Int.J.Curr.Microbiol.App.Sci (2021) 10(01): 1218-1235

International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 10 Number 01 (2021) Journal homepage: http://www.ijcmas.com

Review Article https://doi.org/10.20546/ijcmas.2021.1001.146

Alternate Bearing in Fruits Trees: A Review

Ashok Kumar1*, B. D. Bhuj2 and C. P. Singh2

1Department of Horticulture, SGT University, Gurgram, Haryana, [NCR Delhi], India 2College of Agriculture, G.B.P.U.A &T- Pant Nagar, U.P., India

*Corresponding author

ABSTRACT

Alternate Bearing is an alternating pattern of large and small crops occurring in many fruit species that is internally regulated by the plant. Alternate bearing in mango appeared to be related to complex relationships between vegetative and reproductive growths and it is varied according to the cultivar. Flowering is the main event that set the stage for mango K eyw or ds production each year. For the attaining the fruit flower initiation is very important and it is

Mango (Mangifera very complex phenomena in mango. Flowering is the main event that set the stage for mango production each year. For the attaining the fruit flower initiation is very important indica L., Fruit production, Cultivar and it is very complex phenomena in mango. In mango trees flowering is make them evaluation, especially challenging for physiologists, breeders, and growers. North, east and central Breeding , Irrigation Indian commercial cultivars showed the biennial bearing is very serious problem, while most of the south Indian varieties bear regularly. Therefore, different control measures for Article Info the biennial bearing are application of different chemicals, smudging, pruning etc. most

widely used in view of its high potential mango production. This review classifies the Accepted: multiple hypotheses as internal, genetic, carbohydrate resources and hormones or 12 December 2020 environmental, abiotic and biotic stresses. The biennial bearing or alternate bearing habit Available Online: of mango (Mangifera indica L.) is a major problem for its commercial cultivation for 10 January 2021 getting expected productivity, alternate bearing, alternate year cropping, irregular bearing or cropping, periodicity in mango cropping, biennial bearing, are all synonymous terms which are different from the unfruitfulness and shy cropping.

Introduction is internally. Regulated by the plant. This alternate bearing pattern is common in many Mango (Mangifera indica L.) is an evergreen of the perennial trees and shrubs but is not tree in the family Anacardiaceae grown for its universal. Apple is one of the heavily-studied edible fruit. The mango tree is erect and fruit crops with regard to alternate bearing branching with a thick trunk and broad, because of its high economic importance. rounded canopy. The tree produces dense Alternate bearing is an important economic clusters of flowers with cream-pink petals on problem for a number of fruit and nut growers branched panicles. Alternate Bearing means worldwide. Under normal conditions, olive an alternating cropping pattern of the tree that trees produce heavy crops one year (the “on”

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Int.J.Curr.Microbiol.App.Sci (2021) 10(01): 1218-1235 year) and light ones the next (the “off” year). few QTLs associated with AB, and suggested Experience has shown that large olive yields that hormone-related genes are likely to play a tend to lead to smaller crops the following role in the phenomenon. Once a woody year. The potential light crop is predictable perennial plant has passed the juvenile period from the limited amount of new growth when it cannot be induced to flower and has present in the trees. The previous heavy crop reached its adult phase of reproductive limits shoot growth and, because flowers are competence, a proportion of its meristems produced only on the new shoots of the will initiate floral organs annually. previous season, the tree's potential for olive production is reduced. This alternate bearing Flowering in temperate tree species can be is one of the most important limitations of divided into several stages that include flower natural extensive olive cultivation. induction, flower initiation, flower differentiation, and blooming. Flower The mechanism(s) by which the developing initiation is the key developmental stage for crop influences return bloom and yield the fruit trees, particularly for horticultural crops following year is not fully understood. Two such as the apple (Malus×domestica Borkh.), hypotheses have been suggested. The because it determines the success of “nutritional” hypothesis holds that return commercial orchards (Buban and Faust, bloom and yield are proportional to tree 1982)(4) by its influence on fruit quantity and carbohydrate status. Lack of carbohydrate in quality (Link, 2000)(21), as well as stability the ON year directly or indirectly reduces of production from year to year (Schmidt et flowering the following year. Support for this al., 1989)(32). Flower initiation can be hypothesis has been provided by showing strongly limited by an excessive crop, leading positive correlations between carbohydrate to the phenomenon known as biennial bearing levels and AB status, whereas others have (Jonkers, 1979; Monselise and Goldschmidt, shown no consistent relationship between tree 1982) (20, 26, 14). Commonly used terms carbohydrate status and floral intensity at related to alternate bearing include biennial return bloom. The “hormonal” hypothesis bearing and irregular bearing. Biennial proposes that developing fruit produce an bearing is characterized by large yields of inhibitor that directly or indirectly reduces small sized fruit in „on‟ years, and low yields, flowering in the spring following the ON sometimes even no fruit, in „off‟ years. This crop. alternation is a widely spread phenomenon, occurring in both deciduous and evergreen Although a number of studies have shown trees, and in different tree families and correlations between abscisic acid or indole- species such as nuts (hazelnuts, pecans, 3-acetic acid and AB status, no direct pistachios, and walnuts), temperate fruits evidence has been provided for their (apple, apricot, pears, and prunes), subtropical involvement in the return bloom. Gibberellins fruits (avocados, citrus, and olives), tropical (GA) is well-known inhibitor of flowering in fruits (litchis and mangos), and forest trees citrus; thus, fruit-produced GA has been (beeches, oaks, pines, and spruces) presumed to be involved in AB. Despite these (Monselise and Goldschmidt, 1982)(14). findings, the roles of carbohydrates and hormones in AB remain unclear and more Although generations of scientists have tried research is needed to identify factors affecting to understand this phenomenon, the cause of floral intensity following ON and OFF years. alternate bearing is still largely unknown Genetic analysis of AB in apple identified a (Hoad, 1978; Jonkers, 1979; Monselise and

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Goldschmidt, 1982; Bangerth, 2006, 2009) through the pedicel than annual bearing (19,20,26,14,3). External factors cultivars do (Hoad, 1978)(19), and the peak (photoperiod, temperature, and water stress), activity of GA in apple seed coincides with FI internal factors such as the carbon-to-nitrogen (Luckwill, 1970)(23), it has been difficult to ratio and hormones (auxins, cytokinins (CKs), obtain convincing evidence for the transport abscisic acid, ethylene, and gibberellins of GA from seed in sufficient quantities to (GAs)), as well as interaction with other inhibit FI. Bangerth (2006)(3) proposed that organs (leaves, terminal shoot growth, and auxin could be the mobile signal and might fruit) affect flower formation in apple (for stimulate GA synthesis in the meristem. In reviews, see Hanke et al., 2007; Bangerth, this model, GA and auxin could potentially 2009) (17,2). The negative relationship act as FI-inhibiting signals working in between fruit development and flower bud concert, GA as the primary messenger that differentiation is one of the most investigated stimulates the synthesis/transport of the causes of flower set variability in apple, as the second messenger auxin. However, differentiation of flower buds in apple characterization and quantification of both overlaps with embryo development in the GA and auxin in the meristem still need to be previous season's fruit (Harley, 1942; Foster performed and, moreover, an inhibitory effect et al., 2003)(18,13), leading to competition of GA/auxin and stimulation by CK on the between flower initiation and fruit formation. expression of genes related to FI remain to be demonstrated (Bangerth, 2006)(3). Experiments using „Spencer Seedless‟, which can bear both parthenocarpic and seeded fruit, Technologies to induce regular bearing in suggested that seed development rather than mango nutritional competition may be a factor in alternate bearing (Chan and Cain, 1967; The flowering phenomenon in mango is a Neilsen and Dennis, 2000)(7,27). The number complex one. Normally, it crops heavily in of seed per fruit or per bourse (flowering one year (on year) and bears less or no crop growth unit) has an effect on biennial bearing, the following year (off year). Again, it yields which can be overcome by a high vegetative heavily the next year. Thus the rhythm of growth rate of the bourse shoot itself (Chan bearing in mango is not strictly „alternate' but and Cain, 1967; Grochowska and „irregular' or „erratic'. Research findings have Karaszewska, 1976; Hoad, 1978; Neilsen and clearly indicated that this phenomenon is Dennis, 2000) (7,15,19,27). Seed are known mostly due to varietal as well as to contain relatively large amounts of environmental factors in addition to the hormones (Luckwill, 1974) (22), and auxin orchard management practices including (indole acetic acid (IAA)), GA, and CK have pruning, nutrition, irrigation and plant been implicated separately, and in protection. combination, as being responsible for hormonal control of floral induction (FI). Possible causes for irregular bearing

IAA and GA may act together or Varieties independently to inhibit FI in perennial fruit trees, whereas CK is likely to be the hormone Among the most important commercial enhancing FI (Bangerth, 2006)(3). Although varieties of the North Dashehari, Langra, the spur (short fruiting shoot) tissues of Chausa, Fazri and South, Neelum ( biennial bearing cultivars receive more GA Kazaladdu), Banganapalli ( Sappatai)

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Bangalora (Kizhimooku, Totapuri) Kalepad Regular pruning is very essential and Senthura (Chinnaswarnarekha) are moderate to heavy bearers and are considered Need based fertilizer application based on the to be fairly regular. Choice varieties such as soil test report have to be followed. Spraying Alphonso (Gundu), Imam Pasand of Potassium nitrate at 2 per cent + NAA 40 (Himayuddin), Mulgoa, Peter (Pairi, ppm (or) Potassium dihydrogen phosphate at Nadusalai) etc., are mostly erratic in bearing. 1 per cent + Potassium nitrate at 1 per cent during October. Spraying of 0.5 per cent urea, Weather conditions if the trees do not flower up to January. In the irrigated orchards, soil drenching of Though mango is a hardy tree an adverse Paclobutrazol at 1 ml /m {+2} of canopy area. weather condition can convert an „on year' into an „off-year'. Flower induction in mango during 'off’ year Bearing age: Fruit trees purchased from nurseries and garden centres are usually 1- to Alternate bearing is a serious problem 2-years-old when they are sold. The length of prevailing in many choice varieties; rhythm of time from planting to fruit bearing varies with „On‟ (heavy crop) and „Off‟ (lean or no crop) the species of fruit, the cultivar, and whether years occurs consecutively; profitability of the tree is dwarf or standard size (see table). mango orcharding is affected. Commercial Differences in bearing age also exist among varieties of Uttar Pradesh, Dashehari, Langra, cultivars. This is particularly true for apples Chausa, Bombay Green and Lucknow Safeda, and pears. In general, those cultivars that have are alternate bearers. Application of an upright growth habit, such as Red paclobutrazol @3.2 ml per meter canopy Delicious, tend to be tardy coming into diameter through soil drenching during bearing, while those with a spreading growth September is found to induce flowering even habit, such as Jonathan, tend to be early. during „Off‟ year. In case of Dashehari, full dose of paclobutrazol in the first year Deficit rainfall- It is quite evident during followed by half dose in the second year is mango season of 2010 when almost all the required. In Chausa and Langra, regular varieties failed to flower in Tamil Nadu. It is applications are necessary. This technology mainly due to the deficit rainfall which was was found to increase in Dashehari, „On‟ year about 300 mm less than that of the previous yields by about 25 per cent, while providing year's average annual rainfall of Tamil Nadu. 60 per cent of the normal yield during „Off ‟ years. This approach since operates through If frequent showers occur during the period of checking of vegetative growth /vigour, it is fruit–bud differentiation (October November) important to adopt good cultural practices for and flowering (January) with cloudy weather sustaining tree health in the long run. It is and excessive dew, both flowering and fruit widely adopted in Maharashtra state (Konkan set would be adversely affected. Dry and cool region) in Alphonso production. weather with a day /night temperature around 200 / 150 C during winter season trigger Environmental factors flowering induction. Recommended management practices that help to induce Light: Good exposure to sunlight is one of regular bearing in mango the most important factors influencing the formation of flower buds on fruit trees.

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Through the process of photosynthesis, the hardiest species is much higher. The greatest leaves on the tree manufacture sugars used for injury to the flower buds occurs when rather vegetative growth, flower bud formation, and warm periods in the early spring are followed fruit development. If sunlight is limited, the by unseasonably cold temperatures. With tree will continue to grow, but there will not such warm periods, the buds begin to break be sufficient sugars for the formation of dormancy and swell. As the buds become flower buds. Under such conditions, young more active, they become increasingly trees will be slow coming into bearing, the sensitive to cold temperature and are most blossoms will be sparse, and the fruit that sensitive at bloom. forms will be poorly colored. Dwarf trees also will grow larger than anticipated. For these Cultural practices: Cultural practices that reasons, fruit trees should be planted in influence the vigor and vitality of the tree will locations where they will receive maximum affect its ability to bear fruit early and sunlight. Avoid shaded sites near buildings or consistently produce crops. Poor cultural other trees. practices often result in a tree that lacks vigor and vitality. Such trees may start bearing, but Water: The lack of sufficient water, as fruit production is inconsistent from year to experienced under drought conditions, can year. These trees are unable to produce have both a positive and a negative influence enough food reserves to carry a crop, make on the formation of flower buds. If a new growth, and have something left over to temporary drought occurs early in the form flower buds for the following year. This growing season, during the period of flower ultimately leads to biennial bearing. However, bud formation, it can be beneficial in practices that promote excessive vigour will promoting flower buds. However, if the same inhibit or delay fruiting. With excessive drought continued or a prolonged drought vigour the manufactured sugars are utilized developed later in the season, it could result in for vegetative growth and little sugar remains the loss of flower buds. To prevent such a to form flower buds. One of the easiest ways loss, fruit trees should be watered during to judge tree vigour is to observe the amount periods of prolonged drought, particularly if of shoot growth the tree makes each year. they are planted near other trees. Flower bud Generally, a tree capable of carrying a crop is formation occurs between mid-June and mid judged to have sufficient vigour if the average July. If conditions are favorable, the buds terminal shoot growthis in the range of 12 to continue to develop until flowering the 18 inches. More vigor is desired with young following spring. trees, but as the tree approaches bearing age, cultural practices should be geared toward Temperature: Low temperatures during discouraging excessive vigour. winter and spring through bloom can result in the loss of flower buds. During the winter, Fertilization: For young fruit trees in the temperatures below –18°F to –20°F will kill backyard, over fertilization with nitrogen is the flower buds of peaches and sweet one of the major reasons for excessive tree cherries, while the flower buds of apples, vigour and the lack of fruit. Such trees can pears, sour cherries, and plums are able to easily receive too much nitrogen when the withstand colder temperatures. However, if lawn around the tree is fertilized. For this the temperature drops severely following a reason, it is recommended that fruit trees be January or February thaw, the killing fertilized well (about 1⁄4 lb. actual nitrogen) temperature for flower buds of even the just after planting to encourage good growth.

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Then, depending on the tree vigor, either More important, the tree would have very withhold or cut back on the nitrogen until the few, if any, blossoms the following year. tree begins to bear. This means reducing the Fruiting is a devitalizing process, and with the rate of nitrogen applied to the lawn around the competition of a heavy crop, there would be tree. Once the tree is bearing, normal lawn very little manufactured food reserves and fertilizer rates should be adequate for most nutrients available for flower bud formation. trees. To fertilize bearing fruit trees The net result is biennial bearing. To independently of the lawn, use a rate of 0.1 lb. overcome this tendency to bear fruit in of actual nitrogen per inch of the tree trunk alternate years, fruit thinning should be diameter at its narrowest point. The fertilizer practised. should be broadcast under the tree. Observe the amount of terminal shoot the tree makes Pollination: All the precautions to ensure the each year to make adjustments to this production of flower buds may be taken, but recommended rate. without proper pollination, trees will still fail to bear. Many fruit species or cultivars within Pruning and training: Proper training and a species either cannot produce fruit or will pruning dictate the potential production of a produce very little when pollinated with their fruit tree. Fruit trees should be pruned to own pollen. Such trees require pollen from develop a strong framework and improve another cultivar of the same species to be light penetration through the tree. Low light fruitful. This is true for apples, pears, hybrid intensity is the primary reason for few flowers plums, and sweet cherries. Most peaches, sour and poorly colored fruit toward the centre of a cherries, and apricots are capable of setting tree. As with excessive fertilizer applications, good crops without cross-pollination. excessive pruning encourages vigorous shoot growth at the expense of flower bud Pest management: Insect and disease control formation. This is particularly true for young often are thought of as means of producing non-bearing trees. In order to encourage early quality fruit. However, insects or diseases that fruiting on young trees, pruning should be attack the foliage of a fruit tree can affect its kept to a minimum and be confined to potential to produce flower buds. If the attack developing a good framework. For trees that is severe enough, the trees may fail to bear. have begun to fruit, the amount of pruning Timely applications of recommended required each year can be judged by pesticides will control most pest problems on observing the amount of terminal shoot fruit trees. growth. If the average terminal shoot growth is excessive, then less wood should be Factors responsible for biennial bearing removed than was taken the previous year. If terminal shoot growth is less than normal and Several factors like, age and size of shoots, the previous crop was not great, then more climatologically factors, carbon/ nitrogen wood removal compared to the previous ratio and hormonal balance have been season is warranted. For more information on responsible for biennial bearing in mango pruning and training fruit trees, fruit plants. These factors are described below as; Age and size of shoots Growth in mango Fruit thinning: Bearing fruit trees have the takes place in different flushes, which vary in potential of setting more fruit than they are different parts of the country. Early initiation capable of carrying. If all the fruit were left and cessation of growth, followed by a on the tree, they would be small at maturity. definite dormant period, will helps the shoots

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Int.J.Curr.Microbiol.App.Sci (2021) 10(01): 1218-1235 to attain proper physiological maturity which like substances are vital for a floriferous is essential for fruit-bud initiation. In the case shoots in mango. The inverse relationship of regular bearing cultivar Rumani, December between the level of endogenous inhibitor in emerged shoots are capable of producing the the shoot and vegetative growth. flower buds in the following February. However, the growth of mango shoots is They are also suggested that higher inhibitor purely a varietal feature and fruit-bud content promotes flowering in mango. differentiation in regular bearing varieties is Agrawal et al., (1980)(1) described an annual feature. In biennial bearing cytokinine-like substances isolated from stem varieties, it is governed by „on‟ and „off‟ year tips of an alternate-bearing cultivar in „on‟ phase of the trees rather than by the time of and „off‟ years. The estimated levels of origin and cessation of growth of shoots. In an gibberellins in apical buds for 6 months prior „on‟ year, shoots of any size or maturity to the flowering season were reported to be differentiate flower buds whereas in an „off‟ higher in the „off‟ year than in the „on‟ year of year, even the shoots of requisite size and an alternate-bearing cultivar (Pal and Ram, maturity fail to flower. Carbon / nitrogen ratio 1978)(29). Climatological factors Adverse That irregular bearing in mango was caused climatic conditions like rainfall, high by nutritional deficiency, especially by humidity and low temperature sometimes nitrogen. convert an „on‟ year into „off‟ year directly or by promoting the incidence of diseases like In fruit plants, nitrogen and carbohydrate powdery mildew and anthracnose. Frequent reserves play important role in flower bud frost or low temperatures during the flowering initiation, even if these do not form the period adversely affect the fruit set, thereby primary cause of the phenomenon of biennial turning an „on‟ year into a year of low or no bearing. It is quite probable that an production crop. Chen et al., (1985, 87)(8,9) accumulation of these compounds may create reported that the temperature is considered to favourable conditions for the synthesis and be key environmental factor, with low action of the substances responsible for temperatures (19ºC in day and 13ºC in night) flowering. The accumulation of these favourable for fruit bud differentiation. compounds may create a favourable condition Cultural practices The earlier reports that for the synthesis and action of the substances biennial bearing problem is far most part a actually responsible for flower induction in nutritional one appears to be wrong because these plants. There was an increased liberal manuring and irrigation given to the accumulation and metabolism of 20yearsold biennial bearing trees failed to carbohydrates, proteins and amino acids induce regular cropping. constituents in the mature plants compared with the juvenile plants (Davenport, 1997). Thus, it is evident that while nutritional The translocation of phosphorus is involved requirements of the fruit trees must be met for in controlling the alternate bearing in mango. optimum performance of the trees, biennial Hormonal balance Biennial bearing problem bearing cannot be overcome by the addition in mango appears to be closely associated of nutrients. Crop load Generally, moderate with the fruit development process and the blossoming is one of the chief conditions of inhibitory influence of the developing fruits annual fruit bearing in fruit trees. The number on vegetative growth. Higher levels of auxin of fruits retained till harvest is a varietal like substances and an inhibitor (similar to feature. The total number of fruits that are ABA) and lower levels of Gibberellin (GA3) harvested is important because of their

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Int.J.Curr.Microbiol.App.Sci (2021) 10(01): 1218-1235 deleterious influence on the production of biosynthesis (Upreti et al., 2013)(36). new shoots and their subsequent fruit-bud Potassium nitrate is currently recommended differentiation. Therefore, the fruit load in the Philippines for inducing uniform appears to be the main conditioning factor for flowering and for the production of off-season „on‟ or „off‟ year in mango. The potential of fruits in the 'Pico' and 'Carabao' cultivars shoot to form flower buds will depend on the (Madamba, 1978)(24).Davenport (2003)(10) floriferous condition of the tree, which in turn reported that bud break was initiated three will be determined by the amount of fruit load months later by a foliar application of KNO3 carried by the tree in the previous year (Singh, in weakly inductive condition (during warm 1971)(34). Control measures for biennial temperature condition) maximum response bearing in mango Different control measures was observed at about four weeks. Plant are used for the implying the regular bearing growth retardants have been evaluated to in mango. These control measures are stimulate early or more intense flowering, described below as; Proper upkeep and especially in the „off‟ year of alternate- maintenance of orchards. Deblossoming is a bearing cultivars (Davenport and Núñez- more severe form of fruit thinning, employed Elisea, 1997)(11).The efficacy( of daminozide to conserve the reserves of the shoots which and cycocel for increasing flowering in the could otherwise be depleted later on in the „off‟ season of alternate-bearing cultivars has development of fruits. Deblossoming of the been studied (Rath and Das, 1979; Rath et al., panicles with NAA @ 200ppm during „on‟ 1982)(30,31), together with their ability to year effective for the controlling biennial stimulate early flowering (Suryanarayana and bearing in mango. Majumder et al., 1976(25) Rao, 1977; Chen, 1985)(35,8). Smudging reported that the alternate bearing in mango Smudging is an early commercial method for reduced by the removal axillary panicles. The inducing flowering in mango (Wester, partial or complete removal of flowers in the 1920).Sen and Mallik, 1947(33) reported that 'on' year increases flowering the next year. smudging has a stimulating effect on growth, Chemical regulation Ethephon has also been but the nature of growth, vegetative or successful use in India for increasing flower reproductive, depends on other factors and intensity of mango cultivars Langra and concluded that smudging can induce Dashehari during off years (Chadha and Pal, flowering only if the shoot is in condition to 1986)(6). Chen, 1987(18) described flower in mango cultivar Langra. Pruning In precocious bud break and flowering of mango mango trees, pruning is necessary to control shoots in response to an early October the canopy size and to produce high quality application of 100 ppm 6- Benzyl amino marketable fruits by facilitating better purine (6-BA). The paclobutrazol induced ventilation, high penetration of sunlight, easy enhancement in C: N ratio has been reported application of plant protection chemicals and in mango consistently higher production of ease in harvesting (Burondkar et al., 1997; total sugars and reducing sugars with peak Gross, 1996)(5,16). availability at bud burst in apical buds (Upreti et al., 2014)(37). Pruning play an important role in mango trees like encouraging the branching of young trees Besides reducing the gibberellin biosynthesis, particularly in cultivars which do not branch PBZ enhances the ABA content. PBZ induced readily on their own, stimulating the increase in ABA content could be due to the development of new shoots and maintaining modification in the isoprenoid pathway which the tree size (Oosthuyse, 1994)(28).Tip is common for ABA and gibberellin pruning forces a synchronized flush from

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Int.J.Curr.Microbiol.App.Sci (2021) 10(01): 1218-1235 pruned stems, which results in synchronized of many regular bearing Indian hybrid flowering in Keitt mango (Davenport et al., cultivars. The regular bearing Florida 2006)(12). The age of the last flush is the cultivars i.e. „Tommy Atkins‟,„Keitt‟, etc. are dominant factor regulating flowering of also have potential as parents. It is apparent mango. Stems must be generally about 4 to 5 that floral initiation in trees is controlled by a months to be able to induce for flowering in range of factors which may include the next year (Davenport, 2003)(3).Pruning is environmental factors, developmental issues effective for early and higher accumulation of and other interactions with vegetative growth reserves by enhancing uniform post-harvest and PGRs. for flowering in shoots high level flushing and reduces flowering variation of starch, some auxin like regulators and (Oosthuyse, 1994)(28). Growing regular inhibitors and a low level of gibberellins may bearing cultivars Totapuri, Rumani, Neelum be seemed favourable. Maintain of regular and almost all hybrids of mango are having bearing in mango is necessary not only for regular bearing nature. However, two yield sustainability but also for yield increase. cultivars, Neelum and Totapuri, which are Use of some plant growth regulator regular bearers, have been extensively used as (paclobutrazol), shoot pruning, use of fruit set the parents in a hybridization programme to chemicals etc. are found to be the most transfer the regular bearing habit to hybrids. promising approaches for ensuring flowering Neelum has been observed to be a good and enhancing fruit yield under commercial combiner and has contributed to the evolution cultivation

Table.1 Average age of fruit trees

Average bearing Age Crops Times in Year Apple 4-6 Apricot 3-5 Cherry, sour 3-5 Cherry, sweet 5-8 Peach 3-4 Pear 4-6 Plum 3-5

Fig.1 High density Orcharding bearing in Mango

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Fig.2 Flowering and fruiting in off and on Year

Fig.3 Training and Pruning in Avocado

Fig.4 Alternate Bearing (On and off Year) in Mango (Mangifera indica L.)

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Causes for alternate bearing Distinctly alternate bearers: Baldwin, Benoni, Boskoop, Cox Orange Pippin The exhaustion of tree during the period of Selection of regular bearing varieties and heavy crop load and vigorous vegetative planning of orchards in a site with optimal growth with high gibberellin hormone content climatic conditions with good soil and at the time of flower bud differentiation and physical properties reduces the risk of imbalance in Carbon / Nitrogen ratio has been alternate bearing and other cropping considered as some of the major causes for irregularities. Spring flowering deciduous biennial bearing or alternate bearing in mango orchards are preferably planted on sites with low risk of frost or freeze damage Management: Planting of fairly regular bearing varieties like Amrapali, Banganpalli, Cultural practices and pollination: Since Bangalora and Neelum are suggested for the phenomenon of alternate bearing is getting regular fruits, but most of the natural and is internally regulated by the commercially grown varieties in North India, plant, good crop management practices are like Dashehari, Safeda, Chousa and Langra essential to minimize its occurrence. In are alternate bearers. In such trees, regularity general, flower formation is promoted in can be achieved by performing a series of perennial fruit trees under optimal growing management practices such as pruning, flower conditions. Optimal plant growth can be induction, fertilizer application, irrigation and maintained by practising annual pruning, pest control. Mango normally flowers during regular irrigation and maintenance of optimal February-March and is ready for harvest nutrient levels in soil and plant tissue along during June-July. Fruits are borne largely on with judicious use of pesticides. Honey bees previous year‟s shoots, so pruning should not are effective pollinators for apple. Setting the be very severe. Light pruning restricts the beehives in apple orchards during the vegetative growth up to some extent and blooming period enhances the pollination and activates the quiescent fruit bearing buds by fruit set. Management of orchard with above redistributing the endogenous hormonal cultural practices does not reduce the risk of substances and favours flowering, fruiting and alternate bearing directly but the risk of improves fruit yield. After harvesting the cropping irregularities will be managed up to fruits, troop off branches to open the centre. some extent Also remove dead wood, weaker branches and criss-cross branches to allow sunlight to Crop load management: This is the most enter the canopy. important management practice for minimizing alternate bearing. Crop load Site and cultivar selection: Based on the adjustment is very important for regulation of bearing tendency, apple varieties have been yields in the current season as well as for next classified into three groups (Jonkers, season. Crop load management is done by 1979)(75). thinning and pruning methods

Regular bearers: Early Worcester, Golden Chemical thinning: Some of the chemical delicious, Golster, Jonagold, Rome Beauty thinners such as Lime sulphur, carbamates Moderate bearers: Delicious group, Golden (Carbaryl, Oxymyl @ 600ppm), NAA (2.5- spur, Granny Smith, Jonagold, McIntosh, 20ppm), 6-BA (75-175ppm), Ethephon (150- Northern Spy, Red Gold and Rhode Island 600ppm) are used for the chemical thinning Green process in apples.

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Pruning: Pruning removes bearing surface manually thinning the fruits when they‟re (fruit buds) and stimulates vegetative growth one-third their normal size. With apples, all from remaining buds. This promotion of except the biggest fruit in a bunch can be vegetative growth inhibits many of the removed by hand picking. Only one fruit remaining buds from becoming floral. should be allowed to grow in every 10 inch (25 cm.) span on the branch. For apricots, Hand thinning: Hand thinning serves like a peaches and pears, a gap of 6 to 8 inches (15 chemical thinning process. In this method, to 20 cm.) is ideal. excessive crop load is removed by hand thinning. Hand thinning is labour-intensive, Chemical thinning: Certain chemical agents and it must be practised early in the growing are used to control biennial bearing in trees season in order to have a beneficial effect on grown commercially. These chemicals the alternate bearing. effectively thin out heavy crops and encourages even crops. In commercially Return Bloom Sprays: Chemical thinning grown orchards, this labor-saving technique is alone may not be adequate to promote annual preferred to manual thinning. Vydate®, Amid bearing in many of the commercially Thin®, and Fruitone® are some of the important apple cultivars that possess a strong products used for this purpose. In addition to genetic tendency towards alternate bearing reducing heavy crops, active measures to phenomena. In such cases, plant growth promote flowering and fruit setting may be regulators that directly stimulate flower necessary to prevent alternate bearing. They formation should be used. NAA @ 3-5 ppm include: Use of growth regulators to induce or Ethephon @100-200 ppm may be used, flowering Use of phosphorus fertilizers, such starting from five weeks after bloom to eight as bone meal Planting pollinizer varieties to weeks after bloom to get quality yields. help with cross pollination Introducing beehives at the time of flowering to ensure Pruning: Pruning the branches is a pollination Young trees must be carefully preemptive measure to reduce excess fruiting pruned and protected from water stress and in one year to prevent reduced crops in the chemical imbalances to discourage the following year. When some of the flower tendency for biennial bearing. There are also buds are removed by pruning, it promotes many cultivars resistant to alternate bearing. vegetative growth, reducing the chances of heavy fruit setting. Effect of Palobutrazol: Biennial fruits bearing or Irregular bearing or Alternate Thinning: Thinning out the fruits within the bearing is serious problems in fruit first few weeks after the flower petals fall is cropsleading to considerable decline in their found to be effective against biennial bearing. fruits production potentials. Alternate bearing When the energy requirement for fruit bearing means "a condition at which high or optimum is reduced, it promotes the flower formation fruit production in on year or higher and process of the coming year. Thinning may be certain year bear little or no fruit (off-year). performed by hand for the home gardener, or Flower initiation is very important because it through the use of chemicals for commercial is the first step towards attaining fruit. Recent growers. trials have clearly shown that while the extent (quantity) of flowering affects yields, time of Hand thinning: For a tree fruiting every flower emergence has a significant influence other year, a heavy crop can be reduced by on time of fruit maturity. Early flowering

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Int.J.Curr.Microbiol.App.Sci (2021) 10(01): 1218-1235 clearly resulted in early fruit maturity, Paclobutrazol is effective not only in flower therefore, one method to manipulate induction but also in early and off-season flowering isto use the plant growth regulators flower induction in fruit crops. The Mode of particularly the growth retardants like action of plant growth retardants such as paclobutrazol. Paclobutrazol isa member of paclobutrazol is highly specific to cultivar, the triazole plant growth inhibitor group that rate of application, cultivar, developmental is responsible restricts vegetative growth and stages, and climatic condition. Paclobutrazol induce flowering in biennial bearing several holds considerable promise in the fruit crops. manipulation of flowering, yield, and vigor in fruit crops. However, its high potency for Paclobutrazol (PBZ) is responsible for the harmful to nature, slow mobility in the induction and manipulation of flowering, orchard soil, persistence in soil and fruit over fruiting and tree vigor in biennial bearing fruit its long term use. Plant growth retardants are crops. The application of paclobutrazol in the being used widely in chemical manipulation soil promotes flowering and increasing yield of growth and development by modifying in many fruit crops. Besides reducing associated biochemical and physiological gibberellins level, paclobutrazol increase. processes. Among them, paclobutrazol is cytokinin contents, root activity, and C: N considered as one of the most versatile plant ratio, whereas its influence on nutrient uptake growth retardant which restricts vegetative lacks consistency. It also affects microbial growth and induces flowering in many fruit population and dehydrogenase activity in soil. crops like apple, pear, peach, citrus, mango, Paclobutrazol has been characterized as an avocado, litchi, temperate fruits, and nuts. environmentally stable compound in soil and Paclobutrazol (PBZ) is a triazole derivative water environments with a half-life ofmore with which plays an important role in than a year under both aerobic and anaerobic regulating excessive vegetative growth, conditions. However, when it is applied in enhancing and advancing flowering, inducing optimized rate the residual concentration early bearing, managing biennial bearing detected will not be above quantifiable level tendency, establishing a high-density (0.01 ppm) in soils and fruits. It is extensively plantation. Why the application of studied due to its high potential for paclobutrazol in fruit crops? The biennial controlling plant growth and development. bearing is a very serious problem in fruit crop PBZ which is also known as different production. Because biennial bearing or commercial names such as pp333, cultar, alternate bearing in fruit crops is a major bonzi; sadabahar, parley, clipper, etc, is an problem faced by fruit growers. This problem important growth retardant. causes great economic loss to the growers. Irregular and alternate bearing problem-solve Paclobutrazol has been effective in through paclobutrazol is commonly practiced controlling the growth of a wide range of fruit by growers. Paclobutrazol is a synthetic plant crops by inhibiting both sterol and gibberellin growth retardant, which has been used in fruit biosynthesis. The main effect of paclobutrazol tree crops to control vegetative growth and to in the plant is the inhibition of gibberellin induce flowering. biosynthesis, which reduces change in the sink source relationship by reallocating the The alternate flowering in fruit crops might be carbohydrate source towards other organs of due to improper orchard management the plant than the shoot apex. practices, environmental factors, varietal character, Imbalance of hormone, etc. Mode

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Int.J.Curr.Microbiol.App.Sci (2021) 10(01): 1218-1235 of action of paclobutrazol Gas Therefore, twice there commended dose of chromatography-mass spectrometry fertilizers and organic manures should be fed confirmed that PBZ was taken up by roots to the tree from the second year of and translocate acropetally via the xylem to paclobutrazol application. Time of application stems and accumulated in leaves. of paclobutrazol in fruit crops. Usually, it is Paclobutrazol is having anti-gibberellins applied as a soil application in the month of activity which blocks the conversion of ent- September-November in the case of mango. kaurene to ent kaurenoic acid in the The growth retardant paclobutrazol is applied gibberellins biosynthetic pathway, which is after harvest as a soil application or foliar responsible for cell elongation and cell application. Paclobutrazol is applied as Cultar division and ultimately retards plant growth. @ 23 SC to the tree basin soil by making a 15 When gibberellin production is inhibited, cell cm deep and 30cm wide-furrow at a radial division still occurs, but the new cells do not diameter of 1 m from the tree trunk during elongate. That results in the production of last week of September inmango and Litchi. shoots with the same numbers of leaves and Method of application of paclobutrazol internodes compressed into a shorter length. Paclobutrazol applied asFoliar application Paclobutrazol treated trees show increased Soil application TSLP method Soil and plant production of the hormone abscisic acid and trunk injection incorporating in nutrient the chlorophyll component phytol, which are solution Paclobutrazol must be applied beneficial to tree growth and health. It also directly to the soil due to its low solubility, induces morphological modifications of long residual activity, and lack of efficient leaves, such as smaller stomatal pores, foliar uptake. Soil application rather than the increased number, and size of surface foliar application of paclobutrazol hasbeen appendages, thicker leaves, and increased root found to be more responsive in suppressing density that may provide improved the vegetative growth and enhancing there environmental stress tolerance and disease productive growth in mango trees. resistance and it also has some fungicidal Paclobutrazol is a potent inhibitor of activity due to its capacity as a triazole to gibberellin biosynthesis and can be applied as inhibit sterol biosynthesis.The amount of an overall spray,as a soil drench or by way of paclobutrazol residue left in the soil or plant trunk painting; better results have been parts would appear to depend on themethods achieved when used as a soildrench, either in of application, doses and the crop.Guideline the root zone or the collar region of the tree. for use of paclobutrazol on fruit crops The required quantity is mixed in Paclobutrazol should be applied to healthy approximately 1 L of water and poured onto trees. Tree base should be kept weed-free the soil around the trunk in a circular band. before and after its application. Adequate moisture in the soil at the time of application The proper care of fruit orchards provides for and for the following 40-50 days is essential. the necessary concentration of nutrient Paclobutrazol treated trees start producing substances in the plant cells, especially inflorescence in 3-4 months of application. protein matter, and for an optimal ratio of carbohydrates and nitrogen, which stimulates This flush of inflorescence as well as new the setting of flower buds in the harvest year vegetative flushes and flowers should be for fruiting in the next year. In this way, regularly protected from the attack of insects, annual harvests are ensured. To obtain a good pests, and diseases. Paclobutrazol treated trees harvest of high-quality fruit every year a tree are expected to bear a good crop every year. must have 30 to 60 leaves for each fruit. This

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Int.J.Curr.Microbiol.App.Sci (2021) 10(01): 1218-1235 is possible if the tree has many annual shoots; increasing shoot number (growing points) but thus, shoot formation is an important factor in still increasing the total shoot length and total high yield. Moderate flowering is one of the bud number across 2 years. However in the most important conditions for annual fruiting. presence of PBZ, GA significantly and Only a moderately flowering tree is capable successfully reversed the effects of PBZ or of producing a large harvest and setting GA on vegetative growth characteristics and flower buds for the following year‟s harvest. provided a balanced vegetative growth well Abundantly flowering pome trees (apple and below that of the control for 2 years. pear) should have their excess flowers or set Reproductive growth response to soil-applied fruits removed at an early stage of PBZ in the absence or presence of GA Fruit development by growth substances to yield. In this study PBZ use alone decreased preserve nutrient matter for the formation of the fruit yield the year after PBZ application the remaining fruits. Alternate bearing with a slight reduction in yield in the next characterizes only some plant varieties. For year as well. However, the stability of fruit example, some varieties of apple (Slavianka, yield was increased across the 2 years. Pepin shafrannyi) yield annually, others Bienniality indices based on fruit number (Antonovka obyknovennaia, Anis polosatyi) show the extent of year-to-year variation in require special maintenance in order to do so, yield, the larger the index value, the greater and still others (Kandil‟-Sinap, Grushovka the tendency for year-to-year variation. Based moskovskaia) are marked strictly by alternate on these indices PBZ alone slightly increased bearing. Various agricultural procedures and the BI values from 0.21 to 0.23. the stocks to which varieties are grafted also influence the periodicity of fruiting. The bienniality of the fruit yield was thus increased by PBZ use alone in agreement with Vegetative growth response to soil-applied our earlier study (Khurshid et al., 1996a) and PBZ some other reports on high-density dwarf trees by Steffens et al., (1993) and In the absence or presence of GA Growth Zimmerman & Steffens (1995). The reason form Total number of shoots per tree in Trial for lower yield with PBZ in these trees would A was not affected the year after PBZ be the smaller tree size resulting from PBZ application but was reduced the year after. use combined with the use of single tree plots The reason for this could be that the decision which would have lead to crowding of the for shoot number (growing points) would treated trees. The other trials where PBZ have been made between November/ increased yield used large buffered plots December 1992 and PBZ was applied in (Khurshid et al., 1996a,b), which would have September 1993. At that stage PBZ was not eliminated yield reduction because of expected to affect the shoot number. GA competition. PBZ plus GA combination application at that stage in treatments caused recovery of yield for the November/December caused an increase in next 2 years in Trial A and this brought down shoot number in 1994 and a reduction in the BI values from 0.23 to 0.20. This was 1995. The total shoot length and total bud despite vegetative growth still being reduced number were significantly reduced with PBZ and therefore the trees still having substantial alone the year after PBZ application with a competitive pressure. In Trial B, where trees prominent reduction in the second year after received PBZ before the GA treatment, the PBZ application. This shows that GA is not fruit yield completely recovered the year after producing further vegetative growth through treatment and BI values were reduced

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Int.J.Curr.Microbiol.App.Sci (2021) 10(01): 1218-1235 significantly from 0.27 to 0.18. These results perennial fruit trees: still an enigma?, suggest application of GA to the trees which Acta Horticulturae, , vol. 727 (pg. 177- had already received PBZ 2 months 195) previously reduced fruit bienniality more 4. Buban T, Faust M. 1982. Flower bud efficiently than GA application before PBZ induction in apple trees: internal control treatment to the trees. Total fruit number per and differentiation, Horticultural tree Total fruit number per tree followed a Reviews, vol. 4 (pg. 174-263) similar trend to fruit yield and was reduced 5. Burondkar, M.M., Gunjate, R.T., with PBZ application. However, in the Magdum, M.B., Govekar, M.A. and presence of GA and PBZ fruit number Waghmare, G.M.(1997). Increasing recovered substantially. The reverse PBZ productivity of mango orchards by effect by application of GA has been pruning and application of previously reported (Greene 1991; Steffens et paclobutrazol.Acta Hort., 455: 367-74. al., 1992). GA can therefore be used-as a tool 6. Chadha, K.L. and Pal, R.N. (1986). to increase fruit yield and reduce bienniality MangiferaindicaL. In: Halevy, A.C. and in conjunction PBZ to control vegetative (ed.) CRC Handbook of Flowering, growth, when applied in the correct manner. Vol. 5: 211– 30. 7. Chan B, Cain J. 1967. The effect of In conclusion alternate bearing has been one seed formation on subsequent flowering of the major problems. Most of the south in apple, Journal of the American Indian varieties are regular-bearer, whereas Society for Horticultural Science, , vol. north Indian ones alternate-bearer. 91 (pg. 63-67) Paclobutrazol is a promising chemical for 8. Chen, W.S. (1985). Flower induction flower induction in mango. Soil drenching in mango (MangiferaindicaL.) with with paclobutrazol (5g -10g/tree) results in plant growthsubstances. Proceedings minimum outbreak of vegetative flushes National Science Council Part B, Life during September to October giving an early Sciences (Republicof China),9: 9–12. and profuse flowering and more annual yield 9. Chen, W.S. (1987). Endogenous without affecting fruit size and quality. growth substances in relation to shoot growth and flower bud development References of mango.J. Amer. Soc. Hort. Sci., 112: 360-363. 1. Agrawal, A., Ram, S. and Garg, G.K. 10. Davenport, T.L.(2003). Management ,1980. Endogenous cytokinins of of flowering in tropical and mango (MangiferaindicaL.) shoot tips subtropical fruit tree species.Hort. and their significance in flowering. Sci., 38: 1331- 1335. Indian Journal of Experimenta 11. Davenport, T.L., Nunez-elisea, lBiology,18: 504–509. R.(1997). Reproductive physiology. 2. Bangerth F., 2009. Floral induction in In: Litz RE (ed), The Mango, mature, perennial angiosperm fruit Botany, Production and Uses.CAB trees: similarities and discrepancies with International, Wallingford Oxon. pp. annual/biennial plants and the 69-146. involvement of plant hormones, 12. Davenport, T.L., Ying Z., Kulkarni Scientia Horticulturae, , vol. 122 (pg. V. and White T.L.(2006). Evidence 153-163) for a translocatableflorigenic promoter 3. Bangerth F. 2006. Flower induction in in mango.Sci. Hort.,110: 150-159.

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How to cite this article:

Ashok Kumar, B. D. Bhuj and Singh, C. P. 2021. Alternate Bearing in Fruits Trees: A Review. Int.J.Curr.Microbiol.App.Sci. 10(01): 1218-1235. doi: https://doi.org/10.20546/ijcmas.2021.1001.146

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