Citrus Collection for Research relatives, species, varieties, strains, and hybrids provide materials for research on problems of citriculture

W. P. Bitters

Plant source materials for research pea and weighing only a fraction of an Peel colors range from the bright red on citrus problems are available-in one ounce. of the Mlurraya, through the and of the world’s most extensive citrus va- Most citrus fruits are round or slightly yellow colors of the standard orange and riety collections-at the Citrus Experi- flattened or elongated in shape, but those varieties, to the greenish yellow ment Station at Riverside. of the orange jessamine-Murraya-and of the limes, the brown of the Wampee, In the collection, there are citrus fruits the finger limes - Microcitrus - are and the dark blue of the Severinia. -including relatives-of unusual shapes, greatly elongated and banana-shaped in The color of the pulp varies as well, sizes, colors, and tastes, growing on trees appearance. Others-such as C. macrop- and there are several selections of pink- with varying heights, forms, and foliage tera-are conspicuously necked at the pulped . One of these has in addi- characters. stem end and shaped like pears. Some tion a variegated-mottled green and As shown in the lower illustration on are prominently creased and wrinkled yellow-fruit and attractive green and the next page, citrus fruit ranges in size like C. hystrix and the Moroccan rough white variegated leaves, as illustrated in from the shaddock-Citrus grandis- lemon. Fruits of most citrus occur as a the upper photograph on the next page. which may be as large as a person’s head single specimen, but that of the Wampee There are many pink-pulped grape- and weigh many pounds, to the Chinese grows in a cymose cluster like a bunch of fruit and shaddocks. While most fruits box orange-Severinia-as small as a grapes. Continued on next page sunlight struck any part of the structure. trees-Site C-the morning temperature after arrival of the shadow. The interior A good turf was located adjacent to the reached 75F, three and one-half hours heating continued to rise but began to north. later than when the trailer was located level off two hours later. Comparisons of the temperatures re- in the sun-Site A. It cooled down to 75 Although the coolest condition existed corded at Site A, on August 31; Site B, F in the afternoon, two and three-quar- beneath the fig tree foliagesite C- on September 25; and Site C, on August ters hours earlier than in the open. In there was inadequate light inside for 10 are given in the graph on page 10 addition, the temperature remained over reading and close work. However, this because conditions of wind, tempera- 75F during the hot noon period only is attributed largely to the smallness of tures, and humidity were approximately five hours in comparison to the eleven window area. equal. However, the summer of 1954 was and one-half hours at Site A-the bare From the results of these tests, it would unusually cool and maximum tempera- ground check location. appear that the best planting for living tures were considerably below those of The effect of afternoon shade from the shade would be high-branching decidu- normal years. eucalyptus trees-Site B-was striking, ous trees-relatively close to the house More important than the 20F tem- as indicated by the readings of roof tem- Concluded on page 15 perature differential between bare ground peratures. The trailer received direct sun and shade is the resulting delaying action until 12 noon; then as the shade began Effect of afternoon shade is shown in the roof temperature readings where unit is located east of the morning heating and hastening to cover the roof, a 35F drop in roof of eucalyptus group. of the afternoon cooling. Under the fig temperatures occurred in an hour’s time w Site C. Northern exposure of front of unit under fig tree where foliage

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CALI FOR N I A AGRICULTURE, SEPTEMBER, 1955 87 sweet oranges CITRUS 30 Valencia oranges 55 navel oranges Continued from preceding page 10 red-pigmented or- anges 21 have a yellowish or orange pulp, some 13 mandarin limes such as C. hystrix, have a green color 12 acid (Mexican) and seedless (Tahiti) limes and others, such as the Torocco orange, 9 sweet limes 53 shaddocks are a deep red. 43 sour oranges There are many mandarins with thin 12 Bittersweet, chi- notto, Boquet, sour or- rinds that are easy to remove and at the ange types other extreme are fruits that are nearly 58 (light Pulp) all rind. Citrons, for example, may have 9 grapefruit (pink Pulp) a rind 2” thick that can be used to make 32 mandarins 15 satsumas candied peel. 36 The little , unlike most citrus, 7 15 kumauat, kumquat has an edible rind and the fruit is eaten hybrids 6 Calamondin, Cab in its entirety. Fruits like Afraegle and mondin hybrids Aeglopsis are hard shelled and have a 7 trifoliate oranges 16 rind like that of a dried gourd. 12 other trifoliate hybrids There are sweet limes, lemons, man- 14 Ichang, lchang darins, and oranges. Some fruits are hybrids 90 lemon, lemon-like highly aromatic and are frequently used types 42 miscellaneous, as sachets. Others may be dried and used citrus species--citrus as condiments. relatives. Most citrus trees are evergreen, but Recently - by the -a near-citrus rela- agreement of the tive-sheds its leaves during the winter Exploration time, as do many of its hybrids. In the and Introduction Di- spring the flowers appear on these varie- vision of the U.S. ties before the new leaves are in evidence. D.A. Bureau of Plant Citrus leaves vary tremendously in Industry, the Cali- size. They may range from %’’ to 3/s” fornia State Depart- in width and 1” in length on the finger ment of Agriculture -Microcitrus australmica-to 4“ or Bureau of Plant 5” in width and 8” or 10” in length on some of the larger shaddocks. Most Quarantine, and the Leaf types found in citrus species and relatives. A, Hesperethusa; B, Tri- University Of Cali- foliate orange-Pancirus trifoliate; C, Shaddack- Citrus grandis; D, Cit- varieties have a simple, single leaf which fornia-the prohihi- rus macroptera; E, sweet orangditrus sinensis; F, Variegated lemon- may be long and narrow, such as on the Citrus limon; 0, Chinese box orange-Severinia buxifolia; H, Desert desert lime-Eremocitrus-and willow Concluded on page 14 li me-Eremocitrus hybrid; I, Finger lime-Microcitrus australosica. leaf varieties. Leaves of other varieties are compound and may be clover-shaped Fruit types found in citrus species and relatives. A, ShaddockAitrus grandis; B, Chinese box as in the trifoliate orange or may be even orange-Severinia buxifalia; C, Citrus macroptera; D, Citrus hystrix; E, Finger lime-Microcitrus austrolasica; F, Citran4itrus medica; 0, Wampedlousena Iansium; H, Variegated sour orange- more complex as on Murraya, Hespere- Citrus aurantium; 1, Lemon-lime hybrid. thusa, and others. Many varieties have variegated leaves characterized by dif- ferent intensity of green areas in the leaf and light areas devoid of chlorophyll. The shape and size of the trees also vary markedly. A few are inherently slow-growing dwarf trees such as the ; others may be stunted by growing on dwarfing types of rootstocks. A range from bushes to, vigorous trees is thus possible. Certain varieties are sprawling in character; others are quite erect and columnar. There is a citrus type for nearly every need of the landscape gardener. In the fall of 1952, there were 1,544 trees in the Riverside collection repre- senting 713 different accession sources. This does not include newly developed hybrids that are not yet released for com- mercial propagation. Over the past thirty years, 733 other accessions were elimi- nated by natural hazards of frost and disease and because of undesirable fruit types and characters. A summary of present accessions reveals the following number of varieties :

12 CALIF 0 RN IA AGRICULTURE, SEPTEMBER, 1955 been released in the southern counties where it is working and reproducing well, although it remains to be seen how New Mite Predators satisfactorily it will work through the winter months. Large numbers will be four species from Guatemala show used experimentally in mass liberations at critical times in attempts to prevent promise in southern California. the development of injurious plant-feed- ing mite infestations. Since Stethorm feeds on a wide range C. A. Fleschner of mite species, it may be used in this experimental manner not only on avo- The Guatemalan Stethorucasmall, frost may occur in the highlands above cado and citrus but on various truck and black, lady beetle mite predator-is be- 5,000' during the colder months, so it field crops and other trees. This is also ing propagated by the thousand in the was thought that beneficial species col- true of the cheyletid mite and the two insectary at Riverside for ' release in lected from this area could possibly be typhlodromid mites, which-as labora- southern California avocado and citrus established in southern California. tory studies have shown-will feed on groves. Consequently, after methods were de- all mite pests of avocado and citrus trees As a result of an exploratory trip veloped for their propagation, nine except the citrus bud mite. through Mexico and Central America species of these mite predators were Propagation of these beneficial species during the winter of 1953-54 to study shipped to Riverside in the spring of will be continued until they have been the natural balance of pests of avocado 1955, and four of these-one cheyletid given an opportunity to become estab- trees in their native habitat, several mite, two typhlodromid mites, and one lished in southern California groves. species of natural enemies controlling Stethorm-are being propagated. All C. A. Fleschner is Associate Entomologist, mite pests of wild avocado trees were four are new, undescribed species. University of California, Riverside. found in the Guatemalan highlands. Al- Stethorns, particularly, shows promise. The above progress report is based on Re- though Guatemala is a tropical country, Over 7,000 of this predator have already search Project No. 1495.

Yields and Sizes of Lemon Fruits in the Silver FRUIT SIZE Stage of Maturity Grown on Trees in Soil Cul- increase, whereas the magnesium-con- tures That Received Similar Nutrient 5olutions stant in each nutrient-showed minor Continued from preceding page Except for the Ratio of Calcium and Potassium increases as calcium in the nutrient was from each culture were tested in dupli- Diam- increased and potassium decreased. cul. Cat- PO- NO. y: eter cate determinations for their content of ci- tas- of of Lemon fruit therefore responded very um sium fruit :%':, iruir calcium, potassium, magnesium, and so- ins. well to changes in the calcium-potassium dium, the results of which are shown in content in the nutrient solution applied the larger table. The calcium percentage to the soil when the concentration of the in the peel was approximately doubled 1 318 0 12 1134 2.095 applied other nutrient elements was not 2 298 39 23 2335 2.165 varied in any of the cultures. The larger while that of potassium was more than 3 277 77 15 2400 2.169 tripled in the extreme. Hoagland's nutri- 4 237 155 13 . 1503 2.193 table also shows that the calcium and 5 159 310 18 2027 2.228 entpolution regularly contains 159 ppm 6 80 467 19 2227 2.252 potassium percentages in the dry matter of calcium. When the concentration of 7 40 545 11 1299 2.272 of lemon flowers can be markedly af- calcium in the nutrient solution was in- 8 0 622 8 1100 2.374 fected by varying the ratio of calcium to creased above this strength-as shown potassium in the nutrient applied to soil in the larger table-the calcium percent- peel there were very small increases in cultures. The high calcium content of age in the peel made its greatest increase. the percentages of magnesium accom- many irrigation waters should make the Above a concentration of 237 ppm of cal- panying the increased calcium and re- potassium supply of considerable im- cium in the nutrient, calcium percentage duced potassium percentages though portance. in the peel increased only slightly. the magnesium concentrations in the nu- A. R. C. Haas is Plant Physiologist, Emeritus, The peel readily absorbed large trient solutions were similar for all cul- University of California, Riverside. amounts of potassium when the concen- tures. Joseph N. Brusca k Principal Laboratory tration of potassium in the nutrient solu- In the pulp the calcium percentages, Technician, University of California, Riverside. tion was increased and that of calcium while relatively low in comparison with The above progress report is based on Re- was simultaneously decreased. In the those of potassium, showed a consistent search Project No. 1086.

CITRUS Material introduced under current from quarantine to governmental agen- quarantine measures is carefully screened cies for experimental field trials. Continued from page 12 and indexed for various diseases at The variety orchard provides a wide tion of importation bud of wood or cut- the U.S.D.A. Plant Industry Station source of propagating material of mis- tings was modified, and introduction of greenhouses at Beltsville, Maryland. Sat- cellaneous varieties and a varied popula- citrus budwood from other countries is isfactory material can be released to tion of genes for breeding studies. Wide permissible under quarantine measures. California where it will again be placed use of such trees is made in rootstock Quarantine regulations-imposed in in isolation quarantine greenhouses. The tests and in the search for nematode and the 1930's-prohibited importation of introductions will be budded into various disease-resistant stocks. rootstock combinations and into dif- budwood or cuttings from out of state W. P. Bitters k Associate Horticulturist, because of the danger of introducing ferent seedlings to index for miscellane- University of California, Riverside. contagious diseases with the incoming ous virus and other diseases. Material The above progress report is based on Re- material. found to be sittisfactory will be released search Project No. 194.

14 CALI PORN IA AGRICULTURE, SEPTEMBER, 1955