Proc. Fla. State Hort. Soc. 91:56-59. 1978.

CITRUS BLIGHT DIAGNOSIS IN SEVERAL SCION VARIETY/ROOTSTOCK COMBINATIONS OF DIFFERENT AGES Roger H. Young, H. K. Wutscher took up less water by gravity injection than healthy trees AgriculturalResearch, or than trees afflicted with other diseases (6). This finding Science and Education Administration, indicated that the general water-stressed condition of United States Department of Agriculture, diseased trees, which often exhibited leaf wilt (1), was due 2120 Camden Road, Orlando, FL 32803 to impaired water translocation. Leaf zinc deficiency symp toms in trees with blight led Smith (1974) to evaluate zinc M. Cohen distribution in diseased trees (12). He found as much as 8 University of Florida, Institute of Food and Agricultural Sciences, times more zinc in outer layers of trunk and limb wood in Agricultural Research Center, trees with "blight" than in healthy ones, indicating impair P.O.Box 248, Ft. Pierce, FL 33450 ment of normal zinc translocation. Most recently, Wutscher et al. (1977) combined trunk water injection and analysis S. M. Garnsey ofzinc and water-soluble phenolics in trunk wood to dis Agricultural Research, tinguish blight from other diseases, such as exocortis, tristeza, Science and Education Administration, xyloporosis, or foot rot, or from water damage or burrowing United States Department of Agriculture, nematodes (16). 2120 Camden Road, Orlando, FL 32803 This paper reports that trees of several scion variety/ rootstock combinations of different ages, grown on the ridge Additional index words, xylem dysfunction, wilt disease, and in the flatwoods that exhibit blight symptoms, all have young tree decline. similar patterns of water uptake, zinc accumulation, and in creased phenolics. It also reports further evidence that these Abstract. Eighty-four citrus trees exhibiting visual blight common symptoms occur in the absence of tristeza virus. symptoms were evaluated with corresponding healthy trees with the diagnostic tests of water-uptake and zinc and Materials and Methods phenolic levels in trunk wood. Trees with 'blight7 had less Plant material. Citrus trees of different ages, both healthy water-uptake and higher zinc and phenolic levels in the and exhibiting visual blight symptoms (5), located on the wood than healthy trees. These patterns were found in ridge and in the flatwoods sections of the state were evalu diseased trees 6 to 50 years old growing on the ridge and ated. Care was taken in selecting test trees to avoid other on the flatwoods. Diseased trees characterized as "blight/7 ailments such as foot rot, exocortis, tristeza, water damage, "young tree decline" (YTD), and "sandhill decline" by visual poor nutrition, lightning damage, etc. Scion varieties in symptoms, tree age, rootstock, or location had similar cluded Citrus sinensis (L.) Osbeck, cvs. 'Hamlin/ 'Valencia/ patterns of water uptake and zinc and water-soluble phenolic 'Parson Brown/ and 'Pineapple'; C. paradisi Macf. cvs. levels. Blight was diagnosed by the above techniques in the 'Marsh/ 'Duncan/ and 'Ruby'; C. reticulata Blanco cv. varieties 'Valencia', 'Hamlin', 'Pineapple', and 'Parson Brown' Dancy and hybrids 'Temple' and 'K-Early'; C. reticulata X oranges, 'Marsh', 'Duncan', and 'Ruby' grapefruit, 'Dancy' C. paradisi cv. 'Orlando'; and C. reticulata X (C. paradisi X tangerine, 'Nova', 'Robinson', 'Temple', and 'Orlando' C. reticulata) cvs. 'Robinson' and 'Nova.' Rootstock species hybrids; and rootstocks of sour and sweet oranges, rough included C. reticulata cv. Cleopatra; Poncirus trifoliata (L.) and Milam lemons, Cleopatra mandarin, trifoliate orange, Raf. trifoliate orange; C. sinensis X P. trifoliata cvs. Carrizo Carrizo and Troyer citranges, Rangpur hybrid andColumbia and Troyer; C. limon (L.) Burm. f. cvs. rough lemon and Sweet lime. Trees with blight were found with and without Milam; C. aurantium L., sour orange; C. reticulata hybrid tristeza virus. cv. Rangpur; C. aurantiifolia (Christm.) Swing, cv. Colum bia Sweet lime; and C. sinensis cv. Hamlin. One of the earliest reports of "blight" in Florida was in Blight diagnosis. Zinc and water-soluble phenolicsin 1883 by Manville (10). He described a limb blight with trunk wood were determined by methods of Wutscher et al. characteristic leaf wilt on bearing trees over 16 years of age. (16), and water uptake was determined by methods of Subsequent reports by Swingle and Webber in 1896 (14), Cohen (6) and Young and Garnsey (17). Analyses werecon Rhoads in 1936 (11), and Childs in 1953 (4) described a ducted from March 1976 to August 1978. Water uptake is blightlike disease with visual symptoms similar to those expressed as ml/hr or ml/24 hr, zinc as ppm, and water- reported by Manville. The terms "young tree decline" soluble phenolics as mg/g dry weight of tissue. (YTD) and "sandhill decline" (SHD) were coined in the Tristeza virus indexing. Buds or fruit with 1 cm of 1960's to describe a similar disease of relatively young bear stem attached were harvested from suspected trees with ing trees grown in the flatwoods and on the ridge, respec blight the day water uptake was measured and trunk wood tively. The characteristics distinguishing blight, YTD and samples were taken. Tristeza virus indexing was ac SHD are tree age, rootstock, and location. Blight was complished by either grafting buds into 'Mexican' lime in thought generally to affect trees older than 15 years on dicator seedlings (15) or by an enzyme-linked immuno- sour orange rootstock. Young tree decline was thought to sorbent assay (ELISA) of fruit stem bark (3). For ELISA affect young bearing trees on rough lemon in the flatwoods, tests, OD405 readings twice or more the value for healthy and SHD was thought to affect rough lemon-rooted trees control extracts were considered indicative of tristeza virus of all ages on the ridge (7). Visual symptoms, however, are infection. similar (5). Precise diagnostic techniques have recently been de veloped to complement visual observations of leaf wilt and Results and Discussion zinc deficiency in diseased trees. Cohen, 1974 (6), demon Blight diagnosis. Eighty-four trees exhibiting visual strated that trees afflicted with blight, YTD, and SHD symptoms of "blight" were evaluated with corresponding

56 Proc. Fla. State Hort. Soc. 91: 1978.

healthy-appearing trees in the same groves for water-uptake exact cause of the disease is found or until new evidence is and trunk zinc and water-soluble phenolic levels. Diseased presented to establish more than 1 syndrome, the term trees took up significantly less water and had increased zinc "blight" has precedence for this decline syndrome as pro and water-soluble phenolic levels in outer trunk wood com posed by Smith (13). pared to healthy trees (Table 1). In all but 2 cases, zinc Presence of tristeza virus in trees with blight. Trees of content of trunk wood of diseased trees was greater than several scion/rootstock combinations which showed typical that of healthy trees; water-uptake was always lower, and visual blight symptoms and were diagnosed as being positive water-soluble phenolic levels greater in the trunk of diseased for blight by water uptake and zinc and phenolic assays were trees. indexed for tristeza virus (Table 2). As expected, most trees Reduced water uptake and increased zinc and water- tested were infected with tristeza virus, but some trees with soluble phenolics in trunk wood were found in diseased blight of 'Hamlin' and 'Marsh' on sour orange, 'Nova', trees ranging in age from 6 to 50 years, in trees planted on 'Dancy' and 'Valencia' on rough lemon, 'Valencia' on deep, sandy soils of the ridge and on shallow soils of the Carrizo, and 'K-Early' on Cleopatra mandarin were indexed flatwoods. Typical diagnostic patterns were found in 'Va free of tristeza virus. While indexing may have failed to lencia', 'Hamlin', 'Pineapple', and 'Parson Brown' oranges, detect CTV in one or more individual trees, it is unlikely 'Duncan', 'Marsh', and 'Ruby' grapefruit, 'Dancy' tangerine, that all 15 CTV-negative trees were positive. Blighted trees and 'Temple', 'Nova', 'Robinson', and 'K-Early' hybrids. that indexed free of CTV were reported earlier by Garnsey Typical trees with blight were found on rootstocks of rough and Young (9). Feldman and Hanks (8) indexed over 100 and Milam lemon, sweet and sour orange, Carrizo and trees, both healthy and exhibiting blight, and found a high Troyer citrange, trifoliate orange, Cleopatra mandarin, percentage of trees with tristeza virus. Two trees were found Rangpur hybrid, and Columbia Sweet lime. free of the virus, but it was not indicated whether these were Differences in zinc content of wood between diseased healthy or exhibiting blight. and healthy trees appeared to vary with rootstock suscepti Previous reports have indicated that the physiology of bility to blight. The more susceptible rough lemon and trees affected by blight and tristeza is- quite dissimilar. Carrizo citrange rootstocks showed much greater differences Blight is a xylem disorder with restricted water and zinc in zinc levels than did the more tolerant sour and sweet movement (6, 9, 12, 16, 17). Phloem function is apparently oranges and Cleopatra mandarin. Although insufficient normal and blighted trees have adequate root carbohydrate numbers of groves were available for similar observations reserves (9). Conversely, tristeza is primarily a phloem dis with other rootstocks diagnosed for the presence of blight, order which reduces root carbohydrate reserves (9), but does this observation may provide a clue to determining root- not restrict water and zinc movement in the xylem (6, 9, stock susceptibility. Similar differences were not found with 16). Though tristeza virus is now widespread in Florida and water-uptake or water-soluble phenolic levels in wood. most trees exhibiting blight carry this virus, blight was While these results do not indicate degree of susceptibility, common for many years when tristeza virus was not present they do confirm the presence of the disease in trees of these or was quite rare. For many years we have found trees ex scion/rootstock combinations. More extensive surveys are hibiting blight (identified only by visual symptoms) that needed to establish relative blight susceptibility of different indexed free of tristeza virus. This includes young sweet scion/rootstock combinations. orange on rough lemon in flatwoods sampled prior to 1968. Based on our results and those of Cohen (6) and Ander Failure to transmit or perpetuate blight also argues against son and Calvert (2), it is apparent that the physiology of involvement of tristeza virus which is readily transmissible. trees affected by blight, young tree decline, and sandhill de The dissimilarity of the 2 diseases, coupled with our data cline is the same. These 3 disease names were established indicating that blight can occur in the absence of tristeza arbitrarily by tree age, rootstock, and location rather than on virus, strongly indicates that tristeza is not a causal agent a physiological or pathological basis. We feel that until an or part of a causal complex in the blight syndrome.

Table 2. Tristeza virus indexing of trees diagnosed positive for blight.

Trees with tristeza virus + blight/trees with Method blight of Scion Rootstock Age Locations (No.) indexing

Hamlin Sour orange 30 R 0/5y Mexican lime graft Marsh Sour orange 45 F 0/3y Mexican lime graft Valencia Rough lemon 18 F 0/ly Mexican lime graft Nova Rough lemon 18 R 3/4 ELISA* Valencia Rough lemon 50 R 2/2 ELISA Valencia Carrizo citrange 15 R 2/2 ELISA Hamlin Carrizo citrange 15 R 4/4 ELISA K-Early Cleopatra mandarin 10 R 0/2 ELISA Dancy Rough lemon 35 R 2/4 ELISA Parson Brown Cleopatra mandarin 10 R 2/2 ELISA Valencia Carrizo citrange 6 F 2/3 ELISA Temple Cleopatra mandarin 12 F 1/1 ELISA Hamlin Sour orange 14 F 3/3 ELISA Orlando Sour orange 14 F 3/3 ELISA Valencia Rough lemon 14 F B/2 ELISA Hamlin Rough lemon 9 F 4/4 ELISA Total 30/45

*R = ridge; F = flatwoods. yOnly water-uptake measurements were made for blight diagnosis. xELISA = enzyme-linked immunosorbent assay.

58 Proc. Fla. State Hort. Soc. 91: 1978. Literature Cited 9. Garnsey, S. M., and R. H. Young. 1975. Water flow rates and starch reserves in roots from citrus trees affected by blight and tristeza. 1. Allen, L. H., Jr., and M. Cohen. 1974. Water stress and stomatal Proc. Fla. State Hort. Soc. 88:79-84. diffusion resistance in citrus affected with blight and young tree 10. Manville, A. H. 1883. Limb-blight. Pages 82-83 in Practical orange decline. Proc. Fla. State Hort. Soc. 87:96-101. culture; including the culture of the orange, lemon, lime and other 2. Anderson, C. A., and D. V. Calvert. 1970. Mineral composition of citrus fruits as grown in Florida. Press of Ashmead Bros., Jackson leaves from citrus trees affected with declines of unknown etiology. ville, Fla. Proc. Fla. State Hort. Soc. 83:41-45. 11. Rhoads, A. S. 1936. Blight—A non-parasitic disease of citrus trees. 3. Bar-Joseph, M., S. M. Garnsey, D. Gonsalves, M. Moscovitz, D. E. Univ. of Fla. Expt. Sta. Bull. 296. 64 pp. Purcifull, M. F. Clark, and G. Loebenstein. 1978. The use of en 12. Smith, P. F. 1974. Zinc accumulation in the wood of citrus trees zyme-linked immunosorbent assay for detection of citrus tristeza affected with blight. Proc. Fla. State Hort. Soc. 87:91-95. virus. Phytopathology. (In press.) 13. . 1974. History of citrus blight in Florida. Citrus lnd. 4. Childs, J. F. L. 1953. Observations on citrus blight. Proc. Fla. State Mag. 55(9):13, 14, 16, 18, 19; (10):9, 10, 13, 14; (11):12, 13. Hort. Soc. 66:33-37. 14. Swingle, W. T., and H. J. Webber. 1896. The principal diseases of 5. Cohen, M. 1968. Citrus blight and "blight-like" disease. The Citrus citrous fruits in Florida.' U.S. Dep. Agric. Div. of Veg. Physiol. and lnd. 49(7):12, 13, 16, 26. Path. Bull. 8. 40 pp. 6. . 1974. Diagnosis of young tree decline, blight, and 15. Wallace, J. M. 1968. Tristeza and seedling yellows. Pages 20-27 In sandhill decline of citrus by measurement of water uptake using Indexing procedures for 15 virus diseases of citrus trees. J. F. L. gravity injection. Plant Dis. Reptr. 58:801-805. Childs, ed. U.S. Dep. Agric, Agric. Handb. No. 333. 7. DuCharme, E. P. 1971. Tree loss in relation to young tree decline 16. Wutscher, H. K., M. Cohen, and R. H. Young. 1977. Zinc and and sandhill decline of citrus in Florida. Proc. Fla. State Hort. water-soluble phenolic levels in the wood for the diagnosis of citrus Soc. 84:48-52. blight. Plant Dis. Reptr. 61:572-576. 8. Feldman, A. W., and R. W. Hanks. 1974. Young tree decline and 17. Young, R. H., and S. M. Garnsey. 1977. Water uptake patterns in sandhill decline; status of indexing investigations. Proc. Fla. State blighted citrus trees. /. Arner. Soc. Hort. Sci. 102:751-756. Hort. Soc. 87:101-106.

Proc, Fla. State Hort. Soc. 91:59-61. 1978.

RATE OF NITROGEN FERTILIZATION AND INCIDENCE OF BLIGHT IN THREE ORANGE GROVES ON THE RIDGE

Carl A. Anderson greater number of trees with symptoms of young tree de University of Florida, cline (synonymous with blight and sand hill decline) in the Institute of Food and Agricultural Sciences, low fertility plots than in the higher fertility plots on the Agricultural Research and Education Center, interior 2 rows of the 4-row beds. It was not clear whether P.O. Box 1088, Lake Alfred, FL 33850 the blight-fertilizer relationship resulted from variations in the supply of an essential element, from interaction between Fred W. Bistline the fertilizer materials and soil components, or from other Coca-Cola Company, Foods Division unknown causes. Calvert had fertilized the trees for 6 years P.O. Box 3216 with a mixture containing N, P, K, Mg, Mn, and Cu at i/2, Forest City, FL 32751 1, and I14 times the rates recommended for trees of similar age (12). Additional index xoords. citrus, young tree decline, sand On the Ridge, many bearing groves receive annual soil hill decline. applications of only 2 fertilizer elements, N and K. (All other nutrients are applied indirectly and in some cases Abstract. Experiments involving 3 rates of liquid nitro very infrequently.) Nitrogen plays a dominant role with gen fertilizer were maintained for 5 years in 3 bearing respect to vegetative growth and vigor (16) whereas the orange groves affected with blight. The rates tested were effects of K are primarily limited to those of fruit quality 125, 200, and 275 Ib. N/acre/year (140, 224, and 308 kg (9). Since the most obvious feature of blight is a decline in N/ha/year), applied in split applications, Vi in January and tree condition, in contrast to a minimal effect on fruit 1/2 in June. The treatments were applied to 6-row plots and quality, N rate experiments^ were initiated in several groves were replicated 3 times in each grove in a randomized block on*■ the. Ridge_^.. •. where- blight1 *. ■. appeared■!.•• to be established.. 11*11 Ther-r-11 design No evidence was obtained from these 3 experiments objective was to study the effect of the fertilizer program, viz. to relate rate of N fertilization and incidence of blight. In 2 N supply, on the incidence of blight. groves near Frostproof, where tree loss to blight was re latively high, blight primarily occurred in localized areas. In Materials and Methods a 3rd grove near DeSoto City, bli?l" ™""^ Differential N treatments were begun in January 1970 lower rate and affected individual trees scattered randomly ^ continued £or g year§ -n s ^^ of beJaring omnge

9 , increased The same experimental treatments and design were used in content of the leaves and lowered the soil pH. all 3 groves. Two of the groves were located near Hickory In 1936 Rhoads (13) stated that the incidence of citrus Lake south of Frostproof. One of these was a very produc blight increased markedly with inadequate fertilization in tive 29-year-old grove of 'Hamlin' orange trees on rough groves where it was prone to occur. Calvert (1) observed this lemon rootstock. The trees were spaced 25 x 25 ft and were hedged occasionally to permit 2-way travel. The 2nd grove, relationship in 1969 in a fertilizer experiment with young 'Valencia' orange trees on rough lemon rootstock in a 29-year-old 'Valencia' orange trees on rough lemon root- bedded grove near Fort Pierce. He found a significantly stock, was located immediately adjacent to the 1st. The soil in these 2 groves was Candler sand (formerly called Lake iFlorida Agricultural Experiment Stations Journal Series No. 1483. land), an excessively drained acid soil underlain with red

Proc. Fla. State Hort. Soc. 91: 1978. 59