Limitations on the Use of Volkamer Lemon as Rootstock for Citrus

Ary A. Salibe and Ede Cereda

ABSTRACT. Performance tests revealed a number of restrictions on the use of Volkamer lemon as rootstock: intolerance to xyloporosis (cachexia) viroid, develop- ment of budunion crease with certain scion varieties and appearance of wood pitting in the presence of severe strains of tristeza virus. Typical crease symptoms occurred at the union of trees of Serrana acidless, Pera Bianchi, Pera Santa Irene, nucellar Pera Vacinada and Pera Comprida oranges and Citrus macroptera scion varieties. Trees of nucellar Serrana orange on the same rootstock were healthy. Tests of four Volkameriana lemon selections for susceptibility to tristeza stem pitting virus, revealed that Acireale was more tolerant than Palermo, while Catania-1 and Catania-2 were intermediate. All selections showed good tolerance to severe strains of exocortis viroid. Orchard surveys showed the occurrence of symptoms of "citrus de- cline" in trees budded on Volkamer lemon. Index words. xyloporosis, budunion crease, tristeza stem pitting.

There is a growing interest in interest in nurserymen and grow- the use of Volkamer lemon, Citrus ers in the use of Volkamer lemon volkameriana as rootstock for as rootstock in SBo Paulo, Brazil. citrus, due to its tolerance to tris- The results of the research re- teza, good resistance to Phytoph- ported here revealed some restric- thora root rot and to "ma1 secco" tions on the use of Volkamer lemon caused by Deuterophoma trachei- as a rootstock for certain citrus phila Petri and because it induces scion varieties and indicated its be- high vigour and productivity to the haviour in the presence of major scions. According to Russo (7, 8) viruses. this citrus type has many charac- EXPERIMENTS AND RESULTS teristics resembling those of Rang- pur lime and may be identical to Reaction to tristeza virus. Canton lemon. Truly, the trees and Eight-month-old seedlings of four fruits of Volkamer lemon are in selections of Volkamer lemon many aspects nearly identical to named Acireale, Palermo, Catania-1 rough lemon and only a few charac- and Catania-2 were infected with teristics remind one of Rangpur a severe strain of tristeza virus lime (12, 16). with the brown citrus aphid, Performance tests conducted in Toxoptera citricida Kirk. Original Brazil of Volkamer lemon as a seeds of these lemon selections rootstock for orange and lemon were obtained from Acireale Citrus scions, yielded excellent results Station, Sicily, Italy, through the (11, 17). This opened the possi- kindness of Dr. Francesco Russo. bility of using this variety as an Colonies of T. citricida were alternate for Rangpur lime, which allowed to feed for several days on has ranked first in most of 100 a nucellar Hamlin orange tree in- rootstock experiments conducted in fected with a severe strain of tris- Brazil during the last fifty years teza stem pitting virus. Aphids (6). The outstanding behaviour of were then transferred to the young Volkamer lemon with tristeza-in- Volkamer lemon seedlings (about fected orange scions indicated that 40-50 adults aphids to each seed- it was tolerant to this virus. This ling) and were killed with insecti- information roused a growing cide four days later. Ten seedlings Ninth ZOCV Conference of each selection were inoculated vere exocortis and the rumple and another ten seedlings left as agent. All three trees inspected noninoculated controls. were healthy, vigorous, with no All seedlings were cut back two trunk symptoms characteristic of months later and three new sprouts exocortis. Trees of same scion allowed to grow. On September variety budded on Rangpur lime 1980, one year after inoculation, were stunted, with severe cracking all sprouts were peeled and rated and bark scaling in the trunk of the for stem pitting, on a scale of zero rootstock. (no pits) to four (severely pitted). Inspections made in the same Average results were: Palermo se- citrus collection on Volkamer lemon lection 2.9, Catania-2 2.7, Catania-1 rootstock, revealed typical symp- 1.6, Acireale 0.4 and all healthy toms of xyloporosis (cachexia) in controls 0.0. No significant differ- two trees of Uruguay sweet lime. ences in growth occurred between The removal of a piece of bark at infected and healthy control plants. the union showed the presence of Field observation of trees on conoid pits and pegs, tissue dis- Volkamer lemon with 21-year-old colorations and gum pockets in the nucellar Baianinha navel orange bark characteristic of the disease scions, and with 12-year-old nu- (1, 2, 14, 15). Stunting of affected cellar Valencia orange scions, in- trees was also noticeable. fected with tristeza virus revealed Inspections for budunion crease. vigorous growth and good produc- The excellent performance of trees tivity, with no visible deleterious budded on Volkamer lemon in the effect due to the presence of tris- preliminary experiments, led to the teza virus. establishment of a citrus collection Reaction to exocortis and xylo- on this rootstock. Varieties were of porosis viroids : Eight-month-old old or nucellar clones according to seedlings of Volkamer lemon grow- the material available. In some in- ing in the field were infected with stances, nucellar and old clones of exocortis and xyloporosis viroids. the same variety were included. Seedlings were of the Acireale se- The citrus collection was es- lection and were grown from seeds tablished at the S. Manoel Experi- taken from a single mother tree. ment Station, in November 1974, Sources of inoculum were a and included: 26 oranges, 12 Bar50 orange tree carrying severe lemons, 10 tangerines, 2 tangors, 5 xyloporosis and a Hamlin orange citrons, 3 sweet limes, 3 sour tree carrying severe exocortis. Ten oranges, plus one limequat, one seedlings of Volkamer lemon were shaddock, one grapefruit, one infected with exocortis and another tangelo and Citrus rnacroptera ten with xyloporosis, with the use totaling 66 varieties. Most im- of three blind buds for inoculation portant commercial citrus varieties of each seedling. Ten noninoculated were represented in the collection seedlings were cut back and one to determine their behaviour and sprout allowed to grow on each compatibility with Volkamer lemon seedling. Periodic inspection, to rootstock. May 1983 (35 months following in- Periodic observations indicated oculation) showed no symptoms of that trees made vigorous growth, exocortis and xyloporosis in the with differences according to the seedlings. scion species or hybrids. Average Inspections were also made of tree heights in May 1982 were: field trees of nine-year-old Lisbon for lemons 4.25 m, Marsh seedless lemon budded on Volkamer lemon, grapefruit 3.05 m, citrons 3.00 m, known to be infected with very se- sweet limes 2.95 m, shaddock 2.90 Other Subjects m, sour oranges 2.81 m, tangors commercial varieties. Volkamer 2.75 m, tangerines 2.60 m, sweet lemon has many outstanding oranges 2.31 m, Orlando tangelo characteristics (8, 11, 17, 18) that 2.15 m, Eustis limequat 1.80 m and recommends its use as rootstock. Citrus macroptera. 1.50 m. In- However, trees of certain scion spections of the budunion by the varieties develop budunion crease removal of a piece of bark, revealed when budded on this rootstock and typical budunion crease symptoms symptoms were similar to those of (4.10) with the following scion some Pera orange and other scion varieties : Serrana acidless, Pera varieties budded on Florida rough Bianchi, Pera Santa Irene, nucellar lemon (3, 5, 10, 13). Pera Vacinada (nucellar Pera pre- Pera orange is the most im- immunized with mild tristeza portant scion variety grown in virus) and Pera comprida oranges Brazil, and includes possibly 50 to and Citrus macroptera. All trees of 60 per cent of all citrus trees in nucellar Serrana orange in the the State of S5o Paulo. Thus, the same collection were healthy. These incompatibility shown by Pera trees with budunion incompati- orange trees on Volkamer lemon bility were conspicuously smaller rootstock drastically limits the use than trees having Valencia, of this rootstock there. Baianinha, and Navel orange The occurrence of budunion scions. crease symptoms in trees of old Wood pitting caused by tristeza line Serrana orange on Volkamer virus was observed in the trunk lemon rootstock and the absence of of the rootstock in trees budded to symptoms in the trees of nucellar the Feijiio Crii and Sanguinea de line Serrana orange raises the Mombuca sweet oranges. Indexing possibility of a transmissible agent showed that these trees were carry- being involved in the problem. ing very severe strains of tristeza Several authors attributed bud- seedling yellows virus. union crease to a genetic incom- Reaction to citrus decline. Ten patibility (4, 9, 13) but a trans- young trees of Baianinha navel missible agent has been indicated orange budded on Volkamer lemon, as the cause of the problem in two years old in the nursery were certain stionic combinations (5). inoculated with buds taken from Volkamer lemons has been trees showing "citrus decline." shown here to be tolerant to exo- This was part of a larger experi- cortis and intolerant to xyloporosis. ment to study this disease which is These results strengthen the idea similar to Florida blight. Two years that it has some characteristics of after inoculation all trees were still rough lemon ( tolerance to exo- apparently healthy. cortis, budunion crease with certain Field inspections in a com- scion varieties) and some others of mercial Valencia orange grove with Rangpur lime (intolerance to xylo- various rootstocks, revealed several porosis). The use of healthy mother trees with symptoms of "citrus de- trees, free from xyloporosis viroid cline" in Volkamer lemon and Rang- is then necessary when using Volk- pur lime rootstocks. amer lemon rootstock. Available information indicates DISCUSSION that Volkamer lemon can be con- Release of a new promising sidered tolerant to tristeza virus. rootstock variety demands per- A certain variation or degree of formance studies and also indexing tolerance appears however to exist for virus and viroid reactions and among various selections, the compatibility tests with major Acireale selection being more toler- 374 Ninth IOCV Conference ant. Severe tristeza seedling yellows consequently some damage to this strains may cause wood pitting and rootstock. LITERATURE CITED 1. CHILDS, J. F. L. 1950. The cachexia disease of Orlando tangelo. Plant Dis. 34: 296-298. 2. CHILDS, J. F. L. 1951. Cachexia, a bud-transmitted disease and the manifestation of phloem symptoms in certain varieties of citrus, citrus relatives and hybrids. Proc. Fla. State Hort. Soc. 64: 47-51. 3. GRANT, T. J., S. MOREIRA, and A. S. COSTA 1957. Observations on abnormal citrus rootstock reactions in Brazil. Plant Dis. Rep. 41: 743-748. 4. GRIMM, G. R., T. J. GRANT, and J. F. L. CHILDS 1955. A bud-union abnormality of rough lemon rootstock with sweet orange scions. Plant Dis. Rep. 39: 810-811. 5. McCLEAN, A. P. D. 1974. Abnormal bud unions of lemon and trifoliate orange rootstock, p. 211-214. In Proc. 6th Conf. IOCV. Univ. Calif. Div. Agr. Sci. 6. MOREIRA, S. and A. A. SALIBE 1969. The contribution of research for the progressive changes in citrus root- stocks for South America, p. 351-357. In H. D. Chapman (ed.). Proc. Intern. Citrus Symp. Vol. 1. 7. RUSSO, F. 1956. Um nuovo e promettente portinnesto per il limone: Citrus volkameriana Pasq., altamente resistente alla Deuterophoma tracheiphila Petri e alle Phytophthorae. Rivista di Agrumicoltura, Acireale, Italia. l(5-6) : 207- 223. 8. RUSSO. F. 1959. Ulteriore contributo di esperienze sul comportamento del Citrus volk- ameriana Pasq. quale portinnesto del limone. Tecnica Agricola, Catania 11 (4-5) : 423-427. 9. SALIBE, A. A. 1961. Scion-rootstock incompatibilities in Brazil, p. 172-176. In Proc. 2nd Conf. IOCV. Univ. Florida Press, Gainesville. SALIBE, A. A. 1965. Studies on bud-union crease of citrus trees. w. 187-191. In Proc. 3rd Con- ference IOCV. Univ. Florida Press, ~ainesvilie. SALIBE, A. A. 1971. Performance of Citrus volkameriana Pasquale as rootstock for citrus. Proc. Primeiro Congresso Brasileiro de Fruticultura, Campinas 1: 367- 373. SALIBE, A. A. 1972. Poliembriony in Rangpur lime and Volkameriano lemon seeds. Proc. I1 Jornada Cientifica da FCMBB, Botucatu 1: 81. SALIBE, A. A. and S. MOREIRA 1961. Algumas incompatibilidades Citrus "Poncirz~strifoliata" no Brasil. IDIA, Tucuman 6 : 92-97. SALIBE, A. A. and S. MOREIRA 1965. Reaction of types of as scion and as rootstock to xyloporosis virus, p. 70-75. In Proc. 3rd Conference IOCV. Univ. Florida Press, Gainesville. SALIBE, A. A. and S. MOREIRA 1968. Incidence of xyloporosis virus in citrus varieties. Ciencia e Cultura SSo Paulo 20 (2) : 267. SALIBE, A. A. and J. TEOFILO SOBRINHO 1972. Characterization of the Volkamericano lemon. Proc. I1 Jornada Cientifica da FCMBB, Botucatu 1: 82. SALIBE, A. A. and M. M. MISCHAN 1981. Performance of Feminello Santa Tereza lemon budded on Rangpur lime and on four selections of Volkameriano lemon. VI Congresso Brasileiro de Fruticultura, Recife, Brazil, Proc. 2: 542-551. SALIBE, A. A. and E. CEREDA 1982. Reaction of Volkamericano lemon to tristeza, xyloporosis and exocortis viruses. XV Congresso Brasileiro de Fitopatologia, SSo Paulo, Brazil. Book of Abstracts, p. 161.