Performance of a Clementine Mandarin with Cachexia-Xyloporosis on Eleven Rootstocks* E. Tribulato, G. Cartia, A. Catara, and G. Continella The Clementine mandarin industry in grafted 1 year later with Comune Italy comprises 8,000 hectares and clementine. Buds were from 10-year-old about 100,000 tons of production. trees grafted on trifoliate orange, with Almost all trees are grafted on sour no symptoms of exocortis, psorosis A, orange rootsock. The Comune variety is concave gum-blind pocket, cristacortis, the most important, and yields seedless or cachexia-xyloporosis. Subsequent fruit of excellent quality. Unfortunately, indexing confirmed the visual diagnosis this variety produces a high percentage except for the last disease. The root- of small fruit and, in many areas, fruit stocks were: sour orange, alemow, set is poor. Physiological stress, such as Volkamer lemon, rough lemon, Cleo- that caused by unfavorable tempera- patra mandarin, Avana mandarin, C. tures and inadequate moisture, induces taiwanica, C. amblycarpa, Troyer and a drop of the weak parthenocarpic fruit- Carrizo citranges, and citrumelo C.E.S. ing. Productivity is increased by inter- 1452. Each stionic combination was planting Avana (Willowleaf) mandarin replicated 18 times in three randomized as a polinizer, which induces seedy blocks. fruits, by girdling, or by gibberellic acid From 1973 to 1978, canopy volumes, sprays. The problems connected with circumferences of stock and scion, the above practices are well known yields, and fruit quality were evaluated. (Damigella et al, 1970). Data for trees on alemow are from only Since rootstocks also influence parth- three plants, free of decline. Symptoms enocarpic fruiting (Krezdorn and of iron chlorosis and virus diseases on Phillips, 1970), in 1968, we started a leaves, fruits, stems, and trunks were field trial to evaluate a clone of Clem- recorded. Bark patches were removed entine on 11 rootstocks. Some years across the bud union to check for xylem later, the clone was found to be affected and/or phloem alterations. Randomly by cachexia-xyloporosis, and the effects selected trees were tested for exocortis, of the disease on the trees were also psorosis A, concave gum-blind pocket, evaluated. Preliminary reports have and cachexia-xyloporosis on Madam been published (Tribulato, 1976; Catara Vinous sweet orange and sour orange et al., 1976). seedlings, and on Parsons Special mandarin and Etrog citron grafted on MATERIALS AND METHODS Volkamer lemon. The trial was carried out in eastern RESULTS AND DISCUSSION Sicily where the productivity of Comune clementine is low. The area is far from Tree performance was greatly in- the coast, on a low hill, and has low fluenced by the rootstocks (table I). humidity. From 1969 to 1978, the Volkamer lemon and C. amblycarpa annual rainfall averaged 530 mm and produced large trees, whereas, Carrizo the net heat accumulation was about and Troyer citranges, which are sensitive 2080°C. The soil is sandy clay with over to lime, produced small trees. Sour 50 per cent lime and about 11 per cent orange produced smaller plants than free lime. other stionic combinations. The rootstocks were planted in 1968, Trees on citranges have shown a neck on a 4.5 x 4.5-m spacing, and were at the bud union (Tribulato, 1976), as *This work was supported by Cassa per il Mezzogiorno, and Consiglio Nazionale delle Richerche, Roma. [2321 Other Citrus Virus Diseases indicated by more than 27 per cent at the bud union: Avana mandarin and difference between the average circum- alemow had typical tiny pits in the ference of the stock and the scion. wood, pegs and gum formation in the Trees on Volkamer lemon showed a bark near the bud union. rapid increase in canopy size until 1975, The final number of trees showing aid a slow increase thereafter. Other symptoms is reported in table 3. All but rootstocks induced a more uniform rate three of the trees on C. macrophylla of increase (fig. 1). showed severe pitting and pegging, poor Table 1 shows the cumulative yield 10 growth, and decline (fig. 2). Two began years after grafting. The first yield was to show wood pitting in 1978 and the obtained in 1973. Yields were highest other is still symptomless. Some trees from the trees grafted on alemow, on C. volkameriana had mild symptoms. Volkamer lemon and rough lemon, in The scion reaction varied with the that order. The poor capacity of sour stock and was present on trees grafted orange to produce high yields of on some symptomless rootstocks (fig. 3). Comune clementine was confirmed by Indexing gave a positive reaction yields only one-third of those produced only on Parsons Special mandarin, on Volkamer lemon. Citranges gave indicating cachexia-xyloporosis poor results in contrast to those ob- infection. tained in Corsica (Blondel, 1973; 1974). CONCLUSIONS Rootstocks did not influence the time of color break, but some induced Rootstocks of the lemon group changes in fruit quality (table 2). Trees (Volkamer lemon, alemow and rough on ~leo~atramandarin bore the smallest lemon) behaved differently from others fruit, as observed for Orlando tangelo and produced greater yields, as ob- on the same rootstock (Krezdorn and served in Florida for Orlando tangelo Phillips, 1970). Citric acid was lower in (Krezdorn, 1977) and in Corsica for fruit from trees on Volkamer lemon, Comune Clementine (Blondel, 1973; and the lowest total soluble solids were 1974). These rootstocks may have a produced on trees on rough lemon and better capacity to overcome nutritional alemow. Volkamer lemon did not differ and water stresses like those after an from other rootstocks in this respect. abundant bloom. These rootstocks may The intensity of iron chlorosis in the possibly play a specific role in the leaves indicated the susceptibility of metabolism of the scion which induces rootstocks to lime. No symptoms were greater parthenocarpic fruiting. observed on alemow, Volkamer lemon, Trees on Volkamer lemon gave an and C. amblycarpa; slight symptoms on annual yield of 26 tonslhectare in 1977 a few trees on rough lemon and Cleo- and 1978, whereas those on sour orange patra mandarin; slight symptoms on bore 10.7 tons. Yields of trees on rough many trees on sour orange, C. taiwanica lemon and alemow were 18 and 24 tons, and Avana mandarin; mild symptoms respectively. The yield for alemow is, of on trees on citrumelo; and severe symp- course, only an indication, because it toms on trees on Troyer and Carrizo refers only to those plants not declining. citranges.' Under our conditions, alemow and Trees on alemow began to decline 6 rough lemon, though lower in total years after planting, with typical symp- soluble solids, did not affect the fruit toms of xyloporosis. In 1975, sour quality badly. orange, Cleopatra mandarin, rough The different rate of canopy increase lemon, C. amblycarpa and C. taiwanica of trees on Volkamer lemon appears re- had no symptoms; C. volkameriana had lated to the onset of fruiting. This a few plants with mild, indefinite reac- rootstock appears to effectively over- tions, mostly pitting and pegging; come the low productivity of Clemen- citrumelo, Troyer and Carrizo citranges tine. From a phytopathological point of had bark indentations and gum deposits view, it is tolerant of concave gum-blind 234 Eighth IOCV Conference pocket, exocortis, scaly bark, tristeza, not been reported for cachexia-xylo- and probably to stubborn (no acorn porosis. In 1976, the original mother fruit or seed abortion in affected trees), trees had gumming at the bud union and but is intolerant of woody gall, crista- wood pitting on the trifoliate orange cortis, Phytophthora spp., and Phoma rootstocks, with no scaly butt. These tracheiphila Kanc. et Ghik., the cause of symptoms appear similar to those ma1 secco disease. Further observations described for gum pocket (Schwarz, are needed-to evaluate the long-term 1975) or gummy pitting (Fraser et al., reaction to cachexia-xyloporosis. 1975). On the basis of other rootstock Though results on alemow are not reactions, we believe that a strain of conclusive, because of the decline caused cachexia-xyloporosis might be respon- by cachexia-xyloporosis, this rootstock sible for the observed symptoms on the appears to be promising for Clementine trifoliate hybrids, but we cannot and could be useful in those areas where exclude the possibility that a second Volkamer lemon cannot be used. transmissible entity was present. This In our experience, rough lemon and also could be responsible for the heavy Cleopatra mandarin appear tolerant of gumming at the bud union observed on cachexia-xyloporosis, whereas in Cali- other rootstocks like Volkamer lemon. fornia and Brazil, they have shown a The results show the insufficiency of variable degree of susceptibility visual checks for cachexia-xyloporosis (Calavan and Christiansen, 1965; detection, even on a susceptible species Moreira, 1968). Sour orange, C. ambly- such as Clementine. Since many factors carpa, Avana mandarin, Cleopatra influence symptom expression, careful mandarin, and C. taiwanica behaved in indexing must be done when a sus- agreement with the literature. ceptible rootstock is to be used. Symptoms on trifoliate hybrids have TABLE 1 INFLUENCE OF ROOTSTOCK ON CUMULATIVE YIELD (1973-78) AND TREE GROWTH. Cumulative Canopy Circumference Difference Rootstock yield volume' of stock* of scion and stock? (kg/tree) (m3) (cm) (%) Vol kamer lemon Rough lemon Sour orange Citrus amblycarpa Citrumelo C.E.S. 1452 Avana mandarin Cleopatra mandarin C. taiwanica Troyer citrange Carrizo citrange Data on canopy volume and trunk circumference refer to the 9th growing year (1978). t Calculated as: scion circumf. - stock circumf. x 100. stock circum. $ Mean values followed by unlike letters differ at the 0.05 level of significance. 5 Mean values of the only three trees not showing decline at the 9th growing year. Data not subjected to statistical analyses.