STATUS OF SUGARCANE YELLOW LEAF VIRUS IN COMMERCIAL FIELDS AND RISK ASSESSMENT IN GUADELOUPE

STATUS OF SUGARCANE YELLOW LEAF VIRUS IN COMMERCIAL FIELDS AND RISK ASSESSMENT IN GUADELOUPE By C. EDON-JOCK 1,2, P. ROTT 3, J. VAILLANT 2, E. FERNANDEZ 3, J.-C. GIRARD 3 and J.-H. DAUGROIS 1 1 UPR 75 Amélioration génétique d espèces à multiplication végétative, CIRAD Département des Cultures annuelles, Station de Roujol, 97170 Petit-Bourg, Guadeloupe F.W.I. 2 Département de Mathématiques et Informatique, UFR Sciences Exactes et Naturelles, Campus de Fouillole, 97159 Pointe-à-Pitre, Guadeloupe F.W.I. 3 UMR AGRO.M-CIRAD-INRA Biologie et Génétique des Interactions Plante-Parasite, Campus International de Baillarguet, TA A-54/K, 34398 Montpellier Cedex 5 France Corresponding author: jean-heinrich.daugrois@cirad.fr KEYWORDS: Yellow Leaf Disease, Sugarcane, Melanaphis Sacchari, Epidemiology. Abstract Sugarcane yellow leaf virus (SCYLV), the causal agent of sugarcane yellow leaf disease, is present in Guadeloupe, but its incidence and distribution in commercial fields was unknown. Therefore, five sugarcane cultivars located in 48 plant cane fields in seven sugarcane growing areas in Guadeloupe were analysed for virus infection and populations of Melanaphis sacchari, the aphid vector of SCYLV. Twenty one of the 48 fields were also analysed in the first ratoon crop. Depending on the area of the field, 200 to 400 leaf samples per field were tested by tissue blot immunoassay to detect the virus, and presence of aphids was determined on 10% of sampled plants. In addition, virus incidence in five fields of second and third propagations of nursery stocks produced from tissue cultured plants was determined. Mean virus incidence in plant cane crops was 6.4%, and it ranged from 0% to 21% according to cultivar and geographical location. M. sacchari was widespread in all areas. Mean virus incidence increased to 11.2% in the first ratoon crop, and it increased in all cultivars except in cultivar B69566. Cultivar B69566 consistently had the lowest virus incidence, whereas virus incidence was consistently high in cultivar R579, even if cultivar B69566 was more colonised by aphids. In the second stage nursery fields, virus incidence ranged from 2.5% to 17.3%. Overall, virus incidence did not increase in the third stage nursery step that derived from the second stage nurseries. SCYLV genotype REU was found in all commercial fields, whereas genotypes BRA and CUB were found only in a few samples from five fields. In Guadeloupe, SCYLV appears to be spread by aphid vectors and infected cuttings. Presence of a major virus genotype suggested that this genotype was more adapted to the local environment, or that the two other genotypes were only recently introduced and have not spread yet on the island. Yield losses may occur in extending cultivars such as R579, as it was shown in Reunion Island. Because variation in virulence exists between SCYLV genotypes, disease impact may vary in Guadeloupe in the future. Introduction Symptoms of sugarcane yellow leaf were first reported in Hawaii in 1988, but this disease has since been found in locations all around the world. Yellow leaf caused severe yield losses in cultivar SP71-6163 in Brazil in the 1990s (Schenck, 2001). The most characteristic symptom is a 995

yellowing of the midrib of sugarcane leaves, but the midrib colouration can also turn pink. These symptoms are not specific to yellow leaf and can be caused by various biotic and abiotic stresses (Vega et al., 1997; Lockhart and Cronjé, 2000). The causal agent of yellow leaf was identified in 1996 (Lockhart et al., 1996), and it was named Sugarcane yellow leaf virus (SCYLV). SCYLV is a member of the genus Polerovirus of the family Luteoviridae. It is composed of a single positive RNA strand. The genome of SCYLV has been sequenced (Moonan et al., 2000), and different genotypes have been identified with specific reverse transcription-polymerase chain reaction (RT-PCR) primers (Abu Ahmad et al., 2006a). SCYLV is spread by infected stalk cuttings and by the aphid insect vectors Ceratovacuna lanigera, Melanaphis sacchari, Rhopalosiphum maidis, and R. rufiabdominalis (Schenck and Leher, 2000; Zhou et al., 2006). Viruses of the family Luteoviridae are generally transmitted to plants by aphids in a persistent, circulative and non replicative manner. The virus particles are absorbed with the sap when aphids feed on infected leaves, and they circulate then from the digestive tract to the saliva gland of the insect (Gray and Gildow, 2003). To date, only M. sacchari has been found in sugarcane fields in Guadeloupe. Presence of SCYLV in Guadeloupe was first reported in 1999 (Daugrois et al., 1999), but it was first identified in 1996 (Daugrois, unpublished data) in leaf samples obtained from CIRAD s germplasm collection. Since then, SCYLV was detected in Guadeloupe by tissue-blot immunoassay (TBIA) in breeding plots, in seed-cane plots, and in some commercial fields. Three SCYLV genotypes have been identified by RT-PCR in breeding plots on Guadeloupe (Abu Ahmad et al., 2006b). However, no data regarding incidence and distribution of SCYLV, and the genetic variants of this virus in commercial fields, have been reported. The aim of this study was to determine the level of SCYLV incidence in commercial fields in different cultivars and regions of Guadeloupe and to assess the impact of sugarcane yellow leaf on sugar production. Materials and methods Plant material and sampling procedure Forty eight fields, six to nine months old in plant cane crop, were selected to represent the major cultivars and geographical regions of Guadeloupe. Seed cane used to establish these fields originated from commercial plant cane fields. These commercial plants issued from multiple step field propagation (at least three) of disease-free seed cane that originated from tissue cultured plants. Five commercial cultivars (B5992, B69566, B80689, R570, and R579) were included in the study. These cultivars were grown in seven different geographical locations: North Basse-Terre (NBT), North East Basse-Terre (NEBT), East Basse-Terre (EBT), North Grande-Terre (NGT), West Grande-Terre (WGT), Central East Grande-Terre (CEGT) and Marie-Galante (MG) (Figure 1). Incidence of SCYLV in the plant cane crop was determined in three fields per cultivar and per location. Incidence of SCYLV in first ratoon crop was determined 4 to 6 months after harvest in 21 out of the 48 plots. All cultivars were present in at least two out of the seven locations. The number of leaves sampled to determine SCYLV incidence varied according to the size of the field: 200, 300 and 400 leaf samples (top visible dewlap leaf) were collected from <0.5 ha, 0.5 to 1 ha, and >1 ha fields, respectively. Each field was divided in five quadrats (one central quadrat and four outer quadrats), and samples were regularly taken from the five quadrats. Second nursery steps of cultivars B5992, R570, R579, established with seed cane from primary nurseries issued from disease free tissue-cultured plants, and commercial nurseries subsequently established with seed cane from the second nursery steps were used to determine incidence of SCYLV as described above, except that plots were not divided into quadrats. 996

NBT = North Basse-Terre; NEBT = North East Basse-Terre; EBT = East Basse-Terre; NGT = North Grande-Terre; WGT = West Grande- Terre; CEGT = Central East Grande-Terre; and MG = Marie-Galante. Fig. 1 Map of the different sugarcane growing areas in Guadeloupe. Determination of aphid populations Presence of M. sacchari was assessed visually on leaves from 10% of sampled plants. A plant was considered as colonised by M. sacchari when at least one nymph, one winged aphid, or one apterous aphid was observed on a leaf. Detection of SCYLV by TBIA SCYLV was detected in leaf samples by TBIA as described by Schenck et al. (1997) with a few modifications. Briefly, midrib sections of leaves were blotted for two seconds on Schleicher&Schuell OPTICRAN BAS 85 0.45 µm reinforced nitrocellulose membranes. Membranes were processed with bovine albumin (SIGMA) for 30 min and then with anti-scylv AS-R2 IgG for 90 minutes. Membranes were then processed with anti-rabbit IgG alkaline phosphatase conjugate antibody produced in goat (SIGMA) for 75 minutes, and FAST TM BCIP/NBT tablets were used to identify infected phloem tissue. Positive reactions (blue colouration) were determined using a stereomicroscope (x 6.3) after wetting the nitrocellulose membranes with distilled water. Identification of SCYLV genotypes Leaves from 11 infected plots were stored at 20 C for identification of SCYLV genotypes by RT-PCR. Total RNA was extracted from one or two groups of 10 bulked leaves using the RNeasy plant mini kit (Qiagen), according to the manufacturer s protocol. SCYLV genotypes BRA- PER, CUB and REU were identified with specific RT-PCR primers as described by Abu Ahmad et al. (2006b). When more than one genotype was found in the bulked leaves, a new RNA extraction was performed with each leaf of the bulk, and the SCYLV genotype was determined as described above. 997

Statistical analyses Virus and aphid incidences were compared after angular transformation [arcsin(sqrt proportion)] of field data with SAS 8.2 GLM procedure (SAS Institute Inc., Cary, USA). Results Incidence of SCYLV and aphid populations in commercial fields in Guadeloupe SCYLV was detected in all five sugarcane cultivars and in all seven geographical locations tested in this study (Table 1). No significant differences were found between the origin of samples within a field: incidence was similar whatever the sampled quadrat (centre or border quadrats) (data not shown). Additionally, in a given geographical location, cultivar infection by SCYLV was similar between the three sampled fields of a sugarcane cultivar, with the exception of R579 in CEGT where SCYLV infection varied from 8% to 35%. However, differences in SCYLV infection between cultivars in a given location were identified in at least three locations, CEGT, EBT and NBT (Table 1). Differences between locations also varied according to cultivar. Highest SCYLV infections were observed for R579 in CEGT, WGT and NBT, for cultivar B80689 in CEGT and for cultivar B5992 in EBT (Table 1). On the other hand, no significant variation of plant colonisation by aphids was found between locations and sugarcane cultivars. Table 1 Progress of incidence of SCYLV and aphid distribution in two consecutive crops (plant cane and first ratoon) in commercial fields. Geographical Location 1 % infected plants % plants with aphids Sugarcane cultivar Plant cane 2 1 st ratoon 3 Plant cane 2 1 st ratoon 3 SCYLV genotype (% of leaves infected by this genotype) B5992 CEGT 2.4 cd 9.3 (1.1) 45.0 ab 77.5 (10.6) REU B5992 WGT 6.6 bc 46.6 ab REU (100%) + CUB (10%) B5992 EBT 16.3 ab 43.3 ab REU B69566 MG 0.0 d 0.0 (0) 50.0 ab B69566 EBT 0.3 d 0.5 (0) 80.8 a 100.0 (0) B80689 CEGT 17.8 a 28.8 (5.3) 37.7 ab 43.4 (37.7) REU B80689 NGT 0.9 cd 6.0 5.4 b 13.3 B80689 MG 0.2 d 13.3 ab R570 WGT 7.3 bc 4.2 b R570 MG 0.0 d 0.3 (0.3) 36.7 ab R570 NEBT 0.5 d 2.0 60.6 ab 43.3 REU R570 NBT 1.3 cd 6.7 55.8 ab 90.0 REU R579 CEGT 21.1 a 23.7 9.2 b 3.3 REU + CUB R579 WGT 15.2 ab 17.4 (2.9) 11.0 ab 30.3 (15.2) REU (90%) + CUB (10%) R579 NEBT 1.9 cd 4.0 (1.4) 32.2 ab 56.7 (28.3) REU (86%) + BRA-PER (14%) R579 NBT 11.3 ab 23.5 42.2 ab 57.5 REU (86%) + BRA-PER (14%) 1 NBT = North Basse-Terre; NEBT = North East Basse-Terre; EBT = East Basse-Terre; NGT = North Grande-Terre; WGT = West Grande-Terre; CEGT = Central East Grande-Terre; and MG = Marie-Galante; 2 mean of three plots per cultivar and location, values followed by the same letter are not different at P = 5% (Student -Newman-Keuls test after angular transformation of data); 3 mean of two-three plots per cultivar and location, except for B80689 NGT, R570 NEBT and NBT, and R579 NBT for which only one plot was sampled, standard errors are given in brackets, when available. In plant cane crop, incidence of SCYLV in single fields ranged from 0 (B69566 in MG and EBT, B80689 in MG, and R570 in MG) to 35% (R579 in CEGT). Virus incidence was the lowest 998

for all sugarcane cultivars in Marie-Galante (MG). SCYLV incidence was nil or very low in fields of cultivar B69566 (0 0.5%) in plant cane and in first ratoon crops in the two sampled areas, although the percentage of plants of this cultivar colonised by aphids in each plot ranged from 35 to 100%. Incidence of SCYLV in single fields of the other four cultivars varied in plant cane according to the field and the geographical location: from 2 to 20% in B5992, from 0 to 22% in B80689, from 0 to 15% in R570, and from 2 to 35% in R579. In all fields, the percentage of plants infected by SCYLV was higher in cultivars B5992, B80689, R570, and R579 in first ratoon crop than in plant crop. The increase in incidence of SCYLV between the two crops ranged from one to six times. Overall, the mean percentage of infected plants increased in the commercial fields by 50% between plant cane crop and first ratoon crop. Because only few replications were available to analyse disease progress from plant cane to ratoon cane crop, no clear difference in disease progress between cultivars or between regions was identified, even if the overall increase between the two crop cycles was significant. M. sacchari was found on leaves of all sugarcane cultivars and in all geographical locations. Percentage of plants colonised by M. sacchari varied between fields in plant cane of all cultivars: from 45 to 77.5% for cultivar B5992, from 50 to 100% for cultivar B69566, from 5.4 to 43.4% for cultivar B80689, from 4.2 to 90% for cultivar R570, and from 9.2 to 57.5% for cultivar R579. Geographical distribution of SCYLV genotypes in Guadeloupe Most sugarcane leaves were infected by a single genotype of SCYLV (Table 1). Genotype REU was detected in all cultivars and in all geographical locations. Genotype BRA-PER was only detected in cultivar R579 in NBT and NEBT, and genotype CUB was detected only in cultivar B5992 in WGT, and in cultivar R579 in CEGT and WGT. Even if two genotypes occurred in the same plot, genotype REU was always the most frequent (86 to 100% of leaves were infected by this genotype). A mixture of genotypes REU and CUB was found only in one leaf of cultivar B5992. Incidence of SCYLV in seed cane nurseries in Guadeloupe Incidence of SCYLV varied between the five seed cane nurseries included in the study. As in the commercial fields described above, cultivar R570 had a significantly lower incidence of SCYLV than cultivars R579 and B5992 when the two nursery steps were considered (Table 2). Table 2 Progress of SCYLV incidence from secondary to commercial nurseries. Geographical % SCYLV infected plants in % SCYLV infected plants Cultivar location 1 secondary nurseries 2 commercial nurseries 2 B5992 CEGT 17.3 (1) 13(1) R570 NGT 7.0 (1) 3 (1) R570 NBT 2.5 (1) 0.5 (1) R579 NBT 8.0 (1) 10.5 (3) R579 NGT 14.0 (1) 25.5 (1) 1 NBT = North Basse-Terre; NGT = North Grande-Terre; and CEGT = Central East Grande-Terre. 2 In brackets: number of fields sampled. Overall, mean infection rate of the two steps was 9.8% and 10.5%, and these two rates were not different. Even if no interaction between cultivars and nursery steps was found, we observed that the percentage of infection by SCYLV of cultivars R570 and B5992 in commercial nurseries (established with cuttings from secondary nurseries) decreased from one step to the other. In contrast, incidence of SCYLV increased in commercial nurseries of cultivar R579 (Table 2). 999

Additionally, for cultivars B5992, R570 and R579, virus incidence in commercial nurseries was similar to mean virus incidence in plant cane of commercial fields of these cultivars (see above). Discussion In this study, aphid populations observed on sugarcane plants varied a lot between fields and sugarcane cultivars, and no relationship between these populations and incidence of SCYLV could be established. Interestingly, the fields of cultivars R570 and R579 that were the most infected by SCYLV had the lowest aphid incidence in plant cane crop. Aphid populations are regulated by numerous predators, and a single enumeration of these populations during a crop cycle is not sufficient to draw conclusions on the influence of the populations of the aphids on disease spread. Incidence of SCYLV varied between sugarcane cultivars and geographical locations. However, because the five cultivars were not represented in all areas, the interpretation of the differences between cultivars and locations is difficult. Some tentative observations on variation between cultivars and location are:! In contrast to the other geographical locations, incidence of SCYLV in the Marie- Galante growing area was nil or very low in the three sampled sugarcane cultivars (B69566, B80689, and R570).! Incidence of SCYLV was always nil or very low in cultivar B69566, whatever the crop cycle and the sampling location, even if this cultivar supported the highest aphid incidence.! Cultivar R579 is the most infected by SCYLV. The very low incidence of SCYLV in Marie-Galante, one of the islands of the Guadeloupean archipelago, suggested that SCYLV was introduced only recently into this geographical location or that the M. sacchari populations on this island are less efficient in transmission of SCYLV than the aphid populations existing in the other parts of Guadeloupe. Further investigations will be necessary to understand the low rates of SCYLV in Marie-Galante. In Guadeloupe, the percentages of SCYLV infected plants in cultivars R570 and R579 were quite different from those observed in these cultivars grown on Réunion Island (Rassaby et al., 2004). On Réunion Island, SCYLV incidence ranged from 21 to 92% in cultivar R579 and from 16 to 96% in cultivar R570. Similarly, incidence of SCYLV in cultivar B5992 in Martinique ranged from 0 to 90% (Daugrois et al., 1999), showing the possibility of high infection rates in this other location of the West Indies (when compared to the highest value of 20% observed in Guadeloupe). Differences in infection capacity or in virulence of virus strains exist (Abu Ahmad et al., 2007) and this could be a reason explaining the variation between the three tropical French islands. Another reason could be vector variation or aphid vector adaptation to local environmental conditions. In addition, only the Guadeloupean industry has a nursery scheme that starts with healthy planting material. This planting scheme may keep virus infection at a lower level than fields established by other means, as it was described in Florida (Flynn et al., 2005). In Guadeloupe, primary field contamination can result from infected seed cane or from viruliferous vectors. However, absence of differences in virus incidence between sampled field quadrats suggests that measured incidences in the plant crop were not only due to aphids but also to infected seed cane. Previous studies performed in Guadeloupe showed that plants at the edges of a SCYLV-free diseased field are the most colonised by winged aphids, and are the most infected by SCYLV (Edon et al., 2006). However, the incidence of SCYLV increased by an average of 50% between the plant and ratoon crops in the study which can only be due to virus spread by the aphid vector. 1000

Reduction of virus incidence between two nursery steps in cultivars B5992 and R570 suggested occurrence of plant resistance (tolerance) restraining multiplication of SCYLV in the new plant growing after planting. However, it cannot be excluded that this variation was caused by irregular patterns of virus infection and because only 40 to 60% of the fields are used from one nursery step to the next. Based on results obtained herein, it is believed that yellow leaf has some impact at the present time on sugarcane production in Guadeloupe. In experimental trials, cultivar R579 showed 19% yield reduction in first ratoon crop when it was 100% infected by SCYLV (Rassaby et al., 2003). Although cultivar R579 is infected at a lower level in Guadeloupe, it is the most infected cultivar. Therefore, one can expect that it also suffers losses in Guadeloupe, or that it will suffer significant losses in the near future because it is one of the most extended cultivars at present time on this island. R570 is a tolerant cultivar and no yield losses have been reported for this cultivar so far. More data are needed for cultivar B80689 which is the most planted cultivar today in NGT. However, impact of yellow leaf on this cultivar is expected to be low because, when stalks of B80689 are infected by SCYLV, the virus is found in only a few vascular bundles (data not shown). This situation may change in the future with modifications of the cultivar status of the host plant, but also with evolution of the causal agent of the disease. Three genotypes of SCYLV have been identified in Guadeloupe, but genotype REU is the predominant genotype at the present time. Genotype REU may be more adapted to the local environment, or the two other genotypes have been only recently introduced and have not yet spread on the island. Further studies of genotype distribution and their pathogenicity in Guadeloupe will be necessary because variation in infection capacity and in virulence has recently been shown to occur between SCYLV isolates (Abu Ahmad et al., 2007). Acknowledgment Many thanks to Pr B.E.L. Lockhart for providing us with SCYLV antibodies. REFERENCES Abu Ahmad, Y., Rassaby, L., Royer, M., Borg, Z., Braithwaite, K.S., Mirkov, E., Irey, M.S. Perrier, X., Smith, G.R. and Rott, P. (2006a). Yellow leaf of sugarcane is caused by at least three different genotypes of Sugarcane yellow leaf virus, one of which predominates on the Island of Réunion. Arch. Virol., 151: 1355 1371. Abu Ahmad, Y., Royer, M., Daugrois, J.H., Costet, L., Lett, J.M., Victoria, J.I., Girard, J.C. and Rott, P. (2006b). Geographical distribution of four Sugarcane yellow leaf genotypes. Plant Dis., 90: 1156 1160. Abu Ahmad, Y., Costet, L., Daugrois, J.H., Nibouche, S., Letourmy, P., Girard, J.C. and Rott, P. (2007). Variation in infection capacity and in virulence exists between genotypes of Sugarcane yellow leaf virus. Plant Dis., 91: 253 259. Daugrois J.H., Jean-Baptiste I., Lockhart B.E.L., Irey S., Chatenet M. and Rott P. (1999). First report of Sugarcane yellow leaf virus in the French West Indies. Plant Disease, 83: 588. Edon, C., Vaillant, J., Sauvion, N. and Daugrois, J.H. (2006). Spatiotemporal evolution of plant infection by SCYLV in a disease free plot. Toward modelling virus spread in tropical conditions. VIIIth ISSCT Pathology Workshop Petit-Bourg, Guadeloupe (FWI), 23 27 January 2006. Flynn, J., Powell, G., Perdomo, R., Montes, G., Quebedeaux, K. and Comstock, J.C. (2005). Comparison of sugarcane disease incidence and yield of field-run, heat treated and tissueculture based seedcane. J. Amer. Soc. Sugar Cane Technol., 25: 88 100. Gray, S. and Gildow, F. E. (2003). Luteovirus-aphids interaction. Annu. Rev. Phytopathol., 41: 539 66. 1001

Lockhart, B.E.L. and Cronjé, C.P.R. (2000). Yellow leaf syndrome. In: A guide to sugarcane diseases. P. Rott, R.A. Bailey, J.C. Comstock, B.J. Croft and A.S. Saumtally (Eds). La Librairie du Cirad, Montpellier, France pp. 291 295. Lockhart, B.E.L., Irey, M.S. and Comstock, J.C. (1996). Sugarcane bacilliform virus, sugarcane mild mosaic virus and sugarcane yellow leaf syndrome. Page 134 in: Sugarcane gerplasm conservation and exchange, ACIAR Proceedings No 67. Croft, B.J., Piggin, C.M., Wallis, E.S., and Hogarth, D.M. (eds). Moonan, F., Molina, J. and Mirkov, T.E. (2000). Sugarcane yellow leaf virus: an emerging virus that has evolved by recombination between luteoviral and poleroviral ancestors. Virology, 269: 156 171. Schenck, S. (2001). Sugarcane yellow leaf syndrome: history and current concepts. In: Sugarcane pathology. Vol. II: Virus and Phytoplasma Diseases. G.P. Rao, R.E. Ford, M. Tosic and D.S. Teakle (Eds). Science Publishers Inc, Enfield, USA pp. 25 35. Schenck, S., Hu, J.S. and Lockhart, B.E.L. (1997). Use of a tissue blot immunoassay to determine the distribution of Sugarcane yellow leaf virus in Hawaii. Sugar Cane, 4: 5 8. Schenck, S. and Lehrer, A.T. (2000). Factors affecting the transmission of Sugarcane yellow leaf virus. Plant Dis., 84: 1085 1088. Rassaby, L., Girard, J.C., Lemaire, O., Costet, L., Irey, M.S., Kodja, H. and Rott, P. (2004). Spread of Sugarcane Yellow leaf virus in sugarcane plants and fields on the island of Réunion. Plant Pathol., 53: 117 125. Rassaby, L., Girard, J.C., Letourmy, P., Chaume, J., Irey, M.S., Lockhart, B.E.L., Kodja, H. and Rott, P. (2003). Impact of Sugarcane yellow leaf virus on sugarcane yield and juice quality in Réunion Island. European J. Plant Pathol., 109: 459 466, 2003. Vega, J., Scagliusi, S.M.M. and Ulian, E. C. (1997). Sugarcane yellow leaf disease in Brazil: Evidence of association with a luteovirus. Plant Dis., 81: 21 26. Zhou, G.H., Li, J.G., Xu, D.L., Shen, W.K. and Deng, H.H. (2006). Occurrence of Sugarcane yellow leaf virus in South China and its transmission by the sugarcane-colonising aphid, Ceratovacuna lanigera. Scientia Agricultura Sinica, 39: 2023 2027. STATUT ET ÉVALUATION DES RISQUES LIÉS AU SUGARCANE YELLOW LEAF VIRUS (SCYLV) DANS LES CHAMPS COMMERCIAUX EN GUADELOUPE Par C. EDON-JOCK 1,2, P. ROTT 3, J. VAILLANT 2, E. FERNANDEZ 3, J.-C. GIRARD 3 et J.-H. DAUGROIS 1 1 UPR 75 Amélioration génétique d espèces à multiplication végétative, CIRAD Département des Cultures annuelles, Station de Roujol, 97170 Petit-Bourg, Guadeloupe F.W.I. 2 Département de Mathématiques et Informatique, UFR Sciences Exactes et Naturelles, Campus de Fouillole, 97159 Pointe-à-Pitre, Guadeloupe F.W.I. 3 UMR AGRO.M-CIRAD-INRA Biologie et Génétique des Interactions Plante-Parasite, Campus International de Baillarguet, TA A-54/K, 34398 Montpellier Cedex 5 France. Email: jean-heinrich.daugrois@cirad.fr MOTS CLÉS : La Maladie de la Feuille Jaune, Canne a Sucre, Melanaphis Sacchari, Épidémiologie. Résumé LE SUGARCANE yellow leaf virus (SCYLV) est l agent causal de la maladie de la feuille jaune de la canne à sucre. Cette maladie est présente en Guadeloupe, mais son incidence et sa distribution dans les champs commerciaux étaient inconnues. Par conséquent, le taux d infection du virus et la 1002

population du puceron Melanaphis sacchari, vecteur du SCYLV, ont été évalués dans la canne vierge de cinq variétés cultivées dans 48 champs dans sept régions cannières de la Guadeloupe. Vingt et un de ces 48 champs ont également été analysés en première repousse. Selon les régions, 200 à 400 échantillons de feuilles par champ ont été examinés par la technique TBIA (immunoempreintes sur membrane de nitrocellulose) pour détecter le virus alors que la présence des pucerons a été déterminée sur 10 % des plantes échantillonnées. Par ailleurs, l incidence du virus dans cinq champs plantés à partir des boutures provenant du deuxième et troisième propagations d une pépinière de base issue de la culture in vitro, a été déterminée. L incidence moyenne de virus dans la canne vierge situait de 6,4% et variait entre 0 % et 21% selon la variété et la zone géographique. M. sacchari était répandu dans tous les secteurs. En première repousse, la moyenne d infection a augmenté à 11,2% dans toutes les variétés, sauf la B69566. Le taux d infection sur cette variété était inférieur à la moyenne même dans des cas de fort taux d infestations par les pucerons, à l opposé de la variété R579 ou l incidence du virus était toujours élevée. Dans les pépinières au deuxième stade, l incidence du virus s étendait de 2,5 % à 17,3%. En général, une augmentation de l incidence du virus dans les variétés de la pépinière au troisième stade, issu du deuxième stade, n a pas été observée. Le génotype REU de SCYLV a été observé dans tous les champs commerciaux, tandis que les génotypes BRA et CUB n étaient présents que dans quelques échantillons provenant de cinq champs. En Guadeloupe, la transmission du SCYLV se fait par des pucerons vecteurs et des boutures infectées. La forte présence du génotype REU indique que ce dernier s adapte mieux à l environnement local alors que l introduction des autres génotypes dans l île est récente, et qu ils n ont pas encore été disséminés. Des pertes de rendement peuvent se produire si la surface cultivée des variétés telle la R579 est étendue comme c est le cas à l île de la Réunion. À l avenir, l impact de la maladie pourrait changer de part la variabilité de la virulence des différents génotypes présents. SITUACIÓN DEL SUGARCANE YELLOW LEAF VIRUS EN CAMPOS COMERCIALES Y COMENTAROS SOBRE SU PRESENCIA EN GUADALUPE Por C. EDON-JOCK 1,2, P. ROTT 3, J. VAILLANT 2, E. FERNANDEZ 3, J.-C. GIRARD 3 y J.-H. DAUGROIS 1 1 UPR 75 Amélioration génétique d espèces à multiplication végétative, CIRAD Département des Cultures annuelles, Station de Roujol, 97170 Petit-Bourg, Guadeloupe F.W.I. 2 Département de Mathématiques et Informatique, UFR Sciences Exactes et Naturelles, Campus de Fouillole, 97159 Pointe-à-Pitre, Guadeloupe F.W.I. 3 UMR AGRO.M-CIRAD-INRA Biologie et Génétique des Interactions Plante-Parasite, Campus International de Baillarguet, TA A-54/K, 34398 Montpellier Cedex 5 France jean-heinrich.daugrois@cirad.fr PALABRAS CLAVES: Hoja Amarilla, Caña de Azúcar, Melanaphis Sacchari, Epidemiología. Resumen EL SUGARCANE yellow leaf virus (SCYLV), agente causal de la enfermedad hoja amarilla, se encuentra presente en Guadalupe, pero su incidencia y distribución en campos comerciales era desconocida. Por tanto, se sembraron cinco variedades en 48 campos en siete zonas de cultivo en Guadalupe donde se evaluaron por infección del virus y determinaron poblaciones de Melanaphis sacchari, el afido vector del SCYLV. En 21 de los 48 campos se efectuaron igualmente evaluaciones en la primera soca. Dependiendo del área en el campo, entre 200 a 400 muestras de hojas por campo se detectó la presencia del virus mediante el método de inmunoensayo de tejido manchado, así como la presencia de los afidos en el 10% de las plantas muestreadas. Además, se 1003

determinó la incidencia del virus en cinco campos de segunda y tercera propagación de semilleros provenientes de cultivo in vitro. El promedio de incidencia del virus en las plantillas fue de 6.4%, el cual varió entre 0% hasta 21%, de acuerdo con la variedad y la localidad. M. sacchari se encontró ampliamente distribuido en todas las áreas. El promedio de incidencia del virus se incrementó a 11.2% en la primera soca, y aumentó en todos las variedades excepto en B69566. La variedad B69566 consistentemente tuvo la menor incidencia del virus, mientras que la mayor incidencia del virus ocurrió consistentemente en R579, a pesar de que B69566 fue la más colonizada por los afidos. En los campos de semilleros de segundo estado, la incidencia del virus varió entre 2.5% hasta 7.3%. En general, la incidencia del virus no aumento en los semilleros en el tercer estado y que se habían derivado del segundo estado. El genotipo REU del SCYLV se encontró en todos los campos comerciales mientras que los genotipos BRA y CUB solamente se encontraron en cinco muestras en cinco campos. En Guadalupe, el SCYLV se encuentra ampliamente distribuido por los afidos así como por el empleo de material de siembra infectado. La presencia mayoritaria de un genotipo del virus sugiere que este genotipo se encuentra más adaptado a las condiciones ambientales locales o que los otros dos genotipos fueron introducidos recientemente y que no se han distribuido ampliamente en la isla. Pérdidas en la producción ocurren en variedades ampliamente cultivadas como R579, tal como se demostró en la Isla de Reunión. Debido a la existencia de variación en la virulencia entre los genotipos de SCYLV, el impacto de la enfermedad en Guadalupe puede cambiar en un futuro. 1004