Evaluation of Cucurbit Germplasms for Resistance to Cucurbit Yellow Stunting Disorder Virus CYSDV

Résumé du livre

Cucurbits are among the major vegetables crops grown in the world. All commercial cucurbit varieties are susceptible to Cucurbit yellow stunting disord er virus (CYSDV) (genus Crinivirus, family Closteroviridae), a whitefly- transmitted viru s that was reported to cause about 50 % yield loss in Lebanon and several Mediterranean countries. Development of resistant varieties would constitute a major advance i n the management of this yellowing disease. A total of 124 cucumber germplasms or accessions were evaluated for their resistance against CYSDV, under controlled inoculation conditions, during three growing seasons. Seven promising accessions were identified, which showed milder symptoms expressed as delayed expression of symptoms and lower percentage of infected plants as compared to the susceptible varieties. None of the accessions tested was immune or highly resistant to CYSDV infection. The relative CYSDV concentration as determined by three serological t ests was highest in middle leaves, lowest in upper leaves and intermediate in the bot tom leaves. Virus concentrations, in middle leaves of most tolerant accessions, were lower than those of susceptible accessions. Virus movement was studied in two tolerant and one susceptible cucumber accession for a period of three weeks after inoculation . The two tolerant accessions apparently have two different resistance mechanisms; the major effect in one accession is through retardation of virus movement while in the ot her it is through reduction of virus replication. Therefore, pooling genes from the two ac cessions may lead to a higher level of resistance. Among the serological techniques used, Tissue blot- immunoassay (TBIA) was very sensitive and most suited for a fast detection in root, crown and apex tissues, while indirect ELISA is quantitative and allows CY SDV detection in 100 micro g of infected leaf tissue. However, it is less sensitive than dot (DBIA), which detects the virus in 100 ng of infected tissue. During blot-immuno assay the course of this study two techniques for diagnosis of CYSDV were developed, DBIA using chemiluminescent detection system and immuno- capture- reverse transcripti on polymerase chain reaction (IC- RT- PCR). DBIA was optimized to quantify CYSDV in infected tissue with similar sensitivity to nucleic acid hybridization; the most ...