Evaluation of tomato genotypes for tomato leaf curl virus (tolcv) resistance

Abstract

Tomato (Solanum lycopersicum, 2n=24) is a widely grown vegetable in India, exhibiting wide variability for plant traits. Worldwide, tomatoes are susceptible to many diseases like damping off, bacterial wilt, early blight, leaf curl virus disease, leaf spot etc. Among them, tomato leaf curl virus disease (ToLCD), caused by whitefly-transmitted begomoviruses is more severe and it can cause up to 100 per cent yield loss. Although, the cultivated tomatoes are susceptible to Tomato leaf curl virus (ToLCV), different levels of resistance were identified in wild relatives of tomato. Utilization of these natural resources will aid ToLCV management through crop improvement. The present study entitled ‘Evaluation of tomato genotypes for Tomato Leaf Curl Virus (ToLCV) resistance’ was carried out at Department of Plant Breeding and Genetics, College of Agriculture, Vellanikkara during 2019-21. The experimental material consisted of 27 tomato genotypes including eight NBPGR (National Bureau of Plant Genetic Resources) accessions, five breeding lines from the World Vegetable Centre, Taiwan, nine commercial hybrids, four KAU varieties and one local collection from Idukki. All 27 genotypes were screened for ToLCV resistance under natural conditions in randomized block design with two replications during January- May 2021. The disease response was assessed after 30 days of transplanting by adopting the score chart suggested by Banerjee and Kalloo (1987). Among the genotypes tested, Ansal was found to be highly resistant, Kaustubh, EC 519806 (S. pimpinellifolium), Arka Rakshak and local collection (Idukki) were identified as resistant genotypes. The genotypes found to be highly resistant and resistant were subjected to whitefly mediated artificial inoculation. The resistant and highly resistant genotypes remained asymptomatic, whereas the susceptible genotypes (Anagha and Manuprabha) exhibited ToLCV symptoms after artificial inoculation. The morphological growth characters such as plant height, number of primary branches per plant, days to flowering and trichome density differed significantly among the genotypes evaluated in the present study. Density of both glandular and non-glandular trichomes on both abaxial as well as adaxial leaf surfaces were recorded. Correlation analysis between trichome density, and disease severity index and per cent disease incidence showed that glandular trichome density on abaxial and adaxial surfaces of leaf was significantly and negatively correlated with per cent disease incidence and disease severity index. However, the negative correlation was stronger between the abaxial glandular trichome density and ToLCV incidence. The glandular trichome density of the resistant genotypes identified in the field screening was found to be high. Non-glandular trichome density on abaxial and adaxial side of the leaf was significantly and positively correlated with per cent disease incidence and disease severity index. Screening for the reported Ty genes using the primers TG178 (SCAR), SCAR-2, P6-25, TY-1/3_K (SCAR), 18IY13 (Indel), SLM 4-34 (SSR) and SLM 10-46(SSR)linked to the ToLCV resistance genes Ty-1, Ty-2, Ty-3, Ty-1/3, Ty-4, Ty-5 and Ty-6 respectively was done in the present study. Seventeen genotypes produced amplicon using TG178 and ten genotypes produced amplicons using SLM4-34. However, there was no pattern in the amplification of the markers TG178 and SLM 4-34. Seven genotypes recorded the presence of Ty-1/3 in homozygous condition (AVTO 1727, AVTO 1726, AVTO 1706, AVTO 1707, EC 538153, EC 620428 and EC 620486) and seven genotypes in heterozygous condition (Ansal, Virang, Aryaman, Durg, Raymond, Abhiraj, Pranay). Four genotypes each carried the resistant allele for Ty-2 in the homozygous state (AVTO 1726, AVTO 1706, AVTO 1707 and AVTO 0922) and in the heterozygous state (AVTO 1727, Ansal, Arka Rakshak and Aryaman). Resistant allele for Ty-3 was present in the genotype AVTO 1726 and AVTO 1707 in homozygous state. Whereas, it was in heterozygous condition in AVTO 1727. None of the genotypes evaluated in the present study revealed the presence of amplicons corresponding to resistant allele of Ty-4 and Ty-6. The resistant genotypes identified in the present study viz., Ansal, Kaustubh, Arka Rakshak, EC 519806 and local collection (Idukki) can be used for resistance breeding. The present study revealed that trichome density can be used as a reliable morphological marker for ToLCV resistance. The donors for Ty-2, Ty-3 and Ty-1/3 identified in this study can be used for gene pyramiding in future breeding programmes.