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