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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.