BSc - MSc (Int.)

The study entitled “Locating donors for genes for biotic stress resistance
in tomato through molecular marker assisted selection” was conducted at the
Department of Seed Science and Technology, College of Agriculture, Vellayani,
Thiruvananthapuram during 2020-2021. The primary objective of the study was
to identify donors for genes for resistance to different biotic stresses viz.,
Tomato Yellow Leaf Curl Virus (TYLCV), verticillium wilt, fusarium wilt, late
blight and root knot nematodes from tomato varieties and elite wild species
through marker assisted selection using gene specific markers.
The study was conducted in 30 tomato genotypes, collected from inside
and outside of Kerala which included wild species as well cultivated varieties.
The genotypes were screened for the presence of genes for resistance to various
biotic stress inducing diseases like Tomato Yellow Leaf Curl Virus (TYLCV),
verticillium wilt, fusarium wilt, late blight and root knot using tightly linked
gene specific SCAR and CAPS markers.
The genotypes resistant to Tomato Yellow Leaf Curl Virus (TYLCV) were
screened for the presence of gene Ty2 located on chromosome 11 using the
SCAR marker TG0302/TY2R1 which amplified a band of size 600 bp for
genotypes with Ty2/Ty2 alleles and 450 bp for susceptible genotypes. None of
the 30 genotypes screened for Ty2 gene were identified to consist the Ty2/Ty2
alleles. Another gene for resistance to TYLCV, ie, Ty3 located on chromosome 6,
was screened using the SCAR marker FLUW25, which amplified the genotypes
carrying Ty3/Ty3 alleles with a band of size 640 bp and 480 bp for genotypes
corresponding to ty3/ty3 alleles. Presence of Ty3 gene was not found in any of
the genotypes screened in the study.
Verticillium wilt resistance in genotypes was screened for the presence of
two closely linked genes, Ve1 and Ve2 of Ve locus. Ve1 specific CAPS marker
Ve1 XbaI, distinguished the genotypes of Ve1/Ve1 alleles with restriction
digested fragments of size 410bp and 332bp from the susceptible genotypes of
restriction digested fragments 410bp, 310bp and 22bp. Ve2 specific CAPS
marker V2LeO3F/V2LeO3R generated restriction digested products, 601 bp and
110
428 bp for Ve2/Ve2 alleles and undigested product of 1029bp for ve2/ve2 alleles.
Among the 30 genotypes screened in the study, IIHR 2374 and Kashi Vishesh
were identified for the presence of Ve1 and Ve2 genes and PNR 7 for Ve2 gene
alone.
The genotypes resistant to Fusarium wilt were screened for the presence of
the genes I3 located on chromosome 7 and I7 located on chromosome 8. The
gene I3 specific SCAR marker P743DF1/R1 amplified a band of size 1270bp for
genotypes with I3/I3 alleles and 1060 bp for genotypes with i3/i3 alleles. None
of the genotypes screened in the study were identified for the presence of I3
gene. The CAPS marker CAPS7774 specific to I7 gene generated restriction
digested fragments of size 612bp and 196bp for genotypes of I7/I7 alleles and
undigested fragment of 808 bp for susceptible genotypes. The genotypes IIHR
2205, IIHR 2374 and Vellayani Vijai were identified for the presence of I7/I7
alleles from the study.
The genotypes resistant to Late blight were screened for the presence of
the genes Ph3 located on chromosome 9 and Ph2 located on chromosome 10.
The SCAR marker Ph3-SCAR amplified the genotypes of Ph3/Ph3 alleles with a
band of size 176bp and 154 bp for the genotypes of ph3/ph3 alleles. Presence of
the gene Ph3 was identified in the genotypes Pusa Ruby, CA 22053, Hisar Lalit,
PKM-1 and Arka Vikas from the study. The CAPS marker dtG63 differentiated
the genotypes of Ph2/Ph2 alleles with a restriction digested fragment of band
size 245 bp from 221 bp of susceptible genotypes. In the study, the genotypes
Shakthi, Pusa Ruby, Nenmara local, CA 22053, Manulakshmi, IIHR 2204, PNR
7 and Solanum torvum were identified for the presence of Ph2/Ph2 alleles.
Resistance to Root knot in genotypes were screened for the presence of
gene Mi1.2 using the SCAR marker Mi23, which amplified a band of size 380
bp for Mi/Mi alleles and 430 bp for mi/mi alleles. From the study it was
confirmed that, none of the genotypes screened for the presence of Mi 1.2 gene
were resistant to root knot.
In accordance with the findings from the study, phenotypic analysis of
the genotypes identified as donors for genes for resistance can be carried out, in
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order to ensure the disease resistance in field conditions as well as the credibility
of the molecular markers used in the study. The genes for resistance to the
diseases studied, located in the 30 genotypes, screened from the study could
indicate the donors for tomato resistance breeding programs.