PhD

The study entitled ―Breeding yard long bean (Vigna unguiculata subsp.
sesquipedalis (L.) Verdcourt) for anthracnose resistance through conventional and
molecular marker analysis‖ was carried out at the Department of Vegetable
Science, College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, during
2019-2022. The objective of the study was to identify molecular marker(s) linked
with anthracnose disease resistance in the F2 segregating population of yard long
bean, using bulk segregant analysis to enable marker assisted selection along with
conventional breeding.
The study was undertaken in six experiments. In experiment I, 50
genotypes of vegetable cowpea collected from different parts of India, including
the released varieties of SAUs and ICAR institutes were screened against the most
virulent isolate of Colletotricum gloeosporioides through artificial inoculation.
Among the 50 genotypes tested, VU 53, with semi-trailing growth habit was
found to be highly resistant with disease severity of 3.67 ± 0.13 %. Three
susceptible, high yielding long podded varieties viz., KAU Deepika, Vellayani
Jyothika and Githika, selected as female parents were crossed with VU 53, the
most resistant genotype as male parent for the development of three hybrids.
In experiment II, two crossing blocks were laid to produce the seeds of
three hybrids and their F2 progenies. The three hybrids were evaluated along with
the parents under replicated trial in the main field for trailing nature, yield and
quality in experiment III. Significant variation was noticed on mean performance
of yard long bean parents and hybrids for most of the characters studied. Earliest
flowering was observed in KAU Deepika x VU 53 (57.33 ± 0.57 days) and
delayed flowering in Githika x VU 53 (71.66 ± 1.15 days). Among the hybrids,
the highest pod length was recorded in KAU Deepika x VU 53 (24.50 ± 1.00 cm),
while the Vellayani Jyothika x VU 53 had the maximum pod girth (2.90 ± 0.10
cm). Maximum pod weight and pods per plant was recorded in KAU Deepika x
VU 53 (19.22 ± 0.58 g and 79.33 ± 0.59 respectively) among hybrids. The cross
Vellayani Jyothika x VU 53 (16.55 ± 0.20 g) exhibited maximum seed weight.
Among the three hybrids, KAU Deepika x VU 53 (1416.00 ± 126.09 g) recorded
the highest yield per plant and was on par with Githika x VU 53 (1343.33 ± 75.06
g). Among the hybrids, KAU Deepika x VU 53 (67.85 ± 0.96 days) was
significantly superior for days to harvest. The longest duration among hybrids was
observed in KAU Deepika x VU 53 (126.56 ± 0.37 days) and the shortest duration
was recorded in Vellayani Jyothika x VU 53 (121.31 ± 0.58 days).
High heritability and genetic advance was recorded for vine length, days to
first flowering, pod length, pod weight, pods per plant, yield per plant, yield per
plot, hundred seed weight and keeping quality. Yield per plant had significant
positive phenotypic and genotypic correlation with pod weight, followed by pods
per plant, length of terminal leaf, seeds per pod, pod length, crop duration,
keeping quality and days to harvest. Pods per plant could be considered as the
most important yield trait for enhancing the yield in yard long bean because of its
high, positive correlation and direct effect with yield per plant along with high
heritability and genetic advance.
In experiment IV, parents, three hybrids and F2 progenies were evaluated
for resistance to natural incidence of C. gloeosporioides in the main field, as
unreplicated trial and without any plant protection measures. All the three F1 were
found to be field tolerant. Out of 175 F2 plants of the cross KAU Deepika x VU
53, 164 plants were susceptible and 11 were resistant. In the case of Vellayani
Jyothika x VU 53, 175 plants were susceptible among the 187 individual F2
progenies observed. Similarly, in the cross Githika x VU 53, 188 plants were
susceptible while 12 plants were found to be symptomless.
The F2 progenies of the high yielding hybrid KAU Deepika x VU 53 were
evaluated for resistance to C. gloeosporioides through artificial inoculation in
experiment V. Out of 196 plants, 185 plants were found to be susceptible whereas
11 plants were resistant which could be utilized in marker assisted breeding
programme. The segregation for anthracnose resistance in F2 plants was in the
ratio 15:1 (185 susceptible plants out of 196), which suggests that the inheritance
of anthracnose resistance may be controlled by two recessive genes.
Bulked segregant analysis was done using the DNA from the resistant
parent, susceptible parent, resistant F2 bulk and susceptible F2 bulk in experiment
VI. Bulked segregant analysis with the SSR primer CLM0008 revealed a
polymorphic band at ≈ 300 bp which was appeared in the resistant parent and
bulk. Bulked segregant analysis with ISSR primer UBC 811 produced
polymorphic bands at ≈ 1100 bp, which were present in resistant parent and
resistant bulks. The identified markers linked with resistance were validated over
the resistant F2 lines obtained.