Breeding yard long bean(Vigna unguiculata subsp.sesquipedalis (L.) Verdcourt) for anthracnose resistance through conventional and molecular marker analysis

Abstract

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.