Field screening of Lablab niger germplasm for 3 years revealed that two cultivars, PLS-24 and PLS-16-1 consistently displayed resistance to pod borer, Adisura atkinsoni Moore larval boring and egg laying. Observations at different intervals of plant growth permitted a comprehensive evaluation of cultivar response to the pod borer complex.
Preliminary tests indicated pod colour, pubescence and fragrance to be associated with the borer resistance in L. niger. However, none of the characters per se imparted resistance or susceptibility, partly or fully. Cumulative effect of the aforesaid characters appeared to impart borer resistance to Adisura. Pod wall did not form a physical barrier to Adisura larval entry. Positive relationship existed with amount of chloroplast and susceptibility, and starch grains and resistance in four cultivars studied for anatomical details. Anthocyanin pigment in the pod wall was associated with resistance in L. niger to Adisura.
Based on field and laboratory evaluations of Lablab niger cultivars to the bean aphid, Aphis craccivora damage, the “local” and H-2, rated as highly susceptible to borers, reacted as resistant and PLS-24 and PLS-16-1 rated as resistant to borers reacted as highly susceptible to the aphid attack. It is therefore imperative that promising Lablab niger cultivars be evaluated for resistance to both the sucking and chewing insect pests.
Under artificial infestation conditions the resistant cultivars exhibited susceptibility to larval boring by Adisura, but confirmed resistance to ovipositional response. Non-preference for oviposition was the most important factor in imparting resistance to the borer damage in L. niger. Factors inducing host preference for larva and for adult were different and independent. PLS-24 and PLS-16-1 contained significant degrees of antibiosis as demonstrated by reduced larval survival, larval and pupal weights, prolonged larval duration and altered sex ratio.
Cultivars that sustained low levels of seed yield loss at high infestation levels were identified as tolerant. MS-9579 and IC-661-1 exhibited low degree of tolerance. Resistant cultivars proved non-tolerant even to slight infestations (ca 10%) received under field conditions.