EVALUATION OF KENYAN DOLICHOS (Lablab purpureus L.) GENOTYPES FOR RESISTANCE TO LEGUME POD BORERS (Maruca vitrata and Helicoverpa armigera) USING MORPHOLOGICAL AND BIOCHEMICAL MARKERS

Abstract

Dolichos (lablab purpureus) is an important highly proteinous human food and animal feeds. It is grown in the tropics and subtropics of the world. Common production constraints of Dolichos lablab are low yields, poor cooking and flavor qualities and susceptibility to diseases and pests which lower the economic value of the crop. Pod borers (Maruca vitrata and Helicoverpa armigera) are major pests that affect the marketability and yield of lablab subsequently hindering its improvement. The objective of this study was to evaluate, eighteen Dolichos lablab genotypes for resistance to Maruca vitrata and Helicoverpa armigera in the field. The study was undertaken in 3 sites; University of Eldoret, KALRO Njoro and KALRO Kakamega. Biochemical and morphological parameters of pods were studied to determine whether they have any influence on resistance and susceptibility of lablab to M. vitrata and H. armigera. The pod damage (%) of each genotype was calculated and given a resistance rating of 1-5 score damage. Genotype G2, Bahati and W7 were resistant to M. vitrata in a scale of 1(0-10%, low infestation), Bahati and W7 were moderately resistant to H. armigera in a scale of 2 (11-30%, moderate infestation). Genotype LG1MoiP10 was susceptible to M. vitrata in a scale of 4 (51-70%, severe infestation) and genotype M5 was intermediate to H. armigera in a scale of 3 (3150%, high infestation). For Morphological parameters, there was positive significant correlation in H. armigera and M. vitrata pod damage with days to maturity, growth habit, and pod attachment. Pod length and pod fragrance were positively correlated to M. vitrata. However, negative correlation was detected in pod thickness, pod pubescence and raceme position to pod damage by both H. armigera and M. vitrata. Biochemical parameters showed positive significant correlation in carbohydrates and protein value to pod damage while negative significant correlation was observed in phenols content with pod damage and number of larvae of M. vitrata and H. armigera. The genotypes G2, Bahati and W7 had high phenol content in mg/g of 10.38, 9.8 and 7.9 and low protein of (7.3, 8.2, 6.9) % respectively while genotype LG1MoiP10 had low phenol content of 3.29 mg/g, and high proteins (10.2%). Genotype M5 had low phenol content of 4.07 mg/g, high sugar value of (1.02 mg/g) and 9.4% protein. KALRO Kakamega had the lowest infestation by both M. vitrata and H. armigera (6%) compared to University of Eldoret and KALRO Njoro which ranged between 27- 36%. High phenol content and some morphological features of genotype G2, Bahati and W7 were responsible for resistance to the pod borers and should be further evaluated for more mechanism of resistance to the pest and stability in several seasons and environments to get a source for resistance to aid in Dolichos lablab breeding.