Screening for Resistance Mechanisms in Cowpea Genotypes on <i>Alectra vogelii</i>

Abstract

Parasitic angiosperm Alectra vogelii Benth is a growing problem in Malawi, particularly with current emphasis on legumes. Therefore, two studies were set in order to understand the possible mechanisms of resistance in cowpea genotypes on their reaction to the parasitic weed. In the first experiment, Mkanakaufiti, IT99K-7-21-2-2XIT82E-16, Sudan 1 and IT82E-16 were grown in Alectra infested and non-infested pots. The experiment (2*4 factorial treatment combination) was arranged in an RCBD and replicated eight times. The second experiment, involved Petri-dish techniques where 4 genotype roots were assessed on their ability to stimulate the germination of A. vogelii as a proxy for germination stimulant production. The experiment was arranged in an RCBD and replicated five times. In the first experiment, data was collected on; the number of days to first Alectra emergence, Alectra shoot counts at 6, 8, 10, and 12 weeks after planting (WAP), Alectra attachment at 5 and 12 WAP, Alectra biomass at 12 WAP, cowpea biomass parameters at 5 and 12 WAP, yield and yield components per pot. While in the second experiment, number of germinated Alectra seeds per Petri dishes was recorded. The results indicated that IT82E-16 (33.25 days) and Sudan 1 (34.25 days) were earlier infested whilst late on IT99K-7-21-2-2XIT82E-16 (38 days) which correlated to the number of Alectra attachments. There were significant differences (p = 0.05) in weekly Alectra counts between cowpea varieties from 6 up to 10 WAP. Mkanakaufiti and IT99K-7-21-2-2XIT82E-16 were observed with no and few Alectra shoots infestation respectively which was an indicator of resistance mechanism in the study. Number of pods, grain weight (g) and harvest index per pot were significantly affected by inoculation protocol with lower yield on infested cowpea genotypes. The same trend was observed on cowpea varieties where Mkanakaufiti (21.9 g/pot) shown higher yield followed by IT82E-16 (12.5 g/pot) which is susceptible but with tolerance ability to the parasitic weed. The study has shown that resistance mechanisms can be categorized as no or few Alectra shoots, death of Alectra shoots and late infestation. In the Petri dishes, only 3 WAP grown Mkanakaufiti root media failed to induce the germination of Alectra seeds while the opposite occurred on IT82E-16, Sudan 1 and IT99K-7-21-2-2XIT82E-16. On the contrary, 4 WAP grown root media of the four genotypes stimulated Alectra germination which shed more light on the seed behaviour in the soil. This is worth exploring as more could be known to what causes termination of Alectra shoots on Mkanakaufiti. Still, intensifying resistant genotypes should be a goal in order to reduce Alectra seed banks in the soil, thereby, increasing cowpea yield.