Screening for resistance to Maruca testulalis Geyer in cowpea (Vigna unguiculata L.) Walp

Abstract

Screening methods were devised to select cowpea genotypes with resistance to yield loss oaused by larvae of Maruca testulalis (Lepidoptera, Pyralidae). More emphasis was placed on flower damage than on pod damage. One hundred and forty genotypes of wild and cultivated cowpeas and four of related Vigna speoies were screened in the first year; 25 of these were selected for rescreening in the second year. Resistance to flower damage was assessed by the ratio of number of pods under unsprayed conditions to number of pods under sprayed conditions and resistance to overall post-flowering damage by ratio of seed yield under unsprayed conditions to seed yield under sprayed conditions. The absolute numbers of pods and seed yields from unsprayed plots were also taken into account. Several genotypes of moderate resistance and one of high resistance were located among cultivars of different origins.

The use of two mating systems in breeding for resistance toMaruca testulalisGey. in cow peaVigna unguiculata(L.) Walp.

“…WJ and UN were generally found to have the most dominant alleles for unsprayed yields, but the most recessive ones for sprayed yields, while the reverse was true for EA and EB. This supported the finding of Woolley & Evans (1979) that there was no correlation between yields under unsprayed and sprayed conditions. Sprayed yields appeared to be controlled by increasing alleles showing partial dominance.…”

“…Five lines resistant or moderately resistant to Maruca and two very susceptible but agronomically preferred lines were selected using the screening data of Woolley & Evans (1979). The resistant line was Wake Jaba (WJ), an introgressive type between Nigerian weedy and cultivated subspecies.…”

“…The design and planting date for the trial were chosen using experience from previous screening trials (Woolley & Evans, 1979). A vigorous susceptible cow pea was planted on the edges of the unsprayed experiment 44 days before the main trial was sown on 4 August 1975 to act as a source of Maruca adults for the trial.…”

“…The most important damage is that caused by larvae of the moth to flowers and buds, while later instars also attack green pods; total crop loss may occur (Raheja, 1976). Woolley & Evans (1979) developed a repeatable method of assessing resistance to Maruca, using as a variable the ratio of yield under unsprayed conditions to yield under conditions of complete insecticidal protection from the time that the first flower buds appear. The yields assessed were number of pods per plant, which is reduced only by damage to buds and flowers, mainly by Maruca, and seed yield per plant, which is reduced by all post-flowering pests, including Maruca.…”

Alternative methods of interpreting measurements of resistance to the leafhopper Empoasca kraemeri Ross and Moore in the common bean, Phaseolus vulgaris L.

“…The variable Yu/Yp has been used by WOOLLEY & EVANS (1979) to measure resistance to Maruca testulalis GEYER in cowpea, Vigna unguiculata (L .) Alternatively, the unprotected yield per plant of each genotype in each replication (Y u) can be divided by the protected yield per plant of the same genotype in the same replication (Yp) .…”