Abstract
Flower thrips [Megalurothrips sjostedti (Trybom)] is the most damaging insect pest on cowpea. However, information regarding the nature of gene action governing the inheritance of resistance to thrips is not available for cowpea genotypes in Uganda. This study was carried out to determine the inheritance pattern of cowpea resistance to flower thrips. Five resistant cowpea genotypes and three susceptible genotypes were crossed in full diallel mating design. F2 progenies were evaluated along with the parents in alpha lattice design with two replications under natural thrips infestation at Kabanyolo, Arua and Serere in Uganda. Combining ability analysis was performed using method one and model one of diallel analysis. The results showed that the environmental effects were highly significant (P<0.001). Additive, dominance and epistasis effects had major contributions. The broad sense heritability varied from 18 to 42% for thrips damage scores and from 0 to 6% for thrips counts. The estimates of narrow sense heritability were low for thrips damage score (2 to 18%) and thrips counts (0 to 9%). Genotypes TVU-1471 and TVU-1509 were identified as good transmitters of resistance to flower thrips. Crosses TVU-1509 x NE5, TVU-473 x Sanzi, TVU-123 x Sanzi, TVU-123 x TVU-473, and TVU-473 x TVU-1509 presented significant (P<0.05) and negative SCA effects for thrips damage scores and thrips counts and would be the most useful in breeding as some of their progenies would have high resistance to flower thrips. This study provides the basis of an efficient breeding program of cowpea for flower thrips resistance. Key words: Damage score, gene action, Megalurothrips sjostedti, Vigna unguiculata.
Highlights
Cowpea [Vigna unguiculata (L) Walp] is one of the most important legume crops grown in semi-arid tropical regions in Africa (Afiukwa et al, 2013)
The non-significant differences observed among genotypes for thrips counts per flower indicated that both the susceptible and the resistant genotypes supported almost similar number of thrips suggesting that the mechanism of resistance to flower thrips in the resistant genotypes is probably tolerance
The higher values of GCA compared to SCA observed during the damage assessment dates (44-51DAP) in this study were a good indication as reported by Acquaah (2012) that great genetic progress could be achieved in breeding for resistance to flower thrips in cowpea by focusing on the thrips damage scores and thrips counts
Summary
Cowpea [Vigna unguiculata (L) Walp] is one of the most important legume crops grown in semi-arid tropical regions in Africa (Afiukwa et al, 2013). Crop Sci. the ten leading producers of cowpea and is ranked 8th in Africa (Ronner and Giller, 2012; Ddamulira et al, 2015). In Uganda, cowpea is ranked 4th after beans, groundnuts, and soybean (Ddamulira et al, 2015). Cowpea is mostly grown in the drier eastern and northern parts of Uganda (Dungu et al, 2015). This is because the crop is tolerant to drought and adapted to warm weather, it can produce significant yield where other legumes like beans fail to grow. The species Megalurothrips sjostedti appears most destructive in Uganda, causing 20 to 100% yield losses under severe infestation (Karungi et al, 2000b)
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