Screening and breeding for resistance to maize stem borers and Eldana in West and Central Africa

Stem borers are one of the major constraints limiting maize productivity in Africa. The most important species reducing maize yield in West and Central Africa are Sesamia calamistis, Eldana saccharina and Busseola fusca. Both the pink stem borer (Sesamia calamistis Walker (Pyralidae) and the sugarcane borer Eldana saccharina Hampson (Noctuidae) infest and reduce maize yields in the lowlands of West and Central Africa. Host pant resistance is very effective in managing the pests and researches conducted in the sub-region have identified promising genotypes with resistance to the two borer species. Such genotypes have been utilised to develop improved varieties with better levels of resistance. Genetic studies revealed that both additive and non-additive gene actions are important in varying degrees for the different components of resistance. The improved varieties are being strategi- cally deployed on-farm while other adapted varieties are being improved for resistance to enhance their usefulness. Progress made in screening and breeding for stem borer resistance in the region is discussed

Genetic variance components and GGE interaction of tropical maize genotypes under Northern leaf blight disease infection

Disease infection is a major destructive concern in agricultural production, thus a common point of interest in breeding procedure. Evaluation of breeding improvement on plant disease resistance greatly reveals that high yielding selection in disease-free regions indirectly improves yield in diseased environments. Forty-five F1 hybrids and their 10 parents were assessed in 2016 and 2017 cropping season across five environments using 5 × 11 alpha lattice design to: (1) estimate the genetic variance components among tropical maize hybrids under NLB disease infection, and (2) study the genotypes’ agronomic performance and stability in NLB diseased environments. Data were recorded for major agronomic traits. Highly significant mean squares were recorded for environment, genotype and genotype × environment interaction for traits under study indicating distinctiveness of the test environments. Higher proportion of specific combining ability variance over general combining ability variance across test environments shows the predominance of dominance gene effects over additive gene for the inheritance of the traits under study. Significant and positive genetic correlations recorded for the test environments indicate that the hybrids reaction across the significant and positively correlated environments was consistently related signifying similar ranking of the hybrids for NLB disease resistance across test environments. Therefore, either of the test environments would be adequate for selecting NLB disease resistance germplasm. The most stable hybrids across test environments were all derived from resistance parental lines

Progress in breeding for resistance to maize stem borers sesamia calamistis and Eldana saccharina in West and Central Africa

The pink stem borer (Sesamia calamistis Walker (Pyralidae)) and the sugarcane borer (Eldana saccharina Hampson (Noctuidae)) are among the most damaging pests of maize in West and Central Africa, a region where IITA invests considerable effort in improving productivity of maize-based systems. The use of host plant resistance (HPR) is central to any Integrated Pest Management (IPM) programme; therefore, development and use of maize varieties with resistance to Sesamia and/or Eldana are integral to IPM activities in the region. Early research efforts resulted in the establishment of mass rearing facilities and screening procedures for both insect species, and the development of maize genotypes with resistance to Sesamia and/or Eldana. S1 selection has been used successfully to improve levels of resistance. New genotypes with resistance to both borer species have been developed by either broadening the genetic base of existing genotypes or by classifying the developed genotypes into heterotic groups and pooling each group to form a reciprocal pool for further improvement. Artificial infestation has identified levels of cross resistance in a number of genotypes. Inbred lines with resistance to either of the borer species have been isolated and tested. Stem borer resistant varieties are currently being grown on-farm in Nigeria, Ghana and Cameroon. There is, however, the need to correctly classify the mechanism of resistance in the identified genotypes to improve efficiency of selection and to combine different mechanisms of resistance into different genotypes

Effect of high temperature drying on seed longevity of Bambara groundnut (Vigna subterranea) accessions

Open Access Article; Published online: 25 Nov 2020In this paper, we considered the effects of different drying regimes on the subsequent longevity of Bambara groundnut seeds. Freshly harvested Bambara groundnut seeds from 27 genebank accessions were divided into five samples. One sample (control) was immediately dried at 17°C/15% RH and the other samples were dried at 45°C/35% RH for up to eight days, before transfer to 17°C/15% RH. After drying, seed moisture content was raised to 10.9% before packing the seeds in aluminium foil packets and placing at 45°C. Samples were removed at regular intervals for germination tests to compare seed longevity. Initial drying at the higher temperature resulted in a faster reduction in seed moisture content. The effect of the different drying regimes on subsequent longevity was not significant for most accessions. Nonetheless, the seed longevity of smaller-seeded accessions was perhaps enhanced by initial drying at a higher temperature; in contrast, initial drying at 17°C appeared to be the best drying treatment for larger-seeded accessions. Overall, the results suggest that initial drying at a higher temperature was beneficial for reducing processing time and for some accessions would be beneficial for seed longevity, but further work is required to understand for which seed lots

Comparative Performance of Lowland Hybrids and Inbred Rice Varieties in Nigeria

The objective of this study was to compare the grain yield performance of lowland hybrids with that of some inbred varieties of rice in Nigeria with a view to identifying which of the two groups exhibits higher grain yield. Yield potential of 14 rice varieties comprising 10 commercial hybrids, 2 inbred varieties and 2 lowland NERICAs were evaluated at the Africa Rice Center, Ibadan Station during 2008 wet and 2009 dry seasons. The experiment was laid out in a randomized complete block design with three replications. Agronomic data were collected on days to 50% flowering, days to maturity, plant height, number of panicles per m2, panicle length, number of tillers per plant, panicle weight, number of grains per panicle, 1000 grain weight and grain yield. The number of panicles per m2, panicle weight and number of grains per panicle were significantly higher in the hybrids than in the inbred and interspecific varieties. The hybrids had the highest grain yield compared to the inbred and the interspecific lowland NERICA varieties. The results indicated that hybrids exhibited significant yield increase of 13.44% over the best lowland NERICAs and 15.17% over the best inbred variety WITA 4. The number of panicles per m2, panicle weight and number of grains per panicle appeared to be the main traits that contribute to higher grain yield in the hybrids. Therefore, the hybrids with the highest grain yield have huge potential in raising rice productivity in Nigeri

Maize defence mechanisms against the European corn borer, Ostrinia nubilalis Hubner (Lepidoptera: Crambidae)

Maize is arguably the most widely grown crop in the world, but it is often associated with one of its major insect pests, the European corn borer (ECB). The damage caused by this species to maize production is generally variable, but in many cases it is economically significant. This review paper provides an overview of the research findings on the natural plant defence mechanisms against ECB larvae published till now. What is resistance and how it is achieved, what is the chemical response of maize plants to insect feeding and how tolerance can be increased. A short introduction in breeding for resistance and a discussion if the mentioned traits can be used in conventional breeding in order to create maize hybrids less affected by ECB are given