Search Results (4)

The fall armyworm (FAW), Spodoptera frugiperda, a pest of maize native to the Americas first reported in West and Central Africa in 2016, severely threatens maize production and food security in Sub-Saharan Africa. Native genetic resistance is one of the best methods of control of insect pests as it is contained in the seed making it more amenable for use by farmers compared to other interventions and it is also compatible with other integrated pest management (IPM) options. An intensive screening against FAW was carried out by artificial infestation in greenhouse conditions in Kenya between 2017 and 2018 on about 3000 inbred lines available in the germplasm collection of the International Maize and Wheat Improvement Center (CIMMYT). Among these lines, only four showed to be resistant to FAW, but the mechanisms of resistance are not yet known. The objective of this study was to determine the resistance mechanisms specifically non-preference and antibiosis to S. frugiperda in these four selected resistant inbred lines. The studies were conducted under laboratory and net house conditions in Kenya from April 2020 to November 2021. Non-preference was assessed estimating the feeding preference by counting the number of FAW neonates found on each leaf portion, silk portion and grain using binary and multiple choice methods under laboratory conditions, while antibiosis was assessed through the relative growth rate (RGR) and developmental time of FAW larvae on leaves, silks and grains under both laboratory and net house conditions. Among the four resistant maize inbred lines tested, two, namely CML71 and CKSBL10008, exhibited the highest level of antibiosis resistance on leaves. Under laboratory conditions, the larval RGR reduced from 13 mg/d on the most susceptible line to 8 mg/d on CML71. CML71 also showed a good non-preference on leaves compared to other tested lines. Only 6% of neonates choose to feed on CML71 whereas more than 10% choose to feed on the other lines (and 15% on the most susceptible) in multiple choice tests. The non-preference for feeding and lower RGR of larvae on CML71 suggest a biochemical involvement resistance to FAW. Through this study, CML71 is revealed as a highly promising line for use in breeding for native genetic resistance to FAW in tropical maize. Full article

CIMMYT maize lines (CMLs), which represent the tropical maize germplasm, are freely available worldwide. All currently released 615 CMLs and fourteen temperate maize inbred lines were genotyped with 180 kompetitive allele-specific PCR single nucleotide polymorphisms to develop a reference fingerprinting SNP dataset that can be used to perform quality control (QC) and genetic diversity analyses. The QC analysis identified 25 CMLs with purity, identity, or mislabeling issues. Further field observation, purification, and re-genotyping of these CMLs are required. The reference fingerprinting SNP dataset was developed for all of the currently released CMLs with 152 high-quality SNPs. The results of principal component analysis and average genetic distances between subgroups showed a clear genetic divergence between temperate and tropical maize, whereas the three tropical subgroups partially overlapped with one another. More than 99% of the pairs of CMLs had genetic distances greater than 0.30, showing their high genetic diversity, and most CMLs are distantly related. The heterotic patterns, estimated with the molecular markers, are consistent with those estimated using pedigree information in two major maize breeding programs at CIMMYT. These research findings are helpful for ensuring the regeneration and distribution of the true CMLs, via QC analysis, and for facilitating the effective utilization of the CMLs, globally. Full article

Maize (Zea mays, L.) productivity in sub-Saharan Africa (SSA) remains low, despite breeding efforts spanning across decades. Currently, three-way cross hybrids (TWCH) dominate SSA; however, there is the potential to increase yields by using single-cross hybrids. In this study, five new and four elite CIMMYT lines were inter-mated in a half diallel mating scheme to estimate the combining ability of the lines and to determine the stability of their corresponding 36 single-cross hybrids for grain yield under low-nitrogen stress and optimum growing conditions in Zimbabwe and Zambia. The results revealed that the new inbred line CL121290 showed the highest GCA effects under optimum conditions (1.4 tha⁻¹; p < 0.001) and across sites (0.93 tha⁻¹; p < 0.001). The single-cross hybrids G12 (CML311 × DJL173527) and G16 (DJL173887 × CL1211559) were highly stable and were observed as ideal crosses within both the low-nitrogen and optimal environments. However, G18 (CML311 × DJL173887), which was depicted as ideal genotype under the two management conditions, was an unstable genotype. Hybrid G31 (CML311 × CML312) had the least grain yield under low-nitrogen, optimum and across environments. The hybrid G11 (DJL173527 × CL121290) was the highest yielding genotype amongst the new single-cross hybrids and across environments but was unstable and can be recommended for high potential in environments. Overall, the data demonstrated the potential of single-cross hybrids to supplement TWCH in boosting maize productivity under optimal and nitrogen-stress environments in SSA as well as under other areas with similar climatic conditions in the world. Full article

The development of higher yielding maize (Zea mays L.) hybrids adapted to low input small-holder farming systems in sub-Saharan Africa is required. Three-way hybrids (i.e. F1 tester crossed to inbred line) can be produced at lower cost for smallholder farmers, but to achieve this it is crucial for CIMMYT-Zimbabwe maize breeding program to identify new high yielding single cross testers with high combining ability to support the development of new high yielding hybrids for this region. Data collected on the performance of F1 and three-way hybrids from a total of 25 multi-environment trials (METs) located in South Africa (three trials), Zambia (four trials) and Zimbabwe (eighteen trials) grown across two seasons during the period from 2015–2018 to: (i) identify new single cross testers for CIMMYT HG-B maize germplasm; (ii) identify stable and high yielding three-way hybrids. Analyses were conducted using a two-stage approach. Clustering based on yield data, grouped sites into three environment types (ET); low (LY) < 3 t ha⁻¹, medium (MY) 3–6 t ha⁻¹ and high (HY) 6–13 t ha⁻¹ yielding groups. Additive genetic effects of both inbred parents and selected F1 crosses used as parents were more important than non-additive genetic effects for grain yield across ETs. Strong genotype x environment interactions on yield and other traits were observed. It was concluded that F1 hybrids (entry 75, 85, 72 and 28) demonstrated high yield across all environment types, and it is recommended that these be also evaluated as potential three-way hybrids. Single crosses CZL15085/CML566 and CZL15085/CZL13102 from heterotic group B to be used as testers for ET 1 and ET 2 respectively. Full article