Genetic diversity and heterotic grouping of the core set of southern African and temperate maize (Zea mays L) Inbred lines using SNP markers

The establishment of heterotic groups and heterotic patterns is crucial to a successful maize hybrid breeding programme. Molecular markers can be used for differentiating maize into heterotic groups which can be used for maximum exploitation of heterosis. A core set of 45 maize inbred lines was selected from 96 maize inbred lines that were obtained from major breeding programmes in Zambia, Zimbabwe, CIMMYT, IITA, and USA. The 45 in- bred lines were assessed for their genetic diversity and assigned to different heterotic groups using 129SNPs. The genetic distance ranged from 0.03 to 0.99, with the highest distance observed between inbred lines B73 and Mo17 and the least between L3233 and N3. The inbred lines were clustered into four groups which corresponded to the N, SC, BSS, and Lancaster heterotic groups. The genetic divergence among temperate inbred lines was larger than that among tropical inbred lines. Temperate inbred lines with potential to improve the heterotic response of the N and SC heterotic groups were identified. The study has shown that including temperate inbred pairs from established and well-known heterotic groups is recommended for effective molecular characterisation of Southern African maize inbred lines. It is recommended that the genetic distance based grouping should be verified by combining ability studies

Genotypic Variation in Seedling Tolerance to Aluminum Toxicity in Historical Maize Inbred Lines of Zambia

Maize (Zea mays L) is the most important food grain in sub-Saharan Africa and is mostly grown by small-scale farmers under rainfed conditions. Aluminum toxicity caused by low pH is one of the abiotic factors limiting maize production among smallholder farmers. Therefore, breeding maize hybrids that are tolerant to aluminum toxicity will sustain and increase maize production in these areas. Hence this study was undertaken to assess the genotypic variation for aluminum toxicity in maize inbred lines. Fourteen maize inbred lines of historical importance that are used in maize hybrid breeding in Zambia were studied for seedling root variation under different aluminum concentrations using hydroponic conditions. The aluminum tolerance membership index based on three traits (actual root length, relative root length and root length response) classified genotypes L3233 and L1214 as highly tolerant, L5527 and ZM421 as tolerant, and L12, L3234, and ZM521 as intermediate. The high PCV, GCV, and heritability observed for the root traits indicate that opportunities for selection and breeding for aluminum tolerance among Zambian inbred lines exist. Furthermore, the study indicated that a higher genetic gain would be expected from net root growth followed by shoot length response as selection traits, thus supporting the use of root traits for aluminum tolerance screening

Evaluation of Ugandan cassava germplasm for drought tolerance

This paper invested on the increased pressure on prime arable land for agriculture to meet food demand for global population has resulted in shifting agriculture to marginal areas where drought is frequentIncreased pressure on prime arable land for agriculture to meet food demand for global population has resulted in shifting agriculture to marginal areas where drought is frequent. Focusing research towards development of drought tolerant varieties is thus necessary. Replicated field trials for farmer preferred cassava genotypes were established to evaluate their morphological and yield trait responses and adaptability to moisture stress. Results showed significant (P<0.05) differences among genotypes for all the parameters evaluated. Moisture stress resulted in a decline in Harvest Index by 22.34%, Fresh Root Yield by 37.04%, Number of Roots by 19.43%, Dry matter content by 16.58%, Root starch content of 20.81%, Leaf Retention by 25.72% and Plant height by 16.62%. Results therefore, evidently showed that water stress has significant devastating effects on vegetative and yield parameters of cassava. Breeding strategies to develop drought tolerant cassava varieties to cope up with increased water scarcity and semi-arid conditions are thus paramount. Varietal variability in response to water stress reported is a cornerstone in the breeding process. Besides genetic effects were dominant indicating breeding objectives would be easily achieved. Genotypes MH96/0686, Magana, Yellow, TME 204, Nyamutukura, MH97/2961, NASE 1, NASE 2 and NASE 12 were least affected by drought and may provide gene sources for cassava improvement. Genotype x Location was significant (P<0.05) suggesting that rational distribution of genotypes to agro-ecological zones with different levels of drought stress is possible. Some genotypes had stable yield and its components suggesting that cassava can easily adapt to dry environment

Genetic diversity and heterotic grouping of the core set of southern African and temperate maize (Zea mays L) Inbred lines using SNP markers

The establishment of heterotic groups and heterotic patterns is crucial to a successful maize hybrid breeding programme. Molecular markers can be used for differentiating maize into heterotic groups which can be used for maximum exploitation of heterosis. A core set of 45 maize inbred lines was selected from 96 maize inbred lines that were obtained from major breeding programmes in Zambia, Zimbabwe, CIMMYT, IITA, and USA. The 45 inbred lines were assessed for their genetic diversity and assigned to different heterotic groups using 129SNPs. The genetic distance ranged from 0.03 to 0.99, with the highest distance observed between inbred lines B73 and Mo17 and the least between L3233 and N3. The inbred lines were clustered into four groups which corresponded to the N, SC, BSS, and Lancaster heterotic groups. The genetic divergence among temperate inbred lines was larger than that among tropical inbred lines. Temperate inbred lines with potential to improve the heterotic response of the N and SC heterotic groups were identified. The study has shown that including temperate inbred pairs from established and well-known heterotic groups is recommended for effective molecular characterisation of Southern African maize inbred lines. It is recommended that the genetic distance based grouping should be verified by combining ability studies.This article is published as 166. Richard, C., Osiru, D.S., Mwala, M.S., Lübberstedt, T. (2016) Heterotic grouping of a core set of Southern African and temperate maize inbred lines based on SNP markers. Maydica 61: M3. Posted with permission.</p

Physiological and molecular characterization of drought responses and identification of candidate tolerance genes in cassava

This study was carried out to identify candidate drought-tolerance genes and expression-based markers of drought stress in cassava. One drought-tolerant (improved variety) and one drought-susceptible (farmer-preferred) cassava landrace were grown in the glasshouse under well-watered and water-stressed conditions.Cassava is an important root crop to resource-poor farmers in marginal areas, where its production faces drought stress constraints. Given the difficulties associated with cassava breeding, a molecular understanding of drought tolerance in cassava will help in the identification of markers for use in marker-assisted selection and genes for transgenic improvement of drought tolerance. This study was carried out to identify candidate drought-tolerance genes and expression-based markers of drought stress in cassava. One drought-tolerant (improved variety) and one drought-susceptible (farmer-preferred) cassava landrace were grown in the glasshouse under well-watered and water-stressed conditions. Their morphological, physiological and molecular responses to drought were characterized. Morphological and physiological measurements indicate that the tolerance of the improved variety is based on drought avoidance, through reduction of water loss via partial stomatal closure. Ten genes that have previously been biologically validated as conferring or being associated with drought tolerance in other plant species were confirmed as being drought responsive in cassava. Four genes (MeALDH, MeZFP, MeMSD and MeRD28) were identified as candidate cassava drought-tolerance genes, as they were exclusively up-regulated in the drought-tolerant genotype to comparable levels known to confer drought tolerance in other species. Based on these genes, we hypothesize that the basis of the tolerance at the cellular level is probably through mitigation of the oxidative burst and osmotic adjustment. This study provides an initial characterization of the molecular response of cassava to drought stress resembling field conditions. The drought-responsive genes can now be used as expression-based markers of drought stress tolerance in cassava, and the candidate tolerance genes tested in the context of breeding (as possible quantitative trait loci) and engineering drought tolerance in transgenics