Genetic analysis of the maximum germination distance of Striga under Fusarium oxysporum f. sp. strigae biocontrol in sorghum

Maximum germination distance(MGD) is an important component of Striga resistance in sorghum. The objective of this study was to determine gene action influencing MGD of Striga hermonthica and Striga asiatica among selected sorghum lines treated with a biocontrol agent, Fusarium oxysporum f. sp. strigae(FOS) for effective breeding with Striga resistance, and FOS compatibility. Twelve sorghum genotypes were selected based on their Striga resistance, FOS compatibility, and superior agronomic performance. Selected genotypes were crossed using a bi-parental mating design to generate six families for genetic analysis. Agar-gel assays were used to determine low haustorium initiation factor(LHF) using the 12 parental lines, their F_1 progenies, backcross derivatives, and F_2 segregants in two sets. One set had S. hermonthica seed and the other one had S. asiatica seed. Both were treated with and without FOS. Genotypes were evaluated using a split-plot design with three replications and MGD data were recorded followed by generation mean analysis. FOS reduced MGD by 1cm under both S. hermonthica and S. asiatica infestations. Additive, dominance, and epistatic gene actions were involved in the control of MGD of the two Striga species in the evaluated populations. On average, the relative contribution of additive, additive×additive and dominance×dominance genetic effects on the MGD of S. hermonthica and S. asiatica, with FOS, were 20, 33, and 36%; and 21, 32, and 35%, respectively. Breeding methods exploiting these genetic effects may provide enhanced response to selection for Striga resistance and FOS compatibility in integrated Striga management(ISM) programmes.     

Variance components and heritability of traits related to root: shoot biomass allocation and drought tolerance in wheat

Enhanced root growth in plants is fundamental to improve soil water exploration and drought tolerance. Understanding of the variance components and heritability of root biomass allocation is key to design suitable breeding strategies and to enhance the response to selection. This study aimed to determine variance components and heritability of biomass allocation and related traits in 99 genotypes of wheat (Triticum aestivum L.) and one triticale (X. Triticosecale Wittmack) under drought-stressed and non-stressed conditions in the field and greenhouse using a 10?×?10 alpha lattice design. Days to heading (DTH), days to maturity (DTM), number of tillers (NPT), plant height (PH), spike length (SL), shoot and root biomass (SB, RB), root to shoot ratio (RS), thousand kernel weight (TKW) and yield (GY) were recorded. Analyses of variance, variance components, heritability and genetic correlations were computed. Significant (p?<?0.05) genetic and environmental variation were observed for all the traits except for spike length. Drought stress decreased heritability of RS from 47 to 28% and GY from 55 to 17%. The correlations between RS with PH, NPT, SL, SB and GY were weaker under drought-stress (r?≤???0.50; p?<?0.05) compared to non-stressed conditions, suggesting that lower root biomass allocation under drought stress compromises wheat productivity. The negative association between GY and RS (r?=???0.41 and ??0.33; p?<?0.05), low heritability (<?42%) and high environmental variance (>?70%) for RS observed in this population constitute several bottlenecks for improving yield and root mass simultaneously. However, indirect selection for DTH, PH, RB, and TKW, could help optimize RS and simultaneously improve drought tolerance and yield under drought-stressed conditions.     

Genetic resources and breeding methodologies for improving drought tolerance in wheat

Yield gains from rain-fed wheat (Triticum aestivum L.) production, particularly in areas experiencing intermittent and terminal dry spells, can be realized through integrated breeding with promising genetic and genomic resources using appropriate methodologies. This enables targeted recombination of novel genes for drought tolerance and selection of desirable genotypes. Continuous exploration of new sources of genetic variation and introgression of suitable genes into elite drought-susceptible genotypes, including via transgenic approaches, and the use of genome editing could offer exciting future prospects in acquiring drought-tolerant wheat genotypes. This review highlights the available genetic resources, the major wheat genebanks and databases, as well as the breeding methodologies for drought tolerance in wheat, including prebreeding, conventional breeding, hybrid breeding, and genomics-assisted breeding. The potential of genetic modification through the transgenic and genome-editing approaches is also discussed. Emphasis is placed on how best these breeding methods can be brought together to develop strategies aimed at improving drought tolerance in wheat.     

Combining ability and gene action controlling yield and yield components in bread wheat (Triticum aestivum L.) under drought‐stressed and nonstressed conditions

This study determined the combining ability and gene action controlling yield and yield‐related traits in wheat under drought‐stressed and nonstressed conditions. Twelve parents possessing Rht‐B1b and Rht‐D1a genes and their 66 half‐diallel crosses were evaluated under field and glasshouse conditions. Plant height (PH), productive tiller number (TN), kernels per spike (KPS), thousand seed weight (TSW) and grain yield (GY) were recorded. Analysis of variance, heritability, correlation and combining ability analyses were performed. Heritability estimates ranged from 53.00% (TN) to 63.07% (KPS). Yield showed positive correlations with all other traits under all test conditions. Significant GCA effects were observed for all traits recorded across test conditions, except for yield in the glasshouse. All Baker's ratios were less than a unit, indicating predominance of nonadditive gene action. Consistently high positive GCA effects were observed on LM02 for GY; LM02 and LM23 for KPS; and LM04 and LM09 for TSW, while LM17 and LM21 had negative effects for PH. Good general and specific combiners will be used for further breeding and selection.