New techniques for breeding maize (Zea mays) varieties with fall armyworm resistance and market-preferred traits for sub-Saharan Africa

Deploying maize varieties with fall armyworm (Spodoptera frugiperda [J.E. Smith]; FAW) resistance, desirable product profiles (PPs) and climate resilience is fundamental for food and economic security in sub-Saharan Africa (SSA). This study reviewed and identified challenges and opportunities for effective and accelerated breeding of demand-led maize hybrids with FAW resistance and adaptation to the diverse agro-ecologies of SSA. Lessons were drawn on improving breeding efficiency through adequate genetic variation delivered via prebreeding programmes, speed breeding and a reduced breeding stage plan. Appropriate PPs aligned with demand-led breeding approaches were highlighted as foundations for variety design and commercialization. Challenges to accelerated FAW resistance breeding in maize included inadequate funds and modern tools; poor adaptation of some exotic donor parental lines; lack of information on FAW resistance among local varieties; lack of integration of molecular markers associated with FAW resistance and agronomic traits into selection plans; and limited infrastructure for FAW rearing and germplasm screening. Integration of modern breeding tools and scientific innovations were recommended for accelerated development and release of FAW resistant and market-preferred maize varieties.     

Effectiveness of selection at CIMMYT's main maize breeding sites in Mexico for performance at sites in Africa and vice versa

The exchange of elite breeding materials across regions is an important way in which multinational maize breeding programmes access new genetic variation, improve efficiency and reduce costs. Our objectives were to examine whether CIMMYT's breeding programmes for tropical and subtropical environments in Mexico and Eastern and Southern Africa (ESA) can effectively share materials. Sets of selected and unselected lines were evaluated for per se and testcross performance in multiple environments in Mexico and ESA for grain yield, days to anthesis and plant height. Genotypic correlations between performance in Mexico and ESA as testcross and line per se were high (≥ 0.72) for all experiments, and indirect selection efficiency ranged from 67 to over 100% for all traits. Lines selected in ESA or Latin America performed equally well in each region, indicating selection was for broad rather than regional adaptation. Thus, breeding programmes of CIMMYT in both Mexico and ESA can benefit tremendously by exchanging breeding materials and test results, and elite selections from each region should be fast‐tracked for evaluation in the other.     

大波斯菊小孢子发生时期线粒体的动态

运用电镜及电镜细胞化学等方法对大波斯菊小孢子发生时期,即小孢子母细胞到四分休的整个发育过程中的线粒体动态进行了观察。实验表明:在小孢子母细胞减数分裂过程中,线粒体要经受一个复杂的反分化过程。在减数分裂前期的早期阶段,线粒体的数量增加很快;与此同时,一些空白的被称作”spherical inclusion”的细胞器(STs)也随之产生,它们代表着新产生细胞器的退化。造成退化的原因可能是由于细胞器缺少核密码的调控。推测减数分裂后线粒体围核现象可能与ATP、信息大分子及其他物质的传递有关。     

Large-scale screening for maize drought resistance using multiple selection criteria evaluated under water-stressed and well-watered environments

A total of 550 maize inbred lines collected from global breeding programs were evaluated for drought resistance under both well-watered and water-stressed environments. The evaluation was based on multiple measurements of biomass taken before and after the drought stress was applied using the normalized difference vegetation index (NDVI), along with other selection criteria including anthesis-silking interval, leaf senescence, chlorophyll content, root capacitance, final grain yield, and grain yield components. Kernel weight was the most stable trait under drought stress. Correlations between the primary trait (grain yield) and the secondary traits, except the root capacitance and ASI under water-stressed condition, were all significant. Root capacitance had relatively low heritability and low genetic correlation with other drought resistance criteria, and is not recommended as a drought resistance criterion. Significant reduction of NDVI values measured in the afternoon when the leaves became rolling, compared to those measured in the morning when the leaves were open, provides a reliable index for leaf rolling, which however was not significantly correlated with grain yield. NDVIs measured across different developmental stages were highly correlated with each other and with most of the secondary traits as well as, grain yield, indicating that NDVI can be used as a secondary trait for large-scale drought resistance screening. Regression models built based on non-yield drought criteria and yield components explained about 40% and 95% of the variation for the grain yield, respectively. Some maize lines developed in China for temperate regions showed strong drought resistance comparable to tropical maize lines when tested under tropical condition, indicating that temperate lines with a wide adaptability can be used in drought resistance breeding for both temperate and tropical environments.     

Diallel analysis of acid soil tolerant and susceptible maize inbred lines for grain yield under acid and non-acid soil conditions

Maize is not inherently tolerant to soil acidity but due to the ever increasing demand for the crop in the developing world, production of maize on acid soils continues to expand. Breeding for maize acid soil tolerance is the best strategy to improve yield under these conditions. Therefore, the current study was done to determine the general combining ability (GCA) of eight acid-soil tolerant and susceptible inbred lines and the specific combining ability (SCA) of cross combinations of these lines for grain yield under acid and non-acid soils. The eight lines were crossed using a diallel mating design to produce 28 single cross hybrids for evaluation under acid and non-acid soils at four sites for two seasons. Line C2 was the best general combiner under both soil environments while A2/C1 and A1/C2 had the highest desirable SCA effects under optimal conditions. Loss in grain yield and sensitivity to low pH stress was higher among genotypes in light textured soils than heavy soils. Non-additive gene action was more important than additive gene action in conditioning grain yield under both environments. Results revealed that it was feasible to improve grain yield under low pH and optimum soils from the set of genotypes used in the current study.