Brenda L. Gambín

Kernel weight dependence upon plant growth at different grain-filling stages in maize and sorghum

In the present study we tested how assimilate availability per kernel at different grain-filling stages may affect maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) individual kernel weight (KW). These two species have shown a contrasting KW response to increased assimilate availability at similar seed developmental stages. Plant growth rate (PGR) per kernel was used to estimate the assimilate availability per kernel at two stages: around the early grain-filling period when kernel number per plant is also being established, and around the effective grain-filling period. We tested 3 commercial genotypes from each species, and modified the PGR by thinning or shading the stand at different developmental stages. In both species, each genotype showed a particular relationship between PGR around flowering and kernel number, which gave a range of responses in the PGR per kernel set around flowering. Final KW always increased whenever PGR per kernel around flowering was enhanced. Only sorghum showed a consistent KW increase when PGR per kernel during the effective grain-filling period was enhanced. Results confirmed that increasing assimilate availability per kernel will affect maize kernel size only if the potential set early in development is altered. Most important, we showed that linking specific KW sensibility across species at different seed developmental stages using a simple estimate of assimilate availability per seed (i.e. PGR per kernel) at each grain-filling stage helped explain most of the explored genotypic and environmental variability in final kernel size.

Genotypic diversity in sorghum inbred lines for grain-filling patterns and other related agronomic traits

Opportunities for genetic improvement on specific traits require information on available diversity, together with knowledge on heritability estimates and possible trade-off relations among traits. Sixty-five sorghum inbred lines were evaluated for grain filling and other agronomic traits during 2008 and 29 re-evaluated in 2009. Time to anthesis, final grain weight (GW), grain growth rate, duration of grain filling, maximum water content, grain desiccation rate, moisture concentration at physiological maturity, plant height, panicle length, grain number per plant and final yield per plant were measured both years. Results highlighted the available variability for grain-filling patterns in sorghum, and genotypic differences (P < 0.05) for all traits were evident. Final GW variation (16–44 mg grain–1 in 2008, and 20–40 mg grain–1 in 2009) was achieved through different combinations of rate (3.27–9.78 mg degree-days grain–1 10−2) and duration of grain filling (413–853 degree-days). Calculated heritability for grain-filling traits ranged from 0.43 to 0.95, showing GW and maximum water content had the highest values. Grain number showed consistent negative associations with grain growth rate but not with GW due to grain-filling duration variability. This suggests selecting longer grain filling can increase GW (and yield) without negative trade-off relations with grain number.

Adding genotypic differences in reproductive partitioning and grain set efficiency for estimating sorghum grain number

Abstract. Current models of sorghum crop growth predict grain number using a calculated plant growth rate around flowering and a genotype-dependent parameter that describes the relationship between both traits. Few values for this parameter have been reported, being similar within triple-dwarf or single-dwarf sorghum genotypes. This approach narrows genotypic differences in grain number determination mostly to differences in traits affecting biomass production. Relevant traits such as biomass partitioning to reproductive structures and grain-set efficiency are not specifically considered, but both vary across genotypes and could improve grain number estimations. We first explored variation for these traits (CGR, crop growth rate around flowering; PR, biomass partitioning to reproductive structures during this period; EG, grain set per unit of accumulated reproductive biomass) for a set a sorghum commercial hybrids and inbred lines growing under different conditions. Later, we used a second set of experiments to test whether considering genotype-specific PR and EG improved estimates of grain number compared with the current approach used in crop simulation models. Grain number variations (14–63 × 103 grains m–2) due to genotype and environment were a consequence of significant differences (P < 0.05) in all analysed traits (CGR, PR, EG). Biomass partitioning and grain set per unit of accumulated reproductive biomass showed consistent genotypic differences (P < 0.001); however, they also showed significant environment or genotype × environment effects. When these specific genotypic parameters dealing with biomass partitioning and grain-set efficiency were used for estimating grain number in other non-related experiments, the predicted accuracy improved (r 2 = 0.47, P < 0.05, RMSE = 7029 grains m–2) relative to the general approach using a constant parameter for most genotypes (r 2 = 0.14, P < 0.28, RMSE = 12 630 grains m–2) or a calculated parameter for each genotype (r 2 = 0.38, P < 0.10, RMSE = 8919 grains m–2). We propose that these traits (PR and EG) need to be considered and included in sorghum crop growth models, as they help predict grain number performance of different genotypes in different growth environments.

Secondary traits explaining sorghum genotype by environment interactions for grain yield

Abstract. Effective plant improvement depends on understanding grain yield genotype by environment (G × E) interactions. Studies focusing on more heritable (secondary) traits provide a way for interpreting the nature of these interactions and assist selection by adapting hybrids to specific adaptation patterns. The objective of our study was to explore some specific traits to help describe G × E interactions for yield in grain sorghum. A set of 22 representative hybrids were grown at eight different environments varying mainly in water and nitrogen availability. Studied traits were yield, phenology (time to anthesis and grain-filling duration), numerical yield components (grain number and individual grain weight) and physiological components (biomass at maturity and harvest index). The G × E interaction to G component variance represented 3.48 for grain yield, 1.03 for grain-filling duration, 0.87 for biomass at maturity, 0.71 for time to anthesis, and less than 0.5 for the rest of the traits. Although the G × E interaction for yield was large, the relative genotypic contribution of most studied traits suggests that G × E interaction is not a major impediment for attaining high selection responses to these traits. Pattern analysis applied to G × E best linear unbiased predictors defined three genotype and three environmental groups. Environments were grouped suggesting different water stress levels during early or pre-flowering stages, whereas genotype groups depicted different yield responses across environmental groups. Phenology differences among genotypes explained a large portion of the G × E interaction throughout its influence on grain weight. Late flowering genotypes performed poorly in terms of grain weight and yield across all environments, showing that these materials are not the best option for our production system. Longer grain filling contributed to grain weight and yield at environments with low stress levels, particularly when combined with intermediate or short maturity. Early materials contributed to grain weight and yield at the highest stressful environments. We provide useful information to sorghum breeders at temperate environments, and described secondary traits that could assist selection at particular environments.