No abstract

Leaf removal can significantly reduce yield of grain sorghum [Sorghum bicolor (L.) Moench]. Genotype ✕ defoliation interactions for yield have been reported in other crops, but limited information is available in sorghum. This study was conducted on eight sorghum hybrids to evaluate hybrid responses of yield components and grain‐fill traits to N application and post‐anthesis defoliation. A factorial arrangement of three defoliation levels and three N fertilization rates was used in experiments conducted in five Nebraska and Kansas environments. Defoliation treatments (0, 50, and 100%) were applied at 10 d post anthesis. Removal of 50 and 100% of the leaves caused curvilinear reductions in all measured traits. Significant N effects were not observed in all environments. Defoliation ✕ N interactions did not occur for the traits studied. Genotype ✕ defoliation interactions occurred for grain yield, seed weight, seed number, duration of grain fill, and rate of grain fill, indicating that hybrids did not respond the same to defoliation treatments. Hybrids with higher seed number and longer preanthesis period maintained higher grain yields with defoliation. Responses of seed number to N application were similar for all hybrids. Genotype ✕ defoliation ✕ environment interactions were observed for all traits. Environmental interactions need to be considered when using defoliation to differentiate among hybrids in their components of yield and the relationships of these traits to grain yield.

The belowground microbiomes have many beneficial functions that assist plant growth, including nutrient cycling, acquisition and transport, as well as alleviation of stresses caused by nutrient limitations such as nitrogen (N). Here we analyzed the root endosphere, rhizosphere and soil bacterial communities of seven sweet sorghum genotypes differing in sensitivity to N-stress. Sorghum genotypes were grown in fields with no (low-N) or sufficient (high-N) N. The dry shoot weight ratio (low-N/high-N) was used to determine N-stress sensitivity. Our hypothesis was that genotypes tolerant and sensitive to N-stress select distinct bacterial communities. The endosphere and rhizosphere bacterial community structure were significantly different between the N-stress sensitive and tolerant genotypes in the high-N field, but not in the low-N field. However, significant changes in the relative abundance of specific bacterial taxa were observed in both fields. Streptomyces, a bacterial genus known to alleviate plant abiotic stresses, was enriched in the endosphere and rhizosphere of the tolerant genotypes in the low-N field. Our study indicates that sweet sorghum genotypes tolerant to N-stress select taxa that can potentially mitigate the N-stress, suggesting that the interactions between N-stress tolerant lines and the root-associated microbiome might be vital for coping with N-stress.

Yield response to defoliation in grain sorghum [Sorghum bicolor (L.) Moench] can be influenced by time and intensity of leaf removal. Limited information is available for defoliation ✕ environment interactions and the defoliation response of yield‐related traits, stalk rot, and basal stalk lodging. This study was conducted to examine the effect of time and extent of defoliation on hybrid grain sorghum in three eastern Nebraska environments in relation to yield components, duration and rate of grain filling, nonsenescence period, stalk rot, and lodging. Four levels of defoliation (0, SO, 95, and 100%) were applied to plants at 10 d preanthesis, anthesis, 10 d post anthesis, and 20 d post anthesis. Defoliation significantly decreased yield components, grain‐fill duration, grain‐fill rate, and the nonsenescence period, while increasing the occurrence of stalk rot. The most pronounced effects on all traits occurred when plants were defoliated prior to or during anthesis. Significant defoliation level ✕ time interactions and environment ✕ defoliation treatment interactions were observed for all traits. Variance component estimates indicated that environmental interaction comprised 18 to 25% of total variation for the yield components, 5% for stalk rot, and 50% for lodging. Use of defoliation in a limited number of environments may not prove effective in evaluating tolerance to lodging. Small environmental interactions for the stalk rot response suggest that observations from only a few environments are necessary for its evaluation.

Genotype X environment (GE) interaction is an important consideration in plant breeding because of its effects on progress from selection. This study examines the effects of genotype maturity on GE interaction for grain yield and yield components. Fifty-four grain sorghum (Sorghum bicolor (L.) Moench) genotypes included in three maturity groups, early, medium, and late, were evaluated in 48 environments across Nebraska and Kansas in 1978 and 1979. The soil ranged from sandy types (mixed, mesic Typic Ustipsamment) to intermediate types as represented by Typic Haplustoll, course-silty, mesic and fine-silty, mixed, mesic, Aridic Argiustoll, to clay loam at the opposite extreme (deep with high water holding capacity) as represented by fine, montmoriiionitic mesic, Typic Argiuboll. In the analysis of variance combined over years and environments within year, genotype, genotype X year, and genotype X environment within year sums of squares were partitioned into components representing within and among maturity groups. More than half of the interaction effects sums of squares was attributed to differences among maturity groups. The GE interaction increased with an increase in duration of plant growth (maturity). Genotypes showed larger interaction with environments within year than with years, irrespective of maturity. The results suggest that a reliable evaluation of relative genotype performance can be made if the genotypes under test do not include a wide range of maturity. Minimizing differences in maturity among genotypes reduces GE interaction. Testing at more locations or environments at given locations should be done rather than testing in more years. For a desired level of precision, the amount of testing required for a set of genotypes with a wide range of maturity and long-growth duration is greater than that required for genotypes with a narrow range of maturity and short-growth duration. Increasing number of replications per test more than two, environments in a year more than eight, and years of testing more than two, was not effective in increasing efficiency in genotype evaluation, especially in early and medium maturing genotypes.Additiolllll index words: Sorghum bicolor (L.) Moench, Physiological maturity, Variance components, Precision.