Germination and Establishment of Pearl-Millet and Sorghum of Different Seed Qualities Under Controlled High-Temperature Environments

Larger and/or denser pearl millet [Pennisetum glaucum (L.) R. Br.] and sorghum [Sorghum bicolor (L.) Moench] seed have improved field establishment under temperate conditions. Because soil temperatures are higher in the semi-arid tropics and often are a constraint to successful establishment, effects of seed size and density on germination and establishment under high temperatures (up to 50°C) were evaluated. Effects of seed size and seed density on germination of Senegal Bulk millet and Segaolane sorghum were examined at temperatures of 26-50°C using a thermogradient plate. Seed size and density combinations and timing and duration of 40-45°C stress were evaluated for germination in an incubator. Effects of millet seed size and seed density on establishment were determined at constant temperatures of 35, 43, and 50°C. Sorghum had highest germination at 32-40°C and 32-42°C for medium and large seeds, respectively. Medium-sized millet seed showed higher germination over a wider temperature range than small or large seed. Millet germination rate and plumule emergence had optima at 37-38°C. High-density or large sorghum seed had greater radicle emergence at 24 h with 1 or 2-h high-temperature stress; however, with 4 or 8 h of stress, there was no difference among seed sizes or seed densities. Millet germination at 24 h was lower following 8 h of stress than for 1 or 2 of stress. Millet germination at 48 h was lower for large seed than small seed. High-density millet seeds had higher emergence than low-density seeds at a constant 43°C. At 7 days after planting, seedlings from large and medium-sized high-density seeds were taller than from small or low-density seeds.</p

Sorghum seed maturity affects the weight and feeding duration of immature corn earworm, Helicoverpa zea, and fall armyworm, Spodoptera frugiperda, in the laboratory

Citation: Soper AM, Whitworth RJ, McCornack BP. 2013. Sorghum seed maturity affects the weight and feeding duration of immature corn earworm, Helicoverpa zea, and fall armyworm, Spodoptera frugiperda, in the laboratory. Journal of Insect Science 13:67. Available online: http://www.insectscience.org/13.67Corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae), and fall armyworm, Spodoptera frugiperda J.E. Smith, are occasional pests in sorghum, Sorghum bicolor L. Moench (Poales: Poaceae), and can be economically damaging when conditions are favorable. Despite the frequent occurrence of mixed-species infestations, the quantitative data necessary for developing yield loss relationships for S. frugiperda are not available. Although these species share similar biological characteristics, it is unknown whether their damage potentials in developing grain sorghum panicles are the same. Using no-choice feeding assays in the laboratory, this study examined larval growth and feeding duration for H. zea and S. frugiperda in the absence of competition. Each species responded positively when exposed to sorghum seed in the soft-dough stage, supporting evidence for the interactions between host-quality and larval growth and development. The results of this study also confirmed the suitability of using laboratory-reared H. zea to develop sorghum yield loss estimates in the field, and provided insights into the biological responses of S. frugiperda feeding on developing sorghum seed