Thomas G. Chastain

Effects of elevated CO2 and temperature on seed quality

SUMMARY Successful crop production depends initially on the availability of high-quality seed. By 2050 global climate change will have influenced crop yields, but will these changes affect seed quality? The present review examines the effects of elevated carbon dioxide (CO2) and temperature during seed production on three seed quality components: seed mass, germination and seed vigour. In response to elevated CO2, seed mass has been reported to both increase and decrease in C3 plants, but not change in C4 plants. Increases are greater in legumes than non-legumes, and there is considerable variation among species. Seed mass increases may result in a decrease of seed nitrogen (N) concentration in non-legumes. Increasing temperature may decrease seed mass because of an accelerated growth rate and reduced seed filling duration, but lower seed mass does not necessarily reduce seed germination or vigour. Like seed mass, reported seed germination responses to elevated CO2 have been variable. The reported changes in seed C/N ratio can decrease seed protein content which may eventually lead to reduced viability. Conversely, increased ethylene production may stimulate germination in some species. High-temperature stress before developing seeds reach physiological maturity (PM) can reduce germination by inhibiting the ability of the plant to supply the assimilates necessary to synthesize the storage compounds required for germination. Nothing is known concerning the effects of elevated CO2 on seed vigour. However, seed vigour can be reduced by high-temperature stress both before and after PM. High temperatures induce or increase the physiological deterioration of seeds. Limited evidence suggests that only short periods of high-temperature stress at critical seed development stages are required to reduce seed vigour, but further research is required. The predicted environmental changes will lead to losses of seed quality, particularly for seed vigour and possibly germination. The seed industry will need to consider management changes to minimize the risk of this occurring.

Influence of crop management practices on physiologic leaf spot of winter wheat

The response of physiologic leaf spot to winter wheat management practices was examined in the semiarid Pacific Northwest. Winter wheat cultivars exhibited large differences in susceptibility. The dominant cultivar (Stephens) produced in the region was the most susceptible cultivar evaluated. The disease became less severe as the date of seeding was delayed and as the rate of nitrogen fertilization increased. Leaf spot severity was reduced and grain yield increased with foliar application of urea+calcium chloride, but not with application of urea+micronutrients. The disease was more severe in annual wheat than in rotations of wheat with fallow or peas

Residue Management and Herbicides for Downy Brome (Bromus Tectorum) Control in Kentucky Bluegrass Grown for Seed

Recent changes in herbicide registrations and governmental restrictions on field burning raised many management questions for Kentucky bluegrass seed producers, particularly the extent to which useful lives of their stands might be shortened by decreasing crop yields or increasing weed pressure. Tests conducted over the lives of two grass seed stands (1993–1997) evaluated three contrasting methods of postharvest residue management (vacuum sweep, bale/flail chop/rake, and field burn) and 13 herbicide treatments. Downy brome was the primary weed at both the Madras and LaGrande, OR, sites. In nontreated checks and the four least effective herbicide treatments, downy brome populations increased exponentially over time, with year-to-year increases in density averaging 13.1-fold. Competition had easily detected effects on Kentucky bluegrass seed yield at densities of 30 downy brome plants/m2, and crop stands were destroyed beyond 100 to 200 weeds/m2. Both PRE terbacil at 840 g/ha and early POST (EPOST)/late POST (LPOST) split-applied primisulfuron at 20 g/ha per application contained downy brome during the first 2 yr but not the third, when crop injury from terbacil forced reduction in terbacil rate and changes in weed populations overcame primisulfuron. PRE terbacil followed by LPOST primisulfuron, EPOST terbacil plus primisulfuron followed by LPOST primisulfuron, and EPOST/LPOST split-applied terbacil plus primisulfuron achieved excellent control of downy brome until the final years of the study, when control became increasingly erratic as primisulfuron-resistant downy brome proliferated in specific individual plots. Injury from combination terbacil plus primisulfuron treatments reduced yield relative to safest treatments in early years when downy brome population densities were low. Nomenclature: Dicamba; metribuzin; oxyfluorfen; primisulfuron; terbacil; downy brome, Bromus tectorum L. BROTE; Kentucky bluegrass, Poa pratensis L. POAPR.