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Emergence of soybean [Glycine max (L.) Merr.] seedlings in the field is frequently less than predicted by standard germination, but the causes of this emergence failure are not well understood. Hamman et al. (451–457) , explored the influence of soil pathogens and seed vigor on soybean seedling preemergent growth and emergence. The presence of pathogens in the soil, and the use of seed with less than high quality, had a negative impact on both preemergent growth and final seedling emergence. Planting pregerminated seeds did not eliminate emergence failure. Lack of germination alone therefore does not account for lack of emergence; postgerminative, preemergent growth may be more important.
Origin of White Clover
White clover is found is most areas of North America, but its origins are in Europe and the Middle East. Cultivars brought to the new world from Europe escaped in the wild and became naturalized. Gustine et al. (343–347) found that populations of white clover collected from pastures in Georgia, Iowa, Pennsylvania, and West Virginia in the USA and from Prince Edward Island in Canada had surprisingly similar genetic compositions. Their data suggest a common European origin for much of the naturalized white clover in North American pastures.
Mapping Turf with Vehicle-Mounted Remote Sensors
Environmental concerns require turf managers to minimize the amount of nutrients and pesticides used for turf maintenance. Bell et al. (648–651) tested vehicle-mounted optical sensing (VMOS) for mapping plant status over large turf areas. These maps could provide opportunities for early detection of potential turf problems, economic savings for fertilizers and pesticides, and improvements in turf appearance and functional quality. Normalized difference vegetative index maps constructed from VMOS measurements compared closely with turf response to N fertility and turf cover during grow-in. VMOS maps clearly indicated areas of poor nutrition, sparse turf cover, and some irrigation patterns.
Trinexapac-Ethyl on Respiration of Isolated Wheat Mitochondria
Little is known about nontarget biochemical effects on plants from trinexapac-ethyl [(4-cyclopropyl-
-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid methyl ester].
Heckman et al. (423–427)
evaluated the effects of trinexapac-ethyl and 2-oxoglutarate on the mitochondrial electron transport chain of wheat (Triticum aestivum L. ‘Arapahoe’). Trinexapac-ethyl applied at increasing rates reduced respiration of isolated mitochondria, while 2-oxoglutarate did not reduce respiration as had been previously suggested. Further experiments revealed trinexapac-ethyl was possibly interfering with ubiquinone binding sites. Knowledge of this physiological effect will allow for a better understanding of trinexapac-ethyl on metabolism.
Digestibility of Alfalfa Stems
Improving alfalfa (Medicago sativa L.) quality will require greater understanding of the factors that cause the digestibility of alfalfa stems to decline during maturation. Stem tissues of a specific internode were characterized by Jung and Engels (524–534) using microscopy and cell-wall analysis across five stages of development starting during early elongation. Until elongation of the stem internode ceased, almost all tissues were completely digestible, but deposition of secondary xylem after elongation ended marked the beginning of lignification and decreased stem digestibility. Proliferation and lignification of secondary xylem tissue in alfalfa stems must be slowed to reduce the impact of maturity on alfalfa quality.
Grain Yield in Barley
Information is lacking on traits that underlie grain yield performance of Ethiopian barley (Hordeum vulgare L.) landraces. Sinebo (428–437) studied interrelationships among yield and yield-related traits using correlation and path analysis. Grain yield was associated positively with vegetative height, straw yield, mature height, spikes per square meter, kernels per spike, and grain-filling duration and associated negatively with vegetative duration. Vegetative height influenced growth durations negatively. Early shoot height association with yield and time to maturity suggests an adaptive strategy for capturing the early flush of mineralized N and an escape mechanism from season-end drought. Early shoot height can serve as an indirect selection criterion for high grain yield and early maturity.
Saccharum Linkage Maps
Genetic mapping of autopolyploid sugarcane is complicated by the large number of chromosomes and random pairing among homologous chromosomes. The limited subset of markers that can be analyzed with a population of manageable size affects the completeness of the linkage map. In this experiment, Ming et al. (570–583) used two interspecific Saccharum mapping populations to construct four linkage maps representing two major Saccharum species, S. officinarum L. and S. spontaneum L. The compact genome of sorghum was used as a template to assemble a Saccharum consensus genetic map. The extensively mapped sorghum map aided the alignment of individual Saccharum maps and the filling of gaps on the consensus map by mapping information from different Saccharum linkage maps. This consensus map will be a useful tool for future genetic and QTL mapping and marker-assisted selection in sugarcane.
Waterlogged Wheat
Waterlogging stress is one of the limiting factors influencing wheat (Triticum aestivum L.) in heavy rain areas such as Gulf Coast Region. Collaku and Harrison (444–450) provided methods to quantify losses from waterlogging and identified selection criteria for waterlogging tolerance in wheat. They found linear response as the main trend to explain from 92 to 99% of the variability due to waterlogging effect. The average yield loss of 44% was mainly due to the effect of waterlogging in decreasing tiller and kernel number. Screening of wheat genotypes revealed the potential for waterlogging tolerance in the breeding material and identified tolerant cultivars useful for waterlogged environments.
Red Clover Leaf Markings
Red clover (Trifolium pratense L.) typically exhibits light marks on its leaves, but plants without leaf marks also occur. The no mark phenotype is due to a homozygous recessive genotype. Bortnem and Boe (636–636) evaluated the core collection of red clover for frequency of this recessive allele. Estimates of gene frequency for the no mark phenotype ranged from 0.0 to 0.67 for the 82 accessions evaluated. Their data indicated the recessive allele was absent or rare in about 25% of the accessions.
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