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New corn (Zea mays L.) inbred lines from the Germplasm Enhancement of Maize project (GEM) are becoming available to corn breeders. These lines are derived from crosses of adapted and exotic germplasm and differ in quality characteristics such as protein and oil content. It is important to determine if the exotic genes could create seed germination or seed quality problems that could affect farmers' profitability if used in hybrids. In several diverse locations, Munamava et al. (542–548) evaluated for seed quality inbred lines they developed from GEM breeding lines with a wide range of protein and oil values. They found that the location had an effect on seed germination but the origin of the exotic germplasm and the seed composition did not. However, the origin of the exotic germplasm and the seed composition affected seed vigor. Therefore, to prevent unforeseen production problems, it will be important to monitor seed quality as these new lines become available.
Chickpea Osmotic Adjustment
A physiological selection criterion is required for screening drought resistant chickpea cultivars (Cicer arietinum L.) for rainfed areas. Moinuddin and Khanna-Chopra (449–455) screened chickpea cultivars differing in osmotic adjustment capacity in the field under water deficit environments imposed by a line source sprinkler irrigation system. A high osmotic adjustment group had better plant water status, seed yield, and yield parameters than did a low osmotic adjustment group under water deficit. An osmotic adjustment ranging from 0.28 to 0.48 MPa and from 0.37 to 0.71 MPa was recorded for the high osmotic adjustment cultivars and resulted in a yield benefit of 26 and 48% under mild and severe moisture stress, respectively, relative to the low osmotic adjustment group. Osmotic adjustment can be used as a selection criterion for screening drought resistant chickpea.
Seed Vigor Tests Evaluation
Laboratory germination tests do not always indicate seed lot potential performance, especially if field conditions are less than optimal. Seed vigor tests have been proposed to detect differences in potential seed lot performance. Wang et al. (535–541) investigated suitability of various laboratory vigor tests to rank quality of commercial seed lots and to predict seedling field emergence of four forage species. Among the vigor tests used, an electrical conductivity test provided the best estimate of seed vigor for two legume species, but gave the worst indication of seed lot vigor for two grass species. A controlled deterioration test was a better indicator of seed lot vigor for all test species than was than the germination test. On the basis of these results, the electrical conductivity test for forage legumes and controlled deterioration test for both forage legumes and grasses have the potential to be developed as improved vigor tests for ranking seed lot quality and predicting seeding performance.
Legal Liability in Agricultural Production
Transgenic crops have heightened the interest among farmers and seed companies about potential legal liability in agricultural production. The article by Kershen (456–463) provides an introduction to legal liability claims that might be raised in field agriculture related to transgenic crops. The legal liability focus is on tort liability and patent liability. The article presents both the possible claims and the unique issues that are likely to arise in legal liability cases arising from transgenic crops. Risks of legal liability do exist for transgenic crops, including some unique risks, but the risks overall may not be significantly different from legal liability for other crops in agricultural production generally.
Variability in Wheat Water-Use Efficiency
Variability in water-use efficiency (WUE) based on transpiration is expected in response to climatic factors and soil water availability. Abbate et al. (474–483) conducted six experiments throughout the Argentine wheat belt to quantify the effects of pan evaporation, atmospheric relative humidity, potential water use, vapor pressure deficit (VPD), and soil water availability on WUE. With high water availability, VPD was the factor most closely associated with WUE. Water deficiency increased WUE, thus crop dry weight under low relative to high water availability did not relate linearly to relative transpiration, as proposed in previous studies. This response was better represented by a quadratic relationship derived in this study.
Phenotypic Variation in Wild Soybean
Wild soybean (Glycine soja Sieb. & Zucc.) accessions lack much of the phenotypic variation common in soybean [Glycine max (L.) Merr.]. This research demonstrated the great variation in leaflet size and shape that exists among wild soybean accessions and devised a scheme to classify that variation. Chen and Nelson (671–677) report that leaflet shape and size are associated with geographical origin. Accessions from South Korea were generally smaller than those from China, Japan, and Russia. Accessions from China had more leaflet variation than those from South Korea or Japan but those from Russia were the most variable.
Improving Perennial Ryegrass Gray Leaf Spot Resistance
Gray leaf spot, caused by the fungus Pyricularia grisea (Cooke) Sacc., can be a devastating disease on perennial ryegrass. Bonos et al. (575–580) established two perennial ryegrass field experiments in 2000 and 2001 at Adelphia, NJ, that were evaluated for susceptibility to gray leaf spot disease. Parent clones with improved gray leaf spot resistance were selected based on progeny turf plot evaluations in 2000, interpollinated and seeded into turf plots in the 2001 experiment. The high broad-sense heritability estimate (0.92) and similar response of progeny compared with selected parents indicated that parent selection based on progeny tests was a good selection method to predict the combining ability of the parents. It also proved successful in improving gray leaf spot resistance in the next generation, which will be important for the development of more disease-resistant cultivars.
Cadmium Accumulation in Wheat
Various cultivars of bread (Triticum aestivum L.) and durum wheat (T. durum Desf.) accumulate different concentrations of cadmium (Cd) in the grains. Greger and Löfstedt (501–507) investigated whether high levels of Cd in the grains of high Cd-accumulating cultivars is caused by a high Cd uptake in the roots, a high translocation of Cd from roots to shoot, or a redistribution of Cd between the shoot and the grains. Results indicated that there are differences among the cultivars in the ability to accumulate Cd in grains, but the biggest difference was found among durum wheat cultivars. It also found that the differences were related to variations in the Cd translocation from root to shoot and to the Cd concentration in shoot, flag leaf, and grain coats, but not to the uptake of cadmium by roots.
Wheat Genes Associated with Agronomic Performance Traits
The expression of genes associated with agronomic performance traits in wheat (Triticum aestivum L.) are known to be highly influenced by environmental interactions. Using a molecular marker and agronomic performance dataset for a population of chromosome 3A recombinant inbred chromosome lines and an environmental covariate dataset for seven testing environments, Campbell et al. (620–627) constructed individual factorial regressions to explain genotype x environment and QTL x environment interactions. Temperature and precipitation before anthesis had the greatest influence on agronomic performance differences across environments. Seventy-six percent of the environmental interaction associated with a major grain yield QTL was explained by the effect of temperature during preanthesis growth. This study illustrates that combining agronomic and molecular marker data along with environmental covariates can provide a strong basis for explaining differential gene expression across environments.
Genetic Diversity within and among Wild Red Clover
Mosjidis et al. (665–670) quantified genetic diversity (GD) within and among wild red clover (Trifolium pratense L.) using isozymes. Understanding the level and pattern of GD and examination of the correspondence of diversity and gene flow expectations based on predictions using topographic maps developed using interpolated digital and climatic surfaces would help germplasm collection and post-collection efforts to understand patterns of GD in collected germplasm. Diversity measurements indicated that this species had a high level of variability that resides mostly within populations. Gene flow expectations based on predictions using topographic maps coincided with gene flow estimates obtained using isozymes.
Reproductive Characteristics of Lotononis bainesii Baker
Reproductive characteristics can influence seed production and the amount and distribution of genetic variation within populations. Lotononis bainesii Baker is a subtropical forage legume from Southern Africa that earlier researchers reported as having a cleistogamous form of reproduction. More recently, reports suggest that species in the genus Lotononis Section Listia reproduces chasmogamously. The study by Real et al. (394–400) suggests that this species needs pollinators to produce seed and that genotypes exist that are self-incompatible. The use of sequence characterized amplified regions (SCAR) and cleaved amplified polymorphic sequence (CAPS) markers demonstrated that L. bainesii is highly allogamous.
Seed Dormancy of Eastern Gamagrass
Eastern gamagrass (Tripsacum dactyloides, L.), a warm season, perennial grass with great potential for forage and conservation uses, has a high degree of seed dormancy, making establishment difficult. Rogis et al. (549–552) investigated the combined use of stratification and gibberellic acid (GA3) for promoting eastern gamagrass seed germination. Combinations of GA3 and stratification for 4 wk or more did not increase final germination of eastern gamagrass seed above levels attained by stratification without GA3. However, GA3 did stimulate more rapid and greater germination when seed was stratified for 3 wk or less. Once the dormancy was completely broken with 4 wk of stratification, seed germinated more rapidly when GA3 was applied. Addition of GA3 to stratification improved the seed quality of eastern gamagrass above the use of stratification alone.
Maize Gray Leaf Spot Resistance
Gray leaf spot of maize is caused by Cercospora zeae-maydis (Tehon & Daniels) and is an important foliar disease. Improved host resistance is needed for effective disease management. Gordon et al. (628–636), in Ohio and South Africa, evaluated a population of 144 F2:3 maize (Zea mays L.) progeny lines derived from a cross between resistant inbred VO613Y and susceptible inbred Pa405. A selective genotyping strategy was employed to determine SSR molecular markers linked to resistance factors. Significant marker intervals were identified on chromosomes 2 and 4. The markers will provide tools for introgression of the resistance loci to susceptible germplasm.
Bentgrass Hybrids With Dollar Spot Resistance
Dollar spot disease (caused by Sclerotinia homoeocarpa F.T. Bennett) is one of the major management problems encountered with creeping bentgrass (Agrostis stolonifera L.) on golf courses. Current methods of control rely heavily on the use of fungicides. There is a wide range in degree of susceptibility among current cultivars, with a limited number that have improved resistance. Belanger et al. (581–586) report dollar spot resistance in interspecific hybrids between creeping bentgrass and a related species that has good resistance, colonial bentgrass (Agrostis capillaris L.). Such interspecific hybridization for improvement of creeping bentgrass has not been used previously and may be a useful new approach in breeding programs.
Shade and Turf Quality
Low light is a major problem that influences turf quality. Jiang et al. (587–594) found that seashore paspalums (Paspalum vaginatum Swartz) exhibited large variations in low-light tolerance when grasses were exposed to 70 and 90% shade; ‘Sea Isle 1’ was the most tolerant cultivar. In this study, most seashore paspalums showed better turf quality and low light tolerance than ‘TifSport’ and ‘TifEagle’, the two hybrid bermudagrasses (Cynodon dactylon L. x C. transvaalensis Burtt Davy). The responses of turfgrass species or/and cultivars to low light conditions could potentially be used for enhancing turf management practices.
Congruity Backcrossing for Common and Tepary Beans
Congruity backcrossing has been suggested as a method for increasing introgression in interspecific crosses of common beans (Phaseolus vulgaris L.) with tertiary genepool species such as tepary beans (P. acutifolius A. Gray). Muñoz et al. (637–645) applied amplified fragment length polymorphism markers to study the frequency of introgression in genotypes derived from congruity and non-congruity backcrosses between common bean x tepary beans, showing that congruity backcrossing did indeed increase introgression, but that introgression was still below expected levels. The genetic distance between the two species may prevent greater levels of genomic substitution.
Background of U.S. Hybrid Corn Breeding, Climate, and Food
Troyer (370–380) explains which open-pollinated corn (Zea mays L.) cultivars and landmark inbreds persisted into today's hybrids and attempts to explain how and why. Reid Yellow Dent is 51% of the documented U.S. hybrid corn background (Iodent Reid, 13%; Troyer Reid, 12%; Osterland Reid, 11%; Stiff Stalk Synthetic, 8%; Reid per se, 4%; and Funk Reid, 3%). Minnesota 13 is 13%, Lancaster Sure Crop is 13%, Northwestern Dent is 5%, and Leaming Corn is 5%. Five widely adapted, century-old, open-pollinated cultivars surpassed in use tens of thousands of genetically divergent cultivars to account for 87% of the known background of today's U.S. hybrid corn. Adaptedness mattered. U.S. corn breeders are adapting a tropical crop to a temperate climate.
Blending Kentucky Bluegrass Cultivars of Different Quality Performance Levels
Kentucky bluegrass (Poa pratensis L.) lawns and sports turf are traditionally sown as blends of two or more cultivars. Theories abound as to whether the cultivars for a blend should be chosen based on color similarities, pest resistance differences, or laboratory DNA banding patterns. A field study by Brede (561–566) demonstrated that an elite cultivar was nearly always diminished by the addition of an inferior blend component. It detected certain circumstances where a lesser component could be tolerated and even hidden in a blend to help soften the seed price tag, but for the most part, the inferior cultivar decreased lawn quality. This study supports the idea that a single elite cultivar may make a better lawn than a blend of elite and inferior cultivars.
Pollination Timing Effects on Kernel Set and Silk Receptivity
Kernel set in maize (Zea mays L.) is a dynamic process largely impacted by hybrid variability for silk elongation rate, duration of silk receptivity, and silk senescence. In a study by Anderson et al. (464–473), four hybrids were compared by measuring silk growth and silk morphological characteristics while controlling pollination timing. Hybrid silk elongation patterns were unique because silk receptivity and senescence varied, impacting kernel set and stability. These experiments provide a better understanding of the extent of variation in four hybrids for kernel set when time of pollination varies.
Japanese Beetle and Fungal Endophytes on Competition between Turfgrasses and Dandelion
The ability of Neotyphodium fungal endophytes to provide their grass hosts with resistance to above-ground insects has been well documented, and endophytes have been implicated as an important force driving the composition of grassland plant communities. Richmond et al. (600–606) address this issue below-ground by studying the influence of Neotyphodium endophytes and herbivory by soil-dwelling larvae of the Japanese beetle (Popillia japonica Newman) on competitive interactions between grasses and dandelions in turfgrass. Although Neotyphodium endophytes had little effect on the larvae, below-ground herbivory markedly enhanced the performance of dandelion. Results illustrate an important linkage between insects and weeds that is often overlooked in turfgrass management.
Related articles in Crop Science:
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