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Region nurseries include locations with diverse environmental and biotic conditions where genotype x location (GxL) interaction is expected to be large and may result in failure to differentiate genotypes. Collaku et al. (58–63) used a hierarchical cluster analyses based on GxL interaction effects to group testing sites of Uniform Southern Soft Red Winter Wheat Nursery (USSRWWN) for milling and baking quality attributes. Classification of locations of USSRWWN into two main subregions with similar GxL improves cultivar differentiation and contributes to more efficient ways to evaluate resource expensive traints, such as milling and baking quality.
Stand Establishment of Eastern Gamagrass
Eastern gamagrass (Tripsacum dactyloides L.) is a warm-season, perennial grass with high palatability and productivity. However, poor stand establishment, often due to seed dormancy, limits its widespread use. Tian et al. (185–189) studied the effect of the cupule and pericarp scarification on the germination of dormant eastern gamagrass seed. Cupule removal stimulated the germination of some dormant seed, most remained dormant, however. Scarifying the pericarp over the scutellum of the embryo resulted in the germination of all viable seed. Both the cupule and the pericarp are involved in the dormancy of eastern gamagrass seed. However, further investigations of practical dormancy breaking protocols will be required to develop seed treatments that will improve the ease of stand establishment.
Orchardgrass Model Based on Tiller Structure
The digestibility of grazed herbage, particularly for lenient management and low N application, is poorly understood. For a vegetative orchardgrass (Dactylis glomerata L.) sward, Duru and Ducrocq (214–223) proposed a model based on tiller structure rather than on dates of cutting or grazing. For a given growing period, whatever the cutting date and the N application, the digestibility of the youngest fully expanded laminae depended on growth duration outside the sheath only. Because lamina growth duration depends on sheath length and herbage N status, both the digestibility of the youngest fully expanded laminae as well as the digestibility of the green lamina at the whole canopy level can be expressed on the basis of these two easily measurable sward states. The model, thus, could take into account the effect of degree of defoliation and explain the faster decline of herbage digestibility when the N rate is higher or when daily temperatures increase.
Developing Core Collections of Sorghum
U.S. sorghum breeders and growers have shown a strong interest in the exploration and preservation of exotic sorghum [Sorghum bicolor (L.) Moench] germplasm; currently, the collection inventories over 42000 accessions, which is too large a number to screen and evaluate efficiently. Dahlberg et al. (291–296) compared germplasm evaluation techniques based on agronomic descriptors with phylogenetic trees developed from random amplified polymorphic DNA (RAPD) fingerprinting to identify one approach that uses agronomic descriptors that most closely approximate the groupings produced by RAPD markers. These results indicate that no one technique closely approximates the groupings produced by RAPD markers, which underscores the need for further research in the evaluation of techniques used to develop core collections.
QTLs for Root Morphology Traits in Rice
Kamoshita et al. (255–265) examined effects of phenotyping environment on identification of quantitative trait loci (QTLs) for constitutive root morphology traits using 220 double-haploid lines from a cross between an upland japonica and a lowland indica (‘CT9993-5-10-1-M’/‘IR62266-42-6-2’) rice (Oryza sativa L.) in four greenhouse experiments. The results showed the importance of phenotyping environment and suggested prospects for selection of QTLs for deep root morphology, root thickness, and vigorous seedling growth under anaerobic conditions to improve the constitutive root system of rainfed lowland rice. There was some consistency in QTL regions identified, despite the presence of QTL x environment interactions.
New Pastures from Seed
Establishment of new pastures from seed is risky. Forage plants must be able to grow and develop quickly to withstand stresses and develop a productive stand. Sanderson et al. (224–230) examined grazing bromegrass (Bromus stamineus Desv.), prairiegrass (Bromus willdenowii Kunth), and orchardgrass (Dactylis glomerata L.) for their ability to establish rapidly and to yield well in established stands. Grazing bromegrass had more leaves, about twice the number of tillers per seedling, and a greater seedling mass than other grasses, but the larger seedling size and greater tiller density did not translate into greater yield performance in the field. Rapid development of the larger-seeded grasses in a mixed species planting may crowd out smaller seedlings. Therefore, prairiegrass and grazing gromegrass probably should be used at a lower seeding rate or perhaps not used in seed mixtures with small-seeded grasses. Seedlings of these grasses should be fully established by 40 to 50 d after planting under favorable moisture and temperatures in the spring and late summer.
Spectral Radiance to Estimate Biomass and Yield
Available water and N are potentially the most limiting factors affecting corn growth and production. An experiment was initiated by Osborne et al. (165–171) to determine specific wavelengths and/or combinations of wavelengths indicative of water stress and N deficiencies, and to evaluate these wavelengths for estimating in-season biomass and corn (Zea mays L.) grain yield. Near-infrared (NIR) reflectance and the water absorption bands were used to estimate total N and biomass in the presence of a water stress; without a water stress, green and NIR reflectance were used. Remote sensing techniques can be used to evaluate in-season N and water status.
Flowering and Planting Date in Clover
Understanding factors that affect growth and development of crimson clover (Trifolium incarnatum L.) would be important for the development of management practices to optimize forage production and utilization by improving season of use. An intermediate and late maturing cultivar was planted by Butler et al. (242–247) at six dates to evaluate the effect of date to reach 50% bud and 50% flowering on the basis of day of year (DOY), days after planting (DAP), photothermal index, and growing degree days. Date to reach 50% flowering was best correlated with DOY (r = 0.93 and 0.97) and DAP (r = 0.92 and 0.98) for ‘Columbus’ and ‘Tibbee’. Planting after 21 December delayed flowering in Tibbee 2 to 9 wk, whereas Columbus planted after 21 December did not flower. It is important to plant early in the growing season or to use later maturing cultivars to maximize utilization.
Intercepted Light and Soybean Biomass
Purcell et al. (172–177) proposed that increased population density in soybean [Glycine max (L.) Merr.] would increase the amount of light intercepted during a season and biomass produced, provided that radiation use efficiency (RUE) was constant. Over a wide range of populations and maturities, biomass at the end of the season responded linearly to intercepted light up to 400 MJ m-2, but was curvilinear above this value. With adequate soil moisture and nutrients, RUE decreased linearly by 26 to 30% as population density increased. Biomass production at high populations was not limited by light, and productivity may be limited by RUE at high populations.
Productivity in Dwarf vs. Tall Sunflower
Information on drought adaptability of dwarf sunflower (Helianthus annuus L.) cultivars is lacking. Angoli and Entz (152–159) conducted a 2-yr field study at two locations in southern Manitoba under rainfed conditions to compare water relations and photosynthesis of two dwarf sunflower cultivars with those of a standard height hybrid. Whenever cultivar differences were observed, the dwarf hybrid, SW-103 maintained higher pressure potential compared with the tall hybrid IS-6111. Both lower water stress levels (higher water potential) and better osmotic adjustment contributed to higher pressure potential. The second dwarf cultivar Aurora responded differently from SW-103, indicating the presence of genetic variation within dwarf cultivars. The standard height cultivar maintained greater stomatal conductance and higher photosynthetic rate than the dwarf cultivars under the conditions of this study (i.e., ample soil water supply). It was hypothesized that under conditions of low soil water availability, dwarf cultivars may have greater productivity than tall cultivars because of their superior leaf water relations.
Rate of Leaf Appearance in Crimson Clover
Currently there is little information describing growth and development of cool-season annual clovers. Understanding factors that affect growth and development would be important for the development of management practices to optimize forage production and utilization. Butler et al. (237–241) planted two cultivars of crimson clover (Trifolium incarnatum L.) six times from September to March for 3 yr to see if climatic factors could be used to predict leaf appearance. Leaf appearance was primarily controlled by temperature, which accounted for 90 to 99% of the variability. It is important to plant early in the growing season, as soon as moisture and lower temperature allows, to maximize the length of the growing season and possibly total production in grazed environments.
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  S. P. Singh Broadening the Genetic Base of Common Bean Cultivars: A Review Crop Sci., November 1, 2001; 41(6): 1659 - 1675. [Abstract] [Full Text] [PDF]
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