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Fall dormancy has been associated with alfalfa (Medicago sativa L.) winter survival, but dormant alfalfa plants are less productive in summer than are nondormant alfalfa plants. Cunningham et al. (1091–1098) determined how genetic selection that resulted in incremental changes in fall dormancy altered winter survival, root physiology, and expression of cold acclimation-responsive genes. Fall dormant populations had greater winter hardiness, higher root sugar and protein concentrations, and greater expression of a cold acclimation-responsive gene. This cold acclimation-responsive gene may find use as a marker to efficiently identify winter hardy alfalfa plants, especially among semi-dormant or nondormant alfalfa germplasm pools.
Nutrition vs. Yield in Timothy
Forage nutritive value and dry matter (DM) yield are related negatively. Hence, the improvement of both DM yield and nutritive value requires the identification of genotypes that deviate from that negative relationship. Brégard et al. (1212–1219) studied nine timothy (Phleum pratense L.) genotypes in a growth room with limiting and nonlimiting N rates. Genotype differences in forage DM yield were not necessarily associated with changes in biomass partitioning but rather to a greater growth potential of some genotypes. The variability among genotypes for the relationship between DM yield and nutritive value parameters confirms the possibility of selecting for high yielding genotypes with superior forage nutritive value.
Hulless and Rough-Awned Genes in Barley
The effects of the hulless (nud) and rough-awned (Raw1) genes are not fully understood in hulless barley (Hordeum vulgare L.). Choo et al. (1021–1026) studied the effects of these two genes on 11 other traits. Hullessness was associated with low emergence, short plant height, high test weight, low seed weight, or low grain yield, but it was not associated with heading date, maturity, spike density, smut resistance, or scald resistance. Rough-awned hulless barley had more hulless kernels than smooth-awned barley. Propagating segregating materials from hulless x covered crosses in bulk should be avoided because many hulless plants may be eliminated by competition.
Soybeans, N2 Fixation, and Drought
Differences exist among soybean cultivars [Glycine max (L.) Merr.] in sensitivity of N2 fixation to drought. King and Purcell (1099–1107) hypothesized that large nodules may confer drought tolerance because their larger fraction of N2-fixing tissue results in greater sink demand and phloem water supply than small nodules. A drought-sensitive cultivar, KS4895, had numerous small nodules compared with drought-tolerant ‘Jackson’, which had fewer nodules of greater individual mass. Jackson had greater nodule permeability to O2 and photosynthetic C supply to nodules for both well-watered and water-deficit plants compared with KS4895. Drought tolerance of Jackson appears partially due to the advantages of large nodules, but an inherently greater supply of photosynthates to nodules of all sizes under well-watered and water-deficit conditions is also important in continued N2 fixing under water-deficit conditions.
Exotic Germplasm in Maize
The introgression of exotic germplasm could increase the heterosis for grain yield among maize (Zea mays L.) populations. Mickelson et al. (1012–1020) investigated heterotic relationships among BSSS (R) (Reid germplasm) and BS 26 (Lancaster germplasm) from the temperate USA; the southern African cultivars Salisbury White, Southern Cross, and Natal Potchefstroom Pearl Elite Selection (NPP ES); and the subtropical CIMMYT Populations 34, 42, 44, and 47. Low to moderate levels of high parent heterosis was observed for crosses involving Populations 34, 42, 44, and 47 and NPP ES, and higher levels for crosses involving BSSS (R), BS 26, Salisbury White, and Southern Cross. An opposing heterotic relationship was demonstrated between BSSS (R) and BS 26, Salisbury White and Southern Cross, Population 44 and BS 26, and BSSS (R) and Southern Cross, with the best heterotic combination involving Population 44 and BSSS (R). These heterotic combinations can be used directly by breeding programs or as sources of genes to enhance heterosis in existing breeding materials.
Powdery Mildew Resistance in ‘Massey’ Wheat
Powdery mildew, caused by Blumeria graminis (DC.) E.O. Speer f. sp. tritici Em. Marchal (syn. Erysiphe graminis f. sp. tritici), is one of the major diseases of wheat (Triticum aestivum L.) worldwide. Liu et al. (1268–1275) used both RFLP and microsatellite markers to identify quantitative trait loci (QTLs) associated with adult plant resistance (APR) to powdery mildew in winter wheat cultivar Massey. With bulked segregant analysis and interval mapping, three QTLs were identified through analysis of 180 F2:3 lines. The presence of the three QTLs was confirmed with 97 recombinant inbred lines tested for APR to powdery mildew over 3 yr. The molecular markers identified in this study have potential for use in marker-assisted selection and pyramiding of genes for resistance to powdery mildew in wheat.
Linkage Maps and QTL Analysis of DH and RIL Rice
Although molecular linkage maps and quantitative trait locus (QTL) analysis have been extensively done in rice, few reports are available comparing maps and mapped QTLs of DH and RIL populations. He et al. (1240–1246) compared the genetic linkage maps and QTL mapping of six agronomic traits in DH and RIL populations derived from the same rice (Oryza sativa L.) cross. They concluded that the molecular maps and QTL locations were highly conserved between the two populations and that DH populations can reduce distorted segregation characterized by RIL populations. This study indicates that both RIL and DH populations are equally effective in rice breeding and genetic analysis.
Soybean Linkage Groups and Paired Chromosomes
The 20 molecular linkage groups (MLGs) of soybean [Glycine max (L.) Merr.] have been defined but have not been associated with their respective 20 pairs of soybean chromosomes. Cregan et al. (1262–1267) demonstrate that the completion of the development of this set of 20 soybean primary trisomics makes these associations possible. Progeny derived from crosses of two different primary trisomics with normal soybean were analyzed by simple sequence repeat (SSR) markers that had been previously mapped to different soybean MLGs. SSR markers were identified that fit trisomic inheritance. In this manner, MLG J was associated with soybean chromosome 13 and MLG A1 with chromosome 5. This work defines the approach that will be used to develop a universal cytogenetic map of soybean in which all genes and molecular genetic markers are associated with specific chromosomes.
Flooding Tolerance in Soybean
Soil waterlogging is a major environmental stress that suppresses soybean [Glycine Max (L.) Merr.] growth and yield. VanToai et al. (1247–1252) conducted a study with 208 progeny lines of two crosses to identify DNA markers associated with the tolerance of soybean to soil waterlogging. The experiment was conducted in three environments where plants at the beginning flowering stage were subjected to waterlogged soil for 2 wk. A single marker (Sat_064) was identified which was associated with improved plant growth and grain yield in waterlogged soil. The Sat_064 QTL was associated with flooding tolerance and not with maturity, normal plant height, or grain yields, and would allow the selection of flood-tolerant genotypes for breeding without the need of growing and testing a large number of plants in the field.
Spectroscopy Analysis in Purple Coneflower
Near infrared (NIR) reflectance spectroscopy is an empirical technique capable of rapid analysis of a wide range of plant products. At present, there is no rapid method of analyzing chicoric acid in purple coneflower [Echinacea purpurea (L.) Moench], a valuable crop in the U.S. botanical industry. In this study, Gray et al. (1159–1161) quantified chicoric acid in purple coneflower roots by NIR reflectance spectroscopy. The optimum prediction equation produced coefficients of determination for calibration and cross validation of 0.90 and 0.86, respectively. They concluded that chicoric acid in purple coneflower root could be detected accurately by NIR reflectance spectroscopy.
Diverse Clones of Clover
White clover (Trifolium repens L.) populations persist for years in grazing lands primarily through clonal growth, yet retain high genetic variability. Changes in genetic structure of white clover populations were studied on three dairy farms in central Pennsylvania by Gustine and Sanderson (1143–1149) using DNA molecular markers. Random amplified polymorphic DNA (RAPD) profiles were determined for plants sampled repeatedly at randomly selected field points during two consecutive growing seasons. Analysis of molecular variance (AMOVA) of the populations suggested that decreased genetic diversity caused by higher numbers of clones was offset by rapid turnover of clones, thus maintaining genetic diversity of the populations.
NO-3 Efflux and Influx Effects in Cotton Soils
Exposure of plant roots to NH+4 inhibits net NO-3 uptake. Aslam et al. (1130–1136) investigated whether the inhibition of net NO-3 uptake by NH+4 in cotton (Gossypium barbadense L. and G. hirsutum L.) roots is due to inhibition of influx per se or enhancement of efflux. Inhibition of net uptake by NH+4 increased as root NO-3 concentration increased. The results suggest that the NH+4 effect is due to the stimulation of NO-3 efflux rather than inhibition of influx. The presence of NH+4 in agricultural soils may decrease NO-3 uptake efficiency.
Related articles in Crop Science:
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