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Kentucky bluegrass is a widely used cool-season turfgrass with many cultivars that are difficult to distinguish by morphological traits alone. Molecular markers such as RAPDs (random amplified polymorphic DNA) can provide a rapid alternative to classify these cultivars, as well as give an idea whether exotic plant introductions (PIs) are genetically different or redundant. In this study, Curley and Jung (44:1299–1306) collected RAPD markers from 123 Kentucky bluegrass cultivars, PIs, experimental breeding lines, and interspecific hybrids. Multidimensional scaling (MDS) plots were calculated to determine genetic relationships. Most of the PIs were found to be genetically different from the cultivars, only two of the trait-based types were genetically related according to RAPD data, and a high amount of variability among three seedling replicates of each genotype was found. Thus, the PIs are likely to be a useful genetic resource; for most trait-based groups, it will be possible to create blends of similar morphology while maintaining genetic diversity, and some cultivars contained a rather high proportion of nonapomictic, possibly sexually derived off-types.
Plant Species Diversity and Grazing
Plant species diversity is a hot topic in grassland ecology research because of the reported benefits to ecosystem functions. Sanderson et al. (44:1132–1144) review the current evidence relating plant biodiversity to ecosystem function and grazing and discuss the potential application of biodiversity concepts to management of temperate pastures. They conclude that the evidence is limited for diversity effects in pastureland and recommend that research on plant diversity in temperate pastures must move beyond small-scale experiments dealing with primary productivity. Instead, research should focus on grazing trials that measure plant and animal productivity on a range of species at relevant scales so that practical recommendations can be made for grazing management.
Plant Variety Protection
This paper examines the most recent (1991) UPOV modification of Plant Variety Protection systems to provide incentives for prebreeding, and concludes that the system is currently unworkable. Lesser and Mutschler (44:1113–1120) recommend that national bodies manage minimum enhancements for initial variety status. More fundamentally, the application of a single approach for improvements controlled by single or by multiple gene traits is inoperable. They further recommend different criteria be applied depending on the type(s) of innovation that characterizes a new variety.
Review of SCN Resistance QTL Mapping in Soybean
More than a decade of mapping soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) resistance quantitative trait loci (QTL) has led to the discovery of many SCN resistance QTL in plant introductions, as reported in numerous publications. In this review, Concibido et al. (44:1121–1131) summarize and discuss how the genetic mapping information can be used in breeding for SCN resistance. This review also focuses on how these discoveries ushered in the new era of breeding and selection for SCN resistance, also known as marker-assisted selection (MAS), and the eventual sequencing and cloning of candidate SCN resistance alleles for rhg1 and Rhg4.
Popcorn in the USA
Despite the economic importance of popcorn (Zea mays L.) in the USA, its systematics has received little attention. In this study, Santacruz-Varela et al. (44:1456–1467) characterized 56 maize populations, with an emphasis on New World popcorn landraces, for morphological traits, isozymes, and SSRs to elucidate their relationships. Three groups of popcorn were identified: (i) North American Yellow Pearl Popcorns, possibly derived from the Chilean race, Curagua; (ii) North American Pointed Rice Popcorns, which probably originated from traditional, pointed popcorn landraces from Latin America; and (iii) North American Early Popcorns, which show a marked influence of Northern Flint maize. To enhance conservation and use, it is proposed that these three groups be recognized taxonomically as distinct races, and their characteristics, including diagnostic alleles, are provided.
Turfgrass Nitrogen Utilization
Turfgrasses have been shown to have a remarkable ability to assimilate and sequester applied nitrogen with thatch shown to be a significant buffer for applied nitrogen. Some turfgrasses don't produce thatch; are these turfgrasses more prone to nitrate leaching? Engelsjord et al. (44:1341–1347) compared the ability of a thatch-producing Kentucky bluegrass (Poa pratensis L.) to utilize applied nitrogen with a non-thatch producing perennial ryegrass (Lolium perenne L.) turf. While the thatch-producing Kentucky bluegrass was slightly better at storing and utilizing applied nitrogen, the differences between the two species were not large, indicating that turfgrasses, with or without thatch, are very efficient at nitrogen utilization.
Associations among Bread Wheat Yield-Testing Locations
A good understanding of the target environments for a breeding program and how they differentiate the germplasm is crucial in any plant breeding program. Lillemo et al. (44:1163–1169) analyzed 8 yr of yield data from CIMMYT's High Rainfall Wheat Yield Trial (HRWYT) using shifted multiplicative model (SHMM) and incremental sum of squares (ISS) classification analyses. Two major subenvironments were identified. The first consisted of mainly autumn-sown sites with increasing temperature toward maturity, and high association with global yield performance. The second group consisted of mainly spring-sown sites with decreasing temperature toward maturity, and remarkably low association with global yield performance.
Maize Cross-Fertilization by Pollen from Neighboring Transgenic Hybrids
Since the introduction of Bt and other transgenic events into commercial varieties, there is an increasing concern about the preservation of genetic identity and of isolation distance required to segregate nongenetically modified (non-GM) from GM grain production. Ma et al. (44:1273–1282) conducted a systematic investigation in an 8 site-yr study of percentage cross-fertilization in conventional maize (Zea mays L.) populations by neighboring transgenic maize pollens. Their data indicate that it is possible to produce non-GM maize grains by removing the outside rows of non-GM maize plants (about 30 m) neighboring a GM maize field if the acceptance level is set at <1% out-cross.
Preservation of Genetic Diversity
The most important goal of crop genebanks is to preserve genetic diversity for future use in research and breeding. A reason preventing good representation of species gene pool is inadequate sampling during collections because lack of accurate information on the distribution of diversity among natural populations. Probably, the best approach to sampling is to identify an association of genetic diversity with diversity in ecogeographical patterns. del Rio and Bamberg (44:1170–1177) identified ecogeographical associations in an inbred potato species (Solanum verrucosum Schlechtd). It is possibly that the reproductive system improved resolution both in the experimental method and in the genetics of the natural populations themselves. This information could be used to enrich the capture of genetic diversity in future collections.
Oat Kernel Size Uniformity
Improved oat (Avena sativa L.) kernel size uniformity would be desirable for milling applications. Kernel size uniformity can be evaluated either by sequential sieving with slotted sieves, or by digital image analysis. Doehlert et al. (44:1178–1186) found that digital image analysis indicated that kernel size distributions to be bimodal or multimodal in shape. A statistical model was developed that compares the likelihood of a bimodal distribution with normal distributions, and provides means, variances, and numerical proportions of the two putative subpopulations in the bimodal distributions. Results suggest that the two subpopulations are derived from primary and secondary kernels from oat spikelets.
Wheat Coleoptile Length
Semidwarf wheat (Triticum aestivum L.) cultivars with greater coleoptile length are preferred in low-precipitation dryland regions. Bai et al. (44:1187–1194) evaluated coleoptile length and the Rht8 gene in 135 winter wheat cultivars. Only 8% of all U.S. accessions may carry Rht8 gene and these cultivars with Rht8 genes showed no advantage to coleoptile elongation. Results suggested that the presence Rht8 gene might not be necessary to increase coleoptile length in a semidwarf plant type.
Durable Resistance to Septoria tritici Blotch
Breeding wheat (Triticum aestivum L.) for resistance is the most effective means to control Septoria tritici blotch (STB), caused by the fungus Mycosphaerella graminicola (Fuckel) J. Schröt., yet two known resistance genes (Stb2 and Stb3) are not used extensively in plant-improvement programs because no molecular markers linked to either gene are available and their map locations are not known. Adhikari et al. (44:1403–1411) evaluated two doubled-haploid mapping populations derived from crosses between cultivars Veranopolis and Israel 493, which bear Stb2 and Stb3, respectively, with the susceptible Australian breeding line RAC875-2 for disease resistance and molecular mapping, and found that resistance in each cultivar is conditioned by a single major gene. Five molecular markers linked to the Stb2 were identified near the tip of wheat chromosome 3BS, which also contains previously mapped resistances against a wide array of fungal pathogens; one marker was linked to Stb3 on the short arm of chromosome 6D. Mapping these two resistance genes will be of use in breeding durable resistance to M. graminicola.
Primitive Accessions as Sources for Cotton Improvement I
Cotton fiber quality and yield must be improved to meet textile mill requirements and producer demands. McCarty et al. (44:1226–1230) evaluated yield and fiber quality when high fiber strength lines derived from primitive accessions were crossed to commercial cultivars. Cultivars had higher yields and lint percentages while primitive lines had higher fiber strength. Lint percentage, fiber elongation, and strength for F2– and F3–populations were near the midparent values, whereas boll weight exceeded the high parent. Additive, additive x additive, and dominance effects were detected for most yield and fiber quality traits. Primitive derived germplasm may serve as useful sources of genetic variation for pure line development.
Primitive Accessions as Sources for Cotton Improvement II
Primitive accessions of cotton may provide useful fiber traits for cultivar improvement. The ability to predict performance when crossed with cultivars would enhance their utility and encourage their use in breeding programs. This study by McCarty et al. (44:1231–1235) predicted genetic effects for primitive derived lines that were crossed to commercial cultivars. Yield, yield components, and fiber traits were measured and evaluated. Generally, the cultivar parents had higher additive genetic effects for yield and lint percentage and lower additive effects for fiber strength. The correlation between observed progeny values and predicted values were mainly high. This study suggested that crosses between cultivars and primitive derived lines can produce progeny with improved fiber strength and good yields.
Durable Stripe Rust Resistance
Race-specific resistance to stripe rust of wheat caused by Puccinia striiformis Westend. f. sp. tritici may become ineffective as new races develop in the pathogen population. Navabi et al. (44:1156–1162) studied the genetic basis of high levels of race-nonspecific resistance to stripe rust in five CIMMYT-derived wheat genotypes. High levels of resistance in these genotypes appeared to be based on the additive interaction of Yr18 gene and at least three additional genes. Stripe rust resistance in these genotypes is expected to be durable.
Analysis of Sorghum Genetic Diversity
It is now feasible to estimate accurately the genetic diversity of sorghum (Sorghum bicolor L.) germplasm using an exhaustive set of markers that are well distributed across the entire genome. Menz et al. (44:1236–1244) utilized a set of 100 SSRs, 1318 EcoRI/MseI AFLP, and 496 PstI/MseI AFLP markers with known map positions to determine the genetic similarity in a group of B, R, and IS public inbreds. By comparing the different classes of molecular markers, they determined that the distribution of the markers and the coverage of the genome by the markers did affect the classification of genotypes, and that dendrograms of genetic similarity produced clusters that were in better agreement with pedigree information. Also, cluster analyses failed to reveal a clear differentiation between B- and R-lines, suggesting that R- and B-lines do not represent well-defined heterotic groups in this set of public lines. This analysis will assist sorghum breeders in inbred line development and facilitate the development of well-defined heterotic groups for this crop, as well as in the identification of new sources of alleles for sorghum improvement.
Turfgrass Seed Mixtures
Kentucky bluegrass (Poa pratensis L.) is often poorly established when sown in turfgrass seed mixtures with slender creeping red fescue (Festuca rubra L. ssp. litoralis Vasey) and perennial ryegrass (Lolium perenne L.), possibly because of its slow emergence and slow seedling growth. Larsen et al. (44:1315–1322) investigated the effect of sowing Kentucky bluegrass earlier than red fescue and perennial ryegrass on the botanical composition of the established turfgrass. The establishment of Kentucky bluegrass was significantly improved by the advantage in sowing time. Thus, the percentage of tillers of Kentucky bluegrass could be increased by as much as 0.08% for every degree day Kentucky bluegrass was sown before sowing red fescue and perennial ryegrass.
Switchgrass May Help Mitigate CO2 Increases
The role of agriculture in mitigating increases in atmospheric CO2 has not been defined. Switchgrass (Panicum virgatum L.) is a biofuels crop that may help mitigate CO2 increases. Frank et al. (44:1391–1396) evaluated field-grown switchgrass for 3 yr. Above and belowground biomass was separated into components and analyzed for C content. Soil C loss from respiration was determined. Crown tissue contained 50% of total biomass C. The SOC to 0.9-m depth increased 1.01 kg C m–2 yr–1. Soil respiration loss equaled 44% of total plant C. Although half of C biomass is lost by soil respiration, switchgrass has potential for storing significant quantities of soil C.
Selection for Silage Quality in Maize
The objective of the Frey et al. (44:1200–1208) study was to evaluate all cycles of selection for the Wisconsin Fiber Silica High, Wisconsin Fiber Silica Low, and Wisconsin Quality Synthetic (WQS) populations for whole-plant (WP) and stover forage yield and quality at two field locations in Wisconsin in 2000 and 2001. Selection for WP yield and composition of S2–topcrosses was effective for WQS, especially when using selection indices incorporating WP yield, neutral detergent fiber, neutral detergent fiber digestibility, crude protein, and starch. The WQS cycle 2 WP and stover in vitro true digestibility, WP and stover acid detergent lignin, and milk yield per megagram dry matter were similar to the brown-midrib check hybrid F657. Our results indicate that it is feasible to develop silage maize germplasm with both high whole-plant yield and excellent nutritional quality.
Modeling Rice Growth with Hyperspectral Reflectance Data
Seasonal changes of ground-based high-resolution canopy reflectance spectra are studied to model rice (Oryza sativa L.) growth. Results by Yang and Chen (44:1283–1290) suggest that modeling between spectral characteristics/indices and growth parameters can be improved by separating growth into preheading and postheading phases. The multiple linear regression models provide flexibility in choosing narrow bands and exhibit a greater sensitivity to phenological variation.
Resistance to Fusarium Stalk Rot in Sorghum
Fusarium stalk rot of grain sorghum [Sorghum bicolor (L.) Moench] induces lodging and results in reduced grain yield and grain quality. Potential sources of stalk rot resistance were crossed to several tester lines by Tesso et al. (44:1195–1199) to evaluate differences among lines and hybrids for their reaction to inoculation with Fusarium proliferatum (T. Matsushima) Nirenberg. One germplasm source and its corresponding testcross hybrids consistently had low mean disease scores. This line, SC599, represents an excellent source of resistance to Fusarium stalk rot for use in breeding programs.
New Resistance to Greenbug in Barley
The greenbug [Schizaphis graminum (Rondani)] is an extremely damaging pest of barley (Hordeum vulgare L.), particularly in the Southern Great Plains of the USA. One strain of greenbug (biotype G) found throughout this region was once thought not to be a pest of barley. Porter and Mornhinweg (44:1245–1247) found that biotype G is definitely a pest of barley, easily killing several cultivars. Authors reported new sources of genetic resistance to biotype G that should be useful in developing greenbug-resistant barley cultivars.
Moisture Stress and Pasture Species Mixtures
Pastures in the northeastern USA are typically dominated by Kentucky bluegrass (Poa pratensis L.) and white clover (Trifolium repens L.), which are highly susceptible to drought. Skinner et al. (44:1361–1369) evaluated yield, plant water relations, and nutritive value of alternative species mixtures under a range of moisture conditions. A five-species mixture containing chicory (Cichorium intybus L.), orchardgrass (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), Kentucky bluegrass, and white clover had the greatest yield at all moisture levels. Increased yield was due to the robust growth of chicory and to the improved leaf water relations and greater relative growth rates of white clover and orchardgrass.
Peanut Cultivars for Holstein Heifer Pasture
Rhizoma peanut (Arachis glabrata Benth.) is one of few perennial legumes adapted to grazing in the USA Gulf Coast Region. A study by Garay et al. (44:1355–1360) compared pastures of rhizoma peanut cultivars Arbrook and Florigraze for grazing by dairy heifers. In the first 2 yr of grazing, heifer weight gain was similar for the two cultivars, but by Year 3 of Arbrook in pasture, herbage mass had decreased from 89 to 66% while Florigraze percentage remained relatively constant. Greater heifer gains on Florigraze pastures in Year 3 were associated with greater legume contribution. Florigraze rhizoma peanut appears better suited for pasture programs than Arbrook.
Physiological Consequences of Moisture Deficit Stress in Cotton
The effects of drought on the physiology of eight cotton (Gossypium hirsutum L.) varieties was investigated by Pettigrew (44:1265–1272) for insights into the requirements needed to consistently produce higher yields. Drought stunted overall plant growth, reduced the leaf area index, and reduced the amount of sunlight intercepted. During the morning, drought-stressed plants used sunlight more efficiently for higher photosynthesis than well-watered plants. By the afternoon, however, the drought-stressed plants were photosynthesizing at a lower rate than the irrigated plants. The drought-stressed plants' altered photosynthesis between the morning and the afternoon may help explain the irrigation yield response inconsistencies in the southeastern USA.
Improving Effective Population Size of Grasses
Seed sampling methods that enhance effective population size will help maintain the genetic diversity in heterogenetic populations during seed regeneration. Johnson et al. (44:1450–1455) found that in heterogenetic grass populations, sampling a constant number of inflorescences from each plant enhanced effective population size compared with combining all the seeds from each plant. They also found that most of the benefit was derived when only three to five inflorescences were sampled. Inflorescence sampling appears to be a cost-effective method to help maximize effective population size and diversity of heterogenetic populations during seed regeneration. Potential applications include seed regeneration at gene banks, field germplasm collection, and in selection programs when maintaining population diversity is desired.
Stargrass Pasture and Cattle Performance
Stargrass (Cynodon nlemfuensis Vanderyst) is widely used as forage throughout the tropics. A study by Garay et al. (44:1348–1354) measured stargrass pasture and animal responses to stocking rate (SR) and N fertilizer rate at St. Ann, Jamaica. Pregraze herbage mass increased as SR decreased, but herbage crude protein and in vitro digestibility increased with increasing SR and N rate. Cattle daily gain decreased curvilinearly from 
0.70 to 0.30 kg as SR increased from 2.5 to 7.5 head ha–1. Increasing N fertilizer rate increased gain per hectare only at higher SR. Economic return from N fertilization of stargrass pastures is dependent on SR, with greater N rates more likely to be profitable if SR is high.
Wheat–Jointed Goatgrass Hybrids
Hybrids between wheat (Triticum aestivum L.) and jointed goatgrass (Aegilops cylindrica Host.) are known to occur. The production of herbicide-resistant wheat has raised the issue of the potential to move the resistance trait from wheat to jointed goatgrass. Kroiss et al. (44:1429–1433) used SSR markers to determine whether wheat chromatin is retained over two backcross generations where jointed goatgrass was used as the male recurrent parent. Most wheat alleles were retained at the expected frequencies in both generations. The alleles not fitting the expected frequencies were retained at a higher frequency than expected. Recombination between the D genome chromosomes also occurred. It is possible to move a gene from wheat into jointed goatgrass if the BC1 and BC2 generations were produced in the field.
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  S. Weissmann, M. Feldman, and J. Gressel Sequence Evidence for Sporadic Intergeneric DNA Introgression from Wheat into a Wild Aegilops Species Mol. Biol. Evol., October 1, 2005; 22(10): 2055 - 2062. [Abstract] [Full Text] [PDF]
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