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Theoretically, the highest level of erucic acid in rapeseed (Brassica napus L.) High Erucic Acid (HEA) cultivars that can be achieved through classical breeding is 66 mol% (700 g kg-1). Katavic et al. (739–747) used new approaches based on genetic engineering, to develop a B. napus cultivar containing erucic acid levels above 66 mol% (700 g kg-1). Two main target genes: (i) a gene encoding an sn-2-acyltransferase (SLC1-1) from yeast (Saccharomyces cerevisiae L.) and (ii) a gene encoding a seed-specific condensing enzyme (FAE1) from thale-cress (Arabidopsis thaliana L.) have been expressed separately in the HEA cv. Hero. The results demonstrate that in rapeseed (B. napus L.), the proportion of 22:1 is limited by both the rate of 22:1 synthesis and its subsequent incorporation into triacylglycerols. The application of these two transgenic technologies (SLC1-1 and FAE1) can improve the yield of 22:1 and seed oil considerably, and therefore offer new approaches to be combined with others [e.g., expression of the meadowfoam (Limnanthes sp.) LPAT] to focus on the target of producing trierucin in rapeseed (B. napus L.).
CO2 and Yield in Perennial Ryegrass
Perennial ryegrass (Lolium perenne L.) swards showed only a moderate yield response to elevated CO2. In a field experiment, Suter et al. (810–817) examined regrowth dynamics at two atmospheric CO2 levels. Elevated CO2 stimulated tiller number in the early phase of regrowth, enhanced biomass below cutting height, and increased shoot necromass. The results indicate that the gap between leaf photosynthesis and yield at elevated CO2 is due to a sink limitation, caused by a loss of tillers in later growth stages and a change in dry mass allocation.
Coat Proteins AMV Resistance in Pea
In pea (Pisum sativum L.) there is no known effective host-derived resistance to alfalfa mosaic virus (AMV). To determine whether transgenic pea containing and expressing coat protein (CP) sequences display virus resistance, Timmerman-Vaughan et al. (846–853) developed and characterized transgenic pea lines containing the AMV CP sequence and tested these for resistance to three AMV strains. Partial resistance to mechanical inoculation with AMV was observed in the greenhouse and the field. Resistance was only observed in lines with detectable transgene CP accumulation on western blots, suggesting that the resistance is CP-mediated. The results of this study indicate that pathogen-derived resistance can be used to develop peas with resistance to AMV.
Digestibility of Maize
Improving digestibility is a major goal for forage maize (Zea mays L.) breeding programs. Méchin et al. (690–697) used recombinant inbred lines per se and then top-cross to examine the quatitative trait loci (QTL) involved in genetic variation of traits related to silage maize feeding value. Numerous QTL were detected for in vitro digestibility and lignification of cell walls. Several QTL explained more than 15% of the phenotypic variance, but there was only one such QTL for whole plant digestibility. Two QTL for cell wall digestibility and one QTL for lignification were common to both lines and top-crosses. Breeders need to evaluate, and then separately account for, cell wall digestibility and starch content in the search for QTL and in progeny selection.
Drought Stress and Soybean Development
Soybean seed yields are reduced by drought stress almost every year on the southeastern Coastal Plain. Frederick et al. (778–784) report how drought stress affects soybean branch growth and seed yield and alters the distribution of seed yield and yield components between the branch and mainstem fractions. Branch growth and branch seed yield were very sensitive to drought stress, whereas drought stress had no effect on the seed yield of the main stem. Differences in branch seed yield resulting from drought-stress treatment were due to similar differences in the number of seeds produced on the branches. Drought stress had little effect on individual seed weight for seeds from the main stem and branches. Data suggest that drought stress during the early stages of reproductive development reduces soybean seed yield primarily by reducing branch vegetative growth and the formation of seeds on those branches.
Coexistance of Warm- and Cool-season Forage
Producers need information about the ability of cool- and warm-season species to coexist and thrive together. Determining the combining abilities for species presently grown or having the potential to be grown together for forage is important. Springer et al. (818–823) investigated the combining ability effect of growing native, warm-season grasses and legumes in binary mixtures using a combining ability analysis of variance. The compatibility of these species could not be predicted solely on dry matter yields. Compatible mixtures, however, were identified with greater confidence when other variables, such as crude protein concentration, in vitro digestibility, and visual observations, were taken into account. Based on total forage protein (dry matter yield times crude protein concentration), the only compatible grass-legume mixture was indiangrass-Illinois bundleflower.
A Karyotype for Bromis riparius
A molecular cytogenetic procedure, Geimsa C-banding, was used to identify individual chromosomes and to develop a detailed karyotype or chromosome complement diagram for the diploid bromegrass species, Bromus riparius Rehm. (2n = 14; PI 440215). The method allowed Tuna et al. (831–834) to identify chromosomes on the basis of C-banding patterns, chromosome length, and arm ratios, but unequivocal identification of three of the seven pairs of chromosomes was not possible. The method could be used on other species of Bromus, many of which are complex polyploids, including the economically important smooth bromegrass (Bromus inermis Leyss.), to aid in delineating their origin and genomic relationships.
Weed Management Strategies in Soybean
Identifying economical weed management for April-planted soybean grown without irrigation in the midsouthern USA is essential to ensure a profit. In this study, Heatherly et al. (784–791) compared the profits from the imposition of 10 weed management treatments on a determinate cultivar grown in wide rows and an indeterminate cultivar grown in narrow rows. The cheapest weed management was associated with controlling only broadleaf weeds in both narrow-row and wide-row systems, and this resulted in the greatest net returns from nonirrigated early soybean production system plantings over a 3-yr period. Applying these findings will ensure that unnecessary weed management expense will be avoided, and maximum profits from dryland early plantings can be realized.
Ploidy Levels of Buffalograss
Distribution and adaptation of buffalograss ploidy levels in the North American Great Plains is not well-defined. Johnson et al. (909–913) evaluated buffalograsses collected from 242 sites in the southern Great Plains for chromosome number, and related this information to collection-site environment data. Diploids were rare and located near Lubbock, TX. Tetraploids were collected in western regions of the collection area. Hexaploids were the dominant form representing 73% of the collection. Pentaploid buffalograsses were also collected (1.8%), but do not appear competitive in natural or rangeland situations. No clear patterns of relationship between ploidy level and environment exist in this collection.
Selection of Core Collection of Saccharum spontaneum
A suitable subset, chosen to represent the range of diversity of the World Collection of Saccharum spontaneum, is needed to evaluate and exploit the potential of the sugarcane germplasm. Tai and Miller (879–885) used a stratified random sampling procedure based on geographic origin and characterization data to select 75 of 342 accessions of S. spontaneum in the World Collection at the USDA-ARS National Germplasm Repository in Miami, FL. In addition to the efficient use of S. spontaneum germplasm, this core collection should prevent the loss of significant components of the World Collection and enhance conservation research.
Breeding Choices Examined in Pearl Millet
Information on heterosis and combining ability of diverse open-pollinated cultivars, breeding populations, and genepools is needed for efficient choice of breeding methods and parental materials to use in developing productive base populations. Ali et al. (705–711) investigated grain and biomass yield, growth rate, time to flowering, plant height, panicle length, and productive tillers in an 11-parent variety cross diallel of pearl millet [Pennisetum glaucum (L.) R. Br.] evaluated in five field environments in peninsular India. When genotype x environment interactions were significant, ranks of parental general combining abilities were used to identify the environments and parents contributing most to these interactions. Graphs of these ranks in each environment vs. the sum of ranks across environments provided technically simpler, easily interpreted summaries of large and complex data sets, facilitating choice of parents for future broad-based breeding populations for dual-purpose pearl millet improvement targeting peninsular India.
QTL and Selection for Resistance to European Corn Borer
Selection for resistance to European corn borer stalk tunneling in maize could be simplified by performing selection on QTL associated with resistance. In this study, Cardinal et al. (835–845) mapped QTL for resistance to ECB tunneling in a B73xB52 recombinant inbred line population. Nine QTL were detected for ECB tunneling, and they were associated with 59% of the genetic variation. Genetic effects for decreased tunneling were derived from the resistant parent, B52, at six QTL. Several QTL for ECB tunneling reported herein coincided in their position with QTL for resistance to leaf damage by insect pests of tropical maize.
NIR and Prediction of FD in Alfalfa
Estimating fall dormancy (FD) in alfalfa (Medicago sativa L.) is time-consuming and expensive. Kallenbach et al. (774–777) investigated the use of near infrared reflectance (NIR) spectroscopy to determine FD in 11 diverse alfalfa cultivars. Near infrared reflectance spectroscopy accurately predicted the FD class of individual plants (r2 = 0.85) as well as entire cultivars (r2 = 0.94). Plant breeders could use this technique to screen quickly and accurately experimental lines of alfalfa for FD.
Synthetic Germplasms and Wheat Weight
The rate of grain yield improvement in wheat (Triticum aestivum L.) has not increased during the last decade. del Blanco et al. (670–676) investigated the potential of synthetic hexaploid germplasms to provide superior alleles for grain yield and agronomic traits. Synthetic hexaploids contributed to increased kernel weight in derived lines. High yielding lines were identified in several populations.
Intercropping Leek and Celery
In an attempt to substantiate the functionality of enhanced biodiversity, an intercropping system of leek and celery was suggested to improve the weed suppressive ability of the crop canopy. The intra- and interspecific competition between leek and celery (and celeriac) was studied by Baumann et al. (764–774) in field experiments, including treatments which allowed analysis of additive and replacement series, as well as with a hyperbolic yield-density model. The competitive ability of celery and celeriac was higher than that of leek. Intra- and interspecific competition resulted in a reduced produce quality for both crops, and it is concluded that optimization of the intercrop is needed.
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