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A cereal cyst nematode (Heterodera avenae Woll.) resistance gene has been mapped to an interstitial region of rye chromosome arm 6RL in a wheat background (1771–1778). The location of the resistance gene was determined through bioassays on wheat plants carrying each of four different deletion mutants of the 6R chromosome representing terminal deficiencies of the 6RL arm. The deletion mutants were found after screening almost 3800 seedlings of ph1-bph1b genotype, carrying an entire 6R chromosome, for dissociation of group six isozyme markers. The original intention of this study was to isolate wheat-rye recombinant chromosomes, however no wheat-6R recombinants were found.
Synchronous Pollination Improves Kernel Set in Maize
Maize (Zea mays L.) kernel set can be significantly improved through synchronous pollination. In this study, Cárcova and Otegui (1809–1815) analyzed the effect of (i) selective heating of the apical ear, and (ii) pollination rate (different time gaps between early and late-pollinated silks) on final kernel number (KN). Lateral ear heating reduced KN per ear, while tip ear heating did not modify it. The artificial pollination gaps reduced KN per plant drastically (up to 51%). This study confirmed the beneficial effects of synchronous pollination on kernel set, and added evidence of the negative impact of a delayed pollination timing among silks.
Wheat Quality
Superior bread-making ability in hard red spring and winter wheat (Triticum aestivum L.) is a primary objective for most breeding programs. Selection of high quality types is generally based on tests conducted with milled white flour. Whole wheat bread products are becoming more important in the domestic marketplace. Bruckner et al. (1917–1920) looked at the correlation between white flour and whole meal quality parameters for spring and winter genotypes grown at four locations in Montana. White flour performance was correlated with whole meal performance in both spring and winter wheat for most traits, although these correlations tended to higher in winter wheat. White flour performance would provide baseline data for breeders and end-users to select good genotypes for whole meal products. However, identification of the best genotype for whole meal performance may require separate quality analysis.
Meadow Fescue in Southern Wisconsin
Meadow fescue (Festuca pratensis Huds.) is highly adapted to management-intensive grazing (MIG) systems in temperate European climates, but is underutilized in North America. Casler and van Santen (1946–1953) evaluated 160 accessions of meadow fescue and 10 cultivars of tall fescue (F. arundinacea Schreb.) under MIG in southern Wisconsin. Numerous meadow fescue accessions were superior for net herbage accumulation, apparent intake, apparent preference, and crown rust (caused by Puccinia coronata Corda) reaction to all tall fescue cultivars. These accessions, largely from the Black Sea region of Russia, represent valuable germplasm for pasture improvement in temperate regions of North America.
Two-Row vs. Six-Row Barley
Comparative studies on chemical composition between two-row and six-row barley (Hordeum vulgare L.) and between purple and yellow barley are very limited. Frégeau-Reid et al. (1737–1743) studied five chemical traits of 190 doubled-haploid lines derived from a two-row/six-row cross of barley. Two-row lines contained more protein, less starch, and more ß-glucan than six-row lines; while purple lemma lines contained less NDF and less ADF than yellow lemma lines. The four other marker loci (srh, Raw1, Est1, and Est5) had very little effect on the expression of these five traits. Selection for high protein or low ß-glucan is possible in lines derived from two-row/six-row crosses.
Insect Resistance in Soybean
The development of insect resistant soybean [Glycine max (L.) Merr.] cultivars by means of phenotypic selection has met with limited success. In this study, Narvel et al. (1931–1939) identified SSR markers linked to four lepidopteran resistance QTLs and then used these to estimate the extent to which the QTLs were introgressed into germplasm from several breeding programs. A major QTL conditioning antibiosis and antixenosis resistance was introgressed into 13 of 15 genotypes, but minor QTLs were rarely introgressed. Marker-assisted selection may facilitate the development of superior soybean cultivars with a high level of insect resistance and a reduced exotic-parent genome.
Phomopsis Seed Decay in Soybean
Soybean [Glycine max (L.) Merr.] plants infected with Soybean mosaic virus (SMV) may be more susceptible to Phomopsis seed decay. Using two SMV-susceptible cultivars and their SMV-resistant isolines, Koning et al. (1850–1856) investigated the influence of SMV inoculations at the various stages of seed development and maturation on the incidence of Phomopsis spp. seed infection and the effect on seed quality. Phomopsis spp. seed infection was consistently low in SMV-resistant plants and increased up to 14 times higher in SMV-susceptible plants. Seed from SMV-inoculated susceptible plants had low, unacceptable germination and vigor compared with seed from SMV-resistant plants. Infection of soybean by SMV enhanced the incidence of Phomopsis spp. seed infection and reduced seed quality.
Wheat vs. Canola, Pea, and Dry Bean
The productivity of a ‘Kyle’ durum wheat (Triticum turgidum cv. Kyle) crop grown in saline rooting media was compared to that of four alternative crops by Steppuhn et al. (1827–1833): ‘Cyclone’ canola (Brassica napus cv. Cyclone), ‘Radley’ (green-seed) and ‘Carneval’ (yellow-seed) field peas (Pisum sativum cv. green-seed Radley and P. sativum cv. yellow-seed Carneval), and ‘Othello’ pinto dry bean (Phaseolus vulgaris cv. Othello). Hydroponic nutrient solutions were salinized prior to seeding, resulting in near-zero, moderate, and severe salinity treatments (measuring 1.2, 11.2, and 24.9 dS m-1 in solution electrical conductivities, respectively). Under moderate salinity, the durum wheat produced more biomass and grain than the peas and the bean, but not the canola. Under severe salinity, only the wheat and the canola yielded any grain, but only 0.4% and 20.1% of their respective productivity in nonsaline rooting media. The resulting crop salt-tolerance rankings for the test cultivars in ascending order were: ‘Othello’ = ‘Carneval’ < ‘Radley’ < ‘Kyle’ < ‘Cyclone’. None of the alternative crop cultivars, except ‘Cyclone’, warrants recommendation over ‘Kyle’.
Spatial Yield Distribution in Cotton Following Floral Bud Removal
A better understanding of cotton (Gossypium hirsutum L.) compensatory growth after loss of early season floral buds requires an assessment of the actual patterns of spatial yield distribution in damaged and undamaged plants. This study by Bednarz and Roberts (1800–1808) was conducted to determine if spatial yield distribution or yield components are altered in cotton in response to removal of early season floral buds. As the intensity of early-season floral bud removal increased in this study, the probability of harvesting a mature boll decreased in the lower canopy, but increased in the upper canopy. Removal of early-season floral buds also resulted in fewer first-sympodial-position fruit but more third-sympodial-position fruit at harvest. These modifications in spatial yield distribution adequately replaced those floral buds removed early in the season because total seed cotton yield was not different among the treatments at crop maturity.
Eastern Gamagrass Seed Germination and Dormancy
Eastern gamagrass [Tripsacum dactyloides (L.) L.] is recognized as one of the most productive native grasses in North America; however, its potential as a forage grass has not been reached due to difficulty in establishment from seed. Springer et al. (1906–1910) investigated seed germination and dormancy in eastern gamagrass. Seed germination was affected most by caryopsis weight. Seed dormancy of the two cultivars studied was attributed to the fruit case. The force required to open the fruit case did not significantly change after a 4-wk prechill at 0 to 5°C. Under natural conditions, a caryopsis must first overcome the integrity of the cupulate fruit case to germinate. Light, alternating temperatures, freezing and thawing, fire, rodents, and soil microorganisms, to name a few, may be involved in the decay of the fruit case.
Buckwheat Seed Set
A healthy buckwheat (Fagopyrum esculentum Moench) plant produces numerous flowers but few seeds. Taylor and Obendorf (1792–1799) investigated mechanisms responsible for the low frequency of seed set. Although flowers formed continuously for 7 wk, the period of maximum seed set under controlled conditions was brief (1–2 wk). Abortion (
10%) was not a major factor limiting seed set. Eighty percent of the flowers failed to initiate seeds even under controlled growing conditions when hand pollinated. Lack of fertilization accounted for most of the reduction in seed set and increased with plant age at pollination. Late-forming flowers contributed little to seed set and yield management.
Identifying Alfalfa Chromosomes
Alfalfa (Medicago sativa subsp. sativa) chromosomes are very small (2–3 µm in length), they look alike, and 2n = 4x = 32; thus it is very difficult to identify each individual chromosome. Bauchan and Hossain (1921–1926) utilized a computerized image analysis system and C-banding techniques to identify individual chromosomes based on morphometric measurements and their unique banding pattern. There exists considerable variability in the number, intensity, and location of the C-bands; however, this variability is not sufficient to preclude recognition of the homologous chromosomes. The African Population germplasm karyotype of alfalfa developed in this study is suggested as the reference for the development of additional C-banding karyotypes of diverse alfalfa populations.
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