Influence of temperature on nutrient concentration and tetany potential of hardinggrass and tall fescue

Grass tetany (Hypomagnesemia) potential of TAM Wintergreen Hardinggrass and 16 tall fescue lines and varieties was estimated by determining the K, Ca and Mg concentrations in the herbage and the ratio of K/(Ca + Mg) (milliequivalent basis). Data were obtained at four dates during a two‐year period to determine the environmental conditions under which selections should be made to achieve the greatest progress in decreasing the tetany potential of tall fescue and to determine if either of the grasses have high tetany potential in the North Texas area. Hardinggrass had a greater potential to produce grass tetany than tall fescue when grown on the Northern Blackland Prairie of Texas. There were significant differences in K, Ca and Mg concentrations and K/(Ca + Mg) ratio among dates and tall fescue lines. The average temperature for the 30 days before harvest was related to the mineral content and to the K/(Ca + Mg) ratio in all varieties. The K(Ca + Mg) ratio was highest at approximately 18°C but the Mg content fell below the 0.18% required for lactating beef cows when the average temperature for the 30 days before harvest was 22.4°C. Progress could be made in breeding for low grass tetany proneness but selections should be made over a wide range of temperatures considering both the Mg content and ratio of K/(Ca + Mg).     

Effects of initial plant spacing and applied nutrients on stand development and productivity of Texas bluegrass in the Louisiana coastal plain

The native rhizomatous cool‐season perennial grass, Texas bluegrass (Poa arachnifera Torn), has recently been recognized again as a plant with considerable potential for range and pasture plantings. Throughout the first half of this century, sporadic efforts at evaluation and commercial use of Texas bluegrass were thwarted primarily by slow stand establishment and difficulties with seed processing. Subsequent advances in seed harvesting, processing, and planting equipment and selection of superior plant genotypes could reduce effects of these limitations. In much of the southern mid‐ and tall‐grass prairie regions and lower southeastern states where Texas bluegrass appears to have potential, there is no currently available sustainable cool‐season forage grass. Effects of initial plant spacing and lime, phosphorus (P), and nitrogen (N) application were evaluated in a field and a green house experiment on acid infertile Louisiana Coastal Plain soils. Stands from transplanting on 10‐ and 30‐cm spacings were comparable by the third growing season as the sparsely planted stand spread aggressively. The only consistent response to soil amendment was enhanced forage production from N fertilization in the spring. A plant photoperiodic response appears to limit potential to respond to N in autumn and winter. Forage production of dense stands and responses to spring application of N indicate that Texas bluegrass has considerable potential as a productive, sustainable cool‐season forage grass for at least some soils on the southeastern Coastal Plain as well as that recently reported for the southern mid‐ and tall‐grass prairie regions.     

Effect of Mixed-Salt Salinity on Growth and Ion Relations of a Barnyardgrass Species

ABSTRACT

Recent investigations of the plant genome have revealed a large degree of similarity among cereal crops (specifically within the family Triticeae) and other related grass species. Recognition of the close genetic relationship among the grasses indicates that more exotic species, such as weedy grasses, may be exploited by plant breeders to enhance biotic/abiotic stress tolerance in cereal crops. Echinochloa crus-galli (L.) ^{1 1} Mention of company names or products is for the benefit of the reader and does not imply endorsement, guarantee, or preferential treatment by the USDA or its agents. Beauv. (barnyardgrass), a wide-spread, persistent C₄ weed species of agricultural importance, is reported to tolerate high levels of salinity. Growth and ion relations were studied in barnyardgrass using mixed-salt salinity (with final electrical conductivities (ECi) of 3 (control), 7, 11, and 19 dS m^?1 in the irrigation water) to determine whether the mechanism(s) for its salt tolerance are similar to those previously reported for other cereal crops. Such a finding would indicate that barnyardgrass may possess valuable genetic traits. Ion accumulation and ion selectivity ratios in the various treatments were determined from oven-dried shoot tissue. Significant (P < 0.01) linear regressions were obtained between either fresh weight or plant height and ECi. The point of 50% reduction (C₅₀) in fresh weight was predicted to occur at about 13.9 dS m^?1; the C₅₀ value for plant height was at about 22.9 dS m^?1. Statistical analysis of calculated Gapon constants for potassium (K)/sodium (Na) indicated that ion selectivity was not affected until after 11 dS m^?1. Calcium (Ca)/Na selectivity was not significantly affected by salinity. We concluded that, similar to some cereal crops, barnyardgrass maintains growth under saline conditions by maintaining high K/Na ratios, possibly because of better membrane integrity due to high Ca selectivity.     

Texas Bluegrass Responses to Seeding Rate and Fertilization

Texas bluegrass has potential as a cool-season perennial pasture grass for the south-central USA. Slow stand establishment in competitive environments is a limitation. Forage production of this grass increases with nitrogen (N), and rhizome growth increases with phosphorus (P). Stand responses by Texas bluegrass from three seed sources to seeding rate and a complete mixed fertilizer were assessed from 1997 through 2005 on a Louisiana Coastal Plain site. A linear response (R² = 0.39, P ≤ 0.0001) to seeding rate in March 1998 persisted through 2005, even though stands at all seeding rates improved over time. Stands did not differ (P > 0.05) among seed sources. At only the higher seeding rates, rhizome mass increased with fertilization. Soil pH decreased with fertilization, and pH was positively correlated with the final stand rating in 2005. Direct stand responses to fertilization were not detected. Lack of competitive advantage, despite growth responses, and soil acidification with fertilization indicate that increased seeding rates and delayed fertilization may enhance initial establishment of Texas bluegrass in humid environments.     

Different landscape features within a simplified agroecosystem support diverse pollinators and their service to crop plants

Landscape Ecology - Landscape simplification is a main driver of insect decline, threatening crop pollination services. Changes in functional features in simplified agroecosystems may impact the...     

Genetic mapping of a new flowering time gene on chromosome 3B of wheat

The single chromosome substitution lines of chromosome 3B of the Czech alternative wheat variety Česká Přesívka (CP 3B) into two spring varieties Zlatka and Sandra, revealed clear differences in flowering time compared to the recipient varieties. To map this gene(s), recombinant substitution lines for chromosome 3B were produced from crosses of the substitution lines with their recipient parents and genetic maps developed using SSR markers. Two populations were mapped, Sandra//Sandra 3B/Sandra (CP 3B) and Zlatka//Zlatka/Zlatka (CP 3B). Combining the genotype data with phenotype data on flowering time in five independent experiments under natural long day or controlled short day conditions revealed a single flowering time QTL. This gene had an additive effect of 1–6 days, depending on environment and genetic background, and was mapped in both populations to a position in the region of marker Xbarc164 near the centromere on the long arm of 3B. Comparisons of the genetic maps with other 3B maps developed by the authors indicated that the QTL may be homologous to a QTL segregating in UK germplasm.     

Invertase activity as affected by cytokinin-like compounds during potato tuberizationin vitro

Acid invertase plays an important role in plants by hydrolyzing sucrose. Compounds exhibiting cytokinin activity were examined for their effects on acid invertase activity at three tuberization stages of potato,Solanum tuberosum L. Single nodal segments from the cultivar Atlantic were cultured on Murashige and Skoog (MS) medium with 6% sucrose and maintained under a 16-hr photoperiod. Media were supplemented with either 2 mg kinetin/1, 0.1 mg thidiazuron/1,1.0 mg AC243, 654/1 (a benzyl nitroguanidine), or 0.1 mg AC239, 604/1 (a phenyl nitroguanidine). Basal acid invertase activity was measured in stolon segments at three morphologically distinct tuberization stages: (1) “hook,” (2) “swelling,” and (3) “initiation.” The onset of tuber initiation was significantly advanced by kinetin and thidiazuron compared to controls. Stolons elongated during the hook and swelling stages until tubers were initiated. Basal acid invertase activity in stolons cultured on control medium significantly increased from hook stage to swelling stage and then decreased slightly when tubers were initiated. At the hook stage, highest basal acid invertase activity occurred when the segments were treated with kinetin and thidiazuron. Kinetin and thidiazuron induced basal acid invertase activity significantly decreased following the hook stage to tuber initiation. Basal acid invertase activity were significantly lower in stolons treated with nitroguanidines than the control activity following the hook stage of development. During the swelling and tuber initiation stages, nitroguanidines-treated segments showed reduction in basal acid invertase activity similar to segments treated with kinetin and thidiazuron treatments. Tuber initiation was preceded by a stimulation of basal acid invertase activity followed by a decrease prior to tuber initiation. Kinetin and thidiazuron stimulated enzyme activity early in the growth of stolons which may have resulted in faster stolon growth and in earlier tuber initiation. The two nitroguanidines, although able to mimic many cytokinin effects in bioassays, did not seem to act in the same way as kinetin.     

Genetic mapping of the barley Rrs14 scald resistance gene with RFLP, isozyme and seed storage protein markers

The scald susceptible barley cultivar ‘Clipper’ and a third‐backcross (BC₃) line homozygous for the Rrs14 scald resistance gene that originally came from Hordeum vulgare ssp. spontaneum were grown in replicated field trials. The level of resistance that Rrs14 confers against field populations of the pathogen Rhynchosporium secalis, the causal agent of scald disease, was evaluated. The Rrs14 BC₃ line exhibited 80% and 88% less leaf damage than ‘Clipper’ in 1995 and 1996, respectively. Given this effectiveness of Rrs14, research was undertaken to identify a linked marker locus suitable for indirect selection of Rrs14. Based on linkage to a set of previously mapped loci, Rrs14 was positioned to barley chromosome 1H between the seed storage protein (hordein) loci Hor1 and Hor2, approximately 1.8 cM from the latter locus. The Hor2 locus is thus an ideal codominant molecular marker for Rrs14. The tight linkage between Rrs14 and Hor2 and the availability of alternative biochemical and molecular techniques for scoring Hor2 genotypes, permits simple indirect selection of Rrs14 in barley scald resistance breeding programmes.     

Predicting Areas of 137Cs Loss and Accumulation in Upland Catchments

Anthropogenic radioisotopes with long physicalhalf-lives derived from atmospheric fallout remain inthe environment for decades after deposition. Process- and field-based studies within uplandcatchments show that radiocaesium is transported insolution as well as in particulate form. Catchmenthydrology is therefore an important control onradiocaesium transport and natural processes of soildevelopment. The topographic index, from thehydrological model TOPMODEL, has been used as a basisfor the development of a simple model for predictingradiocaesium redistribution in temperate uplandcatchments. The model is particularly suited topredicting ¹³⁷Cs redistribution within uplandenvironments as it is based on topography, which isreadily calculated from digital terrain models withingeographical information systems. A conceptual modelof radiocaesium losses on hillslopes and re-depositionon the valley floor was calibrated with atmosphericweapons testing ¹³⁷Cs inventories from soil coredata for the Raithburn catchment, Renfrewshire, U.K. The model fitted the observations well and showed thatin this catchment a topographic index value of about5.0, for 10 m grid cells, forms the threshold between¹³⁷Cs loss and accumulation. The resultsindicated that about 20% of the total atmosphericweapons testing ¹³⁷Cs deposited in the catchmenthad been transported out of the catchment over theca. 30 yr period since deposition.