Ann R. Blount

Effects of Silicon Applications on Soybean Rust Development Under Greenhouse and Field Conditions

Soybean rust (SBR), caused by Phakopsora pachyrhizi, is one of the most destructive fungal diseases affecting soybean production. Silicon (Si) amendments were studied as an alternative strategy to control SBR because this element was reported to suppress a number of plant diseases in other host-pathogen systems. In greenhouse experiments, soybean cultivars inoculated with P. pachyrhizi received soil applications of wollastonite (CaSiO3) (Si at 0, 0.96, and 1.92 t ha-1) or foliar applications of potassium silicate (K2SiO3) (Si at 0, 500, 1,000, or 2,000 mg kg-1). Greenhouse experiment results demonstrated that Si treatments delayed disease onset by approximately 3 days. The area under disease progress curve (AUDPC) of plants receiving Si treatments also was significantly lower than the AUDPC of non-Si-treated plants. For field experiments, an average 3-day delay in disease onset was observed only for soil Si treatments. Reductions in AUDPC of up to 43 and 36% were also observed for soil and foliar Si treatments, respectively. Considering the natural delayed disease onset due to the inability of the pathogen to overwinter in the major soybean production areas of the United States, the delay in disease onset and the final reduction in AUDPC observed by the soil Si treatments used may lead to the development of SBR control practices that can benefit organic and conventional soybean production systems.

Intake, digestibility, and nitrogen retention by sheep supplemented with warm-season legume haylages or soybean meal

The high cost of commercial supplements necessitates evaluation of alternatives for ruminant livestock fed poor quality warm-season grasses. This study determined how supplementing bahiagrass haylage (Paspalum notatum Flügge cv. Tifton 9) with soybean [Glycine max (L.) Merr.] meal or warm-season legume haylages affected the performance of lambs. Forty-two Dorper x Katadhin lambs (27.5 +/- 5 kg) were fed for ad libitum intake of bahiagrass haylage (67.8% NDF, 9.6% CP) alone (control) or supplemented with soybean meal (18.8% NDF, 51.4% CP) or haylages of annual peanut [Arachis hypogaea (L.) cv. Florida MDR98; 39.6% NDF, 18.7% CP], cowpea [Vigna unguiculata (L.) Walp. cv. Iron clay; 44.1% NDF, 16.0% CP], perennial peanut (Arachis glabrata Benth. cv. Florigraze; 40.0% NDF, 15.8% CP), or pigeonpea [Cajanus cajan (L.) Millsp. cv. GA-2; 65.0% NDF, 13.7% CP]. Haylages were harvested at the optimal maturity for maximizing yield and nutritive value, wilted to 45% DM, baled, wrapped in polyethylene plastic, and ensiled for 180 d. Legumes were fed at 50% of the dietary DM, and soybean meal was fed at 8% of the dietary DM to match the average CP concentration (12.8%) of legume haylage-supplemented diets. Lambs were fed each diet for a 14-d adaptation period and a 7-d data collection period. Each diet was fed to 7 lambs in period 1 and 4 lambs in period 2. Pigeonpea haylage supplementation decreased (P < 0.01) DM and OM intake and digestibility vs. controls. Other legume haylages increased (P < 0.05) DM and OM intake vs. controls; however, only soybean meal supplementation increased (P = 0.01) DM digestibility. All supplements decreased (P = 0.05) NDF digestibility. Except for pigeonpea haylage, all supplements increased (P < 0.01) N intake, digestibility, and retention, and the responses were greatest (P = 0.04) with soybean meal supplementation. Microbial N synthesis was reduced (P = 0.02) by pigeonpea haylage supplementation, but unaffected (P = 0.05) by other supplements. Efficiency of microbial protein synthesis was unaffected (P = 0.05) by diet. Ruminal ammonia concentration was increased (P = 0.01) by all supplements, but only soybean meal and annual peanut haylage increased (P < 0.03) plasma urea-N concentrations. Perennial peanut, annual peanut, and cowpea haylages are promising protein supplements for growing lambs.

Tetraploid bahiagrass hybrids: breeding technique, genetic variability and proportion of heterotic hybrids

Manipulating apomixis for fixing tetraploid bahiagrass (Paspalum notatum Flüggé) hybrids exhibiting superior agronomic characteristics would be a valuable tool for the genetic improvement of this species. The objectives were to create a second generation of hybrids by crossing sexual first-generation tetraploid hybrids (FGTH) and unrelated apomictic FGTH or ecotypes, determine the segregation for mode of reproduction, and estimate the resulting genetic variation and heterosis for several agronomic characteristics. The segregation for mode of reproduction was analyzed using mature embryo sac observations. Field measurements and visual ratings were used to evaluate the growth habit, production of inflorescences, cool-season growth and freeze resistance of hybrids. A ratio of 4.6:1 between sexual and apomictic hybrids was observed. Only 3% of the progeny was classified as highly apomictic. The low proportion of highly apomictic progeny restricts the feasibility of this breeding approach. Large genetic variation was observed among hybrids for growth habit, cool-season growth and freeze resistance. The proportion of hybrids exhibiting heterosis was high for plant height, cool-season growth, and freeze resistance. The tetraploid bahiagrass germplasm contains a large diversity for traits of agronomic importance that can be exploited for the genetic improvement of this species.

Environmental stability and heritability estimates for grain yield and test weight in triticale

Hexaploid triticale has many advantages over both parental species for both grain and forage production in certain environments. Additional information on environmental stability and heritability would be desirable to develop appropriate selection strategies in the production of superior widely-adapted cultivars. The grain yield of 22 diverse genotypes grown at four ecologically-distinct geographical locations [Quincy, FL, USA (approximate geographical coordinates (AGC) = 30°N 84°W, approximate elevation (AE) = 58 m), Plains, GA, USA (AGC = 32°N 84°W, AE = 76 m), Bozeman, MT USA (AGC = 45°N 111°W, AE = 1458 m), and Aberdeen, ID, USA (AGC = 42°N 112°W, AE = 1360 m)] was measured in two years with winter and spring planting dates only at Bozeman and Aberdeen. Test weight (grain weight in a given volume) was determined for two years at Bozeman and Aberdeen at both planting dates and one year at Quincy. Stability analyses indicated that significant (P < 0.01) variation in means, regression coefficients, and deviation mean squares of the genotypes were present for both characters. Realized heritability (h2) estimates were as follows: grain yield ranged from −0.02 to 0.80 with a mean of 0.57; test weight ranged from 0.63 to 1.05 with a mean of 0.93. The results indicated that substantial genetic variation is present and selection for widely-adapted cultivars would be effective for both characters especially test weight.

Potential root depth development and nitrogen uptake by tetraploid bahiagrass hybrids

The objectives were to develop a screening technique to evaluate the tetraploid germplasm of Paspalum notatum Flüggé (bahiagrass) for potential rate of root depth development (RRDD), estimate the variability for RRDD among hybrids, and analyze the association between RRDD and nitrogen (N) uptake. First, a screening technique was developed based on the evaluation of two clones grown in clear acrylic columns of different sizes, filled with mineral or organic substrates. The RRDD response was determined to be constant across substrates, and tube sizes. Second, differences in RRDD among thirteen clones were compared by growing plants in acrylic columns filled with mineral substrate. Genetic variability was identified among the bahiagrass germplasm for RRDD. Greater RRDD values resulted in greater root and shoot mass, indicating that RRDD was related to early vigor. Finally, to evaluate the relation between RRDD and N uptake, labeled N (15N) was injected either at the depth of the deepest root of each clone or at the maximum depth of all clones. Rapid root depth development was a determining factor for rapid access and uptake of nitrogen present in deep soil layers. This relationship might explain why clones exhibiting rapid root penetration also showed greater early vigor.

Selection in Setaria sphacelata for winter survival

Abstract Choice of warm‐season grasses for use in North Florida, United States, is limited because of the cold winters, which are characterised by both radiation frosts and freezes. With the objectives of increasing the adaptation of the forage Setaria sphacelata to these conditions, a breeding programme was undertaken at the University of Florida from 1997 to 2000. A recurrent selection procedure was used for three cycles to select for winter survival and early spring growth after frost and freezes in Gainesville (29.6°N latitude) and for one cycle in Quincy (31 °N latitude). Heritability estimates for the first two cycles in Gainesville and the cycle in Quincy ranged from 0.35 to 0.50 on a family basis. Predicted gains ranged from 10.4 to 17.4% in winter survival over the preceding cycle. These populations were compared in Gainesville to the original population and to cultivars ‘Solander’ and ‘Splenda’ in two experiments, one wide‐ and one close‐spacing. Results showed that selection for winter survival in Gainesville reduced canopy height in the second and third cycles and the reproductive height in the third cycle. Leaf dry matter yield was decreased in the first and second cycles and leaf percentage in the first cycle. These effects were reversed in the remaining cycles. Selection did not have a consistent effect on the width of leaves, length or number of inflorescences, or on total and stem dry matter yields. However, selection for winter survival in Quincy increased canopy height and the number of inflorescences. Selection for winter survival after frosts and freezes in Gainesville was successful because all cycles of selection had a higher survival rate after the winter of 1999–2000 than the original population. This winter, which killed many of the Setaria plants, was effective in providing additional screening for winter survival after frosts and freezes. Further research with this species for Florida conditions appears warranted.

YIELD AND MINERAL CONCENTRATIONS OF SOUTHEASTERN UNITED STATES OAT CULTIVARS USED FOR FORAGE

A shift in oat (Avena sativa L.) production from grain to forage (hay and grazing) is occurring in the southeastern USA. However, most available cultivars were developed for improved grain production, rather than forage yield. We field tested several standard and new oat releases over 2 years, using repeated clippings to determine forage yield, nutrient uptake, and the potential to match plant nutrients with cattle mineral dietary needs. There were no differences in total annual forage yield among the tested cultivars within years but there was a difference between years. Forage tissue phosphorus (P), magnesium (Mg), and calcium (Ca) were sufficient, potassium (K), sulfur (S), and manganese (Mn) were excessive, and iron (Fe), copper (Cu), and zinc (Zn) were occasionally or frequently deficient to meet daily cattle dietary mineral needs. Sulfur, Cu, Fe, Zn, and Mn may be the most challenging to regulate in U.S. Coastal Plain soils at concentrations that satisfy both, oat and cattle nutritional requirements.

Effects of Annual Cool-Season Forage on Bahiagrass Production in Silvopastures

Interest in silvopastoral systems revolves around developing sustainable agriculture that increase food, forage, and fiber production without causing environmental degradation. Limited resource farmers are looking for alternative agricultural systems with possibilities for diversifying their farm products. We evaluated the effects of tree configurations and annual cool-season forage species combinations on the yield and nutritive value of ‘Argentine’ bahiagrass (Paspalum notatum Flügge.) forage in three tree configurations: double-row sets of trees with 15 m wide forage alleys (double-row), fourth row conventionally thinned stand (random-thinned), and open pasture, which acted as a control. A mid-rotation loblolly pine (Pinus taeda L.) was thinned in the summer of 2002 and a stand of Argentine bahiagrass was established in 2003. Cool-season forage varieties that were overseeded into bahiagrass in late fall grew in the winter-spring period. Cool-season forages included ‘Jumbo’ ryegrass (Lolium multiflorum Lam.), ‘Dixie’ crimson clover (Trifolium incarnatum L.), and ‘Cherokee’ red clover (Trifolium pretense L.). The tree configurations reduced dry matter (DM) yield of bahiagrass by 29% and 22% in the randomly-thinned and double-row (silvopastures) treatments, respectively when compared with open pasture. Generally, no differences were found between the two silvopastures. Although effects of cool-season forage production caused reductions in bahiagrass yields in the first summer harvest month (July), no subsequent yield differences were recorded in the following months. While the bahiagrass in open pasture occasionally had greater in vitro organic matter digestibility (IVOMD) than the silvopastures, the double-row tree spacing resulted in greater crude protein (CP) concentrations in the bahiagrass than that grown in open pasture. Bahiagrass digestibility and CP concentration from ryegrass–crimson–red clovers treatment plots were greater than other cool-season forage combinations (ryegrass and ryegrass–crimson clover). Bahiagrass intercropped with annual cool-season forage treatment plots had greater P concentrations compared with bahiagrass alone. This study revealed the feasibility of converting a mid-rotation loblolly pine stand into productive silvopastoral systems that generally support bahiagrass production after cool-season forage production in the winter-spring period. An improved understanding of the tradeoffs between improved silvopastures and depressed intercrop growth, as well as management options to forage production, will aid farmers design systems to improve yield and nutritive value of their pastures.

Foliage freeze tolerance trait diversity in bahiagrass (Paspalum notatum Flügge)

Abstract Freeze protection of bahiagrass in subtropical pastures might be accomplished through genetic improvement of existing diploid (sexual) cultivars, if clones with a leaf freeze tolerance trait (FT) could be confirmed. Clones originally identified as having FT under field conditions were compared under controlled temperatures to confirm those clones that specifically expressed a FT trait. An initial study was undertaken to determine whether damage induced by placing potted plants in freezing temperatures was confounded by low soil temperature, or leaf damage was directly a result of leaf freeze damage. This experiment confirmed that FT was a result of leaf tolerance to freeze injury, not root damage. Stress treatment of 10 h duration at successively colder temperatures (‐1°C, ‐3°C, ‐5°C, and ‐7°C) was evaluated on 26 clones grown in pots. Substantial variation in FT was observed among these clones, with ‘FL67’ being significantly more tolerant, even to temperatures as low as ‐7°C. An additional comparison of 30 clones was done by subjecting a fresh set of plants only to ‐6°C. Superior FT of ‘FL67’ was confirmed, along with the identification of FT in ‘CO6’ and ‘OK2’.

A New Red Clover 2,4-D-Resistant Cultivar to Improve Broadleaf Weed Control and Elucidate the Molecular Mechanism of Resistance

Using recurrent phenotypic selection we have developed a red clover (Trifolium pratense L.) cultivar (FL24D) resistant to 2,4-Dichlorophenoxyacetic acid (2,4-D) after six cycles. Approximately 20,000 seeds were broadcast seeded into metal flats and sprayed with 1.1 kg a.i. ha-1 2,4-D at 4 week (3 trifoliate leaf stage). One month later, 385 (1.95 %) plants were selected for intercrossing. Selection criteria were based on survival and regrowth. Following cycles were based on recurrent half-sib selection. While standard red clover cultivars (susceptible to 2,4-D) died after the recommended 2,4-D application rates, FL24D established a stand with no decrease in total yield relative to the unsprayed treatment. Under unsprayed conditions, FL24D presented one of the highest yields compared to commercially available cultivars. Additionally, FL24D is earlier in spring growth than any other known cultivar in the market. Despite the economic importance of 2,4-D and its use for more than 60 years, remarkably little is known about the underlying genetic architecture or the genetic process by which resistance is acquired in plants. Using remnant seed from the cultivar development, cycle 0 (susceptible) through cycle 6 (resistant), we are studying both the process of acquired resistance and the molecular mechanism involved in such resistance.