Showing papers in "Crop Science in 1988"

Water relations in winter wheat as drought resistance indicators

Abstract: Although drought is recognized as an important limitation to wheat (L.) production in many regions, drought resistance selection techniques are not adequately developed. In 1984–1985 and 1985–1986, field experiments were conducted in Stillwater, OK, to determine potential drought resistance parameters and their inheritance in winter wheat. Single plants of drought resistant ‘TAM W-101’ and drought susceptible ‘Sturdy’, their F and F progeny, and backcrosses of the F to each parent were evaluated under a rain shelter. Tiller number was recorded throughout the growing season. As stress developed during reproductive development, water potential (WP), solute potential (SP), turgor potential (TP), relative water content (RWC) were measured at 7- to 10-d intervals on single leaves until tlag leaf senescence. Tiller number and growth rate were similar among the six populations. Water potential, WP components, and RWC declined with increasing drought stress, but no significant differences among populations were found, in WP, SP, or TP. Relative water content differed significantly among populations under increasing drought stress. TAM W-101 maintained a higher RWC under drought conditions than Sturdy, and had a longer grain-filling period. Comparison of the RWC values among populations indicated that differences were controlled predominantly by genes with additive effects. Narrow-sense heritability (h) of RWC increased as drought stress intensified and reached a maximum value of 0.64 1 wk prior to flag leaf senescence. With this high h, RWC shows promise as a selection criterion for drought resistance in winter wheat.

Lignin constituents and cell-wall digestibility of grass and legume stems

Abstract: Concentration and chemical constituents of lignin are factors that may influence cell-wall (CW) digestibility of forages. This study was conducted to determine the apparent effect of lignin concentration on extent of CW digestion in immature and mature stems of grasses and legumes and to estimate and relate monomeric products of saponification and nitrobenzene oxidation of lignin to CW digestion. The basal 150 mm of stem from cultivars of field-grown alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), smooth bromegrass (Bromus inermis Leyss.), orchardgrass (Dactylis glomerata L.), and red clover (Trifolium pratense L.) were harvested during spring growth. Laboratory evaluations included CW digestibility after 72 h of fermentation, neutral-detergent fiber (to estimate CW concentration), permanganate lignin, alkali-labile phenolic acids in CW, and nitrobenzene oxidation products (NBO). The apparent inhibition of CW digestion by lignin was 62% greater in grasses than in legumes. In grass stems, ferulic acid was positively correlated with arabinose [r = 0.58 (arabinose determined for another study)], whereas p-coumaric acid was positively associated with lignin (r 0.52). The syringaldehyde proportion in NBO increased 61% in grasses and 31% in legumes with stem maturity. The NBO as a proportion of lignin was closely related to CW digestion (r = −0.86) when both grasses and legumes were correlated. The syringaldehyde proportion in NBO was closely related to CW digestion in grass stems (r = −0.93), but not in the legumes (r = −0.23). Thus, there was close agreement between lignin concentration and CW digestibility within grass and legume stems, and the results indicate lignin chemical constituents can be important in accounting for differences in inhibition to digestion between grass and legume lignins. Contribution of the Iowa Cluster Program of the U.S. Dairy Forage Res. Ctr. and Iowa State Univ. Journal Paper no. J-12766 of the Iowa Agric. and Home Economics Exp. Stn. Project 2709.

Forage Quality Characterization of a Chemically Induced Brown-Midrib Mutant in Pearl Millet

Abstract: Based on the negative relationship between lignin and digestibility, one of the most effective means of increasing forage digestibility is by reducing lignin content. Our objective was to chemically induce a brown-midrib (bmr) mutation in pearl millet, Pennisetum americanum (L.) Leeke, and evaluate the resulting mutants for lignin content and similarity to existing bmr mutants in other species. Seeds from two inbred pearl millet lines derived from Tift 23D₂B₁/2 ✕ PI 185642 were treated with either ethyl methyl sulfonate or diethyl sulfate, planted, and selfed in 1984. In 1985 a single plant in one head row exhibited a brown-midrib phenotype, and was selfed. The bmr pearl millet was compared to selfed normal plants from the same head row along with bmr and normal sorghum, Sorghum bicolor (L) Moench., and maize, Zea mays L., in 1986 at two locations. Plants were harvested at anthesis and analyzed for apparent in vitro dry matter digestibility (IVDMD), permanganate lignin, alkali-labile phenolics, and other quality parameters. Lignin concentration in bmr pearl millet was 40 g kg⁻¹ compared to 50 g kg⁻¹ for its normal counterpart, and IVDMD was 726 g kg⁻¹ for the bmr genotype compared to 659 g kg⁻¹ for the normal genotype. The differences in phenolic monomer concentrations between normal and bmr pearl millet were more like those in sorghum than maize. Based on IVDMD, lignin and phenolic monomer analyses, we concluded that bmr pearl millet was similar phenotypically to bmr mutants in sorghum. This trait has excellent potential for improving the quality of forage pearl millet. Contribution from the Purdue Univ. Agric.Exp. Stn. Journal Paper 11366.

Differential Effects of Sodium/Calcium Ratio on Sorghum Genotypes

Abstract: Plant response to salinity is a function not only of the total salt concentration but also of the Na/Ca ratio in the root medium. Calcium transport to the shoot decreases at high external Na/Ca and, in many gramineous species, Ca concentration in the expanding blades may become deficient. This study was initiated to determine the differential susceptibility of sorghum [Sorghum bicolor (L.) Moench] genotypes 'NK 265', 'NB 9040', and 'Hegari' (PI 34911) to the Na/ Ca ratio in solution cultures. Plants were grown in the greenhouse with six Na/Ca ratios at two salinity levels (osmotic potentials = -0.4 and -0.6 MPa.) NK 265 and NB 9040 were sensitive to high Na/Ca molar ratios at both salinity levels (Na/Ca = 34.6 at —0.4 MPa and 52 at -0.6 MPa). Shoot growth was inhibited; blade injury was typical of severe Ca deficiency. In contrast, at —0.4 MPa, Hegari grew best at high substrate Na and the seedlings had no Ca deficiency symptoms. The K:Na selectivity ratios in Hegari shoots were lower than those in either NK 265 or NB 9040 shoots. The tolerance of Hegari to high external Na was attributed to efficient Ca transport to the developing blades. At both salinity levels, low Na/Ca ratio significantly reduced dry matter yield of Hegari shoots. In all three genotypes, shoot Na decreased with decreasing Na/Ca and was preferentially accumulated in the sheaths. The diversity of the sorghum genotypes in their response to external Na/Ca may be utilized by plant breeders to develop a line that is suited to sodic soil conditions. Additional Index Words: Calcium deficiency, Potassium/sodium selectivity, Salinity stress, Sorghum bicolor (L.) Moench. USDA-ARS, U.S. Salinity Lab., 4500 Glenwood Drive, Riverside, CA 92501. Received 7 Aug. 1987. *Corresponding author. Published in Crop Sci. 28:659-665 (1988. S OF SALT-AFFECTED SOILS have shown that increases in exchangeable Na, accompanied by decreases in exchangeable Ca, may result in ion imbalances that adversely affect plant growth. High external Na reduces the activity of Ca ions in the root medium and decreases the amount of Ca that is available for uptake by the plant (Cramer and Lauchli, 1986; Cramer et al., 1986). Calcium concentrations that are adequate under nonsaline conditions may become nutritionally inadequate when the external Na/Ca ratio is high (Bernstein, 1975). Root growth and function may be inhibited, and the processes whereby Ca is transported from root to shoot may be impaired (Lynch and Lauchli, 1985). The cereals are particularly susceptible to Ca deficiency at high external Na/ Ca ratios. Sodium-induced Ca deficiency symptoms have been observed in sorghum (Kawasaki and Moritsugu, 1979), corn (Zea mays L.) (Maas and Grieve, 1987), rice (Oryza saliva L.) (Grieve and Fujiyama, 1987), and barley (Hordeum vulgare L.) (Maas and Grieve, unpublished data). The cereals show striking intergeneric differences in tolerance to saline cultures of equal osmotic potential (OP) with different molar ratios of Na and Ca. A salt stress of —0.6 MPa and Na/Ca = 52 reduced the relative dry matter yield of wheat (Triticum aestivum L., 'Probred' and 'Inia') less than that of rye (Secale cereals L., 'Merced'), or oat (Avena sativa L., 'Curt' and 'Swan') (Maas and Grieve, unpublished data). At —0.4 MPa, rice ('M-201') was more sensitive at Na/Ca = 5 than was the corn 'PiPublished July, 1988