The objectives of this study were to compare corn (Zea mays L.) inbreds and their F1 hybrids with respect to pattern of nitrate (NO3−) uptake during the growth period and partitioning of absorbed N among plant parts. A four‐parent (‘W64A’, ‘WI82E’, ‘A632’, ‘Oh43’), half‐diallel of corn was used. Disappearance of NO3− from solution culture was monitored from 10 days after emergence until 20 days after silking. Plants were then harvested and the distribution of total N, NO3−, and reduced N (RN) among leaf blades, leaf sheaths, stems, ears, and roots was determined.Significant differences in NO3− uptake per plant were found among the 10 genotypes, but there was no relationship between NO3− removed by F1 hybrids and that removed by their inbred parents. Genotypic differences in dry weight, NO3− and RN per plant, and NO3− and RN còncentrations were found in all plant parts. Inbreds W64A and WI82E were especially high in NO3− and RN. Dry weight and NO3− in all plant parts, and RN in all plant parts except ears, were usually greater in hybrids than in inbreds. In general, stem NO3− concentration of the F1 approximated the mid‐parent mean. Concentration of NO3− in other plant parts of F1 hybrids was not related to that of their parents. No relationship between parents and progeny in RN concentration was found in any plant part.In this study, genetic variation in NO3− uptake and partitioning of absorbed N was demonstrated. This variation suggests the potential for genetic improvement of NO3− uptake and N utilization by corn.
A primary determinant of yield in wheat (Triticum aestivum L.) is the number of spike‐bearing tillers per unit area. Many tillers that emerge do not survive to produce spikes. This study was conducted to determine the point in development when tillers begin to senesce and to examine how premature senescence is affected by water deficits and plant population. Cultivars Edwall and Waverly were planted in a 2‐yr field study at two plant densities (168 and 84 kg ha−1 in 15‐ and 30‐cm rows, respectively) and with both irrigated and nonirrigated treatments. The Haun stage of leaf development was monitored weekly on five plants per plot. Tiller mortality was monitored from tiller emergence until maturity. For tillers destined to die prematurely, a reduced rate of leaf emergence and development was evident immediately after tiller emergence. The majority of tillers senesceduring main stem extension, while almost no tillers were lost during grain filling. The maximum Haun stage reached by senescing tillers was normally ≤3 for all tillers excepthe coleoptile (TO) tiller. For this tiller, the maximum Haun stage was ≤4. Premature tiller senescence occurred in both irrigated and nonirrigated plots and was greatest at the higher plant density. Water deficits increased the number of tillers that died but did not affect the stage at which senescence occurred. Tillers that emerged late during plant development were most likely to senesce prematurely.
Grain yield of wheat (Triticum aestivum L.) depends, in part, on carbohydrate reserves available in the stem. This study was conducted to determine the effects of water deficit during the post‐jointing period on quantitative changes in water soluble carbohydrates (WSC; including simple sugars, starch, and fructans) in the stems of spring wheat. Cultivars Edwall and Waverly were planted in 1983 and 1984 at Spillman Agronomy Farm near Pullman, WA, at rates of 84 and 168 kg ha−1 in rows 30 and 15 cm apart, respectively, in both irrigated and nonirrigated treatments. Beginning at jointing, plants were harvested weekly. Stem material was dried, milled, digested with amyloglucosidase, and analyzed for WSC by iodometric titration. Results were similar for both varieties and both years. Anthesis and peak stem carbohydrate concentration occurred 4 to 7 d earlier in nonirrigated than irrigated plants; and physiological maturity of the grain occurred 6 to 14 days earlier. The concentration of WSC in stems increased to between 250 and 380 mg g−1 dry wt. at ≈10 to 14 d after anthesis and then declined to less than 50 mg g−1 dry wt. by physiological maturity of the grain. From the time of peak WSC content until physiological maturity in 1984, 859 to 1235 mg WSC were lost from the stems of irrigated plants but only 619 to 662 mg WSC were lost from stems of nonirrigated plants. The data indicate that stems are an important temporary storage site for reserve carbohydrates in both irrigated and nonirrigated plants.8
Experiments were conducted at two sites for 2 yr in the Pacific Northwest dryland cropping region to determine if seeding rate of small-red lentil could enhance weed control with herbicides and increase lentil seed yield. At Pendleton, OR, and LaCrosse, WA, lentil was planted at 22 or 44 kg ha−1 in one direction in all plots. In one-half of the plots, lentil was cross-seeded at right angles with an additional 22 kg ha−1 to provide seeding rates of 22, 44, 22 + 22, and 44 + 22 kg ha−1. Seeding rate main plots were split into three herbicide treatments and an untreated control. Total weed density was reduced by increasing seeding rate at Pendleton both years when averaged over all herbicide treatments. Seeding rate reduced total weed density to a greater extent when herbicides did not adequately control weeds or when herbicides were not applied at Pendleton in 1992. Increased seeding rate also reduced total weed dry weight at Pendleton in 1992 and 1993 and at LaCrosse in 1993. The suppressive effect of increased seeding rate on weed dry weight was more evident when herbicides were not used or when herbicides gave only partial control. Herbicides generally reduced weed density, but the effectiveness of individual treatments was related to the weed species present and environmental conditions present in each experiment. Lentil aboveground dry weight production increased with seeding rate at both locations; however, only in 1 yr did lentil seed yield increase with seeding rate. The primary benefit from increased seeding rate in this study was to reduce weed density and dry weight.
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