Two photoperiodic cotton (Gossypium hirsutum L.) strains (T185 and T466) which had been empirically selected because of poor performance and two strains (T25 and T256) selected because of enhanced performance under field water stress were evaluated for stress-induced changes in their organic acids and carbohydrates. Profiles and quantitation of organic acids and carbohydrates from aqueous extractions of cotton leaf tissue were determined by high performance liquid chromatography. In all cases, the water-stressed plants showed two to five times greater amounts of organic acids and carbohydrates over the values determined for the irrigated samples. Under stress, sucrose accumulation was observed in wilting strains (poor performers) probably related to rate of translocation out of the leaf. The most dramatic response to water stress was the accumulation of citric acid in strains T25 and T256 as compared to T185 and T466. Citric/malic acid ratios for both the irrigated and waterstressed samples of T25 and T256 were twice those of T185 and T466.Organic acids and carbohydrates have been implicated in various roles in the metabolic and physiological responses of plants to water stress. Early papers by reported that, at low water levels, carbohydrates accumulated in cotton plants which had complete fruit loads. In cotton leaves, drought caused large reductions in starch concentrations, variable effects on sucrose, and an increase in hexose sugar. The gains in sugars were substantial on a relative basis but were minor in actual amounts. They concluded that drought appears to depress carbohydrate utilization by the cotton plant to a greater extent than it does photosynthesis (7).Malic, citric, and oxalic acids are frequently found in large amounts (several percent of the dry weight of the tissue) in mature tissues or organs of plants (4). For cotton, higher concentrations of organic acids are found in the leaves than in other vegetative parts, frequently at 10% of the basis of dry weight (8). The major acids accounting for a total content of approximately 10% of the dry weight of cotton leaves were identified as citric, malic, and oxalic, with malic usually present in the greatest amount. It was reported that drought caused large reductions in concentrations of citric acid with gains in malic acid but with overall maintenance of the level oftotal organic acids (8
Manipulation of crop architecture through the use of chemical bioregulators suggests the potential to improve plant water use and production efficiency. A bioregulator, mepiquat chloride (1,1‐dimethyl piperidinium chloride), was evaluated in field grown cotton (Gossypium hirsutum L.) during 1979, 1980, and 1981 to determine effects on several plant water relations parameters and crop development in a semiarid environment. All experiments were conducted on an Olton loam soil (fine, mixed, thermic family of Aridic Paleustolls). A broadcast, foliar application was made at the rate of 50 g active ingredient (a.i.)/ha during the early square (young floral bud) Stage. Increases in leaf water potential (Ψw), solute potential (Ψw), and turgor pressure (Ψp) in mepiquat chloride treated plants were recorded during midmorning and at daily minimum Ψw. The earliest Ψw increase wass measured 12 days after application. Changes in Ψw ranged from no significant differences to a 0.63 MPa increase in treated plants, 77 days after application under a high soil water level. Increased Ψs and Ψp in treated plants occurred most frequently during the midmorning period and increases Of 0.20 MPa were measured. Improvements in plant water status were not restricted to low soil water availability and occurred across a range of control Ψw from −1.43 to −3.43 MPa. Increased abaxial transpiration rate, associated with decreased diffusive resistance, was measured in treated plants, particularly during the afternoon. No difference in seasonal soil water extraction was measured between treatments, even in tests in which leaf area index (LAI) was reduced 33% by mepiquat chloride application. Leaf area index reductions were attributable to both fewer leaves per plant and reduced leaf size. Differences in the growth parameters between treated and untreated plants were most evident when conditions for growth were optimum. A maximum decrease in plant height of 25 cm was measured 43 days after application in a high soil water level experiment. Reductions of one to two mainstem nodes were measured in treated plants. The number of bolls per plant throughout the season was not altered by mepiquat chloride application, and there were no differences in lint yield as a result of treatment.
Pearl millet [Pennisetum glaucum (L.) R. Br.] production in the West African Sahel is constrained by low, erratic rainfall and low soil nutrient (particularly P) availability. Outdoor pot and growth chamber experiments tested the hypothesis that increasing soil P supply increases transpirational water‐use efficiency (WUET), under waterstressed and non‐water‐stressed conditions. Pearl millet was grown outdoors under semiarid conditions in covered pots containing 85 kg of acid, P‐deficient Betis sand (sandy, siliceous, thermic Psammentic Paleustalf). Plants were treated with four P levels and two water treatments, and harvested at 14‐d intervals. Significant main and interactive effects on WUET due to P level, water treatment, and time of harvest were found. The slope of the curve relating DM to cumulative transpiration (Tcum) increased with P level and water stress when data from all harvests were pooled. In the growth chamber, WUET of nonwater‐stressed plants ranged with increasing P level from 3.22 to 9.12 g kg−1 at 29 days after sowing (DAS) in pots containing 6 kg soil, and from 0.84 to 9.24 g kg−1 at 49 DAS in pots containing 18 kg soil. The ratio of leaf net photosynthetic rate to transpiration 0,WUEGMS,) at 500 μmol m−2 s−1 photosynthetic photon flux density (PPFD) ranged from 1.88μg mg−1 for plants receiving no P to 10.25μg mg−1 for those receiving 0.310 g P 6 kg−1 soil. Between PPFD levels orS00 and 2000 μmol m−2 s−1, plants receiving no P increased WUEGAS to only 3.60 μg mg−1, whereas those receiving higher levels of P increased WUEGAS to as much as 18.2μg mg−1. Our finding that increasing soil P avail° ability increases WUET under water‐stressed and non‐water‐stressed conditions reinforces previous conclusions that water supply in the Sahel and similar semiarid environments cannot be effectively managed for improved crop production without addressing soil fertility constraints.
Because of recently enacted conservation compliance legislation, reduced and no‐till farming systems in which crop residues are left on the soil surface are becoming more important in areas where soils are highly erodible. On the southern high plains of Texas, many producers are planting cotton (Gossypium hirsutum L.) into wheat straw (Triticum aestivum L.). This study was conducted to determine the allelopathic potential of wheat residues on cotton germination, emergence, seedling growth, and lint yield. Laboratory bioassays revealed that cotton seedling development was inhibited by aqueous extracts of wheat straw. Cotton cultivars were screened for the ability to tolerate the inhibitive effects of wheat straw in laboratory bioassays and greenhouse pot studies. Tolerant ‘Paymaster 404’ and intolerant ‘Acala A246’ were identified and used in field experiments that were conducted in 1986 and 1987 to determine the influence of wheat stubble residues on their emergence and yield. Major reductions in emergence only occurred when above ground residues were present in the seedbed. Emergence was reduced by an average of 9% for Paymaster 404 and 21% for Acala A246 when wheat stubble residues were present in the seedbed. The allelopathic effect of wheat stubble indirectly influenced lint yield by affecting population densities. The negative effect of wheat stubble on cotton stand establishment can apparently be overcome by; limiting the amount of above ground residues that are incorporated into the seedbed during planting, increasing the seeding rates, and planting tolerant cultivars.
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