Plants of four cultivars of wheat were exposed during the grain-filling stage in two different experiments to brief episodes (10 or 20 days) of high temperature. About the same number of degree-days above a standard temperature were accumulated in both experiments. While the cultivars differed in detail in their responses, final single grain weight in all cases was reduced by elevating the temperature, and to about the same extent (14%) in both experiments. The numbers of B-type starch granules (but not of A-type) were substantially reduced by warming, but this reduction did not appear to account wholly for the smaller weight of starch per grain resulting from elevated temperature. Nitrogen content per grain was not affected by the warm conditions and, in the experiment with the short duration at the high temperature differential (33/25°C day/night as compared to 21/16°C), percentage nitrogen was significantly increased by warming from 2.61 to 3.05%. It is concluded that starch and nitrogen accumulation in the grain have differing susceptibilities to brief episodes of high temperature during grain-filling.
Elevated temperature during grain filling resulted in reduced single grain weight due largely to an effect of temperature on the accumulation of starch in the endosperm. Wheat endosperm was cultured in vitro on solutions of [14~]sucrose and the responses to variation in temperature within the range 15-35OC were evaluated in terms of the absorption of radioactive sugar, the evolution of I4c02, and the incorporation of radioactivity into starch.At 35°C the level of 14C in the intracellular pool of soluble carbohydrate was higher than it was at 30°C, and the average Qlo for 14C02 production was 2.1. Incorporation of 14C into starch was greater at 30°C than at 25"C, but at 35'C only half as much [14C]starch was produced compared with that at 30°C.Residual effects of exposure of ears to brief episodes of elevated temperature were investigated by culturing endosperm isolated from such ears on [14~]sucrose at a standard temperature (25OC). Two days of exposure resulted in greater amounts of [14~]starch produced, due to accelerated starch deposition, but longer periods (4-6 days) at elevated temperature resulted in substantial reductions in [14c]starch deposition. Exposure to elevated temperature also hastened the onset of chlorophyll degradation in the pericarp of the grain.Two types of response to temperature appear to be involved: a comparatively low temperature optimum for starch synthesis, and an irreversible reduction in the capacity of the endosperm to convert sucrose to starch resulting from exposure of the ears, or the grains themselves, to elevated temperature.
Brief warming of wheat ears reduced total grain weight, due mainly to a reduction in individual grain weight but also to a small reduction (2.6-12.8%) in grain number. Warming of ears reduced the water content of the grain, independently of humidity of the air with which the ears were warmed. Warming ears at high humidity accelerated the rate of dry matter accumulation as compared to warming at low humidity but both treatments resulted in a reduction of final weight per grain. The effect of temperature, and interaction with humidity, on grain dry matter accumulation are not due to changes in the water or osmotic potential of the grain. Warming the ears reduced temporarily the amount of sucrose and other soluble sugars in the grain, but not in the rachis or the floral organs. It seems unlikely that the supply of sugars available for distribution to the grain is depressed by elevated temperature, nor were reduced rates of grain- filling at elevated temperature simpiy related to apparent concentrations of sucrose within the grain: ripening and senescence of the pericarp were hastened by warming the ears, and these responses were not accompanied by reductions in the levels of sugars in the grain.
The hypothesis that reduced grain weight resulting from elevated temperature is the result of a reduction in the supply of assimilates to the grain or lessened availability of sucrose within the endosperm for grain filling has been investigated. Detached ears of wheat were cultured on solutions of sucrose varying in concentration from a level which supports normal rates of grain filling to one above and one below that level. Contrary to expectation, at the low concentration of sucrose the rate of grain filling in detached ears increased more at elevated temperature than it did in ears supplied with higher concentrations of sucrose, or compared with ears developing on intact plants. In other experiments ears were detached and, after a brief exposure to elevated temperature, were cultured on solutions of sucrose. The residual effects of warming, expressed as slower grain filling and lower mature grain weight, were less pronounced at low than at higher concentrations of sucrose. This result also is not in accordance with the hypothesis.
The field efficacy of pre-mixture of pinoxaden plus clodinafop for control of Phalaris minor Retz. in wheat was evaluated in winter 2011-12 and 2012-13 on Research Farm, Department of Agronomy at Punjab Agricultural University, Ludhiana. The study comprised of pre-mixture of pinoxaden plus clodinafop 40, 50 and 60 g/ha, clodinafop 60 g/ha, pinoxaden 50 g/ha and unsprayed control. The results revealed that post-emergence application of pre-mixture of pinoxaden plus clodinafop at 50-60 g/ha recorded effective control of P. minor and recorded the highest effective tillers/m 2 , spike length and wheat grain yield and was significantly better than its application at 40 g/ha and clodinafop during both the years and pinoxaden alone in one year.
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