Automatic plot covers were used in a study of the effects of drought on the yield and water use of two spring wheat genotypes. The experiment tested the effects of drought at different stages of growth on yield and yield components. There was complete control over the water supplied to the plots, and a fully irrigated control treatment was included.The yields of the two genotypes were similar under fully irrigated conditions, but the yield components differed: Highbury had more grains per ear and TW 269/9/3/4 more ears per unit ground area and a higher mean grain mass. An early drought, which began 4 weeks before anthesis, caused a reduction in number of grains per ear in Highbury, which was outyielded by TW 269. Late drought also reduced yields differentially, reducing mean grain mass, and hence grain yield, more in TW 269 than in Highbury. Total shoot dry matter and grain yield were found generally to increase as water use increased. The average water use efficiency was found to depend upon the genotype and treatment.
SUMMARYEarly and late, and short and tall lines were selected from a cross between the winter wheat varieties Norman and Talent. All short selections carried the Rht2 dwarfing gene while the tall ones did not. The selections were compared in field experiments at the Plant Breeding Institute in Trumpington and at The Murrays Experimental Farm of the Scottish Crop Research Institute near Pathhead. In one of the experiments at Trumpington the plots were automatically sheltered from rain and the effects of withholding water before anthesis and withholding water during grain filling were studied.In all trials the early selections gave grain yields equal to or greater than the late selections. There were no differences in number of ears/m2 or in number of grains per ear between the early and the late selections. Mean weight per grain of the early selections was greater than that of the late selections.The short selections gave grain yields equal to or greater than the tall selections, except when water was withheld during grain filling in the sheltered experiment. There were no differences in number of ears/m2 between the short and the tall selections. The number of grains per ear was greater and mean weight per grain was less for the short selections than for the tall selections.It is concluded that for general fitness to U.K. conditions, new varieties should be semi-dwarf, but earlier than current varieties.
Selections for erect-(E) and lax-leaf (L) posture in winter wheat were made from a cross between parents which contrasted in the character. By the F b generation there were consistent, heritable differences between E and L lines. The lines were evaluated in three field experiments and a glasshouse experiment.In an experiment in which plots were automatically sheltered from rain and in which there were three irrigation treatments, there was no treatment-posture interaction, and over all treatments E lines outyielded L lines by 0-26 t/ha. When fully irrigated the water use of both E and L lines between 1 May and maturity was approximately 280 mm. Withholding water caused a reduction in water use and a corresponding reduction in grain yield for both E and L lines.When the four most erect-and the four most lax-leaved lines were considered over all three field experiments, E lines maintained a slight, though not significant, grain yield advantage of 0-17 t/ha over L lines. However, the E lines produced significantly more biomass, averaging 0-7 t/ha more than L lines, and this extra biomass was not produced at the expense of additional water requirement. However, results from the glasshouse experiment suggested that the E lines may be more susceptible to a substantial pre-anthesis drought.It is concluded that varieties of winter wheat with the erect-leaf habit may provide an opportunity of increasing biomass production. In an environment in which a preanthesis drought is unlikely to occur, such varieties may give the highest yields. However, on light soils prone to early drought or at sites which would not permit the maximum expression of leaf area index at anthesis, varieties with a lax-leaf posture may give greater yield. Tanner et al. 1966;Hadfield, 1968;Pendleton et al. i g 6 8 j A n g u S ) J o n e g & W i l s o n ( 197 2) also found The photosynthesis of crops is affected by the that leaf posture was a factor contributing to the distribution of radiation over the leaves in the higher photosynthetic rate of an erect-leaved canopy, and leaf posture is a factor affecting the compared with a lax-leaved cultivar, although the interception of incident radiation and the yield of the lax-leaved cultivar was higher, uniformity with which it is distributed within the probably because of the low values of LAI achieved canopy. The models of Monteith (1965) and de Wit by both canopies and also the inherently higher (1965) predict that crops with erect leaves will yielding potential of the lax-leaved cultivar. have higher photosynthetic rates than those withIn winter wheat (Triticum aestivum L.), LAI lax leaves when leaf area index (LAI) is greater reaches a maximum about 2 weeks before anthesis than 3-4, while at lower LAI the situation will be and then declines to zero during the following reversed. Thus the conditions required for the 8-10 weeks (Watson, Thome & French, 1963), with expression of the advantage of erect leaves may the maximum LAI attained in the United Kingdom occur for only short periods in the life of the ...
Selection for high-(H) and low-(L) drought-induced abscisic acid (ABA) accumulation in spring wheat was made from a cross between parents which contrasted in the character. By the F b generation H and L selections were homozygous for ABA accumulation, which differed between the classes by 80 %. The selections were evaluated in field experiments in which the amount of available water was varied.In one experiment, in which plots were automatically sheltered from rain, H selections outyielded L selections by an average 0'36 t/ha both when fully irrigated and when water was withheld between anthesis and maturity. The extra grain yield of the H selections was not produced at the expense of additional water requirement in either treatment. When water was withheld during the 4 weeks preceding anthesis, the grain yields of H and L selections were similar, but H selections used less water between 1 May and maturity. Averaged over all treatments the ratio of grain yield to water use was greater for H selections than for L selections by 0-12 t/ha/100 mm. Withholding water caused a reduction in water use and a corresponding reduction in biomass production in both sets of selections.In two trials in which plots were either irrigated weekly or received natural rainfall only, the ratio of grain yield to water use was again greater for H than for L selections, by an average 0-10 t/ha/100 mm.It is concluded that in spring wheat, selection for high levels of ABA accumulation in response to water stress may provide an opportunity of increasing grain yield and water-use efficiency.
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