Leaf Photosynthesis, Leaf Permeability, Crop Growth, and Yield of Short Spring Wheat Genotypes Under Irrigation¹

Abstract

Because of the expected importance of photosynthetic activity to yield, the relationships of leaf photosynthetic traits to crop growth rate and yield in 48 genotypes of spring wheat, were examined under irrigation in northwest Mexico. There were three tall and 33 short (Norin 10-derived) bread wheats (Triticum aestivum L.), eight short durum wheats (T. turgidum L.) and four triticales (X Tritosecale Wittmack). Photosynthetic activity (A) and leaf permeability viscous air flow (LP) were measured weekly using 14CO, uptake and an air flow porometer, respectively.Genotypic effects on A (range 14.7 to 20.4 mg dm-* hour -*) and LP (range 5.7 to 11.1 permeability units) were highly significant but species effects were small and nonsignificant. Looking now exclusively at the short bread wheat group, A was unrelated to specific leaf weight or to LP A on the first sampling at 4 weeks before anthesis and preanthesis crop growth rate (g -z day-*) were weakly c orrelated ( phenotypic r = 0.42, significant at the 0.05 level), and both these traits were positively correlated with mature plant height (r = 0.56, significant at the 0.01 level, and 0.68, significant at the 0.05 level, respectively). A was also positively correlated with crop growth rate during grain filling (r = 0.46, significant at the 0.01 level) and with yield (r = 0.45, significant at the 0.01 level; yield range 516 to 860 g m-Z). These correlations arose because of the positive influence of days to anthesis on all three traits and probably reflect an increase in sink size (more kernels -z) with l ater a nthesis. Y ield w as positively correlated with LP (r = 0.56, significant at the 0.01 level); the correlations remained significant (r = 0.46, significant at the 0.01 level) after allowance for the negative effect of plant height on both (LP was unrelated to anthesis date). While the cause of this correlation may be indirect, the testing of LP as an early generation selection criterion is suggested. Effects of major Norin 10 dwarfing genes on these relationships are discussed.

Regulation of Photosynthetic Rate of Two Sunflower Hybrids under Water Stress

“…and differences in leaf structure, cell size, or stomatal frequency. Small but consistent differences in assimilation were detected between hexaploid wheats under well-watered field conditions (9), but such differences between other wheat genotypes were attributed to ploidy (2). Substantial differences (up to 35%) have been reported between cultivars of field bean (13) and in pea (21), the latter attributed to variation in Chl content.…”

“…Genetic variation in rates of photosynthesis per unit leaf area (Pn2) has been reported for cultivars of some crop species (2,9,12). Possible causes of the differences in Pn between genotypes are variations in amounts or activities of specific proteins, pigments, etc.…”

“…In this respect, productivity of plants is greatly decreased by water deficiency in most parts of the world and much emphasis is given to improving the drought tolerance of varieties (2). However, the effect of water stress on the mechanisms of CO2 assimilation (3-5, 16, 19, 25) has not been analyzed in sufficient detail, in genotypes differing in assimilation capacity, to show how the photosynthetic mechanism may be modified to improve assimilation under water stress (9,16,21,25,26). The main limitation to assimilation under water stress is suggested as inhibition of photophosphorylation which decreases RuBP regeneration rather than the enzymatic or light reactions (4,5,16), but varietal responses have not been examined.…”

Differences between spring wheat cultivars in early growth

“…We consider a range of 5-10% to be realistic for genotypes in breeding nurseries. This estimate is based on C0 2 assimilation measurements of single leaves at high light published by DUNCAN & HESKETH (1968), PEARCE et al, (1969, EVANS & DUNSTONE (1970), KHAN & TSUNODA (1970a, CRISWELL & SHIBLES (1971), DANTUMA (1973), ASAYet al (1974, KISHITANI & TSUNODA (1974), FISCHER et al (1981, AUSTIN et al (1982), MAHON (1983), EVANS et al (1984), andYAMAUCHI &YOSHIDA (1985). Values of Amax change with conditions for growth during leaf development and with leaf age.…”

Studies on endogenous hormonal changes during grain development in wheat genotypes

“…Norin 10, eight short durum wheats and four triticales were examined by Fischer et al (1981), and among the short bread wheats, photosynthetic activity four weeks before anthesis and pre-anthesis growth rate were positively correlated with the mature plant height.…”