Manipulation of leaf area and its effect on grain yield in droughted wheat

Abstract

Modification of crop leaf area could have considerable consequences on grain yield where soil water is limited. To test this, leaf area was artificially reduced to examine the effect on three wheat cultivars in two different drought situations-one where all the water was supplied just prior to sowing, and the other where half of the water was supplied before sowing and half after sowing on eight separate occasions. Leaf area was modified by detillering and two leaf-cutting treatments, Plants were grown individually in pots 1 m tall by 0.1 m diameter at a crop density of 100 plants/m2. Leaf area and water use were measured weekly for all plants, and at maturity the yields of grain, straw and leaves, and the yield components, were measured. The defoliation treatments reduced total cumulative leaf area by about one-half. This in turn reduced the rate of early water use and resulted in the highest grain yields and harvest indices. The ratio of leaf weight to total plant weight was inversely associated with yield both within and across treatments, suggesting an excessive investment in leaves. This was also indicated in an adjacent experiment where the same cultivars, watered daily, had a similar leaf weight to that of the droughted plants, yet yielded considerably more grain. Water use efficiency (the ratio of above-ground dry weight to total water used) also had a significant influence on grain yield. These results suggest that it may be worth while modifying leaf area development in wheat genetically to improve yields under some dryland conditions.