Ra. Fischer et al., Wheat yield progress associated with higher stomatal conductance and photosynthetic rate, and cooler canopies, CROP SCI, 38(6), 1998, pp. 1467-1475
Grain yields of eight representative semidwarf spring wheat (Triticum aesti
vum L.) cultivars released in northwest Mexico between 1962 and 1988 have i
ncreased linearly across years as measured in this region during 6 yr under
favorable management and irrigation. To understand the physiological basis
of this progress and possibly assist future selection for grain yield, lea
f traits were determined during 3 yr in the same study. Stomatal conductanc
e (g(s)), maximum photosynthetic rate (A(max)), and canopy temperature depr
ession (CTD), averaged over the 3 yr, were closely and positively correlate
d with progress in the 6-yr mean yield. The correlation was greatest with g
(s) (r = 0.94, P < 0.01). Compared with the overall yield increase of 27%,
g(s) increased 63%, A(max) increased 23%, and canopies were 0.6 degrees C c
ooler. Carbon-13 isotope discrimination was also positively associated with
yield progress (r = 0.71, P < 0.05), but other leaf traits such as flag le
af area, specific leaf weight, percentage N and greeness were not, nor was
crop growth rate around anthesis. The causal basis of the leaf activity int
errelationships is reasonably clear, with both increased intercellular CO2
concentration and increased mesophyll activity contributing to the increase
in A(max). However, causal links to the yield progress, and the accompanyi
ng increase in kernels per square meter, are not clear. It is concluded tha
t g(s) and CTD should be further investigated as potential indirect selecti
on criteria for yield.