It is often thought that concentration on yield
stability may come at the expense of high yields
in good years; however, yield penalties in more
favorable conditions do not necessarily accompany
drought tolerance (Fig. 2).
Yield stability is harder to select
for than improved yield is, because
selection in breeding programs
requires many years and
many sites for evaluation. However,
there is evidence for a genetic
basis for yield stability and,
hence, an opportunity for gain
(9). Transgenic approaches are
also likely to improve yield stability
(10). There are several clear
examples where single genes
have been able to substantially
increase yield, notably to drive
domestication (to control tiller
number, branching, and seed
number) and the green revolution
(for dwarfing). Initial results
suggest that a gene conferring
increased drought tolerance may
also have a widespread impact
on yield (10).