Challenges and Opportunities for Enhancing Sustainable ... - IITA

Cowpea genetics and breeding
presence of the DLS trait did not have a significant effect on the first-flush grain yield of
the heat-tolerant lines (there was a nonsignificant decrease of 295 kg/ha). If this decrease
in yield is real, it does not represent a large penalty in that the DLS trait has the potential to
increase second-flush grain yield by up to 2000 kg/ha (Ismail and Hall 1998). Performance
of the four sets of lines was evaluated in a soil environment where there was substantial
death of non-DLS lines after producing the first flush of pods (73% of the plants died
compared with < 1% for DLS lines). The presence of the heat-tolerance genes did not
have a significant effect on the proportion of plants that died (nonsignificant increases of
10 percentage points in non-DLS lines and 1 percentage point in non-DLS lines occurred
as shown in Table 5).
The overall conclusions are that (1) the DLS trait can greatly enhance plant survival
after the first flush of pods is produced and may only cause a small decrease in first-flush
grain yield; and (2) the heat-tolerance trait can substantially increase first-flush grain yield
and may only slightly enhance the tendency for premature plant death in non-DLS lines
with no effect on lines having the DLS trait.
Table 4. First-flush grain yields of four sets of lines with and without heat-tolerance and
with and without the delayed-leaf-senescence trait.
Delayed-leaf-
Senescent
senescence lines lines Average
kg/ha
Heat-tolerant lines 3168 3463 3316
Heat-susceptible lines 2248 2613 2430
Average 2708 3038
The heat-tolerance effect was very highly significant whereas the delayed-leaf-senescence and interaction
effects were not significant at the 5% level and the CV was 19.3%.
Note: Data are average values for 10 lines per set from an experiment at Shafter, CA, USA in 1998 (Ismail
et al. 2000).
Table 5. Percentage of plants that died after producing the first flush of pods for four sets
of lines with and without heat-tolerance and with and without the delayed-leaf-senescence
trait.
Delayed-leafsenescence
lines
Senescent
lines
Percentage of plants that died
Heat-tolerant lines 1 78
Heat-susceptible lines 0 68
The delayed-leaf-senescence effect was very highly significant whereas the heat-tolerance and interaction
effects were not significant at the 5% level.
Note: Data are average values for 10 lines per set from an experiment at Riverside, CA, USA in 1998
(Ismail et al. 2000).
Conclusions
Cowpea cultivars can be bred that combine chilling tolerance at emergence with heat
tolerance during flowering and pod set. These cultivars could have enhanced yield
stability in subtropical zones such as those in California. Cowpea cultivars can be bred
that combine early flowering with heat tolerance during flowering and pod set and
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