Challenges and Opportunities for Enhancing Sustainable ... - IITA

Cowpea genetics and breeding
1.2
Breeding cowpea for tolerance to
temperature extremes and adaptation to
drought
A.E. Hall 1 , A.M. Ismail 1 , J.D. Ehlers 1 , K.O. Marfo 2 , N. Cisse 3 , S. Thiaw 3 , and
T.J. Close 1
Abstract
Cowpea exhibits incomplete emergence when soil temperatures are below 19 o C.
Chilling tolerance at emergence appears to be conferred by a dominant gene encoding
a dehydrin protein. Seed immunoblot assays facilitate breeding for this trait.
Cowpea can exhibit floral bud suppression and low pod set when night temperatures
are higher than 17 o C. Heat-tolerance genes enhanced flowering, pod set, and grain
yield under hot subtropical conditions but with no difference between tolerant and
susceptible lines in hot tropical conditions. In glasshouse studies, heat-tolerant lines
had high yields under both long and short days but heat-susceptible lines only
exhibited low yields in long days. Delayed leaf senescence can enhance drought
adaptation of early cowpea cultivars by enabling them to produce a greater second
pod flush if the first flush is damaged by drought. Genetic studies demonstrated
that combining the delayed leaf senescence and heat tolerance traits could breed
cultivars with enhanced yield stability.
Introduction
In subtropical zones, such as the San Joaquin Valley of California, cowpea is sown in the
spring (Hall and Frate 1996). Early sowing can result in high grain yields if it enables the
crop to escape hot summer weather that can hinder reproductive development (Hall 1992).
If sowing is too early, however, and the soil is cooler than 19 o C, chilling damage can
cause slow and incomplete emergence (Ismail et al. 1997). This paper will discuss research
showing that breeding cowpea for both chilling tolerance at emergence and heat tolerance
at flowering can partially solve these problems for subtropical zones. We also will discuss
studies of whether genes that confer heat tolerance during reproductive development in
subtropical zones have any adaptive value for cowpea grown in tropical zones in West
Africa. Cowpea in the Sahelian (annual rainfall of about 200 to 500 mm) and dry savanna
(annual rainfall of about 500 to 700 mm) zones of West Africa can experience both heat and
drought stress (Hall et al. 1997a). Cowpea cultivars that begin flowering early can escape
drought in some locations and years and produce useful yields of grain. Unfortunately,
the early cowpea cultivars tend to be very sensitive to droughts that occur during early
stages of reproductive development (Thiaw et al. 1993). A delayed-leaf-senescence (DLS)
trait has the potential to enhance the drought adaptation of cowpea in the dry savanna
1. Department of Botany & Plant Sciences, University of California, Riverside, CA 92521, USA.
2. Savanna Agricultural Research Institute, PO Box 483, Tamale, Ghana.
3. Centre National de Recherches Agronomiques, BP 53 Bambey, Senegal.
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