Final version of Tropical Legumes II Project Report for Phase 1 - icrisat

most efficient and IT99K-7-21-2-2 was the least under low phosphorus conditions. Among the early
maturing lines, IT03K-351-1 formed the largest nodular tissue under low phosphorus conditions and
depended least on higher soil available phosphorus for nodule formation and development. In the
other genotypes however, nodulation was relatively low under low phosphorus conditions but the
increase in nodule mass development in response to the high soil available phosphorus ranged from
83 to 515%. Genotypic differences in phosphorus utilization under both low and high phosphorus
conditions were not extensive (P ≤ 0.05) even though IT00K-1263 appeared to have performed better
under low phosphorus conditions than most genotypes within the early maturity group.
Screening of germplasm lines for drought tolerance
Over 1,200 cowpea accessions among the germplasm maintained at IITA were randomly selected
and screened for drought tolerance in the field. The screening was carried out during the dry season.
Drought stress was imposed by withdrawing irrigation at five weeks after sowing while none stressed
plots were irrigated until plants matured. Data were collected on number of days to flower, extent of
wilting, and number of days to maturity as well as mean seed weight and total seed weight per plant
(see Figures 5-6 and 5-7). Most plants flowered and matured earlier when drought stressed. Drought
stressed plants also produced lower grain yield per plant. Many of the germplasm lines remained
green even at seven weeks of no irrigation. However, a few of these plants did not flower and therefore
produced no seeds but remained green and stunted.
About 190 accessions with enhanced drought tolerance were identified from this screening activity.
These selected lines were further evaluated in pots placed in the screen house. Drought was imposed
on the potted plants from three weeks after sowing and those that survived for more than four weeks
thereafter were regarded as being most drought tolerant. Some of these lines were selected and used in
making crosses among them and between them and some farmer-preferred varieties.
Frequency
1000
900
800
700
600
500
400
300
200
100
0
Non stressed
Stressed
Frequency
1200
1000
800
600
400
200
Non Stressed
Stressed
36.9-45.8 45.9-54.8 54.9-63.8 63.9-72.8 72.9-81.8
No of days
0
0.32-10.31 10.32-20.31 20.32-30.31 30.32-40.31 40.32-50.31 50.32-60.31
weight
Figure 5-6: Number of days to flowering
Figure 5-7: Seed weight (g) per plant
Making crosses and developing segregating populations
The best of the germplasm lines in terms of enhanced drought tolerance were crossed to one another
and also to improved breeding lines that farmers had selected during PVS. There were over 200 cross
combinations comprising single crosses, three way crosses and double crosses. These have been
advanced to F8, F7, F6 and F5 generations, depending on when the crosses were made. Additional
crosses have been made using lines obtained from our collaborating NARS breeders’ nurseries. Selection
will be made from these segregating populations for plants with superior drought tolerance and also
possessing traits desired by farmers and consumers.
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Engaging Smallholder Farmers | Tropical Legumes II Project