Challenges and Opportunities for Enhancing Sustainable ... - IITA

Cowpea genetics and breeding
Table 2. Index of new gene symbols.
Gene symbol Character Reference
bcm Resistance to black- Arshad et al. (1998)
eye cowpea mosaic virus
Bk-2 Black pod color Aliboh et al. (1996)
fa Fasciated plant Adu-Dapaah et al. (1999)
Dhp Dehiscent pod Aliboh et al. (1996)
Gr Green shoot color Uguru (1995)
P1 Pleiotropic gene for Joshi et al. (1994)
axil, calyx, corolla pod
tip, and seed colors
pms Partial male sterility Singh and Adu-Dapaah
(1998)
ps Photosensitivity Ishiyaku and Singh (2001)
Ptc Calyx pigmentation Biradar et al. (1997)
Pt Calyx pigmentation Biradar et al. (1997)
Pc Calyx pigmentation Biradar et al. (1997)
Rds1 Resistance to drought Mai-Kodomi et al. (1999)
Rds2 Resistance to drought Mai-Kodomi et al. (1999)
Rt1 Rough seed coat texture Singh and Ishiyaku (2000)
Rt2 Rough seed coat texture Singh and Ishiyaku (2000)
Vsm V-shaped mark on leaves Aliboh et al. (1996)
plant pigmentation (Table 3). It has also been observed (by the author) that all the cowpea
varieties with brown rough seed have no pigmentation on any plant part except for a faint
purple tinge on the inner margins of the standard petal. Also all the cowpea varieties with
white rough seed have purple pigmentation on the joints (bases of the branch, peduncle,
petiole, and leaflets), which are always inherited as one gene. However, the pigmentation
of whole stem, petiole, peduncle, and pod is independent of the pigmentation on the joints.
It has also been observed that whenever the calyx is pigmented, the pod tips are also pigmented
and this is independent of other pigmentation. Another interesting pigmentation
pattern is present in the cowpea variety Kamboinse local. It has dark purple pigmentation
on the stem, petiole, peduncle, joints, calyx, and pod, but the flowers are completely white
except for a purple dash in the back of the standard. The cowpea varieties listed in Table
3 represent a good set of differentials for different pigmentation patterns and efforts are
under way to use them in planned genetic studies to elucidate inheritance pattern and
interaction, if any, of specific plant pigmentations.
Genetics of disease resistance
Inheritance of, resistance to several cowpea diseases has been reported between 1995 and
2000. Vale et al. (1995) studied the inheritance of resistance to cowpea severe mosaic
comovirus (CpSMV) using cowpea variety Macaibo as the resistant parent and Pitiuba
as the susceptible parent. The F 1
plants were uniformly susceptible and F 2
segregated into
a ratio of three susceptible to one resistant, indicating involvement of a single recessive
gene pair for resistance. The authors have mentioned that Macaibo is immune to CpSMV.
Arshad et al. (1998) studied the inheritance of resistance to blackeye cowpea mosaic
(BlCMV) in six cowpea varieties: IT86F-2089-5, IT86D-880, IT90K-76, IT86D-1010,
IT86F-2065-5, and PB1CP3. The segregation pattern in F 2
, and backcross populations
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