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Bioscience Methods 2014, Vol.5, No.2, 1-8
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was the most susceptible to
C. maculatus
infestation
and this is followed by cultivar MIT03K-337-6 based
on the following parameters assessed: oviposition, %
adult emergence, weight loss and seed viability.
The results obtained on percentage seed damage and
pest tolerance have further showed that cultivars
MIT04K-399-1, MIT07K-299-92, IT96-610,
MIT06K-281-1, MIT07K-187-24, MIT06K-121,
MIT07K-304-9 and EIT07K-291-69 were resistant,
while cultivars IFE BROWN was the most susceptible
to
C. maculatus
. Damage inflicted by cowpea bruchid
consists of the consumption of seeds, loss or
conversion of nutrients, reduced germination of seeds
and contamination with filthy materials composed of
insect fragments, exuviae, excreta and moulds
(Odeyemi, 2005).
Resistance could be anti-nutritional factors such as
tannins, phytate and oxalate which had been reported
by Singh and McCain (1963).
Anti-nutritional
factors are plant’s secondary metabolites which act
to reduce food nutrient utilization (Soetan, 2008).
Anti-nutritional factors affect susceptibility of grains
to insect attack. However, anti-nutrients is not an
inherent feature of a compound but depends on the
metabolic processes of the ingesting animal (Akande
et al., 2010). The reason for anti-nutritional factors in
plants seems to be as a way of storing nutrients or as a
means of defence from destruction by insect pests and
grazing animals (Harborne, 1989). It has been
reported that tannins help in growth regulation and
also protect the plants from predators like insects
(Fasola and Egunyomi, 2005; Fasola et al., 2013).
Phytate, oxalate and tannins contents were high in the
resistance cowpea cultivars with more phytate than
oxalate. The mean phytate obtained in this study was
about three times higher than that of oxalate. This
agrees with an earlier report by Afiukwa et al. (2011)
who worked on variations in seed phytic and oxalic
acid contents among Nigerian cowpea accessions and
their relationship with grain yield.
The result revealed significant variations in the
anti-nutrients among the cultivars. The amount of
phytate, oxalate and tannins ranges from 2.58 mg/g to
3.92 mg/g, 0.42 mg/g to 0.92 mg/g and 0.21 mg/g to
0.56 mg/g respectively. These values compare well
with 2.58 – 3.87 mg/g for phytate and for oxalate with
mean values of 3.10 and 0.78 mg/g reported for ninety
nine cowpea cultivars by Afiukwa et al. (2011).
Cowpea seeds should always be adequately processed
to avoid phytate-related health risks especially among
individuals who depend largely on cowpea for protein.
Thus, oxalate related problems are not likely to occur
in healthy persons, except among individuals that
consume large amounts on a long-term continuing
basis and individuals with especial vulnerability to
oxalates such as those with kidney disorders, gout and
rheumatoid arthritis. Fortunately, most processing
methods significantly reduce the anti-nutrients or
totally eliminate some of them (Udensi et al., 2005
and 2007; Philips, 1993; Afiukwa et al., 2011). This
study revealed variations in the anti-nutrients among
the cowpea cultivars. These variations affect the
susceptibility of
C. maculatus
infestation. With recent
advances in biotechnology and plant breeding, it is
possible to transfer desirable characters from resistant
varieties in other to improve their resistance to cowpea
bruchid. Alternatively, cultivars MIT04K-399-1,
MIT07K-299-92, IT96-610, MIT06K-281-1,
MIT07K-187-24, MIT03K-337-6, MIT07K-304-9 and
EIT07K-291-69 with high degree of resistance to
C.
maculatus
could be cultivated by farmers. This will go
a long way in ensuring food security in Nigeria.
Acknowledgement
The author are grateful to Alh. Remi Adeleke, CGIAR,
International Institute for Tropical Agriculture, Ibadan, Oyo
State, Nigeria, for the supply of cowpea cultivars. The
comments by three anonymous reviewers towards improving
the quality of this research work are acknowledged.
References
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Variations in seed phytic and oxalic acid contents among Nigerian
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