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Bioscience Methods 2014, Vol.5, No.2, 1-8
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Each trial replicate was terminated when no adult
emergence for five consecutive days. The
developmental period were also recorded.
In calculating % weight loss, the contents of each
container were sieved to remove dust, frass and any
insect present within the seeds. The seeds were
re-weighed and the % weight loss was determined as
the difference between the initial and final weights of
seeds in each replicate divided by the initial weight
multiplied by 100 as described by Odeyemi and
Daramola (2000).
After re-weighing, the numbers of damaged cowpea
seeds were evaluated by counting wholesome and
bored or seed with bruchid emergent holes. Percentage
seed damaged and pest tolerance were calculated
according to the method described by Lephale et al
.
(2012) as follows:
Susceptibility indices (SI) were calculated according
to the method of Dobie (1974) and is given as;
1.3 Anti-nutritional composition of different
cowpea cultivars
1.3.1 Oxalate
Total oxalate was determined according to Day and
Underwood (1986) procedure. To 1 g of the ground
powder, 75 ml of 15 N H2SO4 was added. The
solution was carefully stirred intermittently with a
magnetic stirrer for 1 h and filtered using Whatman
No 1 filter paper. Twenty five ml of the filtrate was
then collected and titrated against 0.1 N KMnO4
solutions till a faint pink colour appeared that
persisted for 30 seconds.
1.3.2 Phytate
Phytate was determined using Reddy and Love (1999)
method. four grammes of the ground sample was
soaked in 100 ml of 2% HCl for 5 h and filtered. To 25
ml of the filtered, 5 ml 0.3% ammonium thiocyanate
solution was added. The mixture was then titrated with
Iron (III) chloride solution until a brownish-yellow
colour that persisted for 5 min was obtained.
1.3.3 Tannin
Tannin was determined using the method of Trease
and Evans (1978). One ml of the methanolic extract
was treated with 5 ml Folin Dennis reagent in a basic
medium and allowed to stand for colour development.
The absorbance of the reaction mixture of each sample
was measured at 760 nm spectrophotometrically.
1.4 Data Analysis
Data were subjected to analysis of variance (ANOVA)
and treatment means were separated using the New
Duncan’s Multiple Range Test. The ANOVA was
performed with SPSS 16.0 software (SPSS, 2007).
2 Results
2.1 Seed damaged and Pest tolerance.
There was no seed damaged in 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. The result
revealed that the above cultivars had 100% pest
tolerance. Cultivars IFE BROWN, MIT03K-337-6,
MIT04K-219-2 and MIT07K-292-10 were the most
susceptible cultivars to
C. maculatus
infestation with
18.98%, 20.03%, 29.04% and 30.94.63% pest
tolerance respectively (Figure 1). Generally, it was
observed that those cultivars that had least seed
damage, had higher % pest tolerance. Consequently, %
pest tolerance varied directly with number of
undamaged seed.
2.2 Anti-nutritional contents of different cowpea
cultivars
Table 1 presented the anti-nutritional contents of
different cowpea cultivars. The result clearly showed that
cowpea seeds contain more phytate than oxalate and
tannin. The mean phytate obtained in this study (3.10
mg/g) is about three times higher than that of oxalate
(0.78 mg/g) and five times higher than tannin (0.31mg/g).
Cultivar MIT04K-339-1 (3.92mg/g) had the highest
amount of phytate and cultivar MIT03K-337-6 (2.58
mg/g) had the lowest amount of phytate. The amount of
oxalate ranges from 0.42mg/g to 0.92mg/g. Cultivar
IT96-610 (0.56 mg/g) recorded the highest amount of
tannin and cultivar MIT03K-337-6 (0.19 mg/g)
recorded the lowest amount of tannin (Table 1).
generation
F1 50% of
emergence
of
Time
100
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F1 of
number
for e Log
SI
lity
Susceptibi
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Index