Comparative Resistance of Maize populations to the maize weevil,Sitophilus zeamais Motschulsky
Date
2011-03-31
Authors
Siwale, Julius
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Abstract
Storage losses present a major threat to food security among the small-holder farmers in
Africa. The Maize weevil, Sitophilus zeamais Motschulsky, is one of the most important
storage pest for which breeding for resistance is the best option for reducing storage
losses. A study was conducted to identify maize cob and grain characteristics conferring
resistance to the maize weevil in selected maize genotypes. Field and laboratory
experiments were conducted using 52 maize genotypes of varying resistance to the pest.
Field experiments looked at husk cover length and husk cover rating, while laboratory
experiments focused on grain hardness, protein content, cob and grain weight loss and
Dobie's susceptibility indices. Results from the field showed that there was no initial
maize weevil infestation from the field on the cobs harvested. Genotypes were
significantly different for husk length and husk cover rating scores (p<0.001), with
landraces having longer husks (mean, 88 mm) and better husk cover score ratings (mean,
1.8) than hybrids (mean, 35 mm and 3.0, for husk length and cover rating scores,
respectively) and open pollinated varieties (OPVs) (mean 48 mm cover length and score
2.1). Genotypes were significantly different (p<0.05) for grain hardness. Grain protein
content was not significantly different among the genotypes (p>0.05). There was no
correlation between protein content and grain hardness across genotypes (r=0.14 among
all genotypes; r=0.20 among hybrids; and r=0.26 among OPVs). However, there was
significant correlation between protein content and grain hardness for resistant OPVs
(r=0.82) only. Husk parameters measured did not discriminate the tested genotypes for
weevil resistance because there was no initial infestation from the field, while the grain
protein content tended to be related to hardness, which could be used as a proxy for
resistance to the maize weevil. Genotypic differences in grain weight loss due to feeding
by the larvae and adults of the maize weevil were highly significant. The genotypes also
differed significantly in the Dobie's index of susceptibility. The two landraces used in the
study did not show any superiority in resistance over the hybrids or OPVs. Similarly,
OPVs were not necessarily superior to hybrids according to the Dobie's index of
susceptibility. Out of the best nineteen genotypes according to Dobie's index of
susceptibility fifteen were hybrids. It was therefore concluded that it is possible to
develop hybrids or OPVs that are as resistant as or even better than some landraces.
Since only two landraces were included in this study, and these were from the same
district, it is recommended that a larger number of land races and from different parts of
Zambia be screened for resistance to the maize weevil. The landraces with superior
resistance could then be used in crosses to develop hybrids and OPVs with increased
resistance to the maize weevil. An attempt at analysing for ferulic acid content in the
maize grain failed due to mechanical faults on the only available Gas
chromatography/mass spectropy machine in the chemistry department at the University
of Zambia. The analysis of ferulic acid could have provided further information on the
mechanisms of resistance in the maize materials studied. It is necessary that in future
Zambian parental maize lines and landraces get characterized for ferulic acid content.
Description
Keywords
Corn--Diseases and pests , Sitophilus , Granary weevil