Comparative Resistance of Maize populations to the maize weevil,Sitophilus zeamais Motschulsky

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Siwale, Julius
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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.
Corn--Diseases and pests , Sitophilus , Granary weevil