Xenia effect on resistance to maize weevil and larger grain in maize
Munyao, William Muthui
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Maize (Zea mays) is a preferred staple as well as a cash crop in Sub-Sahara Africa, contributing to 34-36% of the daily caloric intake in Kenya. Maize production is constrained by several factors among them biotic factors. The key biotic factors leading to post-harvest losses are the maize weevil and the larger grain borer both of which cause grain weight losses in the range of 21-35%. Maize is an open pollinated crop and pollen from other sources influences grain characteristics in the year of crossing, an effect known as xenia. The xenia effect on resistance to maize weevil and larger grain borer is not known. The objective of this study was to determine the occurrence and level of xenia effect on resistance of F2 grain to maize weevil and larger grain borer. Fourteen genotypes (4 resistant and 4 susceptible to maize weevil) and 6 commercial genotypes, were used. The 14 genotypes were grown in 12 crossing nurseries using un-replicated nursery design. Crossing was done using maize weevil and larger grain borer resistant and susceptible genotypes as pollen parents in addition to sib, self, grouped-sib and open pollination treatments to generate F2 grain for evaluating xenia effect. Protein, oil and starch contents, hardness and 100 grain weight of the F2 grain were determined. Shelled and unshelled F2 grained were screened for maize weevil and larger grain borer resistance. Xenia effects were calculated by subtracting sib-mating treatment means from other treatment means for maize weevil and larger grain borer resistance traits evaluated. Xenia effect on F2 grain to maize weevil in cross pollination was a decrease in grain weight loss of 8.41%. Self and sib-pollination treatments xenia effects on resistance of F2 grain to maize weevil and larger grain borer were not significantly different which suggests that these treatments had no xenia effect on F2 grain resistance to these pests. Open pollination increased the starch content of F2 grain by 0.9% but reduced the oil and protein content by 0.16% and 1.03%, respectively. Group-sib pollination increased the oil and protein content by 0.14% and 0.34% respectively but reduced starch content by 0.41%. There was a decrease in F2 grain hardness in all treatments that ranged from 9.96% in cross pollination to 19.19% in open pollination. The decrease in hardness in cross pollination meant that the percent weight loss should have increased. But in contrary the percent weight loss decreased, suggesting that xenia effect in cross pollination influenced other factors that contributed resistance to maize weevil. The protein content of F2 grain was negatively correlated with percent dust weight, and percent grain weight loss and number of live insects. This means that percent grain weight loss, percent dust and number of live insects may be the best traits for determining xenia effect of F2 grain. The percent grain weight in the crosses between resistance and resistant and resistance with susceptible were not significantly different suggesting that xenia effects are as a result of dominance gene. It is evident from the results that xenia has effect on F2 grain resistance to maize weevil and larger grain borer and therefore screening for these pests should take into account this effect.