Resistance of maize to the maize weevil: II. Non-preference

Although there have been significant advances in improving maize for grain yield, progress in developing varieties resistant to the maize weevil (Sitophilus zeamais Motsch.) has been limited. In this study, fifty-two hybrids were evaluated against the maize weevil for non-preference in free choice experiment to study gene action determining inheritance of this mechanism of resistance. Eighteen inbred lines, six each from southern Africa, Mexico and CIMMYT-Zimbabwe were used to make the hybrids. Lines were mated among sub-groups of three each, according to a North Carolina Design II scheme. F2 grain of the hybrids was evaluated for non-preference resistance under controlled temperature and relative humidity conditions. Maize weevil preferred some hybrids, and caused grain weight losses ranging from 0.85 to 8.45% after 70 days of feeding in a free-choice environment with equal access to all maize genotypes. The maize weevil preferred 'SR52', a local commercial hybrid that we used as the susceptible check (6.62% weight loss), and other local hybrids (6.02 to 6.80% weight loss), to 'Oaxaca 179' (the resistant check), which incurred a weight loss of 3.50%. Four percent of the experimental hybrids incurred less than 2.0% grain loss and were classified as resistant, while a further 29% of hybrids were moderately resistant to weevil attack. General combining ability effects (GCA) of lines used as male and female parents were significant (P Key Words: Maize, maize weevil, insect resistance, non-preference, Sitophilus zeamais RESUME Bien qu'il y a eu des progres significatifs dans l'amelioration des rendements grains du mais, le developpement des varietes resistantes au charancon du mais (Sitophilus zeamais Motsch.) a ete limitee. Cinquante deux hybrides ont ete evalues pour la non-preference au charancon du mais dans des essais libres pour etudier l'action du gene determinant l'heritage de ce mecanisme de resistance. Dixuit lignees de familles, dont six chacuns sont de l'Afrique du sud, du Mexique et CIMMYT-Zimbabwe ont ete utilises pour former des hybrides. Les ligneens ont ete croisees entre les sous-groupes pour chacun des trois, selon le plan de protocole II de Corolina Nord. Les grains F2 des hybrides ont ete evalues pour la resistance a la non-preference sous conditions controllees de temperatures et d'humidite relative. Les charancons du mais ont preferre certains hybrides et ont cause des pertes de poids variant entre 0.85 et 8.45% apres 75 jours d'alimentation dans un environnement libre ayant meme access a tous les genotypes. Le charancon du mais a preferre 'SR52', un hybride commercial local, qui a ete utilise comme temoin susceptible (6.62% de perte de poids), et un autre hybride local (6.02 a 6.50% de perte de poids) et l''Oaxaca 179' (temoin resistant) qui a encouru une perte de poids de 3.50%. Quatre pourcent des hybrides des essais ont subi moins de 2% de perte de grains et ont ete clasifies resistants, alors que 29% des hybrides ont ete moderement resistants a l'attaque du charancon du mais. Des effets d'habitude a la combinaison (GCA) des lignees utilisees comme des parents mâles et femelles ont ete significatifs (P Mots Cles: Mais, charancon du mais, resistance de l'insecte, non-preference, Sitophilus zeamais (African Crop Science Journal 2001 .9(2): 441-450)