Resistance of sorghum grain to maize weevil, Sitophilus zeamais Motsch

Abstract

The objectives of this study were to screen seeds of 169 exotic converted sorghum lines for resistance to the maize weevil, Sitophilus zeamais Motsch, and determine physical and morphological kernel properties influencing the degree of resistance. Preliminary screening using free- and no-choice tests were conducted at 27 °C and 60 [plus or minus] 3% RH to eliminate obviously susceptible lines. Standard resistant and susceptible checks, MP-10 shallu and karfir 60, respectively, and hybrid rearing sorghum seeds were used as controls in all tests. For free-cho8iice tests, 225 unsexed weevils 10 [plus or minus] 3.5 days old were placed in the center of specially designed trays and the weevils allowed to move freely to the seeds confined in the compartment. The trays were maintained in an incubator. The number of adults present in each sorghum line was recorded after a 7-day exposure period. This test was replicated four times. The no-choice method used small vials (2.2 cm diameter and 2.5 cm high) containing 50 sound sorghum kernels and in which six female and here male weevils were confined for a seven day oviposition period. The no-choice test was replicated six times, with the first two replications conducted at 27 °C and a humidity range from 40-80%. The other four replications were tested at 27 °C and 60 [plus or minus] 3% RH. The total number of emerged progeny were recorded 55 days post oviposition. Correlation analysis of the number of adults present in the free-choice and number of emerged progeny in the no-choice tests showed significant positive correlation (r = 0.32) at the .05 level. From the preliminary screening test, 22 sorghum lines were selected based on their performance (those producing the lease number of emerged progeny) in all six replication in the no-choice test and least preference to the adult weevils in the free-choice test. Standard checks and rearing seeds also were included in the selected screening..