An assessment of plant resistance to the sorghum midge, Contarinia sorghicola, in selected lines of Sorghum bicolor

Abstract

During a 4-year period, plant resistance in sorghum to Contarinia sorghicola was studied. Experiments were conducted (1) to determine the relative level of resistance to the sorghum midge possessed by selected lines previously reported as resistant, (2) to determine the mechanisms involved in the midge resistance exhibited by such lines, (3) to screen converted exotic lines for additional sources of midge resistance, and (4) to study 1 aspect of plant and 1 aspect of insect biology; namely, pseudoresistance in sorghum and the feeding process of sorghum midge larvae. Comparison of the mean threshed weights of seed obtained from caged and exposed panicles of 4 sorghum lines (TAM 2566, SC 423, TAM 428, and TX 7000) in a yield test showed that yield reductions following exposure to sorghum midge infestation are smallest for TAM 2566. Results of comparisons of adult emergence from 6 sorghum lines failed to show any differences in the level of resistance possessed by TAM 2566, SGIRL-MR-1, AF 28, or SC 423. In studies of the mechanisms of resistance, evaluation of the results of yield, adult emergence, and carvopsis development data failed to identify tolerance as an important mechanism of resistance. However, analysis of the caryopsis data indicated that weight gains of TAM 2566 and TAM 428 were greater than SC 423 or TX 7000 during the period when late-instar larval feeding could be expected. Nonpreference by ovipositing females was shown for the following lines, listed in order of increasing undesirability to females: SGIRL-MR-1, AF 28, TAM 428, Sc 423, and TAM 2566. When cages spikelets of each of 5 resistant lines at anthesis were each infested with 3 ovipositing females, antibiosis in the form of greater larval mortality was indicated by reduced numbers of larvae and pupae found in spikelets of TAM 2566 and SGIRL-MR-1. Larval measurements showed that larvae reared in the spikelets of TAM 2566 and SC 423 were significantly shorter and narrower than larvae found in TAM 428 or TX 7000 spikelets. Results of a test in which the number of eggs found in infested spikelets was compared with adult emergence 17 days later also indicated that fewer individuals reached the adult stage in TAM 2566 than in the check...