FLORET MORPHOLOGY OF SORGHUM MIDGE-RESISTANT SORGHUM

Differences in sorghum, Sorghum bicolor (L) Moench, spikelet character istics at the time ovipositing sorghum midges, Stenodiplosis sorghicol a (Coquillett), are in the field have been proposed as a major cause o f resistance. Ovipositing sorghum midges were most abundant on panicle s of susceptible RTx430 sorghum (7.6 per panicle) and least abundant o n resistant sorghums (mean of 2.7). Percentages of kernels that failed to develop were greater for susceptible (62.9) than resistant sorghum s (25.7). Sorghum midge-resistant sorghums as a group had shorter stig mas (0.92 mm), filaments (0.96 mm), and anthers (1.80 mm), but wider ( 0.70 mm) and longer (1.03 mm) ovaries than did susceptible sorghums (1 .27, 1.24, 2.09, 0.67, and 0.96 mm, respectively). However, these diff erences were not consistent among individual genotypes. Sorghum midge abundance and damage were highly significantly correlated. But, abunda nce of sorghum midges and resulting damage were not consistently corre lated with sizes of sorghum floral parts. This lack of consistent corr elation, especially for individual sorghum genotypes, indicated differ ences in sizes of floral parts are not as important as time and tightn ess of glume closure as a major cause of sorghum resistance to sorghum midge.