VARIABILITY FOR FORAGE QUALITY, SILAGE QUALITY, AND AGRONOMIC TRAITS IN FORAGE SORGHUM

The variation among 49 F(,1) forage sorghum {Sorghum bicolor (L.) Moench} hybrids from a 7 x 7 cross classified design was explored in 1979 and 1980 for heading date, plant height, lodging, and Brix, and for the following quality traits in both fresh-dried and ensiled samples: dry matter (DM), crude protein (CP), in vitro dry matter disappearance (IVDMD), neutral detergent fiber, acid detergent fiber, acid detergent lignin, and ash. Additional quality determinations, made only in silage samples, included pH, lactate, and NH(,3) levels. Data were not homogeneous for many of the traits. Single year means for most traits were significantly different among entries and among hybrid means averaged over male parents, while many traits were not significantly different when averaged over females. Parental means for males generally had a wider range of variation than for females, and a larger range for most traits was present among the hybrids in 1980 than in 1979. Mean squares for the traits that were homogeneous and could be analyzed over years indicated that significant differences among hybrid means over males and over females were present only for IVDMD in fresh-dried samples, DM in silage, and for Brix. For all traits, the year effect appeared to be responsible for a large proportion of the observed variation. Genetic ratios that gave indications of the magnitude of general and specific combining ability were calculated from mean squares. General combining ability effects appeared to be of most importance for DM, CP, and IVDMD in fresh-dried samples, and for DM, pH, and lactate in ensiled samples, and for Brix. Simple correlation coefficients between traits measured on silage and on fresh-dried samples from the same hybrids were also calculated. The traits DM, CP, and IVDMD gave the highest correlation coefficients, but none was large enough to suggest a high degree of reliability in prediction. The lack of homogeneity over years for many of the traits studied increases the difficulty of improving the quality of forage sorghum or forage sorghum silage by breeding. Further studies to improve predictive reliability between years are needed. However, data from these studies do suggest that progress could be made in the improvement of IVDMD of forage sorghum. When measured in fresh-dried samples, significant differences among hybrids averaged over both male and female parents were shown for this trait; it was affected relatively little by year effects, and it exhibited high GCA effects