Four sorghum (
Sorghum bicolor
(L) Moench) Parental lines RTx430,BTx3197, RTx7000, and B35; and their F
1, reciprocals, F
2, and backcross progenies were evaluated during the reproductive phase in two green house experiments to understand the number of genes involved in the expression of high water potential Ψ and high osmotic potential π. The experiments were conducted at Texas A&M University during 1989 and 1990. Plants were well watered until anthesis, after which water was withheld, and measurements were then taken at two weeks interval. Cultivars differed significantly in all traits at all levels of drought stress. B35 and BTx3197 generally maintained higher Ψ and π compared to RTx7000 and Rtx430. Crosses made with B35 resulted in hybrids which were lower in Ψ and π, but higher in dry matter production. These were attributed to hybrid vigor and poor osmotic adjustment capacity. Crosses made with BTx3197 generally maintained higher Ψ and π and were predominantly lower in dry matter, which was associated with better osmotic adjustment capacity. Comparison between F
1 and reciprocals indicated cytoplasmic influence. Depending on the parental combinations, the F
1 means showed higher or lower Ψ and π when compared to either of their parents. Inheritance was proposed to be under multiple gene control with dominant and recessive epistatic effects. Heritability estimates indicated that either B35 or BTx3197 could be used as a parent for the improvement of plant water status. Correlations were found between dry matter accumulation and Ψ and percent moisture loss, and between relative water content and Ψ. These are unlikely to be useful in selection work because of expense and time required for measurement. Indirect selection would be more appropriate for improvement of drought tolerance.
