INHERITANCE OF OSMOTIC ADJUSTMENT TO WATER-STRESS IN 3 GRAIN-SORGHUM CROSSES

Water stress is one of the major constraints to the grain yield of sor ghum in tropical and sub-tropical areas of the world. Osmotic adjustme nt has been widely proposed as a plant attribute that confers adaptati on to water stress. The inheritance of osmotic adjustment to water str ess was investigated in a series of generations derived from the three possible bi-parental crosses between two inbred sorghum lines with a high capacity for osmotic adjustment (Tx2813 and TAM422; high-GA lines ) and one with a low capacity (QL27; low-GA line). Broad-sense heritab ility on a single-plant basis was generally found to be high. Analysis of segregation ratios by the mixture method of clustering identified two independent major genes for high osmotic adjustment. The line Tx28 13 possessed a recessive gene which is given the symbol oal; the line TAM422 possessed an additive gene which is given the symbol OA2. There was some evidence that there may be other minor genes which influence the expression of osmotic adjustment in these crosses as two putative transgressive segregants, with higher osmotic adjustment than the par ents, were identified from the cross between Tx2813 and TAM422. Popula tions of recombinant inbred lines were developed and characterised for osmotic adjustment for two of the crosses (QL27 x TAM422, low-GA x hi gh-OA; Tx2813 x TAM422, high-oal x high-OA2). These will be used to co nduct experiments which test hypotheses about the contribution of the high-osmotic-adjustment genes to the grain yield of sorghum under a ra nge of water-stress conditions.