INFLUENCE OF RATE OF DEVELOPMENT OF WATER-DEFICIT ON THE EXPRESSION OF MAXIMUM OSMOTIC ADJUSTMENT AND DESICCATION TOLERANCE IN 3 GRAIN-SORGHUM LINES

An experiment was conducted to quantify the effect of rate of developm ent of water deficit (R(Psi)) on the expression of maximum osmotic adj ustment (OA) and desiccation tolerance (DT) in three grain sorghum lin es, TAM422, Tx2813 and QL27. DT was determined as the lethal relative water content (RWC(L)) and lethal leaf water potential (Psi(L)) Of lea ves, i.e. the value of these traits just prior to tissue death. Five r ates of development of water deficit were generated by using different soil volumes in which the decrease in leaf water potential ranged fro m 0.093 MPa day(-1) to 0.153 MPa day(-1). The expression of maximum OA increased markedly with a reduced R(Psi), for all three lines. In con trast, DT decreased only slightly with a reduced R(Psi). The three lin es differed for expression of maximum OA and DT. Both TAM422 and Tx281 3 had higher maximum OA, higher RWC(L) and lower Psi(L) than QL27. The re was a significant line-by-R(Psi) interaction for the expression of OA and DT. The interaction was much smaller than the effect of lines f or the expression of maximum OA. Therefore, the absolute level of OA f or the three sorghum lines and the magnitude of the difference between them changed with the R(Psi) without affecting their ranking. As with maximum OA, the interaction for RWC(L) was smaller than the Line effe ct. The RWC(L) of TAM422 and QL27 was stable across rates of developme nt of water deficit. The results indicated that low R(Psi), increased the expression of OA and decreased Psi(L) but had little effect on RWC (L). While line-by-soil-volume interactions were observed, these were largely explained by the increase in magnitude of the variation for th e traits as R(Psi) decreased and were not the result of changes in ran k of the lines among soil volumes. Therefore, the current screening st rategy is considered to be appropriate for examining genetic variation for OA and DT in grain sorghum. Opportunities exist for using smaller pots and soil volumes where large numbers of genotypes are examined.