RELATIONSHIP BETWEEN GRAIN-GROWTH AND POSTANTHESIS LEAF-AREA DURATIONIN DWARF, SEMIDWARF AND TALL ISOGENIC LINES OF WHEAT

Experiments were carried out during 1992 and 1993 growing seasons usin g in the former year 2 (an early and late) sowing dates. Plants of thr ee isogenic lines (standard height, semidwarf and dwarf) of wheat, wer e grown under field conditions with no restrictions on water or nutrie nt availability with the objective of determining whether differences in rate of grain growth and in final grain weight were related to diff erences in leaf area duration postanthesis (LAD). A logistic and an op timization model were used to estimate the components of final grain w eight and their performances were compared. The optimization model app eared more appropriate than the logistic to estimate final grain weigh t and their components (i.e. rate of grain growth and duration of grai n filling). The dwarf line presented the lowest average gain weight fo llowed by the semidwarf and standard height lines, respectively. Howev er, changes in grain weight due to the action of Rht alleles were inde pendent of the LAD, suggesting that reductions in grain weight due to delayed solving dare could be associated with a direct effect of tempe rature on grain development. Changes in final grain weight were associ ated with changes in rate of grain growth, but not with duration of th e grain filling period, demonstrating that rate of grain growth was th e main factor responsible for final grain weight.