ADAPTATION OF CORN (ZEA MAYS L.) KERNEL DEVELOPMENT TO CONDITIONS OF DROUGHT AND THERMAL STRESS

Part I. We studied the effect of water and thermal stress on maize grain growth and development. Kernel growth was more sensitive to water and thermal stress during the lag than during the linear-filling phase. The higher sensitivity of seed development to stress during the lag phase was not a consequence of a lack of carbohydrate availability to the grain. On the other hand starch synthesis was inhibited by high temperature. Our data suggest that both stresses may mediate kernel size by reducing endosperm sink capacity established during the lag phase.;Part II. We considered the concept of managing maize for more conservative growth as a means of reducing late-season drought in Mediterranean areas. Limiting vegetative growth through early defoliation altered the patterns of leaf expansion and reduced the total leaf area of maize. This reduction in leaf area resulted in a reduction in pre-silking evapotranspiration. Soil water savings were associated with an average 37% and 31% increase in yield and harvest index, respectively.;Kernel growth rate was unaffected by a water deficit that completely inhibited photosynthate production. Kernel growth was maintained by a relocation of stored assimilates from non-grain parts of the plant to the grain. The high stalk moisture content, the independence of grain and whole plant water status, and the intrinsic tolerance of growing seed to direct water stress permitted translocation to proceed in spite of severe leaf dessication.