THE ASSOCIATION OF BIOMASS ALLOCATION WITH GROWTH AND WATER-USE EFFICIENCY OF 2 TRITICUM-AESTIVUM CULTIVARS

We investigated traits that might improve performance of wheat (Tritic um aestivum L.) in a dry environment, and examined if the response to drought is different for cultivars with a contrasting biomass allocati on pattern, using two cultivars with either a high (Katya) or small (M exipak) proportion of biomass allocated to the leaves. Plants were gro wn in pots placed in the field, under well-watered conditions and unde r intermittent drought. Katya allocated a greater proportion of its bi omass to both leaves and roots, and a smaller proportion to stems than Mexipak did. The growth rate of Katya was not higher despite a higher investment in leaf area and a slightly higher rate of photosynthesis, possibly due to concomitantly higher respiratory losses. Under well-w atered conditions, the efficiency of water use for growth was higher f or Katya than for Mexipak, due to a lower water use at a similar growt h rate. Differences in water use per plant were determined by the rate of water loss or uptake, rather than by the amount of roots or leaves . A high water use efficiency was independent of growth rate. We concl ude that a lower rate of water use due to a lower transpiration per un it leaf area linked with a high leaf area can contribute to improve th e performance of wheat cultivars in a water-limited environment.