The Effects of Early Season Drought on Stomatal Conductance, Leaf-air Temperature Difference and Proline Accumulation in Sugar Beet Genotypes.

Limited water for irrigation and the coincidence of early growth of sugar beet (Beta
vulgaris L.) with the late growth of winter cereals in the Northeast (NE) of Iran, force
farmers, to allocate their limited irrigation water to the cereal crops and thus their sugar
beet crop is subjected to an early water stress. Finding cultivars which are able to withstand
early water stress without a significant yield reduction is critical to the farmers’
economy. This study was conducted over a two-year period (1998 and 1999) to evaluate
the response of nine sugar beet genotypes to drought stress and to determine the crop
traits associated with drought resistance. The results showed that stomatal conductance,
leaf-air temperature difference and proline accumulation were associated with levels of
water stress in sugar beet genotypes. Among these indices, leaf-air temperature difference
was a more precise parameter to measure. A negative correlation between Δ T (leaf -air
temperature) and stomatal conductance was found. The correlation coefficients for 1998
and 1999 were -0.87 and -0.58, respectively. There was a positive correlation between Δ T
and proline accumulation in sugar beet genotypes. The correlation coefficients for the
1998 and 1999 experiments were 0.61 and 0.49, respectively. The shoot: root ratio (S:R)
measured at the end of the stress period showed that genotypes with a lower S:R often
had a greater stomatal conductance. In general, genotypes with a lower S:R at the end of
the stress period usually had a greater root dry weight. The correlation coefficients of S:R
with root dry weight at the end of the stress period were -0.96 and -0.65 for 1998 and
1999, respectively.