Rcn. Rao et al., CROP GROWTH, WATER-USE EFFICIENCY AND CARBON-ISOTOPE DISCRIMINATION IN GROUNDNUT (ARACHIS-HYPOGAEA L) GENOTYPES UNDER END-OF SEASON DROUGHTCONDITIONS, Annals of Applied Biology, 122(2), 1993, pp. 357-367
Ten groundnut genotypes were grown under adequately irrigated conditio
ns or subjected to drought during the pod filling phase (83-113 days a
fter sowing) in a medium deep Alfisol at the ICRISAT Centre during the
1986-1987 post-rainy season. Crop growth was measured in both treatme
nts, but transpiration (T) and water-use efficiency (W) were quantifie
d only in the drought treatment. Leaf samples from both treatments wer
e assayed for discrimination against (CO2)-C-13 fixed in leaves (DELTA
) to examine the relationships between DELTA, crop growth, and W under
field conditions. The shoot dry matter accumulated during the period
of drought (Y) ranged from 72-150 g m-2 and was closely related to tra
nspiration. This indicates scope for selection of traits and practices
to increase T. Water-use efficiencies ranged from 1.38-2.50 g kg-1 an
d were inversely related to DELTA in eight out of the 10 genotypes. Fo
r the other two genotypes, there was evidence that T was under-estimat
ed by field measurements. Water-use efficiency and transpiration were
not correlated suggesting that these two traits might be combined thro
ugh breeding. Variation between genotypes was greatest for the partiti
oning of total dry matter to pods (73%), followed by water-use efficie
ncy (31%) and transpiration (29%). Crop growth rates were negatively r
elated to DELTA under irrigated conditions but not under drought.