178 V. G. Kakani et al.
Genotypes used in this study differed in their response to temperature treatments.
Genotypes did not differ in their vegetative weight, indicating that source was not
limiting. Thus, processes like photosynthesis or respiration, responsible for source,
are not much altered. In contrast, pod yield was reduced in both the genotypes.
A greater reduction in pod yield of > 70 % occurred in TMV 2, while it was
only around 23 % in ICGS 11. This indicates that ICGS 11 is more tolerant to high
temperature than TMV 2. The greater tolerance of ICGS 11 to high temperature can
be attributed to maintenance of a significantly higher partitioning under increas-
ing temperature conditions. This higher partitioning is due to greater sink strength
in ICGS 11 than in TMV 2. Such genotypic differences for reduction in pod yield
when exposed to high temperature were reported in several independent studies
(Talwar et al. 1999 ; Prasad et al. 1999a, 2000 ; Wheeler et al. 1997 ). In a screening
study conducted in 1991 in Sahelian region of Africa, Ntare et al. ( 2001 ) demon-
strated that groundnut genotypes significantly differ in their pod yields in hot envi-
ronments due to the effects on partitioning.
Under water stress conditions, a greater reduction in vegetative weight and pod
yield occurred in ICGS 11 than in TMV 2. Although the reductions were greater
in ICGS 11 under water stress, this genotype had higher vegetative and pod yield
under irrigated conditions. This is due to greater accumulation of assimilates and
higher partitioning of these assimilates to pod yield (Table 8.6). Under water stress,
only a slight decrease in flower number occurred in ICGS 11, which did not sig-
nificantly influence the peg and pod number. No such decrease in flower number
occurred in TMV 2. In addition, the genotype ICGS 11 had a higher WUE when
compared to TMV 2. This allowed the genotype to accumulate greater biomass even
under water stress conditions. Hence, genotype ICGS 11 was tolerant to both high
temperature and water stress conditions over TMV 2.
8.5 Conclusions
It can be inferred from this study that genotypes that are tolerant to water stress are
also tolerant to high temperature under field conditions. Mechanisms that a geno-
type adopts to overcome stresses differ. However, genotypes with the ability to
establish greater biomass and with a significantly greater partitioning of biomass
to pod yield would be suitable for sustaining higher yields in SAT areas with high
temperature and water stress. Genotypes with greater WUE are also more useful
for the SAT. Thus, screening of groundnut genotypes for both temperature and wa-
ter stress tolerance in field conditions are essential before recommending them for
SAT and before using them for further breeding of new genotypes to these stresses.
Controlled environments can be used for screening genotypes to high temperature
for specific processes and experiments under field conditions need to be adopted to
identify the various mechanisms for tolerance involved.