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Wheat Information Service
Number 91: 1-4 (2000)
Research article
Assimilate transportation efficiency in diverse
wheat accessions in the absence of leaf photosynthesis
Jagadish Rane1* and Shantha
Nagarajan2
1Directorate of Wheat Research, Karnal, India
2IARI Regional Station, Karnal, India
Summary
In order to elucidate assimilate transportation efficiency,
diverse wheat accessions were subjected to defoliation and potassium
iodide induced leaf senescence. Grain development in response to
these treatments was compared with that under late sown condition,
which exposed the crop to high temperatures. It was observed that KI
(0.25%) sprayed at the time of anthesis severely affected grain
growth by interfering with both the assimilate supply and other
processes associated with grain formation. On the contrary,
defoliation reduced only the grain weight but not the grain
number/spike. Defoliation could also partly explain the response of
late sown crop to terminal heat stress. It is concluded that KI
(0.25%) can not be used to screen wheat accessions for assimilate
transportation efficiency. It is suggested that lower concentration
of KI or any other desiccant with no effect on processes in the
developing grain needs to be tested and used for screening large
number of accessions.
Introduction
Late sown wheat is invariably exposed to temperatures greater
than 30C during grain development in North Western Plains Zone of
India (Nagarajan and Rane 1998). Hence, improvement of heat tolerance
in wheat is one of the major objectives of breeding programs in this
region. However, the limited progress made so far is mainly due to
the lack of suitable techniques for screening large number of
accessions. Widely proposed screening methods like canopy temperature
depression (Reynold et al. 1994) and membrane thermostability (Fokar
et al. 1998) are rarely used by breeders because of complexity
involved in handling large number of accessions.
Translocation of assimilate accumulated in stem during grain, growth
under stress environment is one of the promising traits for selection
of stress tolerant genotypes. Translocation of the assimilate
responds to drought stress, removal of leaves and senescing agents
such as potassium iodide (KI) particularly during grain growth in
wheat (Nicolas and Turner 1993), pearl millet (Mahalakshmi et al.
1994) and triticale (Royo and Blanco 1998). KI when sprayed at
appropriate time bring about gradual decrease in chlorophyll content
and photosynthesis. As a result, developing grains are forced to
depend on the amount of assimilate stored in stem and its
translocation. Reduction in stem biomass of wheat plants in response
to elevated temperatures has also indicated increased utilisation of
stem reserves under heat stress conditions (Stone et al. 1995).
The present study was conducted with two objectives viz., evaluation
of large number of diverse wheat accessions for the ability of
translocating the assimilate accumulated in stem and to explore the
possibility of using potassium iodide for screening for this trait.
The ultimate aim was to develop breeder friendly, efficient and rapid
technique to screen early generation breeding material for heat
tolerance.
*Corresponding author
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