Executive Summary
In our previous RIRDC funded
projects (CST-2A and UQ-91A), we demonstrated that seed treatment with
spermine and gibberellic acid (GA) increased seedling vigour of rice at
low temperature. And foliar application of osmoprotectants (spermine, and
glycinebetaine) offered significant cold tolerance by reducing spikelet
sterility in rice cultivars Amaroo and Doongara. In this project, we have
investigated if higher natural spermine- and GA-accumulating ability of
rice cultivars will result in higher cold tolerance, and determined if
the cultivars with higher cold tolerance at the seedling establishment
stage will also have higher cold tolerance at reproductive stage.
We exposed 32 diverse rice
cultivars and 30 recombinant inbred lines (RILs) between Millin and HSC
55 to cold (18/13 °C) and normal temperature (28/23 °C) treatments
in controlled glasshouses during seedling establishment and reproductive
stages. Spikelet sterility, the accumulation of spermine and GA, and engorged
pollen grain numbers were determined.
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Cold tolerance at seedling (biomass)
and at reproductive (spikelet fertility) stages of 32 rice cultivars and
RILs showed considerable similarity.
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We have identified segregating
genetic material for seedling cold tolerance in F3 population between Australian
cultivars and African rice, and in the RILs.
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Cultivars that accumulated greater
amount of spermine in the seedlings were more cold tolerant and its higher
accumulation in the flag leaves resulted in reproductive cold stress tolerance
(reduced spikelet sterility).
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Higher GA content in the seedlings
resulted in greater seedling cold tolerance. However, GA content in the
flag leaves at reproductive stage showed no association with spikelet sterility.
Cold tolerant cultivars, which
accumulated high spermine, also produced more viable pollen grains,
leading to low spikelet sterility.
These findings are
highly useful for the agronomists and plant breeders involved in developing
cold tolerant rice cultivars. Firstly, initial screening could be done
at seedling stage to predict reproductive cold stress tolerance of rice.
Secondly, the measurement of spermine and/or GA or the molecular markers
associated with these will serve as selection tools in breeding for cold
tolerance. Thirdly, the African rice has the potential to significantly
contribute to cold tolerance in Australian cultivars.
Last updated: August
2005 Copyright RIRDC
http://www.rirdc.gov.au/reports/RIC/05-090sum.html
