Abstract:
Sri Lankan wild rice, Oryza nivara and O. rhizomatis, are two threatened species occurring
in habitats characterised by different patterns of dry and wet periods. Both species have
dormant seeds at dispersal, and little is known about their germination phenology. The aim
of this study was to determine the germination strategies of these species, to contribute to
their conservation. We hypothesized that seed germination behaviour is related to their
habitat conditions. Germination phenology was studied by evaluating the prevailing
environmental conditions that seeds experience after dispersal, i.e., a dry condition followed
by a wet condition. Immediately after harvest, seeds were exposed to nine types of dry-
storage conditions (0, 2, 4, 6, 8, 10, 12, 18 or 20 months) at 25°C and ~ 60 % RH. Four
replicates each of twenty seeds were incubated on moist filter paper at 25°C for 12 hrs/12hrs
under light/darkness for germination testing. Twenty seeds with Four replicates were used in
the germination test. Seeds retrieved after 6, 8, 18 and 20 months of dry storage, were
subjected to 1, 2- and 4-weeks of flood treatment. Seed germination of both species increased
with increasing dry-storage periods until 12 months. Under prolonged dry storage, seed
germination declined for O. rhizomatis (6 weeks – 44 %) and none of the seeds germinated
in O. nivara. In O. rhizomatis, short flooding treatment (1 week) elicited higher germination
(64%) compared to just dry-stored seeds, while prolonged flooding (2-4 weeks) had the
opposite effect. Conversely, there was not a significant effect of flooding on seed germination
for O. nivara. Overall, our results show that prolonged drying breaks dormancy in both
species, a strategy to prevent seed germination right after dispersal, when high risk of drought
may result in low seedling survival. The species also show distinctive dormancy cycling
caused by either prolonged flooding (O. rhizomatis) or drying (O. nivara), which may
contribute to their different geographical and ecological distribution. The increase in
precipitation expected with climate change may constrain recruitment success due to lack of
sufficient dry after-ripening and/or an excess of flooding. This risk might be especially high
for the endemic O. rhizomatis. These results can guide conservation and restoration by
identifying optimal drying and flooding conditions for seed germination and storage.
