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We found that the seedlings of indica rice cultivar Dular showed chlorosis but the seedlings of japonica rice cultivar Lemont remained green under natural low temperature in early spring. Using an F2 population of Lemont Dular, we found that the difference of cold tolerance at seedling stage between Dular and Lemont is controlled by a single major gene, with the chlorosis allele being recessive. We named the gene cisc(t). With the help of SSR markers, cisc(t) was mapped in a 5.5 cM interval between SSR markers RM257 and RM242 on chromosome 9.

Random Amplified Polymorphic DNA (RAPD) and Inter-simple Sequence Repeat (ISSR) methods were used to detect the genetic diversity of 57 allelopathic rice accessions which were introduced from 10 countries or areas. A total of 12 RAPD primers and seven ISSR primers were indentified with polymorphism among the entries. For RAPD markers, 85 polymorphic bands were produced, percentage of polymorphic bands (PPB) were 69.4%. For ISSR marker, 34 polymorphic bands were generated, PPB were 53.0%. The result from the clustering analysis by UPGMA indicated that those accessions from the same geographical location were clustered into one group. It was also found that some rice accessions with higher allelopathic potential were clustered together, implying that the genes conferring allelopathy in those rice accessions might be isolocus. However, some rice accessions with different allelopathic potential clustered into the same group performed lower level of generic polymorphism which was attributed to oriented selection for other traits in breeding program. The estimates of correlation coefficient of RAPD and ISSR based on the genetic similarity matrices were significantly correlated.