Bentazon Tolerance in Rice (Oryza sativa L.) Mutants

Abstract

After several screening cycles for bentazon-tolerant rice from rice mutant pools mutated by NaN3, line ben41 (M7) was proved as the most tolerant one, and twelve surviving seedlings were transplanted n the field. Subsequently, six plants were harvested at maturity, i.e., Ben41-1, 2, 4, 5, 6 and 7 (M7). Changes in plant height of the rice offsprings (M8) from these 6 lines except Ben41-5 clearly showed a genetic separation. Analysis of ED50 of bentazon, based on injury index, for rice seedlings revealed that 4 mutant lines, Ben41- 1, 3, 4 and 5, were more tolerant than the control cv. TNG67, wheras no tolerance difference was observed among tested mutants. Assessment of photosystemⅡactivity showed the activity in the susceptible line FSK decreased to 15% of control within 3 days after bentazon treatment (DAT), wheras the inhibition of the same system in tolerant Ben41-5-H5 was recovered to a significant level by 5 DAT. Further analysis of bentazon metabolism showed that less residual bentazon coupled with a higher glucosylation was detected in 3 tolerant lines as compared with FSK. However, the specific activity of bentazon-6-hydroxylase in tolerant Ben41- 1-H1 was similar to that in FSK, suggesting that differential hydroxylation was not a key factor contributing to bentazon tolerance in this tolerant mutant.