INTRASPECIFIC RESPONSES OF 188 RICE CULTIVARS TO ENHANCED UVB RADIATION

Phytotron studies were conducted to determine the intraspecific variat ion in sensitivity of rice (Oryza sativa L.) to enhanced UVB and to te st the hypothesis that rice cultivars originating from regions with hi gher ambient UVB radiation are more tolerant to enhanced UVB. Out of t he 188 rice cultivars (from various rice growing regions and ecosystem s) tested, 143 had significantly reduced plant height, 52 had smaller leaf area, 61 had lower plant dry weight and 41 had less tiller number under elevated UVB radiation (13.0 kJ m(-2) day(-1)) for 3 weeks. Six cultivars showed significant positive growth response to enhanced UVB radiation, although the mechanism is not clear at present. These six cultivars were from the summer rice crop of Bangladesh and from high e levation rice areas where prevailing UVB radiation is most likely to b e greater. However, there was no correlation between the dry matter ch anges under enhanced UVB and the ambient UVB level at the origin of th e cultivar across the 188 cultivars tested. Therefore, cultivars origi nating from regions with higher ambient UVB are not necessarily more t olerant to enhanced UVB radiation.