Natural and Induced Herbicide Resistance in Rice (Oryza Sativa L.) Varieties in Sri Lanka

Weeds along with insect pests and plant diseases are sources of biotic stress in crop systems. Weeds are responsible for serious problems in rice worldwide affecting growth and causing a considerable reduction in quality and quantity in yield. Herbicide-resistant rice varieties in combination with pre-emergent-broad-spectrum herbicides and post-emergent broad-spectrum herbicides improve the effectiveness of weed management in rice fields. Herbicide resistance can be acquired naturally or induced by classical or modern breeding techniques.. High concentration of Glyphosate a pre-emergent-broad-spectrum systemic herbicide is prevalently applied to control rice weeds in Sri Lanka which intern causes severe damages to cultivated rice varieties which are susceptible to Glyphosate. However there are rice varieties with natural Herbicide Resistance (HR). Six traditional and eighteen inbred cultivated rice varieties (Bg Bw At and Ld series developed by Rice Research Development Institute Sri Lanka) were used to screen their natural HR. As observations time taken-to seed germination time taking to flowering; plant height and number of leaves at 12-weeks after sawing leaf-length breadth panicle-length number of seeds/panicles of resistant plants and controls were recorded. Plants with ? 40% resistance were considered as resistant to Glyphosate. Ten inbred rice varieties (Bg250 Bg94-1 Bg304 Bg359 Bg406 Bg379-2 Bg366 Bg300 Bw364 At362) and three traditional rice varieties (“Kalu Heenati” “Sudu Heenati” “Pachchaperumal”) were naturally resistant to 0.25 g L-1 Glyphosate concentration and when increased the concentration (0.5 gL-1) resistance were reduced.. The post-emergent broad-spectrum herbicide Glufosinate is also applied to control rice weeds in Sri Lanka. Two traditional varieties (“Pachchaperumal” “Ma Wee”) and fifteen inbred varieties (At362 Bg250 Bg300 Bg352 Bg357 Bg358 Bg359 Bg360 Bg366 Bg369 Bg379/2 Bg403 Bg450 Bg454 and Bg94-1) were screened for their natural HR resistant to Glufosinate.