Natural Resistance of Sri Lankan Rice (Oryza sativa L.) Varieties to Broad-Spectrum Herbicides (Glyphosate and Glufosinate)

Since studies on herbicide-resistant rice (HRR) are limited in Sri Lanka, the present study conducted to screen the naturally existing glyphosate and glufosinate resistance in traditional and inbred rice varieties. Six traditional varieties and nineteen inbred lines were selected for the study. Complete randomized design with three pots with 10 replicates for each herbicide concentration was employed. Optimal concentrations of glyphosate (0.5 gl −1 ) and glufosinate (0.05 gl −1 ) were applied at 3–4 leaf stages. Varieties ≥50% survival percentage was considered as resistant to respective herbicides. Twelve varieties showed resistance (≥50%) at 0.5 gl −1 glyphosate concentration. Survived plants were monitored and agro-morphological and yield characters/parameters were mea- sured. Fifteen varieties were to glufosinate at 0.05 gl −1 . Even though no significant differ ences (p > 0.05) were observed in growth parameters across control and treated plants, there was a yield penalty. Nine varieties (At362, Bg352, Bg359, Bg366, Bg369, Bg379-2, Bg403, Bg454, and Pachchaperumal) indicated moderate resistance to both glyphosate and glufosinate. The emerged HRRs indicated varying responses of agro-morphological and yield characters across the type of herbicide and the variety. Glyphosate reduced the growth parameters and yield penalty compared to glufosinate treated varieties. These HRR varieties have a higher potential in rice breeding programs and in develop ing HR rice varieties in future. Bg305—1%) lethal 0.05 gl −1 glufosinate 0.5 gl glyphosate. rice varieties Bg250—83%, Bg300—96%, Bg352— 100%, Bg357—53%, Bg359—100%, Bg360—96%, Bg366—73%, Bg369—83%, Bg379/2—93%, Bg403—100%, Bg450—57%, Bg454—97%, Bg94/1—73%, Pachchaperumal —53%) showed natural resistance under glufosinate application and 12 rice varieties (At362—75%, Bg352— 50%, Bg359—55%, Bg366—65%, Bg369—60%, Bg379/2—65%, Bg403—60%, Bg454—55%, Ld365—70%, Kaluheenati —55%, Kuruluthuda —55%, Pachchaperumal —70%) were able to sur vive under glyphosate application. Results indicated that nine varieties (At362, Bg352, Bg359, Bg366, Bg369, Bg379-2, Bg403, Bg454 and Pachchaperumal were resistant for both glyphosate and glufosinate