EFFECT OF THIOBENCARB AND BUTACHLOR ON PHOTOSYNTHESIS, CARBOHYDRATE CONTENT, AND AMYLASE AND PROTEASE ACTIVITY IN RICE (ORYZA-SATIVA) AND BARNYARD GRASS (ECHINOCHLOA-CRUS-GALLI)

A pot experiment was conducted during 1989 to study the effect of thio bencarb and butachlor on photosynthesis and carbohydrates ia rice (Ory za sativa L) and barnyard grass [Echinochloa crus-ga[Ii (L.) P. Bcauv. ] plants raised alone and in combination with each other. Besides, the activity of amylase and protease was studied in seedlings raised in p etri-dishe kept in an incubator. Stomatal conductance and CO2 concentr ation along with photosynthesis and carbohydrate content of leaves wer e recorded at 15, 30, 45 and 60 days after transplanting rice and sowi ng the seeds of barnyard grass. These were treated with 0, 1.5, 3.0 an d 4.5 kg/ha thiobencarb and butachlor separately. The concentrations o f herbicides in petri-dishes were 0, 25, 50 and 75 ppm and enzymes wer e assayed at 24, 78, 72 and 96 hr after sowing. The herbicides did not allow barnyard grass to germinate in pots. Crop-weed association did not affect stomatal conductance, total carbohydrates, starch and reduc ing sugars in leaves but decreased the photosynthesis of the grass. Th e herbicides did not reduce these factors in rice leaves. In barnyard grass the rate of photosynthesis was more, though its internal CO2 con centration and stomatal conductance was low. The herbicides reduced th e alpha-amylase activity with increase in concentration. Sharp increas e in alpha-amylase activity was observed at 96 hr in both the species. Protease activity was maximum at 48 hr in rice and at 24 hr in barnya rd grass. Both the herbicides reduced the protcase activity at 25 ppm but increased it at 75 ppm in both the species.