Healthy seeds of different varieties of rice (PD 6, NDR 359, PD 16 and PS 5) and wheat (UP 262, UP 2628, PBW 175 and UP 2554) were germinated and fourteen days after germination, young rice/wheat seedlings were transferred to half strength of Hogland solution (pH ) containing either recommended levels of Zn ( mg Zn L-1 ) or no Zn for four days. For solidification of medium w/v agar- agar was mixed in the Hogland solutions of both –Zn and +Zn. Prior to solidification, mL of bromothymol blue dye solution prepared in 60 % ethanol and was mixed to agar nutrient solution. Twenty five mL of nutrient agar medium with +Zn or –Zn was poured in glass petri plates of 10 cm diameter and one seedling of each rice/wheat variety from +Zn or –Zn lot was transferred to the respective nutrient agar medium in duplicate. The colour change near roots under +Zn and –Zn were monitored and photographs were taken after 48 hrs in case of rice and 72 hrs in case of wheat for recording the extent of change in colour of the nutrient medium in the rhizosphere of all the rice and wheat varieties. In rice NDR 359 substantially reduced the pH in vicinity of roots (more yellow area around roots) than in Zn sufficient medium indicating possibly a better activity of the proton efflux pump to enhance Zn uptake under Zn deficient conditions. In Zn deficient conditions, Zn inefficient genotype UP 262 failed to substantially reduce pH in the vicinity of roots (less yellow areas around the roots) however, this variety under Zn sufficient conditions could reduce the pH of the growth medium (more yellowing around the roots). | Effect of Zn application on rhizosphere acidification in rice and wheat varieties of varying Zn sensitivity
