Relative efficacy of paclobutrazol, propiconazole and tetraconazole as stress protectants in wheat seedlings

Abstract

The stress protective effects of triazoles including paclobutrazol, a plant growth regulator, and two fungicides, propiconazole and tetraconazole, are compared. Wheat (Triticum aestivum L. cv Katepwa) seeds were imbibed for 18 h in distilled water (Ck) or in aqueous solutions of each triazole (50 mg L-1). Seeds were then air dried, planted in sectioned plastic flats and grown in a greenhouse. After 10 days, one set of seedlings were allowed to continue growing under optimal conditions while additional sets were exposed to various stresses including high temperatures, drought and spray with the herbicide paraquat. Compared to wheat leaves from plants grown under optimal conditions, heat stress decreased shoot fresh weight, fluorescence values and chlorophyll levels. It also increased ion leakage. All symptoms of damage were alleviated by the triazoles, with paclobutrazol being the most potent. Similar trends were found under acute drought conditions, where seedlings treated with paclobutrazol had the highest percent survival and the most shoot regrowth upon rewatering. Paclobutrazol was also the best triazole in protecting wheat leaves from damage caused by paraquat, a free radical generator. It is concluded that while all the triazoles have the potential to be stress protectants, paclobutrazol was consistently the most effective.