Physiological and biochemical response of potato (Solanum tuberosum L. cv. Kara) to O-3 and antioxidant chemicals: possible roles of antioxidant enzymes

An Egyptian cultivar of potato (Solanum tuberosum L. cv. Kara) was grown in the field at two locations in northern Egypt: a 'rural' and a 'suburban' site, from October 2000 and November 2002. The antiozonant ethylenediurea (EDU) and the fungicide chlorothalonil (1,3-benzenedicarbonitrile-2,4,5,6 tetrachloroisophthalnitrile) were applied as a foliar spray to plants at both sites. it was found that foliar injury symptoms were reduced greatly in plants treated with EDU and/or chlorothalonil, and the yield of treated plants was higher than that of the untreated ones, with the EDU having a greater protection than chlorothalonil.. Antiozonant (EDU) and fungicide (chlorothalonil) combination sprays were even more effective in reducing O-3 injury. Moreover, the percentage of protection was higher in the rural area than in the suburban one, and this was associated with higher levels Of O-3 recorded in the rural area. The response to O-3, EDU, and chlorothalonil of the leaf antioxidant scavenger system was examined. Antiozonant-treated plants had the highest reduced glutathione/oxidised glutathione ratio. The results suggest that EDU and chlorothalonil do not act directly as antiozonant to inhibit O-3 injury but act through maintaining some antioxidant enzymes during O-3 exposure. To the best of knowledge, this is the first report demonstrating the marked enhancement of yield and plant oxidative enzymes by fungicides as a mechanism of protecting plants against noxious oxidative stress from the environment in the developing world.