Evaluation of genetic resources of peach and nectarine for powdery mildew resistance by physiological parameters

The knowledge about plant physiology has a great importance for a better understanding of peach resistance mechanisms against Sphaerotheca pannosa var. persicae Woron. During 1997-2000 studies on the physiological changes due to this fungus have been carried out on three cultivars belonging to different resistance classes, at the Research Station for Fruit Tree Growing Baneasa Bucharest, located in the southern part of Romania. Research has been focused on: ions transport through membranes, permeability index, total electrolyte content, photosynthesis, respiration intensity, catalase activity along with chlorophyll, carotene and xanthophyll content. There is a correlation between ions transport speed and resistance to powdery mildew, high speed being observed infected cultivars. The total electrolytes content was always higher in the healthy biologic material compared to the infected one. A decrease in the permeability index values was noted in the powdery mildew infected cultivars compared to the uninfected ones. Photosynthesis was drastically reduced in powdery mildew affected trees. Moreover the amount of chlorophylls and photo assimilation was reduced. Catalase activity was less intense in powdery mildew sensitive trees and also a high increase of their respiration was noted.