Growth and physiological responses of chestnut calli to crude extracts of virulent and hypovirulent strains of Cryphonectria parasitica

The effect of crude extracts (CEs) of virulent (V-E-I) and It hypovirulent (H-E13) Cryphonectria parasitica strains on growth and physiological activities of chestnut calli was investigated on cell cultures obtained from either a susceptible Castanea sativa or a resistant Castanea mollissima chestnut species. The V-E4 CEs significantly reduced calli fresh weight in both species when used at 50 and 500 mug g(-1) and, in general, showed an inhibitory effect on either O-2 uptake and H+-ATPase activity. Only the highest (500 mug g(-1)) concentration of H-E13 CEs had a detrimental effect on callus growth, whereas the lowest one (5 mug g(-1)) induced a slight, but significant early increase in callus fresh weight of both genotypes. The O-2 uptake and H+-ATPase activity were enhanced by the presence of H-E13 CEs. The decrease of callus growth and physiological activities, caused by V-E4 CEs, was attributed to toxic compounds produced by the C parasitica virulent strain, whereas the stimulatory effects of H-E13 CEs on the overall callus metabolism seemed to be due either to the lack or very reduced amount of phytotoxic compounds and to growth-regulating substances produced only be the hypovirulent strain of the fungus.