Phytoalexin production by cypress in response to infection by Diplodia pinea F.Sp. Cupressi and its relation to water stress

Predisposition of cypress saplings to extreme water stress enhanced the development of cankers caused by Diplodia pinea f.sp. cupressi, and augmented fungal colonization in the bark and xylem, in comparison with normally watered plants. Production of two phytoalexins, cupressotropolone A and B in the bark, which commenced soon after the inoculation, was lower in plants predisposed to water stress. In Plants treated with (aminooxy) acetic acid, a metabolic inhibitor, the cankers were significantly longer, and the content of phytoalexins was significantly lower, than in nontreated plants. Treatment of the bark of initiated cankers with a solution of 15% methanol, to extract soluble constituents, enhanced the subsequent development of the cankers, and significantly reduced the content of both phytoalexins in the bark, in comparison with untreated plants. Neither of the phytoalexins was detected in the extractive fluids. The results suggest that the terpenoid phytoalexins greatly inhibit canker development.