PHYTOALEXIN INDUCTION IN THE SAPWOOD OF PLANTS OF THE MALOIDEAE (ROSACEAE) - BIPHENYLS OR DIBENZOFURANS

Following fungal inoculation or natural infection, five biphenyl phyto alexins (aucuparin and its 2' and 4' oxygenated derivatives) were indu ced variously in the sapwood of Aronia, Chaenomeles, Eriobotrya, Malus (three spp.) and of Sorbus aucuparia. By contrast, 14 dibenzofuran ph ytoalexins were induced variously in sapwood of Cotoneaster (7 spp.), Crateagus, Cydonia, Mespilus, Photinia, Pseudocydonia, Pyracantha, Pyr us and two Sorbus spp. (S. chamaemespilum and S. domestica). These wer e five cotonefurans, three eriobofurans, five pyrufurans and a 2,3,4,7 ,8-pentaoxygenated dibenzofuran trimethyl ether. No plant has yet been found to produce both types of phytoalexin, although o-hydroxybipheny ls are theoretically precursors of the dibenzofurans. The ability to s ynthesize either biphenyls or dibenzofurans appears to be genus-specfi c, except in the case of Sorbus. In 18 of the 38 species tested, these phytoalexins were accompanied by constitutive antifungal phenolics, m ost of which appeared to be released from bound (glycosidic) forms dur ing the infection process. These were identified variously as hydroqui none, p-hydroxyacetophenone, acetovanillone, 5,7-dihydroxychromone, ch rysin, sakuranetin and naringenin. Woody members of the subfamilies Pr unoideae and Spiraeoideae failed to yield any phytoalexins on inductio n, but did contain constitutive antifungal compounds. The limited freq uency of the phytoalexin response within the family as a whole is cons idered in relation to the accumulation of constitutive antifungal agen ts in these plants.