THE EFFECT OF A PHYTOTOXIN FROM ALTERNARIA BRASSICICOLA ON BRASSICA POLLEN

A methanol-soluble extract from the culture filtrate of Alternaria brassicicola (Schw.) Wilts., grey leaf spot, markedly inhibited pollen germination and pollen tube growth of Brassica napus L., Brassica campestris L. and Brassica oleracea L. in hanging drop culture at concentrations comparable to those causing death of B. napus secondary embryoids. The extract was partially purified by Sephadex column chromatography, and the fractions obtained were tested for their inhibitory capacity. Two fractions which killed secondary embryoids also inhibited pollen germination. The methanol-soluble extract and inhibitory fractions from Sephadex chromatography were further tested using a thin-layer chromatographic bioassay which showed that the original extract could be separated into at least four inhibitory compounds. The potential of the techniques used for screening and selection for resistance to compounds toxic to plants is briefly outlined.