ABSTRACT
Botrytis cinerea Pers ex Pers is a ubiquitous, necrotrophic, pathogen which invades a wide range of plants through senescent, moribund or wounded tissue. Floral infection and rot of soft fruits such as raspberries and strawberries is also widespread and damaging. In the case of viticulture, the infection of the grape berries by Botrytis has important consequences. If the rate of tissue damage is slow (noble rot), the berries may be used to produce a valuable dessert wine; if it occurs at a high rate, then damage and soft rotting are considerable, and the crop is worthless. Previous studies using a variety of hosts, have pointed to the important role of pectic enzyme secretion by the pathogen in causing maceration and cell death of host tissues. There is also evidence that low mol wt polysaccharides produced by B.cinerea are phytotoxic, but evidence for the role of organic acids is still not convincing. In this review, evidence is presented from a detailed investigation of the phytotoxic fractions secreted in the germination fluid and early mycelial growth phase (up to 48h) by the pathogen, using carrot root tissue as the host system. As well as confirming the presence of a phytotoxic pectic enzyme (characterized as an endopolygalacturonase with a mol. wt. of 49,000 d), and 2 low mol. wt polysaccharides (5000, 10,000d), a phytotoxic, high mol. wt. (63,000d), glycoprotein was identified. The implications of this study are discussed in relation to the mechanisms involved in cell death, host resistance and latency.
