Phenotypical differences among B. cinerea isolates from ornamental plants

B. cinerea is a common pathogenic fungus which causes Botrytis blight (Grey mould) in most ornamental plants. It may be responsible for serious preharvest diseases and postharvest losses in fruits, vegetables and flowers. In this work, several B. cinerea isolates from ornamental plants (Chamelaucium uncinatum, Pelargonium x hortorum, Euphorbia pulcherrima, Lantana camara, Lonicera japonica, Hydrangea macrophylla, and Cyclamen persicum) affected by Botrytis blight in the south of Spain were studied. All the isolates were confirmed as B. cinerea by PCR using a specific 750-bp molecular marker, which is present in all strains of this species but absent from other species of Botrytis. The isolates were evaluated by reference to mature conidia length, sclerotia production, and growth rate. Conidia, conidiophores and hyphae were described by light microscopy and some by cryogenic scanning electron microscopy (Cryo-SEM). Conidium length was measured by using an eyepiece micrometer at 400x power, whereas the growth rate was assessed from differences in colony diameter between the third and fourth day of growth in potato-dextrose agar culture medium at 26 degrees C. B. cinerea showed a high degree of phenotypical variability among isolates, not only as regards visual aspects of the colonies but also in some morphological structures such as conidium length, conidiophores, sclerotia production, and hyphae. Differences were also observed in the growth rates. Conidiation was insignificant in the isolates from H. macrophylla, and P. x hortorum, where the overall appearance was white in all the growing stages, whereas isolates from L. camara, C. persicum and C. uncinatum were mainly grey or brown in mature stages. The longest conidia were obtained in isolates from H. macrophylla and C. persicum (17-18 microm) and the lowest in C. uncinatum (9 microm). All the isolates, except L. camara, developed mature sclerotia after approximately 16 days in the conditions used. H. macrophylla had around 72 sclerotia per colony, whereas C. persicum had only nine after 28 days. The growth rate of isolates from L. camara was the highest (1.64 cm/day). Such phenotypical variability may result in a differential response to plant growth regulators if plants are infected by Botrytis in the early stages of growth. In this way, we confirm, as we have done in other published studies, that isolates show different responses to some plant hormones and inhibitors.