A real-time PCR assay for detection and quantification of Botrytis cinerea in Pelargonium x hortorum plants, and its use for evaluation of plant resistence

A reliable EvaGreen-based qPCR assay was developed for the relative quantification of fungal and plant DNAs in the Botrytis cinerea-Pelargonium× hortorum pathosystem. Primers, designed on RPB2 (DNA-dependent RNA polymerase subunit II) gene sequences directed the amplification of a specific 149 bp product for B. cinerea. No cross-reactivity was observed in DNA extracted from several nontarget fungi and bacterial, and in pelargonium plants, with the exception of the closely related species Botryotinia pelargonii and Botrytis fabae. This assay allowed for quantification of as little as 1.55 pg fungal DNA and 9.95 pg plant DNA, and detection of the pathogen in both symptomatic and asymptomatic pelargonium plants. The qPCR protocol is suitable for studying cultivar resistance and induced resistance in pelargonium plants, which requires accurate quantification of the pathogen in diseased host tissue. This assay allowed us to establish that the Pelargonium×hortorum cvs. ‘XL Boomerang’ and ‘Eroica 2000’ showed high foliar resistance to B. cinerea with respect to the susceptible cv. ‘Fernando’, and that spray applications of 0.3 mM acibenzolar-S methyl markedly protect pelargonium plants against gray mold. The protection for plants treated with chitosan (0.2 %) did not reach significance.