A greenhouse screening assay for Botrytis tulipae resistance in tulips

As a leaf pathogen, Botrytis tulipae severely affects tulip bulb production. Chemical control is not desired for environmental reasons. Thus, resistant cultivars can play an important role in the control of this disease. To select genotypes resistant to B. tulipae, a reliable screening assay is needed. A greenhouse test was developed to establish resistance at clonal level. Removal of the wax layer by soft rubbing of the leaves was essential to obtain a homogeneous distribution of the spore suspension on the leaves. Small lesions were found within 24 hr after inoculation. Continuous leaf wetness was obtained by regular water evaporation. This was essential to obtain rapidly spreading lesions. After eight days, leaves of susceptible genotypes were completely destroyed. Large differences in resistance were found within tulip genotypes. Feeding additions to the inoculum suspension enhanced the infection process, but were unnecessary. Plants inoculated before flowering were less sensitive to B. tulipae than plants inoculated at flowering. Plants inoculated after flowering were most sensitive to infection. Ranking of resistance for the tested genotypes before or after flowering however remained nearly the same. The influence of factors involved in the screening test and the implications for resistance breeding are discussed