In vitro screening for Botrytis leaf blight resistance in Lilium species

The plant genus Lilium is an economically important ornamental flowering monocot that is highly susceptible to leaf blight diseases caused by the fungus Botrytis elliptica. We designed an efficient in vitro screening system using a detached leaf disk assay to identify Lilium cultivars with resistance to B. elliptica. Optimal culturing conditions for the B. elliptica in vitro screening assay were established in which fungal isolates were grown on potato dextrose agar medium for 2 weeks at 25 °C under 12 h UV-A light. Healthy 2 weeks old in vitro grown leaf tissue from the susceptible cultivar 'Siberia' was inoculated with 2.0 × 103 spores·mL−1B. elliptica, and incubated in the dark for 12 h at 25 °C. Seven days after inoculation, until blight symptoms on leaves with a significant disease index (DI) rate were observed. Using the standardized in vitro screening system with 'Siberia', we evaluated 30 different Lilium cultivars. The DI rates significantly varied among the different cultivars, suggesting that 30 cultivars could be classified into 3 groups: strong resistance (group A), moderate resistance (group B), and susceptible (group C). In order to elucidate the role of disease resistance (R)-genes in resistance/susceptible cultivars upon Botrytis infection, several well known marker R-genes were evaluated for their differential mRNA expression pattern through Real-time quantitative polymerase chain reaction (qRT-PCR). In general, qRT-PCR shows a remarkable up-regulated mRNA accumulation pattern of those genes in resistance (group A) as compared to that in susceptible (group C) cultivars, which further validating the accuracy of our in vitro screening system. This in vitro screening system is flexible and cost-effective, and will contribute to cultivar identification for Botrytis leaf blight in multiple Lilium cultivars.