Evaluation of resistance to Botrytis elliptica in Lilium hybrid cultivars

Gray mold disease, caused by the fungus Botrytis elliptica, is one of the major diseases affecting Mum species, and it has become a limiting factor in the production of ornamental lilies. To support selecting and breeding Botrytis-resistant cultivars, a total of 50 Mum cultivars belonging to seven hybrid types were evaluated using a detached leaf technique for resistance to B. elliptica. Through resistance evaluations, Oriental x Trumpet and Oriental hybrid cultivars were classified as resistant lines, while Asiatic and Trumpet hybrids were classified as susceptible lines. A highly resistant (HR) Oriental hybrid, 'Sorbonne', and a highly susceptible (HS) Asiatic hybrid, 'Tresor', were selected for further study of early host-parasite interactions. After infection, B. elliptica grew faster and more easily on the leaves of 'Tresor' than on those of 'Sorbonne' during initial infection; when 'Tresor' leaves were completely infected, only a few lesions were observed on 'Sorbonne' leaves. Biochemical differences between these two cultivars were found following inoculation with B. elliptica, as shown by studies of reactive oxygen species (ROS) and the enzymatic antioxidant system. Rapid accumulation of H2O2 and center dot O-2(-) to trigger a defense response was detected in HR 'Sorbonne'. Meanwhile, higher levels of antioxidant activity, including SOD, POD and CAT, were found in HR 'Sorbonne' than in HS 'Tresor' before 48 h post-inoculation, but antioxidant activity was reduced with subsequent infection progress. These large and timely increases in ROS and antioxidant activities could be the main contributors to the high resistance of the 'Sorbonne' cultivar.