Field and laboratory screening of anthurium cultivars for resistance to foliar bacterial blight and the induced activities of defence-related enzymes

Bacterial blight (BB) caused by Xanthomonas axonopodis pv. dieffenbachiae (Xad) is the most destructive disease of ornamental anthurium. In the present study, foliar resistance of 21 anthurium cultivars were assessed under shaded field and laboratory conditions by injection inoculation of 3 × 10⁸ cfu/ml Xad; disease severity was evaluated using a pretransformed rating scale after symptoms survey. Then six selected cultivars with different resistance levels were evaluated for the induced activities of six defence-related enzymes. The obtained results indicated that the same cultivar shared identical resistance under both conditions, but there was a great variation among the cultivars. Anthurium cv. Pink Champion and Manaka showed the highest resistance, and five other cultivars were highly susceptible. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) and phenylalanine ammonia-lyase (PAL) in the resistant cultivars increased much faster and reached much higher peak levels than those in susceptible cultivars. Further analyses revealed that the relative resistance index (RRI) significantly positively correlated with the activities of SOD, APX, POD and PAL, but not with catalase (CAT) and polyphenol oxidase (PPO), suggesting that early rapid accumulation of SOD, APX, PAL and POD might be an important mechanism of defence against Xad and could serve as one of the valuable physiological indices for the prediction of BB resistance in anthurium germplasm. Consequently, the identified resistant cultivars and the induced defence enzymes will facilitate the phytopathological research and enhance blight resistance selection in future breeding.