Evaluation of Shiranuhi, a Hybrid of Kiyomi Tangor and Nakano No.3 Ponkan, for Resistance to Citrus Canker in Growth Chamber

Citrus canker disease is caused by bacteria Xanthomonas axonopodis .pv. Citri. Shiranuhi cultivar, a hybrid of Kiyomi tangor and Nakano No.3 ponkan was evaluated for resistance to citrus canker based on initiation of disease, percent area of lesion infected and growth rate of bacteria in the leaf under growth chamber condition. Significant differences between susceptible plant and resistant plants were observed in these assays. Resistant plants showed delayed disease symptoms compared to the susceptible plants after spray inoculation of the pathogen. The resistant verities, satsuma, yuzu, and Shiranuhi showed symptoms after six days where as susceptible, mexican lime showed the symptoms just after three days of inoculation. 18 days after inoculation, percent area of lesions developed on leaf and disease severity differed significantly in susceptible and resistant plants, and were ranked as follows: mexican lime > early satsuma =Shiranuhi =yuzu (P <, 0.01). However, 30 days after inoculation, percent area of lesion was further differentiated into resistant and highly resistant plants. That was ranked as follows: sweet orange> early satsuma =Shiranuhi =Kiyomi > yuzu (P < 0.01). These results indicate that host reaction to the bacterial was more distinct when the disease developed for a longer period. Growth rates of a citrus canker bacterium during 16 40 h also were distinct after infiltration into leaves of susceptible and resistant plants, and were ranked as follows: sweet orange> early satsuma =Shiranuhi =Kiyomi =yuzu (P < 0.01). Based on these results, we concluded that Shiranuhi is resistant to citrus canker as compared to Kiyomi, early satsuma, and yuzu.