Resistance mechanisms of cabbage cultivar “Shinsei” against infestation of the diamondback moth - effect of leaf angle and hardness of outer leaf

Various studies have been conducted on the mechanisms of host plant resistance (HPR) of cabbage against the diamondback moth (DBM). Understanding the role of wax-bloom has been a major focus of these studies. Our study distinguishes itself from previous research by focusing specifically on outer leaf angle and leaf hardness. The resistance mechanism of cabbage cultivar “Shinsei” against DBM was examined. Generally outer leaves of “Shinsei” cabbage have an erect position when compared with a common cultivar, “Kinkei 201.” Lethal effects of rainfall on II instar larvae on the outer leaves of “Shinsei” and “Kinkei 201” were investigated with an artificial rainfall system. The results showed that mortality of II instar larvae on the outer leaves of “Shinsei” was higher than that on outer leaves of “Kinkei 201.” Compared with II instar larvae on prone outer leaves, II instar larvae on erect outer leaves were killed more frequently by artificial rainfall. Tests showed that experimental results between erect and prone leaves were similar in both cultivars. First instar larvae took longer to mine into the outer leaves of “Shinsei” than into those of “Kinkei 201” and the probability of success in mining into the leaf was lower on “Shinsei” than on “Kinkei 201.” Artificial diets mixed with methanol extracts from outer leaves of each cultivar were fed to I instar larvae. However, there were no significant differences between mining rates on both artificial diets. On the other hand, outer leaves of “Shinsei” were harder than outer leaves of “Kinkei 201.” These results showed that the difference of leaf hardness was the cause of the difference in mining time and success rate. We concluded that the major HPR mechanisms of “Shinsei” were outer leaf angle and hardness.