Study On Mechanisms Of Resistance To Black Spot Disease In Non-Heading Chinese Cabbage

The objective of this paper was to study the physiological and biochemical mechanism to black spot disease in non-heading Chinese cabbage. The results were as follows:1. Changes of BcAF, BcPR4 and Bcchi that had been cloned in non-heading Chinese cabbage were studied by semi-quantitative PT-PCR after Alternaria brassicicola infection on two non-heading Chinese cabbage materials ('Suzhouqing' and 'Duanbaigeng').The results showed Bcchi, BcPR4 and BcAF were induced both in 'Suzhouqing' and 'Duanbaigeng'. Bcchi and BcPR4 reached the peak 24 h after inoculation. BcAF in 'Suzhougqing' which reached the peak at 12 h, was earlier than that in 'Duanbaigeng'. In the whole prossece, more Bcchi, BcPR4 and BcAF were induced in 'Suzhouqing' than that in 'Duanbaigeng', which indicated that Bcchi, BcPR4 and BcAF play an impotant role in the resistance to black spot disease.2. After Alternaria brassicicola infection on two non-heading Chinese cabbage materials ('Suzhouqing' and 'Duanbaigeng'), APX both in disease-resistant material and disease-susceptible material were lower, while PPO, SOD, CAT activities and O₂^- were increased after infection. PPO, SOD activities and O₂^- in 'Suzhouqing' were higher than that in 'Duanbaigeng', while CAT activity was lower than that in 'Duanbaigeng'. As to PAL activity it was increased in 'Suzhouqing' but decreased in 'Duanbaigeng'. POD activity and H₂O₂ content were increased in the two materials after inoculation, and the content of H₂O₂ could be lowered quickly in 'Suzhouqing'. Thus it could be considered that compared with disease-susceptible material, disease-resistant material was able to produce more PPO, PAL and O₂^- that may resist the infection of Alternaria brassicicola, and was able to produce more ROS in short time to promote antioxidant enzymes activities, which could maintain lower ROS level and reduce the damage of ROS after inoculation.3. 0.5 mmol·L^-1 SA was used to spray leaves of 'Duanbaigeng' which is susceptible to black spot disease at two-leave and one heart stage, and semi-quantitative RT-PCR was done to detect the expression of Bcchi, BcPR4, BcAF in leaves. Alternaria brassicicola was inoculated 24 h after SA treatment. The results showed the expression of Bcchi, BcAF and BcPR4 was significantly induced and enhanced by SA in 'Duanbaigeng'; SOD, POD, PPO activities of leaves pretreated by 0.5 mmol·L^-1 SA increased dramaticly compared with those water-treated after inoculated with Alternaria brassicicola, while CAT activity and the content of H₂O₂ were lower than that in water-treated leaves. SA can reduce the disease index which indicates systematic acquired resistance induced by SA plays an important role in the resistance to Alternaria brassicicola in non-heading Chinese cabbage.