番茄枯萎病对植株维管束危害及抗氧化系统影响的研究

为了在早期诊断和确定番茄枯萎病的发生, 本文采用溶液培养方法研究了番茄(Lycopersicon esculentum Miller)幼苗剪根接种不同浓度枯萎病菌后染病植株维管束受害程度和抗氧化系统的响应。试验设4个病原菌梯度处理, B1(10⁴ cfu·mL^-1)、B2(10⁶ cfu·mL^-1)、B3(10⁷ cfu·mL^-1)、B4(10⁸ cfu·mL^-1), 以不接病原菌为对照; 分别在接种病原菌后4 d、8 d、12 d、16 d、20 d测定维管束褐变情况和抗氧化系统的变化。结果表明, 在水培条件下, 接种病原菌16 d植株维管束出现褐变, 其受害程度随病原菌接种浓度提高而增大; 维管束中病原菌只在B4处理中有检出。番茄叶片中丙二醛(MDA)含量随接种时间呈先降后升趋势, 12 d开始逐渐上升, 20 d达到最高, 各接菌处理均显著高于对照, 且B4处理显著高于其他处理; 过氧化物酶(POD)活性先缓慢下降, 12 d后回升, B4则急剧上升; 多酚氧化酶(PPO)活性逐渐上升, 接菌16 d时达到高峰; 随接菌浓度的提高, MDA含量、POD和PPO活性均有所增加, 尤以接菌浓度为10⁸ cfu·mL^-1时3种指标显著高于其他处理, 分别是未接菌植株的13.1倍、12.9倍和1.9倍; 而培养时间对番茄叶片中过氧化氢酶(CAT)活性的影响没有明显规律, 对照菌株CAT活性显著高于各接菌处理, 说明CAT活性对番茄枯萎病病原菌没有响应。本研究结果表明, 结合番茄茎的维管束褐变现象, 认为番茄叶片中MDA含量、POD和PPO活性可作为早期判断番茄是否感染枯萎病的重要指标。

Response of antioxidant system and vascular bundle browning to tomato Fusarium wilt

To facilitate early diagnosis and identification of tomato wilt disease caused by Fusarium oxysporum, tomato seedlings were cultured in liquid medium, and their vascular bundle browning and antioxidative system response after infection with different concentrations of F. oxysporum were investigated. Five concentrations of F. oxysporum - B1 (10⁴ cfu·mL^-1), B2 (10⁶ cfu·mL^-1), B3 (10⁷ cfu·mL^-1), B4 (10⁸ cfu·mL^-1) and CK (the control without pathogenic bacteria) - were used in the study. The antioxidant system variations and vascular bundle browning were assessed after 4, 8, 12, 16 and 20 days of inoculation. The results showed that under hydroponic conditions, vascular bundle browning occurred at 16 days after inoculation with F. oxysporum. Browning severity was positively correlated with inoculant concentration. Vascular bundle pathogen content was detected only under B4 treatment. Melonaldehyde (MDA) content of tomato leaves initially decreased followed by an increase with the passage of time. It started rising gradually on day 12 and reached the maximum on day 20 after inoculation. MDA contents in inoculation treatments were higher than the control and B4 treatment was significantly higher than the other treatments. Peroxidase (POD) activity initially decreased slowly but picked up 12 days after inoculation, followed by a sharp rise under inoculant concentration of 108 cfu·mL^-1. Polyphenol oxidase (PPO) activity increased gradually until reaching its peak value 16 days after infection. MDA content and activities of POD and PPO increased with increasing inoculant concentration, and were highest at inoculant concentration of 10⁸ cfu·mL^-1, which respectively were 13.1, 12.9 and 1.9 times of the un-inoculated control. No changes were observed in catalase (CAT) activity within the entire culture experiment. CAT activity of control treatment was higher than that of inoculation treatments, and was not affected by F. oxysporum inoculation. When combined with vascular bundle browning, MDA content and POD and PPO activities were important indicators for early diagnosis of tomato Fusarium wilt.