Studies On The Mechanism Of Exogenous Application Of Cold Resistant Agent On Alleviating Chilling Injury Of Banana Seedlings

Banana is a fruit, native to tropical and subtropical regions. The chilling injury could easily occur when the fruit are stored lower than 11°C. In China, most banana growing regions suffer varing degrees of chilling damage every year. When suffering chilling stress, the plant shows yellowing leaves, browning fruit peel, abnormal fruit ripening, which adversely affect the commercial value of the fruit; serious damage can even lead to the death of the whole plant. Chilling injury causes a serious impact on the banana industry, so the study on the mechanism and prevention of banana chilling injury is of great significance.Using ’Brazil’ banana seedlings(Musa, AAA group, cv. ’Brazil’) and artificial climate box, simulating the temperature change of 24 hours a day during the cold wave in Guangzhou(the lowest temperature is 4°C), we investigated the occurrence of chilling injury, selected the cold resistant agents which alleviate chilling injury of banana seedlings, and explored their anti-chilling mechanism from photosynthetic, physiological and biochemical respects. The main results were as follows:1. Among the nine cold resistant agents tested, two were selected with optimal concentration to alleviate the chilling injury of banana seedlings. Spraying Shan’ao 300-fold dilution and Yuntaisu 7500-fold dilution could effectively reduce the chilling injury index of banana seedlings, reached the significant level(P<0.05). The treated banana seedlings grow better than the control when transferred from low temperature to normal temperature.2. Spraying cold resistant agent effectively suppressed a decrease in the chlorophyll content and the chlorophyll a/b ratio. From low temperature to normal temperature, the chlorophyll a/b ratio of banana seedlings increased rapidly; the chlorophyll content of banana seedlings sprayed with cold resistant agent was 20% higher than that of control, and brightness and saturation were significantly higher than control.3. Low temperature reduced the photosynthesis of banana leaves. The photosynthesis at low temperature was only 31% of that at normal temperature. The photosynthesis of cold resistant agent-treated banana seedlings was about 1.7 times of the control. One day at low temperature, the stomatal closure and the photosynthesis decreased significantly; when kept for 2~3d, the photosynthesis maintained a relatively low level.4. Cold resistant agent inhibited the cell membrane permeability, and the increase of malondialdehyde(MDA) and free proline content. It also enhanced the activities of superoxide dismutase(SOD), peroxidase(POD) and catalase(CAT) of banana leaves under chilling stress, thus improving the cold resistance of banana seedlings.