| Walnut(Juglans regia L.) is an important woody oil tree, and it has high economic value. Late frost injury occurred frequently in recent years, and caused great losses. The late frost injury occurred on April 19 th to 20 th, 2013 in south-central of Hebei province which resulted in walnut yield reduced by 60% to 99%. In order to study the mechanism of the frost injury, the supercooling point, freezing point, electrolyte leakage rate, semi-lethal temperatures, protection activities, osmolyte contents in leaves and ovaries of walnut before the frost injury were studied in demonstration base of Hebei Lvling Fruit Industry Co.,Ltd, then the frost injury and the effect of cutting out the frozen shoots after the frost injury were studied. The results showed that:1. The walnut trees in the 6 bases of Hebei Lvling Fruit Industry Co.,Ltd. were in the shoot elongation stage at the time of late frost occurrence, the lowest night temperature was-1.8~-3.7℃ at that time, the walnut yield reduction was 39%~99% in different bases; There existed very significant positive correlations among the duration low temperature index and the female flower preservation rate and the average fruit number per plant, the correlation coefficients were 0.958 and 0.923, and there existed significant negative correlation between the duration low temperature index and the yield reduction percentage, and the correlation coefficient was-0.914.2. The freezing indexes of different cultivars ‘Lvling’, ‘Xiangling’,‘Liaoning NO.1’,‘Shangsong NO.6’,‘Zhonglin NO.1’ and ‘Qingxiang’ were 41.97%, 52.65%, 54.88%, 67.58%, 74.93%, 99.67%, 82.69% and 100.00% respectively in the same place; The freezing indexes of different shoots of the 6 cultivars whose lengths were less than 5 cm, 5-10 cm and above 10 cm increased gradually with the shoot length increased., and the freezing indexes of the 3 kinds of shoot of ‘Lvling’ were 54.98%, 64.01%, 80.50% respectively, while those of ‘Qingxiang’ were 71.85%, 81.33%, 90.26%.3. In the different places, the freezing indexes of ‘Lvling’ which were grown on the top of hill and low-lying area were 50% and 98%; The freezing indexes of ‘Lvling’,‘Xiang ling’,‘Zhonglin NO.1’,‘Shangsong NO.6’ at the altitude of 125 m were 45.93%, 46.33%, 54.18%, 62.14%,those at the altitude of 114 m reached 100%.4. The total storaged nourishments in single bud of long branches were higher than the shorts ones. There existed positive correlations among the total storaged nourishments ofsingle bud after frost and the shoot length after accessory bud sprouting; There existed very significant positive correlations among the total contents of starch and total potassium in stem xylem and the shoot length, the correlation coefficients were 0.992, 0.992 respectively; There also existed significant positive correlations among the total contents of the soluble sugar.5. The supercooling points and the freezing points in leaves of ‘Lvling’, ‘Xiangling’, ‘Liaoning NO.1’, ‘Shangsong NO.6’, ‘Zhonglin NO.1’, ‘Qingxiang’ were lower than the ovaries. The supercooling point and the freezing point in leaves of ‘Lvling’ were 1.17℃, 1.4 lower than that of ‘Qingxiang’, those in ovaries were 1.4℃ ℃, 1.39 lower than that ℃of ‘Qingxiang’. The supercooling points in leaves and ovaries, the freezing points in ovaries of ‘Lvling’ and ‘Xiangling’ were very significant lower than those of the other cultivars, and the freezing point in leaves of ‘Lvling’ was very significant lower than those of the other cultivars.6. The semi-lethal temperatures in leaves of ‘Lvling’, ‘Xiangling’, ‘Liaoning NO.1’, ‘Shangsong NO.6’, ‘Zhonglin NO.1’ and ‘Qingxiang’ were-3.33℃,-2.96℃,-2.81℃,-2.63℃,-2.31 ℃and-2.25 ℃respectively, and that of in leaves of ‘Lvling’ was very significant lower than those of the other cultivars; the semi-lethal temperatures in ovaries of the 6 cultivars were-2.62℃,-2.58℃,-2.39℃,-2.05℃,-1.80 ℃and-1.07 ℃respectively, there had no significant differences between ‘Lvling’ and ‘Xiangling’, but they were very significant lower than those of the other cultivars.7. The SOD, POD activities, soluble sugar and soluble protein contents in leaves and ovaries of ‘Lvling’, ‘Xiangling’, ‘Liaoning NO.1’, ‘Shangsong NO.6’, ‘Zhonglin NO.1’ and ‘Qingxiang’ showed the trend that increased first, and then decreased as the temperature dropped; The temperatures that the SOD, POD activities and soluble protein contents in leaves of the 6 cultivars reached the peaks were at-4℃,-4℃,-3℃,-3℃,-3℃,-3 ℃respectively, and those in ovaries were at-3℃,-3℃,-3℃,-3℃,-2℃,-2 ℃respectively; The temperatures that the soluble sugar contents in leaves of the six cultivars reached the peaks were at-3℃,-3℃,-3℃,-2℃,-2℃,-2 ℃respectively, and those in ovaries were at-3℃,-2℃,-2℃,-2℃,-2℃,-2 respectively.℃8. The contents of MDA, proline and the production rate of O2-· in leaves and ovaries of the 6 cultivars increased gradually as the temperature dropped; There had differences of the increased and the temperatures that they reached the peak of the different cultivars. The contents of them reached the peaks were at 5℃.9. The accessory and dormant bud sprouting rate and the fruit set percentage of the plants whose the injured shoots were cut out immediately after the frost for 10 days were 80.84% and 27.75%, whereas those frozen shoots which weren’t cut out were 41.16% and 12.22% respectively.10. The results of the comprehensive evaluation for protection activities, accumulations of toxic substances, osmolytes contents in different varieties indicated that the average memberships in leaves of ‘Lvling’, ‘Xiangling’, ‘Liaoning NO.1’, ‘Shangsong NO.6’, ‘Zhonglin NO.1’ and ‘Qingxiang’ were 0.531, 0.530, 0.523, 0.493, 0.486, 0.483 respectively, those in ovaries were 0.518, 0.487, 0.486, 0.463, 0.461, 0.431 respectively. That indicated that the frost resistances of the 6 cultivars, from high to low, were ‘Lvling’, ‘Xiangling’, ‘Liaoning NO.1’, ‘Shangsong NO.6’, ‘Zhonglin NO.1’, ‘Qingxiang’ in turn. |
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