| Non-heading Chinese cabbage ( Brass ica campestris ssp. chinensis Makino) is widely cultivated in the area of Yangtze river, but the high temperature in summer is a limiting factor of growth. So the author studied physiology, biochemistry and the morphology under heat stress of non-heading cabbage at seedling stage and adult stage, and the correlation between the above indexes and the heat injury index (LIII) .On the base of the HII as an index to measure the heat-resistant ability of the cultivar,the feasibility of screening heat-resistant cultivars from the seed stage was also discussed. 1 Heat injury index ( HJ1) HLI reflects the heat resistant ability of different non-heading Chinese cabbage cultivars. The correlation between HI1 at seedling stage and at different stages after transplanting is declined with the time prolonging (r8d=O.782, rI~d=O.S5S). 2 Morphological indexes and heat resistant ability The heat-resistant cultivars always grow fast at seedling stage, at which stage the petiole length and the leaf area may be used as the heat-resistant indexes. Most of the morphological indexes at adult stage are all significantly negatively correlated with the HII, just as leaf area, leaf weight, petiole weight, petiole thickness, plant weight and plant height, and et al, of which the petiole thickness and its weight was most significantly correlative with the 1-111 (r thickness~0?88, r weighf~O.938). Also there~ s a significantly negative correlation between the root weight, the root length and the I-III.And the stoma density shows less correlation with the heat-resistant ability. 3 Physiologic, biochemistic indexes and heat-resistant ability I-ILL is significantly or most signicantly correlated with the germination capacity, germination velocity, germination rate under heat stress, which could be used as heat-resistant indexes. The cutivars with high seedling viability and adult plant viability also reflects their high heat-resistant 3 ability ( r scedling~0-7?5?r adult plant0?5 )? There is a signicantly or most significantly negative correlation between the content of chlorophyll a, chlorophyll b, total chlorophyll and the Fill, respectively. But the ratio of chlorophyll a I b is less significantly correlative with the HIt. Experiments show the content of chlorophyll is more important to heat-resistance at seedling stage than that at adult plant. The relative electric conductivity of leaf at normal temperature could be used as a heat resistant index. It was better to place the leaf in water for 6?10 hours at normal temperature, or for about 10 hours at 40CC. It was no necessity to think about the effect of the area or the weight of leaves to the result when they are in a certain scope. POD activity?in root was much higher than that in leaf, both of which are significantly positively correlative with the I-ill ( r root=0?7 1, r leaf~~O.8 12 ).POD activity in heat-resistant cultivars is lower than that in heat-sensitive cultivars. 4 Seed vigor and heat-resistant ability Seed vigor was much concerned with the HII.In this experiment the germination result of perpendicular plate was more reliable than that of horizontal plate. Three methods, germinating at different temperature, germinating by seeds aged for different time and treating the germinated seedling at different temperature, were used to measure...
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