Initial Establishment Of The Tolerances To Weak Light In Tomato Seedlings And The Study Of Their Chloroplast Ultrastructure

Tomato (Solanum lycopersicum Mill.) is one of the most important world-wide protected vegetables. In recent years, researches about low light tolerance in tomato breeding have become more and more at home and abroad. During the breeding procedure process, choosing right parents parent selection is the key factor to cultivate low light tolerant tomatoes low-light-tolerant varieties. However, it is hard to select original materials for breeding, so there is a demand to establish an easy evaluation system to evaluate low light tolerance in tomatoes.In this research, the low light condition was simulated by shade net. We used multivariate statistics analysis method to discuss seventeen character indices of eleven tomato cultivars under different low light conditions. The character indices are as follows, basal angle, open angle, dropping angle, bend degree, accumulation of leaf area, specific leaf weight, Chi a, Chi b, Chi (a+b), Ca/Cb, stomatal conductance, transpiration rate, photosynthetic rate, reducing sugar content, sucrose content, starch content character indices. According to the results of the comprehensive analysis by taking multivariate analysis of variance, factor analysis and cluster analysis of cultivars, and then observed the variation in the ultrastructure of their mesophyll cells with the aid of transmission electron microscope (TEM). In this way, the research could try to gives some scientific theoretical bases to evaluate low-light-resistance of tomato cultivars. The main experimental results are as follows:(1).Under moderately low light condition(450-600μmol·m-2·s-1), the results of multivariate analysis of variance showed that differences of dropping angle, bend degree, accumulation of leaf area, Chi b, Chi (a+b),Ca/Cb, reducing sugar content, sucrose content, and sucrose content reached significant level (P<0.05) of different tomato cultivars at their seedling stage. These character indices could be summarized into five main factors with the cumulative contribution rate of84.181%. The Euclidean distance between the cultivars according to factor scores were calculated in the cluster analysis. Final results indicated that, under moderately low light condition, the sequencing of low light tolerance of the eleven tomato cultivars were T1<T4<T3<T6<T10<T7<T9<T8<T2<T5.(2).Under severely low light condition (200～420нmol·m-2·s-1), dropping angle, bend degree, accumulation of leaf area, specific leaf weight and other eleven character indices reached extremely significant level (P<0.05) or significant level (P<0.01) of different tomato cultivars at their seedling stage. The eleven character indices could be summarized into five main factors with the cumulative contribution rate of84.968%. After taking cluster analysis according to factor scores, the eleven tomato cultivars were grouped into three typical clusters. Cluster1(T1, T5, T6, T10, T11) was low-light sensitive category, cluster2(T4, T7, T9) was moderately low-light-resistant one, cluster3(T2, T3, T8) was severely low-light-resistant category.(3).Differences of tolerance to different low light condition in different tomato cultivars.In this study, the eleven cultivars were unified fertilizer and water management. After different low light treatment, their tolerance to low light showed different manifestation to a certain degree. T3and T4were not very low-light-resistant under moderately low light condition, but they showed preferable low-light-resistance when they were under severely low light condition. T10was severely low-light-resistant cultivar under moderately low light condition, and it was also the most low-light sensitive one when it was under severely low light condition. T5performed normally when it was under severely low light condition, however, under moderately low light condition, it showed excellent low-light-resistance. Therefore, when choosing suitable tomato cultivars in protected cultivation, T2and T5were priority choices, T3, T8, etc could be applied in breeding experiment as experimental materials in extremely low light condition.(4). Comparing constitutions in main factors effected tolerance to low light of tomato under different low light conditions.Under moderately low light condition, these main factors effected tolerance to low light constitute photosynthetic pigment factor, leaf growth angle factor and dry matter factor (carbohydrate level factor). Under severely low light condition, the results indicated that photosynthesis factor, photosynthetic pigment factor, dry matter factor, leaf growth angle factor and leaf growth factor were the main factors. Presumably, severely low light condition could have a complicated influence on low-light-tolerance of the tomato, in the future research, further study can be carried out.(5). correlation between low-light-tolerance of tomato and variation in their chloroplast ultrastructure of leaves.Observations of the variation in the chloroplast, mitochondria and other organelles ultrastructure of leaves of different tomato cultivars showed that, the low-light-tolerance of tomato cultivars was correspondent with damaged conditions in their ultrastructure of leaves. Variations in the ultrastructure of leaves of different low-light-tolerant tomato cultivars were obvious different, i.e. ultrastructure of leaves in tomato cultivars with severely low-light-resistance suffered lightly under the low-light-intensity stress and ultrastructure of leaves in low-light sensitive tomato cultivars suffered heavily.