The characters of plants behave variously when stressed by adversity, and the range of variation of some certain character of different varieties under the stressed conditions is not completely identical. Consequently it is necessary to apply more than one index to give a comprehensive evaluation on stress resistant. In this article, taking the heat tolerance of different rice species at grain filling stage as an example, a comprehensive evaluation method that combines subordinative function method with principle component analysis and uses hierachical cluster analysis to do an quantitative classification has been set up to study the plants’ stress resistant.
Principal component analysis can transfer many correlating indexes into several independent comprehensive indexes with little original information lost. Based on the test results which show that significance of difference is above the significant point, five correlated characters which have very close relationship with the effect of rice’s heat tolerance at its filling stage are chosen. They are grain plumpness, imperfect grains percentage, density of full-filled grains, chalky grains percentage, and degree of chalkiness. By taking the heat tolerance coefficients of the five characters of evaluated varieties as the target and using principal component analysis, the five correlated single indexes are transferred into two independent comprehensive indexes with contribution ratio of accumulative total of more than 85%. Then according to heat tolerance coefficients and standardization eigenvector of five respective characters of each variety, two comprehensive indexes’ scores of every evaluated variety can be calculated accurately. The D value, comprehensive evaluation value of each variety’s heat tolerance at its filling stage, can be deduced after calculating the subordinative function values of the two comprehensive indexes scores and using the contribution ratio of the comprehensive indexes to deduce the weight coefficient and then to weight sum. As the D value is a pure number between 0 to 1, the intensity difference of the stress resistant in different species and stress resistant grades of different species can be distinguished by using hierachical cluster analysis to do a quantitative classification and combining the produce requirement in reality.
The statistical test of the group of external independent sample and the result proved by practice show that the comprehensive evaluation method set up by this study has an ideal effect. It can give an objective and precise evaluation on the comprehensive heat tolerance at the grain filling stage of different varieties.