Abstract:

In this study， we selected 82 white clover germplasm lines from Sichuan and Guizhou， as well as the widely used cultivars ‘Haifa’ and ‘Huia’ to evaluate the aluminum （Al） tolerance of white clover germplasm resources in southwest China， with a view to identifying superior germplasm resources for this region. Hydroponics was used to observe the growth parameters of different germplasm lines under Al exposure （4 mmol·L^-1） for 15 days at the seedling stage， then we preliminarily screened nine lines with differing Al tolerance by subordinate function analysis. We further observed the growth and physiological changes of nine germplasm lines under Al tolerance. Subordinate function analysis was used to calculate the Al tolerance scores of the nine selected germplasm lines and principal component analysis was used to compare the contribution rates of different evaluation indexes， and hematoxylin staining was carried out to observe the active Al content of the germplasm lines. It was found that the growth and physiological performance of white clover were inhibited when the white clover germplasm lines suffered from Al toxicity. With Al toxicity， the shoot length （SL）， root length （RL）， dry weight （DW）， greenness （G）， relative water content （RWC）， chlorophyll content （Chl）， photochemical efficiency （F_v/F_m）， and performance index （PI） of white clover were significantly decreased （P<0.05）； While the electrolyte leakage （EL） and malondialdehyde content （MDA） of white clover were significantly increased （P<0.05） and the root tips of white clover were stained with hematoxylin. The preliminary evaluation of relative growth indexes showed that the white clover germplasm lines with strongest Al tolerance were Tr016， Tr056， Tr060， Tr062， and Tr077， while Tr009， Tr021， Tr040， Tr048， and Tr075 had relatively weak Al tolerance. The multivariate evaluation further confirmed Tr016 and Tr060 had the strongest Al tolerance， on the contrary， Tr021 had poor at Al tolerance. The principal component analysis suggested that， for the Al tolerance evaluation of white clover， the relative SL， RL and DW could be regarded as growth identification indexes， while identification indexes for physiological stress could use photosynthetic parameters （Chl， F_v/F_m， PI） and MDA. The results provide data on white clover Al tolerance to support selection and breeding decisions， as well as a reference information for evaluation systems to detect Al tolerance.

Key words: white clover, germplasm resources, aluminum tolerance, Al-tolerance evaluation indexes, subordinate function