Comprehensive evaluation and screening for chilling-tolerance in tomato lines at the seedling stage

Tomato is one important vegetable but with low chilling tolerance. Though research on tomato chilling tolerance has been reported, the evaluation method has not identified. In the present study, seedlings of 48 tomato lines were treated with chilling stress (4/4 A degrees C, day/night) for 8 days, and the chilling injury index (CII) was then determined. Four physiological indexes including electrolyte leakage, total chlorophyll (Chl) content, the chlorophyll fluorescence parameters Fv/Fm and I broken vertical bar PSII were measured in leaves of tomato seedlings before and after the treatment. It was found that CII, and the electrolyte leakage increased, while the total Chl content, Fv/Fm, and I broken vertical bar PSII decreased in response to chilling stress. Based on the chilling tolerance coefficients (CTCs) of four physiological indexes, the comprehensive evaluation value (D) of each tomato line was calculated by principal component analysis (PCA), and subordinate function analysis. The D value had significant correlation with CIIs and CTCs of the physiological indexes, which suggested that D value could accurately predict the chilling tolerance of tomato lines. Based on the D values, 48 tomato lines could be divided into four groups by cluster analysis: chilling-tolerant (15 lines), medium chilling-tolerant (21 lines), low chilling-tolerant (seven lines), and chilling-sensitive (five lines). Meanwhile, linear equation was constructed. Therefore, this work provides a comprehensive and accurate method for evaluating chilling tolerance in tomato.