Screening of Low Phosphorus Tolerant Germplasm in Cotton at Seedling Stage and Comprehensive Evaluation of Low Phosphorus Tolerance

To establish an evaluation system for low phosphorus tolerance in cotton varieties (lines), screen low phosphorus tolerant cotton germplasm and evaluate different types of phosphorus efficiency, and lay the foundation for studying the physiological mechanisms of low phosphorus tolerance in cotton and mining low phosphorus tolerance genes.

Using 140 cotton cultivars (lines) from different cotton regions at home and abroad, 21 traits such as biomass, root-related indexes and phosphorus efficiency-related indexes were measured under low (10 μmol·L^-1 KH₂PO₄) and normal (500 μmol·L^-1 KH₂PO₄) phosphorus treatments in a hydroponic experiment. The index of low phosphorus stress tolerance was calculated for each index. Using the integrated affiliation function method, principal component analysis, regression analysis and cluster analysis were conducted to classify the low phosphorus tolerance of each cotton variety and to comprehensively evaluate the low phosphorus tolerance and phosphorus efficiency type of each cotton variety.

Compared with the normal phosphorus treatment, the mean values of total phosphorus accumulation, total phosphorus content, aboveground dry weight and total dry matter weight of the tested cotton varieties decreased more under the low phosphorus treatment, while the mean values of root average diameter, specific root area, root tips number and phosphorus use efficiency increased. Under low phosphorus treatment, the coefficients of variation of each index ranged from 6.04% to 47.79%，the coefficients of variation of root indexes such as specific root tips density, root tips number, specific root length and root average diameter were higher than those of normal phosphorus treatment, and the coefficients of variation were 47.49%, 42.13%, 40.19% and 19.16%, respectively; the principal component analysis of the 21 indexes of low phosphorus stress tolerance showed that the cumulative variance contribution of the six principal components reached 77.21%, and the comprehensive low phosphorus tolerance value (D) was calculated using the affiliation function method. The D-value regression equation was established by multiple regression analysis to determine the six low phosphorus tolerance indices and perform systematic clustering to classify different cotton varieties (lines) into three categories: low phosphorus tolerant, intermediate and low phosphorus sensitive.

Total dry matter weight, phosphorus use efficiency, root fresh weight, total root length, root surface area and total phosphorus accumulation were identified as indicators for the evaluation of low phosphorus tolerance in cotton.