Heat Tolerance of Cotton Genotypes Assessed by Electrolyte Leakage, Chlorophyll Fluorescence Analysis and Performance in the Field in Pakistan
Apr 26, 2019
Germination and emergence of 117 cotton accessions were tested in the laboratory at 43oC and 30oC. The absolute heat tolerance of detached leaves of the 117 accessions was tested by chlorophyll fluorescence analysis (CFA) and by electrolyte leakage tests. The heat tolerance of whole plants was examined in a large, modified growth chamber. The relationships between temperature, net photosynthesis, stomatal conductance, transpiration and transpirational leaf cooling were examined using an automated CIRAS infra-red gas analyzer to measure gas exchange parameters while applying defined profiles of increasing leaf temperatures. An early-sowing field experiment at Multan examined the responses of 16 cotton lines to early heat stress. CIM443, CIM 438, BH89, GH8, NIAB78 SLS1 and 1269/93 were more heat-tolerant than Acala SJ2 at the germination stage. The chlorophyll fluorescence assay (CFA) revealed that CIM448 and CIM435 performed better than CIM443, but SLS1 performed badly in CFAs. Of the wild species, G. sturtianum was least tolerant, while Thespesia populnea was the most heat-tolerant wild relative. The hexaploid G411 (G. hirsutum cv. NC8 x G. australe) was the most tolerant interspecific hybrid. Electrolyte leakage tests largely confirmed these results. CIM448 and NIAB 313 were less leaky than Acala SJ2, while DNH40 was susceptible to heat damage. Only the electrolyte leakage test gave data which correlated well with yields in the field experiment.