Abstract
The aim of the present study was to examine the diversity for heat tolerance in a set of 105 accessions using some key morpho-physiological attributes. The data was standardized by calculating percent change over control, and used for phonetic analysis and construction of dendograms based on distance matrix (all primary data is given as supplementary material listed in statistical analysis section of Materials and Methods). These distance matrices were then used for the unweighted pair group method with arithmetic mean (UPGMA) cluster analysis using the sequential agglomerative hierarchical nonoverlapping (SAHN) method. The cluster analysis indicated some potential attributes that could be effectively used to screen germplasm for heat tolerance. Among the growth attributes, shoot fresh and dry weight was a much stable indicator than root biomass. The alterations in the concentration of chlorophyll (Chl) b played a significantly better role in clustering of various genotypes than those in Chl a. Since leaf osmotic potential was fairly maintained in most of the barley accessions under study, the notable change in leaf water and osmotic potentials seemed to be the fundamental reason for the clustering pattern. The alterations in stomatal conductance (g(s)) and intercellular CO2 concentration (C-i) were of foremost importance for clustering gas exchange parameters. The changes in electron transport rate and nonphotochemical quenching were of major importance for clustering based on chlorophyll fluorescence. Thus, it can be concluded that the thermo-tolerance and yield of barley when grown under high temperature stress can be enhanced by improving these attributes.