Nondestructive phenomic tools for the prediction of heat and drought tolerance at anthesis in Brassica Species

Oilseed Brassica species are vulnerable to heat and droughtstress, especially in the early reproductive stage. We evaluated plant imagingof whole plant and flower tissue, leaf stomatal conductance, leaf and budtemperature, photochemical reflectance index, quantum yield of photosynthesis,and leaf gas exchange for their suitability to detect tolerance to heat (H)and/or drought (D) stress treatments in 12 Brassica genotypes (G). A replicatedfactorial experiment was set up with 7 d of stress treatment from the beginningof anthesis with various levels of three factors H, D, and G. Most phenomicstools detected plant stress as indicated by significant main effects of H, D,and H×D. Whole plant volume was highly correlated with fresh weight changes,suggesting that whole plant imaging may be a useful surrogate for fresh weightin future studies. Vcmax, the maximum carboxylation rate of photosynthesis,increased rapidly on day 1 in H and H+D treatments, and there were significantinteractions of G×H and G×D. Vcmax of genotypes on day 1 in H and H+Dtreatments was positively correlated with their harvested seed yield. Vcmax onday 1 and day 3 were clustered with seed yield in H and H+D treatments as shownin the heatmaps of genotypic correlations. TPU, the rate of triose phosphateuse, also showed significant positive genotypic correlations with seed yield inH+D treatments. Flower volume showed significant interactions of G×H and G×D onday 7, and flower volume of genotypes on day 7 in H was positively correlatedwith their harvested seed yield. There were few interactions of G×H or G×D forleaf stomatal conductance, leaf and bud temperature, photochemical reflectanceindex, and quantum yield of photosynthesis. Vcmax, TPU, and volume of flowersare potential nondestructive phenomic traits for heat or combined heat anddrought stress tolerance screening in Brassica germplasm.