Physiological response and productivity of pot marigold (Calendula officinalis) genotypes under water deficit

Pot marigold (Calendula officinalis L.) is an industrial plant in which the selection of drought tolerant genotypes based on yield, oil content, and physio-chemical traits is desirable. The experiment was conducted at Research Farm of Agricultural Sciences and Natural Resources University of khuzestan located in the northeast of Ahwaz, Iran during 2015-16 and 2016-17. The experiment was designed as a three-replicate, split-plot, randomized complete block, in which the main plots consisted of the three irrigation regimes [after 35% (I-1), 60% (I-2) as well as 85% (I-3), exhaustion of available water in the soil] and the subplots consisted of the nine pot marigold genotypes ('Ahwaz', 'Tehran', 'Isfahan-m1', 'Isfahan1', 'Candy-man', 'Gitana', 'Zen-gold', 'Isfahan-m2', and 'Isfahan2'). Drought increased catalase (CAT), peroxidase (POX), and Ascorbate peroxidase (APX) activities, as well as malondialdehyde (MDA), leaf and root proline, extract contents, and water use efficiency, but reduced seed oil content, dry petal yield, and extract yield, seed yield and seed oil yield. Ahwaz genotype had the highest seed yield, and seed oil yield under all irrigation regimes. The Candy-man genotype produced the highest dry petal yield and extract yield. These results indicate that the effects of drought on measured traits depended on drought level, genotype, and measured trait, suggesting that selection of genotypes for drought tolerance and production of desired traits is possible. In this regard, plant breeders might be able to use APX, CAT, and PDX activities as chemical markers to select drought tolerant genotypes.