Screening of forty Indian Amaranthus hypochondriacus cultivars for tolerance and susceptibility to tropospheric ozone stress

Tropospheric ozone stress adversely affects crop cultivars growth and productivity variably. The variable response of crop cultivars raised the need for identification of ozone (O3) stress-tolerant cultivars as an adaptive option. In the present study, forty cultivars of Amaranthus hypochondriacus were screened for susceptibility and tolerance to ozone stress. The cultivars were exposed to ambient (AO3) and elevated (EO3) ozone levels in free air ozone enrichment (FAOE) facility and monitored for foliar ozone injury symptoms appearance and yield attributes response. Foliar ozone injury symptoms on Amaranthus cultivars were interveinal yellow or black spots. Foliar ozone injury was observed in almost half of the cultivars and the maximum foliar injury (> 75%) was observed in cultivar IC-5527. The maximum yield reduction (> 90%) was observed in cultivars IC-4200 (94.9%) and IC-5569 (91.4%) compared to other cultivars. The results showed that Amaranthus cultivars exhibited variable response towards ozone stress where foliar ozone injury does not always correspond with grain yield reductions. Among the indices, Relative Yield Index (RYI), Stress tolerance (TOL), Abiotic Tolerance Index (ATI), Susceptibility Index (S) and Stress Susceptibility Index (SSSI) were positively correlated with relative yield loss in all the cultivars under ozone stress. With the help of cluster analysis and principal component analysis (PCA), the cultivars were categorized into ozone tolerant, moderately ozone tolerant and ozone susceptible category. The most tolerant cultivars were IC-5527 and IC-1733 which exhibited lower yield losses whereas the most susceptible cultivars were IC-3599 and IC-7924 having high foliar injury and maximum yield losses as compared to other cultivars. The most ozone tolerant cultivars of Amaranthus identified in this study may be recommended for cultivation to farmers in the areas experiencing EO3 during the Amaranthus crop growth period.