Temperature stress tolerance in small cardamom (Elettaria cardamomum Maton) upon root colonization by endophytic fungus Piriformospora indica

Abstract

Elettaria cardamomum Maton, one of the most valuable and ancient spice crops, is generally vulnerable to abiotic stress factors. The major factor that contributes to this specificity of the plant is the temperature. Piriformospora indica symbiosis with cardamom reduces the negative effects of temperature stress. This study was aimed to identify temperature stress tolerant genes in P. indica co-cultivated cardamom plants and evaluation of chlorophyll and mineral content. P. indica colonized cardamom plants already established in JNTBGRI experimental field for a period of 1.5 years were exposed to temperature stress (ambient temperature). The changes in plant phenotypes and biochemical parameters were measured. To identify temperature stress tolerant genes conferred by P. indica, the leaf transcriptome of colonized and uncolonized plants were analyzed after 24h of temperature stress induction. Results obtained showed that colonization of cardamom roots by P. indica revealed significant variation in leaf number, leaf length and tiller number of temperature stressed plants compared to control (p < 0.05) for a period of 6months at 30 days intervals. In addition, chlorophyll a, b, a + b and carotenoid contents were increased in the leaves of the colonized plants under temperature stress conditions improving photosynthetic efficiency. Mineral estimation revealed that plants treated with P. indica increased the accumulation of Ca and Mg elements. Furthermore, the expression of the antioxidant enzymes catalase, ascorbate peroxidase and superoxide dismutase were significantly upregulated by 4.83, 4.12 and 4.67 folds respectively in P. indica inoculated cardamom plants during temperature stress. This improvement in the transcripts of antioxidant enzyme genes (Catalase [CAT], Ascorbate peroxidase [APX] and Superoxide dismutase [SOD] could be correlated with a significant increment in antioxidant enzyme content. In conclusion, P. indica has the potential to enhance the cardamom growth under temperature stress and alters the activities of enzymatic and non-enzymatic antioxidants 100 and chlorophyll content which would help them to grow in high temperature zones of Kerala.