Endophytic Fusarium clavum confers growth and salt tolerance in Cucumis melo

Abstract

In the present study, we investigated the in-vitro and in-vivo effects of root endophytic fungal species isolated from squirting cucumber Ecballium elaterium on morphological, physiological and biochemical mechanisms of muskmelon (Cucumis melo) in response to salt stress. A total of 23 endophytic fungal isolates belonging to nine different genera were initially screened for their salt tolerance potential in saline medium. Endophytic Fusarium clavum EeR24 exhibited maximum salt tolerance in screening studies and was selected for further studies. Seedlings of C. melo were inoculated with F. clavum EeR24 and one week later were subjected to two salt (100 and 200 mM NaCl) and control (no salt) treatments in a growth chamber and greenhouse experiments. In growth chamber assays, seedlings treated with F. clavum EeR24 exhibited significant increase in growth and biomass under both controlled and saline conditions. Under greenhouse conditions, F. clavum EeR24 significantly improved morphological and physiological traits including plant height, weight, number of leaves, membrane stability, electrical conductivity, photosynthesis, stomatal conductance and transpiration, in C. melo in response to salt stress. Endophyte colonization also led to decreased absorption of Na+ (36–42 %) and Cl- (23–33 %) ions and an improved K+ (35 %) absorption. Under saline conditions, endophyte colonization improved catalase (24–37 %), guaiacol peroxidase (31–42 %) and superoxide dismutase (16–22 %), chlorophyll and phenolic content by 30–64 %, compared to non-colonized plants. Lipid peroxidation activities significantly decreased by 45 % and proline accumulation increased by 18 % in endophyte-colonized compared to non-colonized plants. Histochemical analysis indicated that under saline conditions, endophytic colonization reduced levels of H2O2, superoxide ion production and cell mortality and increased lignin deposition. The endophytic isolate F. clavum EeR24 also exhibited plant growth promoting activities by producing hydrolytic enzymes, IAA, and phosphate solubilization. Furthermore, a study on spatial colonization of the endophyte, using either conventional Petri-plate counts or RFP-tagging, indicated that F. clavum was able to penetrate the root tissues of C. melo. Conclusively, the endophyte F. clavum EeR24 is an effective salt stress reducer and melon growth promotor; hence can be further taken into account for development as an eco-friendly bio-fertilizer to confer salt stress tolerance in melon.