Antioxidant enzymes associated with resistance to Fusarium oxysporum f. sp. melonis race 1.2 in melon

Fusarium wilt of melon, Cucumis melo L. (Cucurbitaceae) caused by Fusarium oxysporum f. sp. melonis (FOM), induces severe symptoms, thus dramatically limiting the yield in melons globally. Incorporating genetic resis-tance in cultivated crops is considered the most efficient and sustainable solution to control root rot diseases. However, resistance to FOM in melon is quantitative in nature, and the mechanism is poorly understood, and the information about melon-FOM race interactions is still limited. This study explored the changes in the eight antioxidant enzyme activities; catalase (CAT), chitinase (CHI), beta-1,3-glucanase (GLU), peroxidase (POX), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), superoxide dismutase (SOD), and as well as total phenol contents (TPCs) in roots of two resistant 'Shante-F1' and 'Khatooni' and two susceptible 'Shante-T' and 'Shahabadi' melon accessions, over the time courses of 7, 14 and 21 days (dpi) following inoculation with an isolate of FOM race-1.2.The results revealed that the up-regulated of this set of defense-related enzymes was a key factor against FOM race-1.2 infection, with levels being elevated up to 3-fold in the resistant accessions. In addition, biomass growth parameters (BMPs), roots and shoots (fresh and dry weights, heights, diameters and roots volume) following inoculation displayed almost similar trends observed for the enzyme activity in resistant melon accessions in comparison to susceptible ones. Thus, studying the physiological metabolic pathways of the related enzymes appears to be an important biochemical marker for breeding programs aiming to elucidate the FOM race 1.2 resistance mechanisms in melon. A better insight in melon defense responses can help to establish biochemical characteristics for the selection of resistant melon sources and provide a theoretical basis for disease control and breeding of melon plants with higher levels of resistance to FOM race 1.2 isolates.