Priming with fungal elicitor elicits early signaling defense against leaf spot of broccoli underlying cellular, biochemical and gene expression

The phytopathogen Alternaria, which causes leaf spot disease in broccoli plants, has developed the ability to adapt to changing climatic conditions with the failure of conventional fungicides. To restrict its infection and further spread, the application of novel molecules that have the ability to trigger innate immune responses of the plants to concurrent pathogenic invasions is essential. In this context, the current study was set out to assess Trichoderma-derived trehalose molecules' beneficial effects from inciting resistance mechanisms in broccoli plants against Alternaria brassicicola at histochemical, biochemical and genetic levels. From the results of the greenhouse experiment, it was evident that trehalose proved to be an exceptional elicitor in combating broccoli leaf spot disease. The induced resistance is positively associated with an early hypersensitive reaction expressed in the primed seedlings. Additionally, the deposition of histochemical such as callose and phenols was found to be accelerated in the tripartite system at 24 and 48 h after post-inoculation (hpi). At the biochemical level, the activities of the enzymes chitinase (CHI), catalase (CAT) and allene oxide synthase (AOS) were significantly enhanced in trehalose-treated broccoli plants inoculated with A. brassicicola. The enzymatic activities were further validated by quantitative real-time polymerase chain reaction (qRT-PCR) analyses wherein the relative expressions of the corresponding gene transcripts were up-regulated in trehalose primed plants. Conclusively, the investigation results have provided vital insights into the histochemical, biochemical and gene expression underlying the enhanced induced systemic resistance against broccoli leaf spot disease.