Biochemical defense mechanism associated with host-specific disease resistance pathways against Rhizoctonia solani AG3-PT potatoes canker disease.

MAIN CONCLUSION: Screening for resistance in 40 potato genotypes to Rhizoctonia solani AG-3PT-stem-canker, antioxidant enzymes activity as well as total phenol compounds were documented. Rhizoctonia solani AG-3PT-stem-canker is one of the most devastating diseases that leads to severe economic losses in potatoes, Solanum tuberosum globally. Crop management and eugenic practices, especially the use of resistance can be effective in reducing the disease incidence. However, the information about potato-R. Solani interaction is still limited. This study explored screening for resistance in forty potato genotypes to R. solani, analyzing biomass growth parameters (BGPs), as well as antioxidant enzymes activity of which peroxidase/peroxide-reductases (POXs), superoxide dismutase (SOD), polyphenol oxidase (PPO), catalase (CAT), phenylalanine ammonia-lyase (PAL), ß-1,3-glucanase (GLU) and total phenol compounds (TPCs) were taken into account. In addition, we analyzed up-regulation of two gene markers (PR-1 and Osmotin), using reverse transcription quantitative PCR (RT-qPCR). For which, the resistant 'Savalan', partially resistant 'Agria', partially susceptible 'Sagita' and susceptible 'Pashandi' were selected to explore the trails in their roots and leaves over the time courses of 1, 2 and 3-weeks post inoculation (wpi) following inoculation. Cluster analysis divided potatoes into four distinct groups, based on disease severity scales (0-100%) significance. The BGPs, shoot and root length, fresh and dry weight, and root volume were also significantly higher in infected potatoes compared to non-inoculated controls. Antioxidant enzymes activity also indicated the highest increased levels for POX (fourfold at 3wpi), CAT (1.5-fold at 3wpi), SOD (6.8-fold at 1wpi), and PAL (2.7-fold at 3wpi) in the resistant genotype, 'Savalan', whereas the highest activity was recorded in TPC (twofold at 1 wpi), PPO (threefold at 3wpi), and GLU (2.3-fold at 1wpi) in partially resistant genotypes. Although the defense-related enzymatic activities were sharply elevated in the resistant and partially resistant genotypes following inoculation, no significant correlations were between the activity trends of the related enzymes. The two related gene markers also showed comprehensive transcriptional responses up to 3.4-fold, predominantly in resistant genotypes. Surprisingly, the PR-1 gene marker, basically resistant to Wilting agent Verticillium dahlia was overexpressed in resistant 'Savalan' and 'Agria' against R. solani AG3-PT. Similar results were obtained on Osmotin gene marker resistant to late-blight P. infestans, and early-blight Alternaria solani that similarly modulates immunity against R. solani. Furthermore, there was a significant correlation between resistance, enzyme activity, and gene expression in the aforesaid cultivars. Studying the physiological metabolic pathways of antioxidant enzymes activity appears to be an important direction in research to elucidate resistance to R. solani in potatoes.

Effectiveness of alginate coating on antioxidant enzymes and biochemical changes during storage of mango fruit.

The climacteric nature of mango makes it ripen quickly and increases its postharvest losses. The objective of the present search was to evaluate the efficacy of 1%-3% sodium alginate edible coating for maintaining the postharvest nutritional quality and increasing the marketability of the mango fruit during storage at 15 ± 1°C and 85 ± 1% relative humidity. Results revealed that the quality characteristics including acidity and ascorbic acid content were not affected by the alginate treatments. In contrast, treatment with 3% alginate significantly reduced weight loss and maintained higher firmness (2-fold), total phenols (1.3-fold), and flavonoids content (1.7-fold), as compared with the control. Higher antioxidant capacity was observed in the 3% alginate treatments than the control. Polyphenolxoidase activity in the coated mango remained below 30 U/g FW, while it was increased continuously in the uncoated samples during the storage. Fruits coated with alginate exhibited a higher antioxidant enzyme activity during storage. Sodium alginate had no significant effects on the external color parameters except the a* value. Generally, it was concluded that the mango storage life and its valuable nutritional characteristics were increased by applying the alginate edible coating. PRACTICAL APPLICATIONS: Recently, the edible coatings by natural sources have been widely demanded by consumers due to its nontoxic and biodegradable characteristics. Mango fruits as a climacteric high-nutritional tropical fruit being climatic have a limited shelf life and the maintenance of its quality is still a major challenge for the consumers. The results of this study showed that using sodium alginate coating at 3% concentration had a significant effect on preventing water loss, color changes and preserving antioxidant properties, phenol and flavonoids compounds of mango fruit during storage. Therefore, alginate coating as a biodegradable compound can be used to maintain the quality during the shelf life of fruits and vegetables.