Induction Of Disease Resistance Using BTH And Harpin On Hami Melon And Their Effects On Postharvest Behavior Of Fruit

Melon seedlings (cv. Queen) were sprayed with BTH and Harpin, then inoculated with Erysiphe cucurbitacearum .The results showed that both inducers decreased the disease index of plant .The induction effect was increased with the concentration of elicitors. The optimum concentration was of 100μg/ml and 90μg/ml for BTH and Harpin,respectively. The average induction effect reached of 78% and 73.5%. Considering of statistical leval and the cost of the inducors, assay concentration of BTH and Harpin was screaned as 50μg/ml and 60μg/ml. The treatment of BTH and Harpin induced locally and systemically PRs activity in melon seedlings. When treated the first leaf with BTH and Harpin, a higher peroxidase activity (POD) were observed in 'Hongmicui'(resistance cultivars ) and 'Queen'(bearing disease cultivars). Chitinase(CHT)and β-1.3-glucanase (GLU) activities were also induced in 'Hongmicui'(resistance cultivars ). POD activity reached maximum after 6 and 10 days of inoculation in the first and second leaves, respectively. There was a positive relationship between POD activity and cultivars resistance on Hami melons. CHT activity reached maximum after 8, 13 and 24 days of inoculation in the first, second and forth leaves, respectively. GLU activity reached maximum after 5, 8 and 13 days of inoculation in the first, second and forth leaves, respectively. The treatment of three elicitors (BTH ,Harpin and Kangdufeng) had new band of POD isozyme in resistance cultivars (Hongmicui) and darker bands in bearing disease cultivars (Queen) and resistance cultivars (Hongmicui). The preharvest treatment of BTH and BTH combined with Amistar controlled effectively Powdery Mildew and Bacterial Spots in the field. The treated plant had a lower disease index. Preharvest treatment significantly influenced on weight and total soluble solids (TSS) of fruit at harvest. However, no significant difference was found on hardness. Preharvest treatment with BTH had a smaller lesion area when harvested fruit inoculated with Fusarium sp. However, no significant difference was found on lesion area inoculated with A.alternata. BTH preharvest treatment also reduced significantly cracks and disease of fruit, increased the marketable rate of melons after stored at cold storage. However, no significant difference was found in the marketable rate of fruit after stored or transported for a long distance at ambient temperature.