Influence of Humic Substances on Cucumber Seeds Storability and Root Rot Diseases Incidence under Salinity Conditions

Abstract

Seed germination is a complex process, which is regulated by many factors including storage. The present study aims at assessing the validity of stored cucumber seeds under stressed-soil. In-vitro experiment was conducted to investigate the influence of soaking of stored cucumber (Cucumis sativus L.) seeds produced during three consequent years (2015, 2016 & 2017) in five concentrations of humic substances (HS'c) solution (0.3, 0.6, 0.9, 1.2 & 1.5%) for five different intervals (30, 90, 150, 210 & 270 min), on germination percentage (G%), germination velocity (GV) and vigor index (VI). Another In vitro experiment was conducted to assess the direct effect of HS'c on two nutritional media for Rhizoctonia solani and Fusarium solani mycelial growth, sclerotial productivity & viability, conidia viability. Greenhouse experiment was conducted to assess the effect of soaking cucumber seeds in HS'c and spraying with salicylic acid (SA) (100 and 200mg L-1) twice on growth parameters of cucumber seedlings, and controlling the root rot disease caused by R. solani and F. solani under saline conditions (2.36, 4, 5 & 6 dS m-1). The results indicate that T5 (0.3% for 210 min.) for 2015 and 2017 and T4 (0.3% for 150 min.) recorded the highest values for all studied parameters. No morphological changes were observed for the highest pathogenic two fungal isolate's mycelial growth on both fungal strains. R. solani was affected less than F. solani for the presence of different HS'c into nutrient media. 1.5% HS concentration had a reduction effect on the radical growth of fungal isolates, R. solani sclerotial production (30%) and viability (53%) and F. solani conidial viability (58%). Root rot disease was affected differently by seedling treatments of HS'c and/or SA under the four salinity conditions. The combined treatment; soaking seeds in 0.3% HS (for different period/year) and spraying seedlings with 200 SA had significantly reduced the disease incidence (DI) and disease index of both R. solani and F. solani specially in the lowest and highest salinity conditions.