الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 194 |  |  |
| | | from | 194 | | |
Abstract
The effectiveness of some alternative abiotic agents such as chitosan (CHT), xanthan gum (XAN), propolis (PROP), sodium carbonate (SC), sodium bicarbonate (SBC) and potassium sorbate (PSO) to deter net blotch disease of barley (Hordeum vulgare, L.) caused by Drechslera teres Sacc. (D. teres) were evaluated compared to the propiconazol fungicide at its recommended dose (0.25 ml/l). In vitro experiments, the direct effect of the tested substances at various concentrations on the mycelial growth, spore germination and germ tube elongation of D. teres were determined. Propiconazol and PSO at 0.5 % completely inhibited the mycelial growth and spore germination, followed by PSO at 0.25 % with high percentage of inhibition (98.5 %). The efficacy of CHT and salts substances showed high inhibition effect on spore germination than mycelial growth. Meanwhile, XAN treatment hadn’t any direct effect against mycelial growth, spore germinations, and germ tube elongation. In vivo trials under greenhouse conditions, disease responses at both seedling and adult stages were scored as (a) type of infection and incubation period (b) sporulation on the lesion (c) count of lesions developed and (d) measurement of lesion length. Propiconazol, CHT (0.1 and 0.15 %) and PSO (0.25 and 0.5%) were the most effective in the reducing all disease components at both seedling and adult stages, followed by XAN at 0.3% except for conidial sporulation factor. The applications of PROP (0.6%), SC and SBC at 0.5% proved high activity against net blotch disease on adult barley plants under greenhouse conditions compared to field applications. The ability of tested substances to trigger physiological defense reaction in plant tissues were manifested during the assessment of some defense related enzyme activities, notably peroxidase (POD), chitinase (CHS) and phenylalanine ammonialyase (PAL). The higher activity of POD was obtained by propiconazol, followed by XAN 0.3%, PSO 0.25%, PROP 0.6% and both concentrations of CHT (0.1 and 0.15%), while the application of SC (0.25 and 0.5 %) and SBC at 0.5 % showed the lower increase in enzyme activity than untreated plants. Activity of CHS showed the highest increase response with PROP at 0.6% and CHT (0.1 and 0.15%), followed by XAN (0.3%) and PSO at 0.5%. Meanwhile the lowest response was investigated with propiconazol, SC and SBC treatments. All treatments significantly increase the activity of PAL enzyme except for PROP treatments. The highest activity of PAL was observed in plants treated with propiconazol , SBC ( 0.5% and 0.25%) followed by PSO (0.5%), SC (0.5%), and CHT (0.1 and 0.15%). Field experiments were conducted with the protective and curative activates at two locations, the course of net blotch severity development and disease epidemic expressed by area under disease progress curves (AUDPC), apparent infectious rate and terminal severity on different leaf positions. Two applications of CHT and propiconazol treatment reflect the higher activity with moderately to slightly high in the combat of the disease development, followed by the application of PSO with moderately to slightly low protection level. XAN treatment was not enough with two-times of applications to suppress the total time duration of net blotch development. The lowest activity was obtained by PROP with non-significant different with control on most of all disease components in both experimental trials. Yield potentiality (Thousand-kernels weight (TKW) and the number of kernels per head (KN/H) were decreasing with the high net blotch severity. CHT and propiconazol foliar applications provided greater TKW and KN/H, followed by the application of PSO.