الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
:The nine isolates of S. cepivorum obtained from different localities of Upper Egypt were able to infect Giza 6 onion cultivar and produced typical symptoms of white rot. The pathogenic potentialities of the tested isolates ranged from moderate to severe. Isolates No. 5, 7, 8 and 9 of the pathogen formed less frequently numbers of large irregularly shaped black sclerotia (0.5-2 cm in diameter) on infected bulb tissues beside that known as microsclerotia which are numerous, black, spherical and their diameter not exceed 0.2 cm and formed by all pathogen isolates.
2- Trichoderma viride and T. harzianum were capable to antagonize growth of S. cepviroum isolates in vitro. They showed different inhibitory effect against growth of different pathogen isolates on PDA medium ranged from moderate to severe.
3- In greenhouse treated infested soil with the pathogen isolates No. 5 and 7 with both antagonists at transplanting time, significantly reduced percentages of infection and white rot severity on Giza 6 onion cultivar and numbers of the pathogen sclerotia in soil. The least disease incidence % and the lowest numbers of sclerotia in soil were achieved by T. viride.
4- Treated Giza 6 onion plants with combined treatments of the biocide (BioHealth) and the plant growth promoters (Algarin and Inicium) caused significant reduction in incidence of onion white rot in greenhouse and in field plots (naturally or artificially infested with pathogen isolates). Rasing the tested biocide rate had no effect on incidence of the disease in the greenhouse, however, it caused the highest reduction in infection % and the highest marketable bulb yield in the field.
5- Soil treatment with N-allyl sulphide and N-propyl sulphide (at the rate of 200 ppm), before onion transplanting, reduced significantly both percentages of infection and white rot severity on Giza 6 onion cultivar and numbers of the pathogen sclerotia in infested soil (with the pathogen isolates No. 5 and 7). Numbers of pathogen sclerotia in soil are decreased by shorting treatment time, before transplanting, from 3 to one week. However, the only treatment time reduced incidence of the disease was one week before transplanting date.
6- Soil treatment with the tested organic sulphides and T. viride at different times before onion transplanting reduced significantly both percentages of infection and white rot severity and numbers of the pathogen sclerotia in infested soil with the pathogen isolates. The highest reduction in incidence of the disease and in numbers of sclerotia in soil was achieved by organic sulphide + T. viride combined treatment one week before transplanting date.
7- Soil treatment with single or combined treatments of T. viride or T. harzianum and the tested organic sulphides one week before onion transplanting caused significant reduction in both disease incidence and numbers of the pathogen sclerotia in infested soil with the pathogen isolates. The lowest infection %, disease severity % and numbers of the pathogen sclerotia in soil was achieved by combined treatments (organic sulphides + antagonists) compared with single treatment with each of them alone.
8- The chemical resistance inducers SA, AA and ASM, at 250-1000 ppm concs, inhibited significantly growth of the pathogen isolates No. 5 and 7 on PDB medium. In general, the lowest percentage of inhibition is caused by 250 ppm conc.
9- Treating Giza 6 onion transplants before transplanting by dipping in SA (100 & 200 ppm) or AA (50 & 100 ppm) or ASM (50-100 ppm) or by twice sprays on grown plants (15 and 30 days after transplanting date) or by combined treatment (dipping + spraying) induced the resistance of onion plants to white rot, since, percentages of infection and disease severity were significantly decreased in treated plants compared with untreated ones. In general, lowest disease incidence in different treatments of the tested resistance inducers was achieved by combined treatments followed by spray treatments and finally dipping treatments. Also, no significant differences were existed within reduction in disease incidence caused by the tested concs. of resistance inducers.
10- Treating Giza 6 onion plants with different resistance inducers and different methods of applications increased accumulation of total phenols and free SA and levels of PO and PPO in treated plants compared with healthy or diseased untreated plants. In general, the combined treatments of the tested chemicals (dipping + spraying) caused the highest increase in levels of total phenols, free SA and the tested oxidative enzymes followed by spraying treatments and finally dipping treatments. Rasing the tested concs. of chemical resistance inducers increased accumulation of phenolic compounds and levels of the tested enzymes compared with untreated control.