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Onion has great economic importance as a cash crop, it was and still one of the most important vegetable crops not only in Egypt but also globally. It is cultivated worldwide especially in warm regions It considered the tenth vegetable crop in Egypt the Top 10 Commodities of Production in Egypt 2018 and the center eighth of the Top 10 Country of Export Quantity of Onions About 216,500 tonnes in 2018 (Faostat,2020). Meanwhile, onion is considered the first crop in Egypt for fresh use, cook, and export. onion is attacked by a number of pathogens from seed to harvesting stages and subsequently by post-harvest pathogens that affect production at quantitative and qualitative standards. Considerable, fungal diseases, especially purple blotch in onion was the most important diseases which affect production.
The major goal of this study is to throw some light on disease incidence, distribution, and survey of a purple blotch of onion in different growing regions, isolation, and identification of the causal pathogen at microscopic examination. Moreover, pathogenicity tests, also morphological and cultural characteristics of the pathogen. On the other hand, the antagonistic action effect of different botanical, bio-agents, and fungicides against the causal pathogen was studied.
Obtained result can be summarized in the following:
1- In this study data indicated that a disease survey in the field of onion from 2017 till 2019 revealed that, the purple blotch disease was presented in all the observed Governorates i.e. Giza, Menofia Qalyubia and Sharkia, Governorates. Also, the highest percentage of disease survey was obtained in Qalyubia , Shalaqan city being (61.1%) followed by Menofia, El-Sadat city being (57.6%), Giza, Geraza city (57.1%), Qalyubia , shoubra El-khama city(52.5%)and Sharkia, El-Gosak city (45.7%) Governorates, while the lowest percentage of disease survey was noticed in Qalyubia , Qalyub city (28.5%). Also, the results showed that the highest percentage of A. porri fungal isolates was reached about (85.7%) compared with the percentage of 16.39% was other fungi.
2- The isolated fungi from onion leaves were A. porri, Cladosporium spp., Stemphylium sp., Chaetomium sp. and Trichoderma spp. and cultural characterization for isolates. The fungus A. porri was the most occurred and frequent of all isolated fungi
3- The tested fungal isolates were significantly various in their responsibility to cause the disease. Pathogenicity tests showed that, (Qu3) was the most pathogenic fungal isolate the percentage was 50% followed by (QU4) 40% and (Qu5) 40% followed by (SHg4) the percentage was 33% then (Ms14) was the lowest pathogenic fungal isolate 1.2%. Whilst Stemphylium sp. isolate code (Qu10) and (Qq2) not gave disease symptoms when onion leaves were inoculated with Stemphylium sp.
4- Morphological characterization of virulence isolates of A. porri by using slide culture technique and checked under light microscope to studied for conidiophores attachment of conidia to conidiophores, branching of conidiophores, colour, shape, beak width, beak length, spore body length, spore body width, number of transverse septa, length and width of conidia.
5- This study was extended to include the botanical control of the causal pathogen of purple blotch disease. The results show that, all the tested botanical extracts (aqueous extracts) Neem, Garlic, Moringa and Bougainvillea sp. at 5%and 10% concentration and (oil extracts) black Seed, Cinnamon, Cloves and Garlic at 50ppm and75ppm reduced percentage of mycelial growth rate of pathogen at various degrees, in vitro so that used it in pots experiment which showed Bougainvillea sp. at 10% concentration (aqueous extract) and Garlic at 50ppm concentration (oil extracts) reduced percentage of disease severity purple blotch and the best botanical treatment so that used Bougainvillea sp. and garlic oil in field, it reduce disease and increase production and quality crop on two Cultivar(Giza red and Giza 20).
6- In vitro trials for the biological control, the obtained data showed that T. harzianum was more effective on the mycelium linear growth of the tested pathogenic isolate fungus than Chaetomium sp, Bacillus sp. and Actinomyces sp. Besides, the obtained data showed that, the tested bioagents were Trichoderma sp., Chaetomium sp, Bacillus sp. and Actinomyces sp. action effective against the tested causal pathogen of purple blotch disease than Pseudomonas sp. invitro. so that used it in pots experiment which showed that T. harzianum was more effective on the disease severity of purple blotch on seedling in pots than Chaetomium sp, Bacillus sp. and Actinomyces sp.; and used T. harzianum to effect of purple blotch disease on two Cultivar of onion (Giza red and Giza 20) in field.
The biological control treatments by using fungal and bacterial bioagents was the best method to prevent environmental pollution and to keep human healthy. Biological control of plant pathogens by microorganisms has been considered a more natural and environmentally acceptable, safety, active, alternative to the existing chemical treatment methods and economically the bio-agents cost less than fungicides (Siameto, et al., 2010).
7- Chemical control results indicated that, A. porri was more affected fungus with three fungicides namely, Score, Dithane M45 and Achook were the best fungicides based on the percentage inhibition at 300ppm concentrations were used in vitro and copper oxychloride is the least effected treatment on pathogen in vitro so that used three fungicides namely, Score, Dithane M45 and Achook to application in pots experiment which showed Dithane M45 was more effective on the disease severity of purple blotch on seedling in pots than Score and Achook ;and used Dithane M45 to effect of purple blotch disease on two cultivar of onion (Giza red and Giza 20) in field.
8- Experiments have been done on naturally infected seeds and bulbs from the previous year by cultivating infected bulbs. Infection was classified into five categories based on the percentage of disease severity. Pathogen transmission by the onion seed was investigated, either as internal or external infection type, Five different ratios of blub infection was determined as;14.2%, 25.2%, 41.5%, 61.1%, 87.5%. Also, trials were carried out in the current study to evaluate the efficiency of some botanical, biological and chemical as seed dressing treatments for infected seeds before sowing it, i.e. (Achook, Bougainvillea sp., Bacillus sp., Trichoderma sp. and Score). Results showed that disease severity was increased in the blub produced from previous crop, the number of flower stalk was reduced, and its disease severity was increased. Seeds produced from infected blub showed reduction in germination percentage. The most effective seed dressing treatment on seed germination were obtained by using Score & Achook treatment compared with other seed dressing treatments. All treatments including Score, Achook, Bacillus sp., Bougainvillea sp., and Trichoderma sp.; respectively showed variable seed stimulation of germination compared with plants in the control treatment.