الفهرس 
ACKNOWLEDGEMENTOnly 14 pages are availabe for public view
 |  | from | 185 |  |  |
| | | from | 185 | | |
Abstract
Onion is considered one of the most important economic crops in Egypt, not only for local consumption but also for export. Bacterial rot diseases of onion bulbs are among the most serious diseases of storage leading to sever damage in the yield. The objective of this study was based on two main aims, firstly detection of onion bacterial rot pathogens and secondary an approach of disease control by three ways; biological control by actinomycetes, control using natural compounds and control through induction of plant resistance by chemical inducers. Naturally infected onion bulbs with bacterial rot symptoms were collected from different localities in Dakahlyia governorate, Egypt to isolate the bacterial pathogen(s) which in turn were identified and categorized into five different bacterial pathogens, with different count percentages, namely; Erwinia carotovora subsp. carotovora with the highest percentage (48.14 %), Erwinia cacticida (18.51 %), Erwinia carotovora subsp. atroseptica (14.81 %), Burkholderia cepacia (14.81 %) and Pantoea sp. with the lowest percentage (3.7 %) from which a strain from Erwinia carotovora subsp. carotovora (Ecc) and a strain from Burkholderia cepacia (Bc) were selected as an ideal pathogens of onion bacterial rot to be used in the subsequent tests. Forty five actinomycetes isolates were screened in vitro for their antagonistic capacity against Ecc and Bc from which seven isolates exhibited antagonistic activity against both Ecc and Bc. The most active actinomycetes isolate was identified as a strain of Streptomyces coelicolor (S. coelicolor HHFA2). Three natural products; chitosan (chito), seaweed extract (SW) and humic acid (HA), were used to control onion bacterial rot pathogens; they didn’t exhibit any in vitro antibacterial activity against Ecc nor Bc in the used concentrations. Three chemical resistance inducers; sodium salicylate (SS), ascorbic acid (AA) and thiamin hydrochloride (TH) were used to induce onion resistance against bacterial rot pathogens; they exhibited variable and slight in vitro antibacterial activity against Ecc and Bc in the used high concentrations. Streptomyces coelicolor HHFA2, the three candidate natural products and the three candidate chemical inducers were applied under greenhouse and field conditions for controlling bacterial rot of onion throughout storage. The assessment of disease incidence (DI) for greenhouse grown onion after three months from storage showed that all treatments decreased the DI.. Generally chitosan exhibited the best results in this regard hence the DI was recorded as zero, followed by S. coelicolor, SW and AA, TH, HA and finally SS in which cases the DI was recorded as 9.17, 9.55, 9.55, 14.55, 19.09 and 22.73 % respectively. After three months from storage of the field grown onion the DI was decreased significantly by treatment with HA or TH and it was lower than the control in the rest of treatments, after six months from storage, significant decrease of DI was showed in all treatments, also the same result was obtained after eight and ten months from storage. In general, the reduced DI values trend was more pronounced throughout storage of field onion with time. Based on the aforementioned results, it can be concluded that all the tested treatments can be used as a successful control measures in management of onion bacterial rot diseases in Egypt.