الفهرس 
Angular bacterial leaf spot of cucurbitsOnly 14 pages are availabe for public view
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Abstract
Angular leaf spot of cucurbits is considered as one of the most important bacterial diseases that infect cucurbits in Egypt and worldwide specially United States of America. The disease could infect plants under greenhouse or field conditions. Disease symptoms could show on the leaves and fruits causing huge loss to crop, like the disease outbreak in 2013-2015 in Florida and Georgia, USA. Disease severity increases when the favorable conditions are available for the disease such as low temperature and high humidity during the season.
The causal agent of the disease is P. syringae which has many strains causing different levels of disease severity, because of the diversity in physiological and molecular characteristics among strains. The control of the disease mainly relies on the use of copper bactericides, although, they could cause phytotoxicity for the seedlings in the first two weeks due to their sensitivity to copper compounds in this stage.
So, this study aimed at studying the molecular diversity for the obtained isolates from the disease outbreak occurred in 2013-2015 in Florida and Georgia, USA. Also, determining the virulence factors within the isolates which led to the increased disease severity. The study also aimed at using some nano-copper compounds to control the disease during the first two weeks of planting.
The main results could be summarized as follows:
1- Five strains of P. syringae were isolated from infected watermelon plants in Florida and Georgia, USA.2- The isolated strains were identified according to morphological and biochemical characteristics.
3- A pathogenicity test was carried out for the obtained strains on watermelon, cantaloupe and squash seedlings, and the results showed a variation in the disease severity between strains, where isolate PsM_D was showed the most severe symptoms.
4- The phylogenetic tree constructed based on the MLSA results carried out using 4 housekeeping genes for the five isolated strains compared with other related P. syringae strains that all 5 strains were among genomospecies 1 and are genetically distinct from P. syringae pv. lachrymans.
5- The whole genomes for the collected strains from the disease outbreak were sequenced. The sequences then were compared with other genome sequences for related P. syringae strains to determine the phylogenetic relation between strains.
6- ANI analysis results showed that all collected strains were in the genomospecies 1 group under different phylogroups, although all strains were genetically different from P. syringae pv. lachrymans, confirming the results obtained from the MLSA.
7- T3SS genes profile for the collected strains showed high level of variation between isolates explaining the diversity in the disease severity for those isolates.
8- Phytotoxins genes for the collected strains were determined within the bacterial genomes to determine the ability of bacteria to secrete phytotoxins.
9- The results showed that all strains were able to secrete syringopeptin, mangotoxin, syringolin and syringomycin, and they were not able to secrete coronatine, phaseolotoxin, tabtoxin and syringolide.
10- The effect of some nano-copper composites to control the disease in the first two weeks and the effect of CS-Cu, FQ-Cu, MV-Cu and Kocide 3000+Mancozeb with different concentrations was studied on the growth of P. syringae strain 13-1 and the copper tolerant strain A1513 in vitro. The CS-Cu and FQ-Cu were significantly more effective in reducing the bacterial population.
11- Watermelon seeds (hybrid Starbrite) were inoculated with P. syringae strain 13-1 using two different methods: Vacuum inoculation and seed soaking inoculation, where seed soaking method was significantly more effective in transmitting the disease to the healthy seeds that vacuum inoculation method.
12- Kocide 3000+Mancozeb was significantly more effective in reducing average number of contaminated seedlings using seed inoculation method.
13- FQ-Cu was significantly the most effective in reducing % disease incidence at day 14 followed by MV-Cu, while Kocide 3000+Mancozeb was the least effective compared to untreated control.
14- Kocide 3000+Mancozeb was significantly more significant in reducing area under disease progress curve (AUDPC) followed by MV-Cu and FQ-Cu.