Ruba Abuamsha

Differential resistance of oilseed rape cultivars (Brassica napus ssp oleifera) to Verticillium longisporum infection is affected by rhizosphere colonisation with antagonistic bacteria, Serratia plymuthica and Pseudomonas chlororaphis

The effect of a seed treatment with the antagonistic bacteria Serratia plymuthica (strain HRO-C48) and/or Pseudomonas chlororaphis (strain MA 342) on the infection of oilseed rape with Verticillium longisporum was assessed with ten different cultivars. Soil was inoculated with microsclerotia and mycelium of a V. longisporum culture. Seeds were treated with rifampicin-resistant antagonistic bacteria at a rate of log10 6–7 cells per seed. Resistance against V. longisporum infection did not differ between cultivars and was generally low. A significant disease reduction recorded as area under disease progress curve (AUDPC) was obtained with both antagonistic rhizobacteria with no significant difference between the treatments. Percent of healthy plants was approximately 70% in all bacterial treatments. Significant differences were observed between the cultivars ranging from 46.5% (cultivar Titan) to 72.6% (Trabant). The combined use of both bacteria could not provide additional control effects. The bacterial density in the rhizosphere was not related to the control effect, but increased by log10 2 on infection with V. longisporum. Growth promotion effects were also not related to the control effect. At present, neither the application of chemical fungicides nor breeding for resistance against V. longisporum in oilseed rape can provide a solution for this increasingly problematic plant pathogen. The present results now open perspectives to control V. longisporum in oilseed rape by making use of cultivars, which express resistance against this pathogen on interaction with the antagonistic rhizobacteria S. plymuthica or P. chlororaphis.

Improvement of seed bio-priming of oilseed rape (Brassica napus ssp oleifera) with Serratia plymuthica and Pseudomonas chlororaphis

Abstract Seed bio-priming of oilseed rape (Brassica napus) with the antagonistic rhizobacteria Serratia plymuthica and Pseudomonas chlororaphis was improved. With the imbibition of water, bacteria are transported into the seed where they survive better. To obtain a minimum bacterial density in the seed of log10 5 colony-forming-units (CFUs) seed−1, the bacterial density in the bio-priming suspension should be >log10 9 CFUs mL–1 for S. plymuthica and >log10 8 CFUs mL–1 for P. chlororaphis. Priming duration was reduced from 12 to 2 h for S. plymuthica and 4 h for P. chlororaphis. Among other priming solutions tested, the addition of MgSO4 best supported establishment in the seeds and also improved germination. The optimal bio-priming temperature for S. plymuthica is 28°C and for P. chlororaphis 22°C. Survival of the bacteria inside the seeds was moderately improved by storage at low temperature but considerably prolonged by storage under anaerobic conditions. P. chlororaphis survived significantly longer than S. plymuthica.

Interaction of fluorescent pseudomonads with Pythium ultimum and Rhizoctonia solani in cucumber roots.

The effects of thefluorescent pseudomonadisolate CW2 on hyphae ofPythium ultimum (Trow) andRhizoctoniasolani(Khn)and root colonization were studied in gnotobiotic systems under scanning electron microscopy (SEM). Results of SEM revealed that the frequency of bacterial colonization was higher in cucumber roots infested with the fungi than in healthy roots. Isolate CW2 caused irregular and abnormal fungal growth. Swellings and shrinkages ofP. ultimumand R. Solanihyphae were obvious when cucumber roots were drenched with CW2. SEM studies were also conducted to evaluate the effect of CW2 on hyphae of both fungi on PDA medium.The hyphae ofP. ultimumand R. solanishowed distinct morphological alterations and degradationcompared to untreated healthy control hyphae ofPythium orRhizoctoniawhich were slender and uniform in shape.The results provide direct evidence of bacterial attachment and colonization to f ungal hyphae of both tested spp.and show that fungal growth to be significantly reduced in the presence of isolate CW2.

Role of different additives on survival of Serratia plymuthica HRO-C48 on oilseed rape seeds and control of Phoma lingam.

For optimum inhibition of plant pathogens, biocontrol agents must be maintained at higher density and survive for a long time in the plant system. Biopriming of seeds with bacteria in the presence of different additives provide a promising technique that might improve the efficacy of biocontrol agents and their application. The aim of this work was to test different additives and stickers on the activity of Serratia plymuthica in oilseed rape in controlling Phoma lingam. Seeds were soaked in bacterial suspensions (log10 11 CFU ml) containing one of the following Stickers and additives in a ratio of 1:1:1 (w:v:v): Sodium alginate, Dextran T 40, Polyvinyl alcohol, Methylcellulose, Gum Arabic, Raffinose, Tween 20, and Paraffin oil. Seeds were stored either at room temperature or at 4°C. Number of bacteria inside the seeds was monitored over a period of 12 months. The effect of additives and stickers on bacterial efficacy in controlling Phoma lingam was evaluated in pot experiments. Number of bacterial cells inside the seeds was significantly higher in the seeds coated with GA+MgSO4, RF+MC and PA (log10 7.5 ± 0.2, log10 7.5 ± 0.2 and log10 Original Research Article British Microbiology Research Journal, 4(7): 737-748, 2014 738 7.4 ± 0.4, respectively). Interestingly, bacterial concentration in seeds stored at 4°C was higher than that in seeds stored at 20°C. Moreover, after storage for 8 months, Serratia plymuthica was able to control the black leg disease. Our results showed that some additives and stickers prolonged the shelf life of bacteria inside the seeds and improved the efficacy of bacteria in controlling the disease.