The principal host of E. fawcettii is sour oranges (Citrus aurantium), but it is also

important on grapefruits (C. paradisi), lemons (C. limon), mandarins (C. reticulata) and

some cultivars of oranges (C. sinensis) and tangelos (C. paradisi x C. reticulata). Many other species and hybrids of Rutaceae include susceptible or moderately susceptible cultivars or clones, e. g. calamondins (C. madurensis), C. hystrix, C. limonia, C. nobilis, Poncirus trifoliata, rough lemons (C. jambhiri) and satsumas (C. unshiu). The potential host range extends to other ornamental Citrus and rootstocks. Most cultivars of C. latifolia,Fortunella margarita, oranges and pummelos (C. maxima) are rarely attacked. cultivars of citrons (C. medica), kumquats (Fortunella), limes (C. aurantiifolia) and oranges are highly resistant. Inoculum for new infections consists of conidia, and presumably ascospores, from scabs formed on leaves, twigs and fruits. Conidia are formed abundantly on wet scabs, in a nearly saturated atmosphere, between 20 and 28°C.Germination of conidia and infection do not require liquid water, both processes being possible with dew, fog or under high moisture conditions. A wet period of 2.5-3.5 h is needed for conidial infection. The temperature range required for germination of conidia is 13-32°C, but infection does not take place below 14°C or above 25°C. The incubation period is at least 5 days. The optimal temperature for disease development is 20-21°C. Leaves, shoots and fruits are infected when young, i.e. when leaves are up to 15 mm wide and fruits are not more than 20 mm across.

The pathogen is able to survive in scab pustules on fruits remaining on the tree and on other plant organs, providing the inoculum for the next season. Even in resistant cultivars, the fungus can survive on diseased shoots from susceptible rootstocks (Whiteside, 1988). For more information, see Yamada (1961), Whiteside (1975; 1988).

Biotypes of the fungus virulent on certain hosts are known (Whiteside, 1978). 

Dear Andreas,

Have you got any micrographs?

It's impossible to identify just  by photo of  colony on Petri dish...

Hi Andreas,

From the photo I can't help you with an identification, but if you are still struggling with isolation of the citrus scab fungus, this may help...

I use DST-PDA (Whiteside 1986), a semi-selective medium for the isolation of Elsinoe fawcettii from citrus scab pustules. DST-PDA consists of PDA amended with streptomycin sulphate (100ppm), tetracycline hydrochloride (100ppm) and Dodine 40S (400ppm). 

To isolate, surface-sterilise the scabbed area, then use a scalpel to scratch tiny pieces of the scab onto the media.  Leave it for a week or so, then pick out the “brain-like” growths and transfer them to clean PDA plates.  They will grow very slowly, but are very hard and can be lifted out and transferred with forceps.

Ref:  Whiteside (1986) Plant Disease 70 (3): 204-206.

Good luck.

Are you sure it is an Ascomycete? In my opinion it could be a Phytophthora, and you can easily check this hypothesis considering that in Phytophthora hyphae have no septa. And if it is Phytophthora, then you have plenty of papers dealing with production in sporangia in pure culture. In my experience, P. nicotianae often produces sporangia in the isolation plate, close to the excised plant fragment. But of course this would depend on the species...

Hi,

I agree with Rosario, the colony looks like an oomycetes and there are no septa in the microscope picture.

You should try a V8 medium or similar to try to identify better.

Good luck!

I think more magnification needed to be sure in presence or absence of septa.  And better focusing. On tis photo objective is focused mostly  on the cell walls so we might don't see septa.

Although I agree it maybe oomycete. But maybe not.

Dear Dr. Andreas

Please refer to the following address: slide culture technique for actinomycetes

Sincerely Yours

2015.03.09.MON.04:15

Woo-Sik Jo  on  Daegu City, S.KOREA 

https://www.google.co.kr/?gws_rd=ssl#newwindow=1&q=slide+culture+technique+for+actinomycetes