Dear Elizabeth,

Good day,

There is an important notice here, there is different between colony measurement and growth rate. As an example, if you measure the fungus growth after 7 days of inculcation, this is colony measurement not growth rate. If you measure the growth of fungus daily for 7 days till the fungus cover the plate., this is growth rate. Now, how to calculate the growth rate: as I understand from your question, you are doing Dual culture test.

Then it will be compared to the control plate and transformed into the percentage inhibition of radial growth (PIRG) using the following formula:

PIRG = Rc – Rt x 100%

Rc

Where Rc = radial growth of the pathogen in the control plate

Rt = radial growth of the pathogen toward the antagonist in a dual culture plate.

Wael Alsultan

Thank you for your answer. To clarify, I am not plating 2 cultures in the same plate to look for antagonism/competition. Each plate has a single pure culture. I am screening cultures on agar with different amounts of salt (0ppt, 35ppt, 200ppt). I am simply trying to compare growth rates across treatments.

Is possible to compare the area of growth fungal to the Petri dish area.

area growth fungal : x = area Petri : 100

Elizabeth Kimbrough,

I got it, like this you have to measure growth rate daily till the fungus cover the plate (control) then you have to take the measurement for the last day and dived by total days.

As an example, I want to measure Phytophthora growth rate, usually the fungus covers the plate within 7 days. I take the measurement every day but to calculate, I will take the measurement for day 7 only then dived by 7.

Note: you have to -0.5 (Agar disk).

fyi and old school - some have used "race tubes" http://www.fgsc.net/neurosporaprotocols/How%20to%20measure%20and%20monitor%20line%20final.pdf

These kind of measurement is typical for filamentous organisms that cannot have their cells easily counted like molds. Normally, two measurements of the diameter are taken as the colonies are not always perfectly circular, and from at least 3 individual colonies. Point-inoculations can be easier to interpret and less biased.

Note that this is more of a descriptive measure under specific conditions and not necessarily growth rate. E.g. some species like to grow into the agar, the mycelium density can be different, etc

Thanks Wael Alsultan that makes sense. Also Xabier Vázquez Campos that is a good point that these measurements are more descriptive as they don't account for density or growth habit. My goal is to assay endophytes in different levels of salinity. So the 2%MEA and nutrient agar plates were amended with 0ppt (control), 35ppt, and 200ppt salt and I am comparing growth of endophytes.

I have been informed that another way to compare growth rates (or growth area over time) is to plot the area at each day use a linear regression analysis to compare.

Update: I ended up square root transforming my area measurements and then finding the slope of these three area measurements. I am using this slope in my ANOVA comparisons. This method is from: Estrada, C., Rojas, E., Wcislo, W., and S. A. Van Bael. 2014. Fungal endophyte effects on leaf chemistry alter the in vitro growth rates of leaf-cutting ants’ fungal mutualist, Leucocoprinus gongylophorus. Fungal Ecology 8, 37-45.

could yo tell me the steps you used to measure the area of fungal mycelial growth Elizabeth Kimbrough using image j software please ?

Three columns measured by ruler