In their paper “Mycena citricolor isolates from diverse hosts in Costa Rica: Colony aspect, growth dynamics, reproduction in vitro , and aggressiveness on Coffea arabica." The authors isolate 15 strains of the plant pathogenic Mycena citricolor from multiple host plants and characterizes their morphology, reproduction and aggressiveness grown on coffee leaves using the standard CAI index.
They conclude that M. citricolor on other hosts than coffee serve as a reservoir for inoculum and infection of coffee plants, which is important given the frequent presence as shade trees and common weeds of Avocado trees and Kalanchoë in coffee plantations.

The methods are robust and the indices soundly calculated, and I find that the paper has merit. However, I have some questions and suggestions.

1) M. citricolor is well-known as a pathogen on avocado, and it is so far considered one species (to my knowledge). Is it really true that nobody has considered the shade trees a potential source of M. citricolor infection on coffee plants until now? E.g. Albertin and Nair (2003) (https://link.springer.com/article/10.1023/b:huec.0000043515.84334.76) appear to suggest that avocado shade trees may increase the infection risk with M. citricolor in coffee, and for other fungal diseases like Colletrichium, (https://link.springer.com/article/10.1023/A:1006468103914) or Fusarium, cross-infections are well-described.

2) Which leads to the next question: Why have the authors apparently not tried to do any sort of DNA work on the strains? Do we at all know for sure that there are no species differences between the 15 strains - or at least some phylogenetic signal in the aggressiveness, reproduction or morphologies? I would recommend doing at least a simple ITS phylogeny on the 15 strains and impose the colours, aggressiveness, and reproduction and possible other features as characters to the phylogeny.

3) The discussion section deals almost exclusively with M. citricolor infection.Given the fact that there are other broad-spectrum infectious fungi attacking coffee and other hosts with similar pathology patterns (as in Schroth et al. cited above) - and given that the genus Mycena is known to contain members with a wide ecologic spectrum within one and the same species (see Thoen et al. 2020, https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.16545) - the paper would benefit greatly from just a minimum of a discussion of the findings of the variability of M. citricolor in the light of other comparable infections and the ecological variability within the Mycena genus specifically.