Some fungal Diseases
Posted: Sat Aug 11, 2018 6:32 am
I have been trying to respond to numerous questions about cactus stem lesions and keep repeating myself. So I thought, it might be a good idea to give a few examples of fungal pathogens - some which do attack cacti and others that infect other plants - on this thread. I hope, that this will help the concerned forum user with figuring out, if a fungus is to blame for the condition of their plant. Keep in mind, that this is only a very limited presentation of fungal pathogens you might encounter.
The major classes of fungi you as a grower will experience are the ascomycetes,(which as immature fungi are split into hyphomycete and coelomycete fungi) and the basidiomycetes, of which the most important group is known as rust fungi. A true rust is a rather rare occurrence among fungi. I am only aware of one time, where a rust pathogen was found on the fruit of a Hylocereus plant. Rust colored lesions on cacti are thus not caused be a rust fungus. I am attaching two images of the appearance of rust pustules, but they were not found on cacti.
First, some of the symptoms/signs of Hyphomycete fungi. The images are labeled with the pathogen and its host plant.
One of the features of a hyphomycete is a fuzzy growth which consists of fungal mycelium from which arise structures called conidiophores, which bear spores that are not enclosed.
The next group is called "Coelomycetes". There the spores are enclosed in a structure made up of fungal cells. Depending on the appearance of these structures (cushion-like, with slit-like opening (acervulus), or spherical structures fully enclosing the spores and often with an ostiolar opening (pycnidium). To indicate the small size of these structures, there is either a ruler in mm or a bar visible on the images.
Just to show you what a true rust may look like, I did photograph two kinds of plant leaves. As you can see, the color is not necessarily rusty brown, but can range from off-white to yellow, reddish brown, all the way to black. The rust found on the Hylocereus was identified as an Aecidium, which tells me, that the spores in the rust lesions were most likely yellow, similar to those shown for the pathogen of Fouquieria splendens (last image).
Harald
The major classes of fungi you as a grower will experience are the ascomycetes,(which as immature fungi are split into hyphomycete and coelomycete fungi) and the basidiomycetes, of which the most important group is known as rust fungi. A true rust is a rather rare occurrence among fungi. I am only aware of one time, where a rust pathogen was found on the fruit of a Hylocereus plant. Rust colored lesions on cacti are thus not caused be a rust fungus. I am attaching two images of the appearance of rust pustules, but they were not found on cacti.
First, some of the symptoms/signs of Hyphomycete fungi. The images are labeled with the pathogen and its host plant.
One of the features of a hyphomycete is a fuzzy growth which consists of fungal mycelium from which arise structures called conidiophores, which bear spores that are not enclosed.
The next group is called "Coelomycetes". There the spores are enclosed in a structure made up of fungal cells. Depending on the appearance of these structures (cushion-like, with slit-like opening (acervulus), or spherical structures fully enclosing the spores and often with an ostiolar opening (pycnidium). To indicate the small size of these structures, there is either a ruler in mm or a bar visible on the images.
Just to show you what a true rust may look like, I did photograph two kinds of plant leaves. As you can see, the color is not necessarily rusty brown, but can range from off-white to yellow, reddish brown, all the way to black. The rust found on the Hylocereus was identified as an Aecidium, which tells me, that the spores in the rust lesions were most likely yellow, similar to those shown for the pathogen of Fouquieria splendens (last image).
Harald