The simple answer is yes, in many cases, but it is a little more complicated than yes or no. Infectious diseases are instigated through a perpetrator we term the pathogen. There are a good many of these species which is where the complication lies. Each will have a mode or modes of entering a plant to cause trouble (create disease). The big players are fungi and bacteria, and to some degree viruses. There are others but let’s keep it simple. For instance, bacteria don’t do any direct penetration. That is they don’t just barrel into tissue but instead find a way through a natural opening or through a wound. A natural opening could be flower parts, lenticels, or stomata. Viruses can enter through wounds, and in particular when hitchhiking on/in a vector (like a plant biting insect). Fungi tend to be more of a bully and can directly attack tissue without the need for an easy entry point. They may invade only the cuticle (i.e. the waxy leaf coating), squeeze between cells, or drill right into cells. Many pathogens have the ability to secrete toxins and enzymes to break down cell walls or cells completely.
This all seems grim, so let’s look at a word you included about plants: healthy. In most cases a healthy plant will cope with such attack. Some species (or varieties) will be more resistant than others. Environmental conditions always have bearing. I won’t get into management here but you can be rest assured that keeping your crop as healthy as possible will go a long way in suppressing disease.
