A genetic study was carried out on arbuscular mycorrhizal fungi or “AMF” to test the relative genetic diversity in a certain population. This kind of fungi is very important ecologically but has been studied very minimally in genetics because it reproduces by cloning itself. This leads many people to think that it would have relatively low gene variability within the population; however, it has been found that, “they have evolved to contain a surprisingly high within-species genetic variability, and genetically different nuclei can coexist within individual spores” (Koch et al., 2003). The scientists’ hypothesis was that these “traits could potentially lead to within-population genetic variation, causing differences in physiology and symbiotic function in AMF population” (Koch et al., 2003). This kind of fungi is so important because it carries out symbiosis together with most terrestrial plants on earth; about 80% to be specific (Koch et al, 2003). Most mycorrhizal species carry out tasks like providing the plant with nutrients, water, and pathogen protection in return for products made by the plant from photosynthesis. The authors add that they “improve plant growth by increasing phosphate uptake, and species diversity of AMF has been shown to increase plant species diversity and productivity” (Koch et al, 2003). It is surprising that this fungus has not been studied more in depth because of how much genetic diversity occurs not only within the species, but also within the individual spores. The authors note that, “AMF are coenocytic, with many nuclei coexisting in a common cytoplasm, and one species of AMF has recently been shown to be multigenomic, harboring genetically different nuclei” (Koch et al, 2003). They go no to mention that one of the reasons it hasn’t been studied was because of how difficult it can be to obtain a set of individuals from this species that are representative of the species as a whole. “The aim of the experiment was to measure genetic and phenotypic variation among isolates, among plots, and between treatment” (Koch et al., 2003). There were 16 starting isolates, and those isolates were each transferred to 4 new plates, and then each replicated. This made it so that the total amount of plates was 256 (when contamination of plates was taken into account, it brought that number down to 229. Genetic information about the phenotype and genotype and the relationship between the two were taken over the course of 15 weeks and measured every 3. For the phenotypic data, they “measured hyphal growth rate and spore production because they can be related to life history traits and tillage treatments” (Koch et al., 2003). For the genotypic data, “fresh hyphae and spores were taken for extraction of DNA by using the DNeasy plant mini kit” (Koch et al.,2003). Some of their results included that “Genetic differences among isolates were large, and this was true for all primer pairs (Table 1). A mean of 94.2% of the total population variation was explained by differences between the isolates” (Koch et al., 2003). The scientists concluded that “five-fold differences in hyphal length between isolates, as observed among isolates in this population, have previously only been described between AMF species and have been shown to explain differences in plant phosphate uptake. Thus, the variation observed in phenotypes of this AMF population has indeed the potential to alter plant nutrition and growth, indicating that variation in AMF populations may be ecologically important” (Koch et al., 2003). This is a very interesting conclusion being that these fungi have only evolved such diverse taxa groups about 400 million years ago.

Reference:

Koch, A.M, et al. “High Genetic Variability and Low Local Diversity in a Population of
Arbuscular Mycorrhizal Fungi.” Proceedings of the National Academy of Sciences – PNAS, vol.
101, no. 8, 2369–2374, (2004). https://wwwjstororg.proxy.lib.odu.edu/stable/3371298?sid=
primo&seq=1