Variability in pathogens
Plants like corn are not the only organisms in the corn field that gain genetic variability through mutations and recombination from fusion of chromosomes from haploid nuclei. Although the pathogenic growth of most fungi is with the haploid form, eventually chromosomes from two mating types fuse, meiosis occurs, and new combinations of the two parent’s genetics are formed. This is usually realized when a single gene form of resistance in corn is no longer effective.
The range of sexual of reproduction methodology among fungi is wide. Cellular features of fungi are not completely different than plants and animals. Their DNA is in a distinct nucleus, they have mitochondria for transformation of energy to forms used for growth and function and ribosomes for protein production. While most fungal growth is separated into distinct cells, there are some such as in the Pythium genus in which the hyphae do not have distinct cells and have multiple haploid nuclei. Most of the life in most fungi, the nucleus has only one set of chromosomes, instead of the two sets found in most plants and animals. The process of sex has slightly different definition with fungi. Joining of two cells, and then of two nuclei followed by meiosis in which new combinations of chromosomes are distributed into haploid nuclei can occur without sexual distinctions between the two individuals, or, in some species, only with distinct mating types. It can result in creation of distinct (to us) morphological structures or within the normal appearing hyphae. The requirement for having two, or more, mating types certainly causes difficulty for us humans to completely understand the sex life of many fungi but genetic variability for characters that we follow in corn pathogens seems strong. Because of the ability to asexually reproduce quickly the unique genotype that has found a susceptible host, a new variant has been witnessed often in agriculture, whether produced by mutation or sexual recombination.
A lot of complex biological things are happening in the corn field beyond the biology of the corn plants.
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The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.