Corn Journal
  • Corn Journal
  • Author
  • Stalk Rot Booklet
  • Seed Testing
  • Corn Genetics
  • Pathology
  • Sponsors
  • Contact
"You can see a lot by just looking"-Yogi Berra

Diversity in fungal pathogens

12/10/2015

 
Those of us that attempt to maintain cultures of corn pathogens by growing them in artificial culture quickly become aware that isolates of the same species show considerable variability in growth rate, color, spore production and ability to infect the corn plant.  After several generations on the artificial culture media, some appear to lose the ability to infect plants.
 
Genetic variability in all living things comes from sexual recombination in which uniting of chromosomes from two individuals present new possibilities and form mutations.  A human geneticist once told me that humans have an average of 100 mutations, most of which are inconsequential but are different from their parents.
 
Fungi have sex, in which two ‘sexes’ combine and produce new genotypes that are some random combination of the two original parents.  The sexual stage for many corn pathogens is not easily found and therefore is assumed to not be common.  No problem for many fungi, however, because often their vegetative stage, the filaments (hyphae) of a fungus, often fuse, allowing their nuclei to join in a process similar to sex.  It is called parasexuality (outside of true sex) and can give the same benefit of producing new combinations of genetics.  The third source of variability comes from mutations. 
 
Variability is the source of survival and success of most species of plants, animals and fungi. Most pathogenic leaf fungi that produce enzymes to break down complex carbohydrates in plants basically have to kill the leaf tissue first to obtain nutrition for survival and reproduction.  The northern leaf blight fungus enzymatically drills into the leaf, grows towards the vascular tissue, plugs it up so it wilts at least in a area of a couple inches, killing that tissue. Now the fungus feeds on the dead tissue and produces more spores when moist, allowing it to spread and infect elsewhere on that and other corn plants.
 
If the plant’s initial resistance system cannot prevent infection of the veins, corn breeders have selected for resistance inherited by a single gene (Ht1) that inhibits the fungus from plugging the vein. Consequently the fungus is unable to survive and reproduce.  After being widely used for about 10 years, genetic variants in the fungus increased sufficiently to negate to use of that type of resistance.  The battle continues between genetic diversity in the fungus versus genetic diversity in the corn.


Comments are closed.

    About Corn Journal

    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.

    Archives

    December 2021
    November 2021
    October 2021
    September 2021
    August 2021
    July 2021
    June 2021
    May 2021
    April 2021
    March 2021
    February 2021
    January 2021
    December 2020
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    May 2020
    April 2020
    March 2020
    February 2020
    January 2020
    December 2019
    November 2019
    October 2019
    September 2019
    August 2019
    July 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    March 2017
    February 2017
    January 2017
    December 2016
    November 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015

    Categories

    All

    RSS Feed

© COPYRIGHT 2023. ALL RIGHTS RESERVED
  • Corn Journal
  • Author
  • Stalk Rot Booklet
  • Seed Testing
  • Corn Genetics
  • Pathology
  • Sponsors
  • Contact