For our next group of diseases that attack plants, I’m
reporting on Protoctistas, or “water molds”. They are in the Eukarya Super
Group, and the Oomycota classification. For references, I am using Five Kingdoms, Essential Plant Pathology, and information from my plant diseases course at Merritt College taught by Dr. Ann Northrup in Fall 2012.
Oomycetes were classified as fungi, but later reclassified as Protoctista, since they are more closely related to brown algae. Oomycetes do resemble fungi in that they have filamentous hyphae used for feeding. However, at a cellular level, they do not have cross walls between nuclei; they are composed of cellulous; and their nuclei are diploid (two sets of chromosomes). In contrast, fungi have cross walls between nuclei; are composed of chitin (similar to crabs); and their nuclei are haploid (one set of chromosomes). Water molds are very primitive, and require moist conditions for reproduction. The asexual spores, called zoospores, have flagella and are motile, enabling them to move through moist conditions to a target such as a root. Take a look: http://youtu.be/jQXO4P8cpQQ
Two types of Oomycetes are found, both of which affect plants in the San Francisco Bay Area:
Oomycetes were classified as fungi, but later reclassified as Protoctista, since they are more closely related to brown algae. Oomycetes do resemble fungi in that they have filamentous hyphae used for feeding. However, at a cellular level, they do not have cross walls between nuclei; they are composed of cellulous; and their nuclei are diploid (two sets of chromosomes). In contrast, fungi have cross walls between nuclei; are composed of chitin (similar to crabs); and their nuclei are haploid (one set of chromosomes). Water molds are very primitive, and require moist conditions for reproduction. The asexual spores, called zoospores, have flagella and are motile, enabling them to move through moist conditions to a target such as a root. Take a look: http://youtu.be/jQXO4P8cpQQ
Two types of Oomycetes are found, both of which affect plants in the San Francisco Bay Area:
- Root affecting – water molds that live in garden soils, ponds, and streams
- Foliage affecting – water molds that live above ground, and are adapted for air dispersal (but still require moist conditions)
A water mold disease caused the Irish potato famine in 1845 –
1852. Closer to home, a water mold is behind Sudden Oak Death in the San
Francisco Bay Area. Other water molds cause downy mildews and white blister
rusts.
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