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A REVIEW OF PYTHIUM DISEASES IN ROW CROPS Soilborne Organism is Known for Causing Seedling Diseases and Other Issues By STEVEN KOIKE | TriCal Diagnostics Large, established cauliflower plants can still become infected with Pythium (left), resulting in loss of roots, severe stunting and yield loss (all photos courtesy S. Koike.) It is highly likely that growers, PCAs and other field professionals are familiar with the word “Pythium”. Pythium is the name of a soilborne, fungus-like organism that is notorious for primarily causing seedling diseases. Pythium is notable because many row crops are susceptible to it, the pathogen is very widely distributed and occurs in most cropped ground, and despite the use of IPM tools and strategies, Pythium problems can still show up in row crop production systems. What is Pythium? Pythium is a fungus-like organism. Previously considered to be a true fungus, molecular studies in recent years indicate that Pythium—as well as closely related organisms like Phytophthora and downy mildew—is more closely related to brown algae and diatoms. Formally, therefore, Pythium species are no longer part of the fungal taxonomic group but are classified in the kingdom Chromista, or Stramenopila. The Pythium genus contains over 200 species, most of which are not plant pathogens. There are Pythium species that are pathogens of animals (some of which can infect humans), and many species are saprophytes and only grow on dead and decaying organic material. Pythium species are mostly found in soil environments but are also present in aquatic habitats. Plant pathogenic Pythium species are well equipped to cause problems on row crops. Most of these species form resilient, thick-walled sexual spores (oospores) that can withstand periods of unfavorable dry and warm conditions. These structures enable Pythium to persist in the soil for a long time. When favorable soil conditions are present, mostly in the form of abundant soil water, these Pythium organisms either produce hyphae that grow toward the roots or swimming spores (zoospores) that move through the soil water in search of susceptible plant tissues. Another feature that makes Pythium problematic for growers is the extremely fast growth rate of these organisms. Given suitable soil conditions, Pythium pathogens can rapidly grow from seed-to-seed, seedling-to-seedling The primary symptom of Pythium diseases is the dark discoloration and decay of roots, pictured here on lettuce. and root-to-root. Diverse Pythium Diseases In contrast to many plant pathogens, Pythium causes several different types of problems on crops (Table 1, see page 14). First, Pythium is a seed pathogen. Once placed in the ground, seed can be exposed to Pythium that is residing in the soil. If conditions are favorable for the pathogen, Pythium can invade and colonize the seed, causing it to rot before it can germinate. If the seed germinates, Pythium can cause a decay Continued on Page 14 12 Progressive Crop Consultant March / April 2021
THE BEST WAY TO MANAGE PATHOGENS BEFORE THEY BECOME AN ISSUE. TriClor is chloropicrin based and can be used as a standalone or as a complement to Telone® depending on your orchard redevelopment needs. When targeting soil borne disease and nematodes, TriClor and Telone® can be applied in a single pass. This reduces application costs, promotes early root development, and improves soil health. For more information about TriClor and Telone or to schedule an application contact TriCal, Inc. 669-327-5076 www.TriCal.com Authorized distributor for Telone® *TriClor and Telone are federally Restricted Use Pesticides.
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Page 3 and 4: 4 8 12 18 24 IN THIS ISSUE A New Ge
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Page 9 and 10: Average Yield (lb/ac, 12% protein)
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Page 15 and 16: Pythium pathogens form thick-walled
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Page 24 and 25: New Findings on Limb Dieback of Fig
Page 26 and 27: Figure 3. Left, pycnidia protruding
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Page 41 and 42: References Biofertilizers Market Si
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