Pythium irregulare

Pythium irregulare is an oomycete that causes pre- and post-emergence damping off, as well as root rot. Alternatively, post-emergence damping off occurs when the oomycete infects just after the seed has germinated. In order to identify Pythium irregulare it is necessary to isolate the organism and observe it microscopically. First, it is important to identify that the microbe is an oomycete by looking for characteristics that are specific to oomycetes, such as coenocytic hyphae, zoospores, and oospores. In contrast, most other oomycetes do not have a vesicle and the zoospores form in the sporangia. There are also many genomic tests that can be done to determine species based on specific DNA markers. It is also important to note that many diagnosticians do not identify to the species level because it can be difficult to find all necessary microscopic structures and many management techniques can be applied to all Pythium species. ==Disease cycle==

Pythium irregulare, like most oomycetes, has a life cycle with sexual and asexual stages. During the winter, oospores, which are sexual resting spores, survive in the soil. Oospore germination occurs when the oospore senses chemicals released by seeds or roots. Once germinated, oospores can produce either a germ tube, which directly infects the plant, or a sporangium, which releases zoospores that infect the plant. Sporangium that produce zoospores make up the asexual phase of the life cycle. The zoospores can move through soil when water is present, which is why water is important for disease to occur. Once zoospores reach the root or seed, they encyst, germinate, and infect via a germ tube. Once infection has been established, the pathogen grows hyphae both in and outside the plant and releases enzymes to breakdown plant tissue. The breakdown of tissue provides nutrients for the pathogen, also known as necrotrophy. Once the plant dies, more sporangium can form, release zoospores, and repeat the infection cycle. Alternatively, the hyphae within the dead plant material may also continue to grow and develop “male” and “female” haploid mating structures, known as antheridium and oogonium, respectively. The antheridium then transfers its genetic material to the oogonium (fertilization), resulting in the diploid oospore, which overwinters and starts the infection over again in the spring. ==Management==

Pythium irregulare requires very specific environmental conditions to produce disease, so control of environment is the first step. Because the zoospores require water to be able to move around, preventing standing water will decrease the chance of disease occurrence. Additionally, in greenhouses scenarios it is important to sanitize soil, work benches, and tools with heat or chemicals as well. ==See also==