Phytophthora sojae

Phytophthora sojae is an oomycete and a soil-borne plant pathogen that causes stem and root rot of soybean. This is a prevalent disease in most soybean growing regions, and a major cause of crop loss. In wet conditions the pathogen produces zoospores that move in water and are attracted to soybean roots. Zoospores can attach to roots, germinate, and infect the plant tissues. Diseased roots develop lesions that may spread up the stem and eventually kill the entire plant. Phytophthora sojae also produces oospores that can remain dormant in the soil over the winter, or longer, and germinate when conditions are favourable. Oospores may also be spread by animals or machinery. Phytophthora sojae is a diploid organism with a genome size of 95 Mbp (Millions of base pairs). The natural chemical farinomalein (a metabolite from entomopathogenic fungus Paecilomyces farinosus) has shown potent and selective inhibition (0.15-5 μg/disk) against eight isolates of plant pathogenic Phytophthora sojae. These results suggest that farinomalein might be useful as a candidate pesticide for the treatment of Phytophthora stem rot in soybean. Phytophthora sojae is so similar to Phytophthora megasperma that they’re often mistaken for each other. In the early years of research, Phytophthora sojae and Phytophthora medicaginis were respectively known as Phytophthora megasperma f. sp. glycines and Phytophthora megasperma f. sp. medicaginis. Recent discoveries about their molecular structure, however, proved that they were indeed unambiguous species. Phytophthora sojae infects soybean plants (Glycine max) and many members of the genus Lupinus. They have the ability to infect soybeans at any point during its development process, including during seed development. They cause seed decay and pre- and postemergence damping off when the soil is flooded after planting. Seedling roots may appear to have light brown soft rot as soon as the seedlings begin to sprout from the soil. It also causes root and stem rot and the severity of the infection depends on how susceptible or tolerant the plant is to pathogens. In a highly-tolerant soybean plant, the root rot will simply cause the plant to be stunted and slightly chlorotic instead of killing the plant. In contrast, infection of a low-tolerant soybean plant will most likely lead to the death of the plant. Infection initiates in the roots and then progresses several nodes up the stem, turning the root and the stem brown and the leaves yellow. As the pathogen progresses, the entire plant transforms into an orange-brown color. The wilted leaves bend towards the plant and remain attached as it succumbs to death. Foliar blight is also a symptom of Phytophthora sojae, especially when the plant has recently experienced heavy rain. The soybean plant has an age-related resistance in which the older leaves are not susceptible to foliar blight.