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Powdery scab is a disease of potato tubers. It is caused by the cercozoan ''Spongospora subterranea'' f. sp. ''subterranea'' and is widespread in potato growing countries. Symptoms of powdery scab include small lesions in the early stages of the disease, progressing to raised pustules containing a powdery mass. These can eventually rupture within the tuber periderm.〔Maldonado, M. Loreto Hernandez, Richard E. Falloon, Ruth C. Butler, Anthony J. Conner, and Simon R. Bulman. "''Resistance to Spongospora Subterranea Induced in Potato by the Elicitor β-aminobutyric Acid.''" Australasian Plant Pathol. Australasian Plant Pathology 44.4 (2015): 445-53. Web. 21 Oct. 2015.〕 The powdery pustules contain resting spores that release anisokont zoospores (asexual spore with two unequal length flagella) to infect the root hairs of potatoes or tomatoes. Powdery scab is a cosmetic defect on tubers, which can result in the rejection of these potatoes. Potatoes which have been infected can be peeled to remove the infected skin and the remaining inside of the potato can be cooked and eaten.〔Dennis A. Johnson and Thomas F. Cummings. ''Effect of Powdery Scab Root Galls on Yield of Potato.'' (2015).Plant Disease 99:10, 1396-1403〕 ==Disease Cycle== In general, not a lot is known about the life cycle of Asexual Stage: A zoospore infects root tissue and becomes an uninucleate plasmodium. This plasmodium undergoes mitotic nuclear division (creates many nucli within a single cell) and turns into a multinucleate plasmodium. Then, the multinucleate plasmodium forms zoosporangium, which eventually release more zoospores. This process can happen relatively quickly and can act as an important source of secondary inoculum within a field. Sexual Stage: This stage follows a similar pattern to the asexual stage, but with a few exceptions. It is hypothesized that two zoospores fuse together to form a dikaryotic zoospore (with two separate haploid nuclei, n+n) and then infect the roots. Once the infection occurs, the dikaryotic zoospore develops into a binucleate plasmodium (n+n). This plasmodium will also replication its nucleus to create a multinucleate plasmodium (n+n). The second main different between stages occurs here. The pairs of nucli (n+n) will fuse by karyogamy, and the plasmodium will quickly divide into numerous resting spores within a sporosori (spore sack). These resting spores have three-layered walls and are extremely resistant to the environment, allowing them to persist in the soil for over 10 years.〔 As was stated, most of the life cycle is still unclear. However, the presence of zoospores, plasmodia, zoosporangia, and resting spores have been observed in the field and lab. The ploidy levels and karyogamy events are only theorized. No one has actually proven that there are two cycles and that they have different ploidy levels yet. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「powdery scab」の詳細全文を読む スポンサード リンク
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