The presence of the second mating type (A2) along with the first mating type, allows sexual reproduction and quicker gene recombination, which, leads to more rapid development of resistance to pesticides. Each version is unique in its susceptibility to chemical controls (such as mefenoxam), or if it infects both potatoes and tomatoes, if it is A1(prevalent) or A2(rare) mating type, if sexual reproduction occurs, temperature restraints and quick versus long latent periods. Since then, there have been almost 20 more different genotypes. The outbreaks in the early 1990s were caused by 3 genotypes of Phytophthora infestans (US-6 in 1992 US-7 in 1993-1994 and US-8 in 1998). This disease is capable of wiping out entire potato and tomato commercial fields very quickly under wet conditions and farmers who grow potatoes or tomatoes are at serious risk of losing their entire income from these crops. Since the oomycete that causes late blight produces so many spores, and the spores can travel long distances through the air it is very important that everyone who grows potatoes or tomatoes is able to identify late blight and know how to control it, to avoid being a source of spores that infect potatoes and tomatoes in neighboring gardens and commercial fields. Host Plant: Mainly potatoes ( Solanum spp.) but also tomatoes and other members of Solanaceae family such as petunias, nightshades and tomatillos. For potatoes, these lesions can serve as pathways for other tuber diseases like bacterial soft rot to enter, so late blight symptoms can sometimes be obscured by symptoms of other diseases. On tomato fruit, Phytophthora infestans causes a firm, dark, greasy looking lesion where, under humid conditions, the spore producing structures emerge. Infected potatoes have shallow, brownish or purplish lesions on the surface of the tuber. Symptoms on tomato leaves and stems are similar to those on potato. Lesions turn brown when they dry up and the white spore masses will not be visible. When it is humid, whitish growth (pathogen spores) is produced at the edge of the lesion, particularly on the underside of the leaf. Black lesions appear within 3-7 days of infection of leaves. Late blight lesions can occur on both leaves and stems, and usually occurs after periods of wet weather. infestans infects the foliage of the plants. Unlike the other 60 Phytophthora species that produce soil-borne, root-rotting diseases, Late blight infects foliage, stems, potato tubers and tomato fruits. Sign up for potato blight updates from BlightWatch for daily blight updates in your area.Late Blight, Phytophthora infestans, is an eukaryotic, water mold (Oomycete) which caused the 1845 Irish and 1846 Highland potato famines. In severe cases, the marks can be seen without cutting open tubers. Symptoms on the tubers comprise brown mottled lesions can be seen inside the tubers close to the surface. Heavy rain can wash these spores from the leaves and stems onto the ground where they can infect the tubers. These spores may infect more potato plants directly, or produce swimming spores known as zoospores which infect more plants. The spores which develop from the fungus from these lesions are dispersed in the wind. Lesions can also develop on the stems and appear as pale brown watersoaked marks. This is because late blight is a biotroph and lives on healthy green tissue. The white fungal growth of the fungus is generally seen in the zone between the lesion and healthy plant tissue. Typical disease symptoms comprise pale brown or black water-soaked spots on leaves. These dumps are a concentration of diseased tubers which, if ignored, sprout early in the year and allow the disease to develop. A potato dump is a pile of potato tubers which have been discarded in previous years. Late blight is caused by the fungus Phytophtora infestans and it first became a major problem in Europe in the 18th Century, where it led to extensive destruction of potato crops in Ireland.Īlthough seed and potato volunteers are potential sources of the disease, the key source is potato dumps.
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