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3 Potato diseases and their management


Welcome back to this third lecture of this week. In the last class we talked about important wheat diseases and their management and today we are going to talk about important potato diseases and their management. Among the most important diseases of potato Late blight, early blight, Brown rot or wilt and Common scab are the most important potato blight.

Late blight is caused by Phytophthora infestans and we know that this is the causal agent of irish famine which led to millions of death in 1843-45. The disease is very easy to diagnose where you can see that leaves are getting blighted and in the early morning we can see that sporangiospores they appear out of the blighted regions. The potato tubers also get affected and they become brown in color. These are the sporangium of the pathogen Phytophthora infestans that carry juice spores and these juice spores are the effective agents form inciting the disease. The pathogen survives in the form of Oospores in soil and Mycelium in tubers. So control measures include both management of Oospores and Mycelium. So an IPM practice that’s why includes Cultural practices, Application of fungicide, Use of resistant cultivars and Biological control. Cultural practices are the most important one in this case where we should use Weed free potato fields, because many of the weeds they harbor this particular pathogen. Potato should be grown in high ridges to avoid disease severity and mulching between rows is very important because it can avoid the splashing of the juice spores to the foliage. Then we can also avoid contact between foliage and tubers during harvesting and delay in harvesting is recommended. The foliage should be allowed to dry completely before harvesting of the tubers. Some of the fungicides which are very effective and used for management of the pathogen is Ridomil along with Blitox. Ridomil is a combination of metalaxyl and mancozeb and Blitox also proved effective in management of this particular disease. There are no immune cultivars but there are partially resistant varieties that are available and whenever this partial resistance varieties are available one should go for use of those partial resistant varieties. Biological control includes seed treatment and foliar application with bacillus cereus, Pseudomonas fluorescens which proved reduction in the other disease severity.

Next is Early blight of potato. It is caused by Alternaria solani. The disease symptoms characterised by development of Necrotic lesions where concentric rings are visible. The pathogens survive on potato refuse in the field, in soil or on tubers and it also survive on other solanaceous plants. So cultural practices become very important to manage this particular pathogen. So along with Cultural practices we can also use Fungicides, other resistant sources and biological control for management of the Pathogen. Cultural practices that includes crop rotation, removing and burning of infected plant debris, eradicating weed hosts are most important. Maintaining optimum growing conditions include proper fertilizer application, irrigation and management of other pests. This all methods proved important for management of this particular disease. Grow late maturing and long season varieties and also we should avoid irrigation in cool cloudy weather. So with these practice again has proved effective in management of the particular pathogen. Among the fungicides Mancozeb, Iprodione, Chlorothalonil all proved effective when they are spread as foliar spray. Resistant cultivars are not available in many cases so wherever and it is available it should be used for management of the pathogen. Biological control includes foliar spray and soil application of biocontrol agents like Pseudomonas fluorescens and Trichoderma harzianum. These biocontrol agents has also been effective in management or lowering down the disease severity.

The next disease is Brown rot or wilt of potato. It is caused by a bacterium Ralstonia solanacearum. The pathogen or disease could be distinguished in the field through wilt of the crop plants or infected plants where partial wilting is observed at the very beginning and it also affect the tubers where brown rot is very very evident. These are the common symptoms of the particular disease. The pathogen can survive in soil, seed tubers and alternate cultivated or wild host plants. So there are different modes of survival of the pathogen. So it needs and that is why it is difficult to control the pathogen. So Cultural practices again is one of the major region or major practice that needs to be adopted for management of this particular pathogen. So Crop rotation with non-host plants intercropping and control of weed and root-knot nematode populations are some of the very highly recommended practices. Planting at non-infested production sites and removal of weed or crop residue where the inoculums persist is also recommended. Selection of appropriate planting time to avoid heat, Deep plowing of crop residues, Satisfactory soil drainage, Early and late in the season irrigation management and calcium supplementation to soil. All has become an integrate component for management of this particular disease. Application of chemicals include Thymol oil and Actigard although, successful disease management may not be achieved by these chemicals. So it remains a challenge to find a important chemical for management of this particular pathogen. Resistant cultivars are also not available so it is again a challenge to work for development of resistance sources. Biological control has been effective in certain areas where pouring, dipping and bacterization with Bacillus cereus, Bacillus subtilis and Pseudomonas fluorescens has proved important in reduction of the disease.

The next one is Common scab of potato. It is caused by other bacteria that are Streptomyces scabies. This common scab is again grouped into three different categories where the scab symptoms may be pitted it may be raised or it may be on the surface. So based on these symptoms we can distinguish which type of scab is present in the soil. The main mode of survival of the pathogen is soil. So the IPM practices include Cultural, Chemical, Use of resistant cultivars and Biological. Cultural practices among the chief ones use of disease-free potato. This is one of the major our important cultural practice. Rotate root crops by planting in alternate locations to limit the disease. The most prevalent in dry, alkaline soils, so, decreasing the soil H to less than 5.2 by adding elemental sulfur has proved very very effective. So cultural management is the chief management for this particular disease where reduction in pH is one of the important components. Tilling in a cover crop like mustard, canola and alfalfa- prior to planting potatoes is again very very important. It also helps in reducing the soil pH in management of this particular pathogen. Spreading of agricultural gypsum prior to planting will raise the calcium content in soil that will help build strong cell walls in plants. This is another cultural practice that has proven effective. Adequate irrigation during early tuber development and keeping soil damp for two to six weeks is again a very important practice. Application of chemicals includes seed treatment with sulfur fungicides, Brassicol. This chemical has given good control over the pathogen and reduction in the disease. There are certain resistant cultivars available in certain regions, those should be adopted in those regions specific way. Biological control has not been proved very effective so, there is no potential biological control identified so far for management of this particular disease. So we have seen that these are the important potato plants pathogens and the diseases they cause and again we have seen that it is mostly the cultural practices that has helped us to minimize the disease severity of this particular crop and if we combine these cultural practices along with chemicals one we are going to get a good control over the pathogen.

Thank you.



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