Economically Significant Fungal Diseases of Potato and their Management Essay
Abstract The cultivation of murphy is frequently affected due to assail of assorted diseases caused by Fungis, bacteriums, viruses and roundworms etc P. infestans over-summers as hibernating mycelium in septic tubers in the cold storage. The presence of late blight infection in seemingly healthy tubers collected from morbid field provides new dimension to the epidemiology of this disease. Antifungals like azoxystrobin, fenamidone, famoxadone, iprovalicarb and mefenoxam and their combinations with contact antifungals like mancozeb have shown promising efficaciousness against murphy late blight. Early blight ( Alternaria solani ) , can last as conidiospore or mycelium in dried septic foliage spots in the dirt. Spraies of mancozeb, zineb, ziram, propineb and others like chlorothalonil, captan, Cu oxychloride, Bordeaux mixture, captan etc. have been reported to be effectual against this disease. In Black Scurf ( Rhizoctonia solani ) the fungus perpetuates in the signifier of Sclerotium on the seed tubers or in the dirt. It can last in the dirt for many old ages and has broad host scope. Successful direction of fungous murphy diseases can be achieved chiefly by incorporate desease direction, utilizing immune murphy assortments, following the proper cultural patterns and by chemical intervention of the harvest and, sometimes, of the seed. This reappraisal deals with the of import fungous disease jobs in murphy, their etiology, epidemiology and different schemes for effectual direction.
Cardinal words: Potato, fungus, antifungals, tubers
Potato ( Solanum tuberosum L. ) is an of import vegetable harvest and is cultivated over an country of about one million hectares in India, with the entire production of more than 1.5 million dozenss. Important potato turning provinces are Uttar Pradesh, West Bengal, Bihar, Assam, Himachal Pradesh, Madhya Pradesh, Punjab and Karnataka. One to three harvests per twelvemonth are taken under varied agroclimatic conditions. In India, approximately 80 per cent of murphy harvest is cultivated under semitropical and 20 per cent under temperate to sub-temperate clime. The cultivation of this harvest is frequently affected due to assail of assorted diseases caused by Fungis, bacteriums, viruses and roundworms etc ( Khurana et al. , 1998 ) .
This disease is caused by Phytophthora infestans. Late blight is the most destructive disease of murphy throughout the universe and was recorded in the beginning of 19th century in the Andes Mountains of South America. The disease is believed to hold been introduced into Europe from South America in early 1840s from where it spread to other states and caused a dearth in Ireland ( known as Irish dearth ) during 1845-46 ensuing into deceases of 1000000s of Irish people and an equal figure migrating to other parts of the universe, peculiarly North America. The systemic development of Plant Pathology as a subject started after this dearth. Late blight has the enormous potency to do up to 70 % decrease in the output in a susceptible cultivar. The losingss runing from 20-25 % in Punjab, 40-50 % in Haryana, 15-20 % in Uttar Pradesh and 5-10 % in Bihar and West Bengal have been reported ( CPRI, 1987 ) . In India, one-year losingss due to late blight have been reported to run between 10-75 % ( Dutt 1979 ) . The extent of harm depends mostly at which stage the harvest is attacked and it is normally heavy when infection occurs on the immature harvest phase before tuberization that sometimes can ensue into complete output losingss in epidemic old ages and the losingss vary between 15 to 100 per cent depending on cultivar, harvest phase and the antifungals sprayed ( Thind and Mohan 1998 ) .
The symptoms of late blight appear on foliages, root and tubers. Initially little, water-soaked lesions develop near the tips and borders of the foliages which quickly grow into big, brown to purplish black, necrotic lesions under favourable conditions conditions. During forenoon hours, milky downy growing of the pathogen consisting of sporangiophores and spore case can be seen on the borders of the lesions largely on the bottom of the foliages. Light brown to dark brown lesions appear on root and leafstalks which may stretch subsequently and deaden the affected parts. The affected stems become weak and prostration, doing decease of the works parts above the lesions. Sometime the stamp turning stem tips and nearby immature leaf are attacked in the immature harvest and the workss halt their growing and wither shortly. Since the disease is polycyclic in nature, the full harvest in a field may be killed in one or two hebdomads and the field gives spoilt visual aspect. The tubers may acquire infected by rain-washed spore case from the morbid leaf. The septic tubers show irregular, little to big, somewhat down countries of brown to purplish tegument which extend deep into the internal tissue of the tubers. The septic tuber tissue which is house and dry in the beginning is frequently invaded by secondary pathogens, chiefly bacteriums, in the field or ill ventilated storage topographic points ensuing into soft putrefaction of tubers.
Late blight is caused by Phytophthora infestans ( Mont. ) de Bary which belongs to division Mastigomycotina, category Oomycetes, order Peronosporales and household Pythiaceae. The mycelium is coenocytic, hyaline, branched holding simple to club molded haustoria. Sporangiophores originate from internal mycelium and emerge through pore on the foliages and tubers. These are slender, hyaline, sympodially branched, indeterminate, septate holding side subdivisions with conceited bases. Sporangia are formed on the tip of sporangiophores and are hyaloid, thin walled, lemon shaped, papillate holding up to 30 karyons, mensurating 21-28X12-24 Aµm. The spore case turns to the side on adulthood and sporangiophore growing continues with characteristic swollen nodes. This fungus is heterothallic and requires two coupling types A1 and A2 for sexual reproduction. In India although A1 copulating type is of common happening, prevalence of A2 type has been recorded in Shimla hills after 1984 ( Singh et al. , 1993 ) . Antheridia and oogonia are produced after A1 and A2 copulating types come in close contact. Antheridia are amphygynous while oogonia are spherical. Oospores are 24-46 Aµm in diameter, midst walled and develop after fertilisation. Oospore formation varies depending upon peculiar A1 and A2 combinations and besides on septic murphy genotypes ( Cohen et al. , 1997 ) but self production of oospores in A1 population is besides reported. There has been shift from simple 0 and 4 races to complex 4-8 cistron races of P. infestans after 1965 in India. ( Arora 1990 ) reported that development and fittingness of complex races is dependent on cultivars planted and favourable conditions conditions.
Assorted steps which aim to cut down the primary inoculant and spread of the disease can assist in effectual direction of murphy late blight. These include transgenic attack, healthful steps, usage of healthy seed, cultural patterns, host opposition and usage of antifungals.
Potato ( Solanum tuberosum L. ) tardily blight, caused by Phytophthora infestans ( Mont. ) de Bary, is one of the most detrimental diseases in any harvest. Deployment of immune assortments is the most effectual manner to command this disease. However, engendering for late blight opposition has been a challenge because the race-specific opposition cistrons introgressed from wild murphy S. demissum Lindl. have been short lived and engendering for “ horizontal ” or lasting opposition has achieved merely moderate successes. The high-ranking late blight opposition in a wild murphy relation, S. bulbocastanum Dunal subsp. bulbocastanum, is chiefly controlled by a individual opposition cistron RB. Transgenic murphy lines incorporating the RB cistron have showed strong tardily blight opposition, comparable to the backcrossed offsprings derived from the bodily loanblends between murphy and S. bulbocastanum. RB cistron into murphy utilizing traditional genteelness methods, an option to deploying the RB cistron through familial transmutation ( Lara et al. , 2006 )
Infected seed tubers, diseased halm left in the field and reject hemorrhoids, which may function as primary beginning of inoculant, should be destroyed by firing or proper burying them deep in the dirt. Application of certain chemicals such as Na chlorate or chlorthiamid granules is besides utile for this intent. Volunteer or self seeded workss and weeds which may harbor late blight infection can be destroyed by application of some suited weedkillers.
Use of healthy seed
Since infected seed is the major beginning of primary inoculant for late blight, seemingly septic tubers should be sorted out before and after storage and the reject hemorrhoids destroyed by firing or burying deep in dirt. Potato tubers to be used for seed should be taken from a disease free harvest. The usage of healthy tubers for seed will guarantee healthy and disease free harvest.
Some changes in the cultural patterns may turn out beneficial in cut downing late blight incidence in the field. Proper hilling and earthing up of murphy tubers should be practiced to minimise opportunities of tuber infection. Wider row to row and works to works spacing ensures better incursion of air and sunlight to lower parts of the workss therefore making unfavourable conditions for development of the disease. Cultivation of the blight resistant and susceptible assortments together reduces the rate of spread of the disease epiphytotic ( Bhattacharyya and Singh 1990 ) . Cultivation of murphy with some other harvest like wheat besides slows down spread of the disease. In the north-western fields of India like Punjab and Haryana, early planted harvest ( in September ) by and large harvested pre-maturely after about two months remains free from late blight. Main season fall harvest planted in early October is harvested in January-February and is frequently attacked by late blight. In Himalayan hills the disease by and large appears in late June and in fields in mid-November to mid December. So planting of early maturating assortments in early April in hills and in late September or early October in fields following by dehaulming of workss at 1 % disease strength should turn out beneficial.
Use of immune assortments is regarded as the best agencies of late blight direction. Initially the opposition was derived from Solanum demissum which shortly broke down due to development of specialised races of the pathogen. Early surveies had shown that the opposition in murphy workss to P. infestans was inherited as dominant character and the R cistrons control allergic response in a race specific mode. Later it was realized that the pathogen exists as race composites and has the ability to bring forth new races quickly. In India before simple races like race 0 and 4 were prevailing, but now with the debut of new assortments multigene races are happening both in hills and fields and 11 multigene races are reported utilizing murphy differential lines with 0 to 11 R opposition cistrons. Now the attempts are directed to bring forth assortments holding polygenic field opposition. Such opposition beginnings are available in species like S. demissum and S. stoloniferum and such opposition is governed by a figure of minor and independent cistrons. Field opposition is associated with characters like longer incubation period, reduced pathogen growing within the host tissue, reduced monogenesis and late works adulthood. ( Louwes et al. , 1992 ) have besides reported S. circaefolium bomber sp. circafolium to be a good opposition beginning every bit good against late blight.
The Central Potato Research Institute, Shimla has developed and released several blight immune assortments of murphy for cultivation in different parts of the state including hilly and kick countries which include Kufri Jyoti, Kufri Sherpa, Kufri Badshah, Kufri Jeevan, Kufri Jawahar, Kufri Muthun etc. However, an of import country is still under Kufri Chandramukhi which is extremely susceptible to late blight. In Kufri Jyoti and Kufri Badshah varieties the blight appears about 20 yearss subsequently than Kufri Chandramukhi and these assortments show less foliar infection ( 15-35 % ) till terminal of the season while Kufri Chandramukhi is wholly killed within a month ( Anonymous, 1991 ) . ( Bjor and Mulelid, 1991 ) reported cultivar Pimpernal without R cistrons to possess opposition to tuber blight. Das et Al. ( 1996 ) have developed blight immune ringers of commercial assortments utilizing gamma radiation.
Fungicides form an of import input for pull offing late blight of murphy because host opposition in commercial assortments is frequently broken down by multigene races of the P. infestans. Several antifungals have been reported to supply good control of late blight in India and other states. Bordeaux mixture and Burgundy mixture which were used earlier were subsequently replaced by Cu oxychloride, captafol, mancozeb, zineb, propineb and other dithiocarbamates, chlorothalonil etc. ( Dutt, et al. , 1982 ; Malathi and Jeyarajan, 1995 ) . These have to be used as contraceptive applications before infection is established. Mancozeb is now an recognized antifungal for late blight control in India and is reported effectual by several workers. A preventative antifungal application agenda appears more effectual ( Thind, et al. , 1989 ) for contact antifungals and spraying with these antifungals before usual day of the months of disease visual aspect when the harvest is about six hebdomads old in north Indian conditions gives better control.
In the past two decennaries, several systemic antifungals with significantly better efficaciousness have been found assuring for late blight control. Metalaxyl, an acylalanine antifungal, has proved most effectual against this disease ( Schwinn and Staub, 1987 ) . Oxadixyl, banalaxyl, ofurace and dimethomorph are other specific antifungals holding high efficaciousness against this disease ( Thind and Mohan 1997 ; Mohan and Thind 1999 ) . Dunking of sprouted tubers in 0.1 per cent metalaxyl for 30 proceedingss suppresses the disease ( Singh and Bhattacharyya, 1990 ) . However, inordinate and irrational usage of these phenylamide antifungals may take to the development of opposition in the pathogen. Metalaxyl immune populations of P. infestans have been reported in many states ( Dowley and O’Sullivan, 1991 ; Deahl et al. , 1993 ) including India ( Arora, 1991 ; Thind, et al. , 2001. ) . To avoid the development of fungicide opposition, mixture preparations of systemic and contact antifungals are by and large recommended. Ridomil MZ ( metalaxyl + mancozeb ) is one such mixture being normally used against late blight ( Alam et al. , 1991 ; Thind and Mohan, 1997 ) . Other mixtures which are in usage for late blight control are ofurace + mancozeb, cymoxanil+ mancozeb, dimethomorph + chlorothalonil, dimethomorph + mancozeb, oxadixyl + mancozeb, oxadixyl + Cu oxychloride, banalaxyl + mancozeb and few others. Recently, freshly developed antifungals like azoxystrobin, fenamidone, famoxadone, iprovalicarb and mefenoxam ( a new enantiomorph of metalaxyl ) and their combinations with contact antifungals like mancozeb have shown promising efficaciousness against murphy late blight ( Thind et al. , 2004a, B ) .
Forecasting based fungicide applications cut down the cost of disease direction by cut downing figure of applications. A preventative spray agenda of contact antifungals like dithiocarbamates is recommended as shortly upwind conditions like temperature and comparative humidness become favorable. Phenylamide fungicide mixtures need to be sprayed merely when heavy disease hazard state of affairs prevails in the event of intermittent rains and cloudy conditions.
The disease chiefly affects leaf and may uncommonly happen on root and tubers. The symptoms foremost occur on lower foliages as dark brown, ellipse or angular musca volitanss scattered on the leaf surface. The musca volitanss are normally surrounded by a greensick zone which may widen much beyond the lesion due to the presence of toxin ‘alternaric acid ‘ produced by the pathogen. Under suited climatic conditions, they enlarge quickly to 3-4 millimeter diameter, go irregular and may germinate full foliage lamina. Concentric rings may look on the lesions giving them aim board visual aspect. Large figure of musca volitanss on a individual foliage consequences in aging and dropping. During frequent rains, big dark brown lesions are produced resembling those of late blight but without evident milky growing of the fungus. Infection on leafstalks and stems shows little or elongated dark brown necrotic lesions and the tissue may interrupt at the infection point. Lesions on tubers are dark sunken, unit of ammunition to irregular in form and surrounded by raised boundary lines with implicit in flesh giving dry and coriaceous visual aspect. Tuber infection is uncommon in fields.
Early blight is caused by the demataceous Alternaria solani ( Ellis & A ; Mart. ) Jones & A ; Grout belonging to sub-division Deuteromycotina, category Hyphomycetes, sub category Sporomycetidae, order Moniliales and household Dematiaceae. It has pale to olivaceous brown septate mycelium. Conidiophores may originate singly or in little fascicules through pore from the mycelium nowadays in the dead Centres of musca volitanss and are up to 110 ten 6-10 Aµm in size. Conidia are normally lone, obclavate, oblong to elliptoid, tapering to a beak about of the same length or even longer as that of the conidial organic structure. Conidia are muriform, picket to olivaceous brown, smooth, 150-300 ten 15-19 Aµm holding 9-11 transverse and 0-few longitudinal septa. No perfect phase of the fungus is known.
Different methods such as healthful steps, cultural patterns, usage of antifungals and host opposition can be used for pull offing early blight.
Field sanitation and cultural patterns
Diseased halms and harvest dust should be removed from the infected Fieldss after crop and destroyed in order to cut down the primary beginning of inoculant for the following harvest. Balanced fertilisation of the harvest ensures healthy and vigorous works growing which contracts less disease. Poorly fertilized workss are apt to be attacked more by the disease. Tubers should be allowed to maturate in the field before crop and hurt to the tubers should be avoided. Use of disease free tubers for planting, remotion of morbid harvest dust from the Fieldss and 3-4 old ages harvest rotary motion aid in cut downing the primary inoculant.
Resistance to early blight has been identified in Solanum species such as S. phureja and S. chacoense that has been exploited for genteelness of immune cultivars ( Stewart, et al. , 1994 ) . Among assorted cultivars being grown in the fields of India, Kufri Sindhuri shows good opposition against the onslaught of early blight.
Use of antifungals
Most of the antifungals recommended against late blight can efficaciously command early blight of murphy as good. Spraies of dithiocarbamate antifungals such as mancozeb, zineb, ziram, propineb and others like chlorothalonil, captan, Cu oxychloride, Bordeaux mixture, captan etc. have been reported to be effectual against this disease ( Thind and Jhooty 1982 ; Steinberg, et al. , 1996 ) . These antifungals give better control when used as preventative applications at the induction of the first symptoms. Tebuconazole, a triazole antifungal, has besides demonstrated good efficaciousness against early blight. Recently developed strobilurin antifungal azoxystrobin has been reported to supply good efficaciousness of both late blight and early blight of murphy and tomato.
Integrated disease direction
More than one direction patterns can be integrated for accomplishing better degree of disease control. Genotypes holding moderate degree of opposition can give desired control of early blight with fewer antifungal applications compared to susceptible cultivars and consequence into economical output returns ( Shteinberg et al. , 1993 ) . The strength of fungicide applications can be adjusted in such a manner that reasonably immune cultivars can be sprayed at longer intervals while in instance of assortments with age related opposition it would be better to increase the frequence of sprays towards the terminal of the season. Some counter beings can besides be used in the IDM programme. Two strains of Trichoderma species have been reported counter to Alternaria solani ( Martinez and Solano, 1995 ) . A strain 679-2 of Pseudomonas species can besides suppress this pathogen through production of a H2O soluble metabolite and there was no inauspicious consequence of Cu antifungals. This adversary can be easy integrated with other disease control measures ( Casida and Lukezic 1992 ) .
Root canker and blight stage and the scurf stage are the two distinguishable stages of the disease. There may be pre-emergence decease of the workss or the sprouting may be delayed when the pathogen onslaughts turning tips of the sprouts. If the infection is less, a big figure of sprouts may originate and the affected hills show yellowing of workss which by and large remain scrawny. In root canker stage, the turning tips of sprouts show browning. Sunken, handbill or elongated brown necrotic musca volitanss may besides be observed on the mature sprouts at the point of infection near female parent tuber. Badly affected sprouts are killed. Subsequently, when shoots emerge, similar necrotic lesions are observed on the root which may widen downwards and may wholly deaden the root. In instance of terrible ulcerated lesions, the tops show acrobatics, rusetting and purpling of foliages. Green aerial tubers may besides look on the subdivisions and petiole axes and the disease stage is called ‘aerial tubers ‘ .
The most outstanding symptom of black scurf is the presence of black crust on tubers due to the formation of Sclerotium of the fungus. The pathogen produces a big figure of sclerotia superficially on the surface of turning tubers. These Sclerotium may be difficult or squashy organizing a black crust of scurf on the tuber surface. These are usually seated on the tegument and do non do any harm to the tuber interior. Black scurf stage is more common than root canker in India. Dry putrefaction symptoms on tubers are besides seen if the pathogen enters through lesions.
Black scurf is caused by the fungus Rhizoctonia solani Kuhn. ( teleomorph Thanatephorus cucumeris ( Frank ) Donk ) . The mycelium is septal, chocolate-brown, dolipore type, 5-14 Aµm broad. The sidelong subdivisions of the mycelium are constricted at ramifying point and possess septum near the junction. The Sclerotium are little, brown to black and unlike other fungous Sclerotiums are undifferentiated into rind and myelin. Outer cells of Sclerotium are thick walled and dark in coloring material. Basidial phase of the fungus has besides been reported in some parts of the state on dead murphy halm, which appears as flakey pellicle on the substrate under cool and humid environment.The basidiospores appear onsterigmata originating from barrel shaped to clavate basisdia and are normally four in figure. These are spheroidal to oblong and flattened on one side Different strains of the pathogen have been identified based on cultural and sclerotial characters. Based on anastmosis grouping ( AG ) , R. solani infecting murphy has been assigned to A4 type.
The black scurf pathogen survives in dirt every bit good as through seed murphy tubers and has a broad host scope. Successful direction of the disease can be achieved by following proper cultural patterns and chemical intervention of the seed.
In general, planting of healthy and disease free tubers is helpful in cut downing the incidence of the disease. Change in the day of the month of planting is another of import standard. If the clip between seting of tubers and sprout outgrowth is reduced, less infection is observed. In the hills, the harvests should be sown in spring to cut down root canker and mortification of sprouts. On the other manus, in the fields, early plantation of chief harvest followed by early crop is recommended. Two to four old ages rotary motion with cereals, Brassica and leguminous plants is helpful for the direction of this disease. Green mucking with Dhaincha ( Sesbania cannabina ) reduced the black scurf on tubers by 40 per cent while corn and sunhemp ( Crotolaria juncea L. ) were reported effectual by ( Bhattacharrya, et al. , 1977 ) . The addition in organic affair content of the dirt helps in cut downing the population of the fungus through enhanced activity of the adversaries such as Trichoderma spp. Likewise, dirt amendment with nim tree or margosa bar or with saw dust has been found to cut down black scurf ( Sikka et al. , 1971 ; Singh et al. , 1972 ) . Other patterns like shallow planting and good drainage besides aid in disease decrease.
Seed tuber intervention:
Treatment of seed tubers with chemicals before seting or before hive awaying consequences in effectual disease control. Dipping of seed tubers in 0.25 – 0.5 per cent solution of organo-mercurials such as Emisan-6, Agallol or Aretan for 5-10 proceedingss is widely practiced by the husbandmans. But these erratic antifungals are being banned now because of toxicity and pollution jobs. Certain oxathiin antifungals are besides reported to be effectual against root canker stage of the disease. ( Tanii et al. , 1982 ) reported important control of the disease by dusting or spraying of tubers with Validamycin. ( Khanna et al. , 1991 ) reported good efficaciousness of carbendazim to command the disease.
Dunking of seed tubers with 1 % acetic acid plus 0.05 % Zn sulfate or with 3 % boracic acid has besides been reported effectual ( Somani, 1986 ) . The intervention with boracic acid is more effectual, less toxic and safer than organo-mercurials which are non merely risky but besides affect the outgrowth of sprouts particularly when the temperature is above 30oC. Recently, Thind et Al. ( 2002 ) have reported about complete control of black scurf by dunking septic seed tubers in 0.25 per solution of Monceren ( pencycuron ) , a phenyl carbamide based fungicide, for 10 proceedingss before sowing.
All the belowground works parts except roots are attacked. The works cells multiply quickly at the infection site and bring forth enlarged tissue masses ensuing into wart type symptoms on tubers and beads like projections on roots or runners changing in size from little bulges to big elaborately bifurcate constructions. Warts are usually soft, pulpy, spherical and similar in colour to tubers. The coloring material may alter to green on exposure to sunlight. Sometimes whole tuber may be covered with warts. The coloring material of warts alterations to dark in shadiness as the tubers mature. Sometimes secondary micro-organisms invade the wart tissues doing their decomposition.
Potato wart is caused by the fungus Synchytrium endibiotichum ( Schill. ) Perc. Which is holocarpic and endobiotic in nature. The fungus green goodss spore case which release a big figure of uniflagellate planospores. When planospores originate from different sori, these behave as planogametes and copulate to organize zygospores which act as resting spore case of the pathogen. One race and one biotype of the pathogen have been reported from Darjeeling hills in India. ( Phadtare and Sharma 1971 ) have reported certain other hosts to be infected by the fungus.
The disease chiefly being soil borne in nature is hard to be managed. Assorted steps including quarantines, cultural patterns, host opposition some chemicals have been found effectual in cut downing the disease degree.
Since the disease is soil borne, its obliteration is really hard. Strict domestic quarantine steps enforced in India have helped to curtail the disease in Darjeeling territory of West Bengal merely where it was foremost reported. Sing the hazard of spread of the disease through contaminated dirt atoms, the seed every bit good as tabular array murphies are non allowed to be taken out from this territory and this has helped to incorporate the disease efficaciously.
The pathogen can stay feasible in the infested dirt for several old ages. This warrants practising harvest rotary motion with non-host harvests for 8-10 old ages where the disease has become endemic. The pathogen population in the dirt can besides be reduced through steam sterilisation of the dirt.
Some murphy lines such as Ronda, Edina, Mira from European states have shown considerable opposition to potato wart. Assortments developed by CPRI, Shimla like Kufri Jyoti, Kufri Sherpa, Kufri Jeevan, and Kufri Muthun have demonstrated opposition to late blight every bit good as wart and can play important function in cut downing the disease degree in endemic countries.
The usage of antifungals like mercurous chloride, Cu sulfate, formaldehyde etc. as dirt application, though effectual, but is rather expensive and can ensue into some non-target effects. These can be applied to limited extent to look into the constitution of the pathogen into those countries where it has late been introduced.
Initial symptoms of common strikebreaker appear on tubers as little brownish and somewhat raised musca volitanss which subsequently on enlarge, merge with each other and give corky visual aspect. Scab symptoms on tubers are categorized as shoal and deep pitted. In shallow strikebreaker, the affected tubers show superficial roughened countries, sometimes raised above but frequently somewhat below the tegument of the tubers. The lesions of scab consist of corky tissue which is the consequence of unnatural proliferation of the cells of tuber cuticles due to invasion by the pathogen. The lesions may change in form and size and the colour is by and large light to dark brown. In deep alveolate strikebreaker, the lesions are dark brown or about black and step 1-3 millimeter or more in deepness. They are besides corked in visual aspect and may fall in together affecting full surface of the tuber. Other signifiers of strikebreaker are proliferated lenticels with difficult corky deposition and homocentric series of wrinkly beds of cork around cardinal black nucleus.
Common strikebreaker of murphy is by and large considered to be caused by Streptomyces itchs ( Thaxter ) Waksman and Henrici. However, many species of Streptomycess are now reported to be responsible for doing common strikebreaker, though S. itchs is by and large recognized as its major cause. Other species of Streptomyces responsible for doing mild common strikebreaker are S. griseus ( Krainsky ) Waksman & A ; Hewici, S. collinus Lindenbein, S. aureofaciens, S. longisporoflavus, S. griseoflavus, S. alborgriseolus, S. violanceorber and S. flaveolus ( Dey and Singh, 1983 ) . However, names of some of these species are non included in the Advanced Lists of bacterial names. Glucose asparagines agar, Czapek ‘s agar and Tyrosine-caesin-agar are suited media for the isolation of Streptomyces species. The mycelium of the pathogen is slender, branched with few or no cross walles. The spores are cylindrical or spheroidal produced on particular hyphae that develop cross walls from tip and spores are pinched off. These Streptomycess species are gram positive and aerobic.Among other species in India, ( Singh and Singh, 1991 ) reported S. aureofaciens for motivating assorted types of shoal or deep strikebreaker symptoms on murphy tubers.
As the disease is both tuber and dirt borne, it is hard to command it. However, some direction patterns have been adopted to look into this disease. Healthy and blemish free seed tubers should be selected for seeding in order to cut down the primary beginning of inoculant.
The tubers can be disinfected by dunking them for 10-30 proceedingss in 0.25 per cent aqueous solution of erratic antifungals such as Emisan or 0.5 % solution of Agallol or Aretan ( Singh and Soni, 1987 ) . The intervention has been normally accepted by husbandmans in India. However, due to environmental pollution and wellness jeopardies, erratic antifungals are now being banned. Other tuber intervention chemicals like 3 per cent boric acid and certain antibiotics like Streoptocycline and Plantamycin have besides given satisfactory control.
Since dirt pH and dirt wet are of import factors in the development of disease, they have been exploited for minimising the losingss. Successful control of murphy strikebreaker has been achieved by frequent irrigations of the field at hebdomadal intervals from tuberisation until adulthood ( Singh and Singh, 1981 ) . Green manuring and cultivation of certain leguminous plants before seting murphy has been emphasized as of import cultural patterns in commanding common strikebreaker. Green manure likely increases the activity of certain actinomycetes and other bacteriums which are counter to S. itchs. Delay in seeding besides reduces disease incidence. Four twelvemonth harvest rotary motion with wheat-oat followed by potato-onion-maize besides helps in cut downing strikebreaker in the infested Fieldss ( Singh and Jeswani, 1987 ) .In Russia, S. itchs was reduced by application of high rates of K in combination with N and P fertilisers. In India, Singh and Singh ( 1993 ) confirmed the function of nitrogen-bearing fertilisers in the control of common strikebreaker ( S. aureofaciens ) of murphy. Turning murphies in acidic dirts besides reduces strikebreaker and add-on of sulfur can convey the pH to near 5.5. Application of gypsum is reported effectual to cut down common strikebreaker ( Singh and Soni 1987 ) .
Limited information is available on the usage of immune assortments to pull off this disease as no commercial assortment is known to possess high opposition to scab. Good degree of opposition to scab has been reported in Solanum chacoense and S. phureja. Solanum andigena x S. tuberosum loanblends and ruddy skinned assortments have been found to possess considerable opposition to scab ( S. scarius ) and are being used in the opposition genteelness programme ( Nagaich, 1983 ) . ( Singh and Singh 1992 ) have reported Kufri Sindhuri and some other accessions as resistant to scab caused by S. aureofaciens.
Decisions are irelevant