At the end of the lesson the students will be able --to tell list important diseases of potato and tomato with their causeto identify the disease by observing the symptomto draw life cycle of most important diseasesTo formulate the control strategy for these diseases
Bacterial Disease Bacterial wilt = brown rot Ralstonia solanacearum Blackleg and bacterial soft rot Erwinia carotovora subsp. atroseptica Ring rot Clavibacter michiganensis Streptomyces scabies Common scab S. turgidiscabiesViral Potato leafroll Potato leafroll virus Potato mop-top Potato mop-top virus Potato rugose mosaic Potato virus Y Potato spindle tuber Potato spindle tuber viroid Potato yellow dwarf Potato yellow dwarf virus Potato yellow mosaic Potato yellow mosaic virus Potato yellow vein Potato yellow vein virus Potato virus X Potato virus X Potato virus Y Potato virus Y
Nemic Globodera rostochiensis Potato cyst nematode Globodera pallida Lesion nematode Pratylenchus spp. Root knot nematode Meloidogyne incognita,M. javanica, Phytoplasma infection or anything that constricts the stem, including but not limited to Rhizoctonia canker,Aerial tubers heat necrosis, chemical injury, mechanical injury, wind injuryAir pollution injury Photochemical oxidants (primarily ozone), sulfur oxidesBlack heart Oxygen deficiency of internal tuber tissueHollow heart Excessively rapid tuber enlargementInternal brown spot = heat Oxygen deficiency of tuber accompanying high soilnecrosis temperature Exact cause(s) unknown, chemical injury, viruses or otherStem-end browning pathogens.
Late blight of potato• Great Irish Famine of 1845 to 1847Disease symptoms and signs • necrotic spots, may or may not be surrounded by a pale green border • Older lesions generally have a necrotic center and a chlorotic halo • they coalesce, blighting and killing the entire leaf within a few days.
• a white fluffy growth appears at the lesion edges on the underside sporulating, producing sporangia • Irregular, slightly depressed areas of brown to purplish skin • A coppery brown granular rot usually extends less than one- half inch into the tuber
Management • Healthy Seed-first line of defense • Cultivar Resistance • Removal of Diseased Plants: • Fungicide Spraying: Fungicides – mancozeb @ 0.2% or Copper oxychloride @ 0.3%. If late blight attack is early in the season and weather conditions are favorable, one spray of metalaxyl + mancozeb @ 0.2% may be given
Early blight• Initially on the older, lower leaves• Lesions ﬁrst appear as small spots—dry and papery.• Lesions become brownish black and circular.• Concentric rings of raised and depressed tissue gives the lesions "target-spot" or “bull’s eye” appearance• Adjacent to the lesion is usually yellowed. As new lesions develop and older lesions expand, the entire leaf becomes chlorotic (yellow).
• Tuber lesions are dark, sunken, and circular to irregular in shape, and often are surrounded by a raised, purplish-gray borderManagement of disease•Use a crop rotation•Use tillage practices such as fall plowing that bury all plant refuse.•Select cultivars that have a lower susceptibility to early blight.•Use certified disease-free tomato seed and transplants.•Kill off the foliage at least 2–3 weeks before harvesting to prevent tuber infection•Allow tubers to mature before digging.•Avoid harvesting tubers when conditions are wet, dig when vines are dry•Avoid excessive wounding of potatoes during harvesting and handling.•Although the above measures are important to minimize infection, it is usually necessary toapply fungicide sprays to fully protect plants from early blight.
Fusarium wilt • develop a yellowing of the older leaves. Often the yellowing is restricted to one side of the plant or even to leaflets on one side of the petiole.• the main stem is cut, dark, chocolate-brown streaks may be seen running lengthwise through the stem • tubers may show browning of the vascular ring as well as browning at the stem end
Common Scab Streptomyces scabies• Lesions typically are circular, raised, and tan to brown in color, with corky areas that develop randomly. Lesions may become irregular in shape when they coalesce .• A superficial corklike layer (russet scab) occasionally appears instead of the circular lesions.• In other cases, the lesions are one-half inch deep (pitted scab). These pitted scab lesions are dark brown to black, and the tissues underneath are often straw-colored and translucent.• More than one type of symptom may be present on a single tuber.
Damping off (Phytophthora, Rhizoctonia or Pythium sp.)1. Pre-emergence damping-off:• Results in seed and seedling rot before these emerge out of the soil.• Young seedlings are killed before they reach the surface of the soil.• Since this happens under the soil surface, the disease is often not detected except for the resulting poor stand2. Post-emergence damping-off:• Characterized by toppling over of infected seedlings.• Collar portion rots and ultimately the seedlings collapse and die.
Management•Healthy seed•Seed treatment with Thiram @ 2g/kg of seed before sowing.•Soil treated with Thiram @ 5g/m2 area of the soil/ Formalin•Soil drenching with the same chemical @ 2g/litre of water at fortnightlyinterval.•Soil solarization by spreading polythene sheet over the bed for 30 daysbefore sowing•Application of BAU- biofungicide (T. viride) in soil @ 1.2kg/ha•Continuous raising of nursery in the same plot should be avoided. Additional precautions: a) Thin sowing to avoid overcrowding. b) Light sandy soils for nurseries or use pure fine sand sawdust mixture for raising seedlings. c) Use well-decomposed manure. d) Light but frequent irrigations. e) Raised nursery beds to drain off excess water, and f) Sterilization of soil by burning a 30cm thick stack of farm trash on the nursery bed before seed
Phomopsis Blight Phomopsis vexans• seedling infection-------------damping off symptoms• leaves infected-----------small circular spots appear which become grey to brown with irregular blackish margins• Lesions may also develop on petiole and stem, causing blighting of affected portion of the plant• Fruits infection-------minute, sunken dull and dusky spots which later merge to form rotten areas. The flesh of severely infected fruits rots• At advance stage, numerous pycnidia as small, black pimples embedded in the host tissue are seen.
Control•Healthy seeds•Good field sanitation,•Destruction of infected plant material•crop rotation•Disease resistant variety e.g BAU begun-1&2•Seed treatment with hot water (51oC for 15 minutes)/Thiram (2 g/kg seed)•Spraying with Zineb (Dithane-Z-78) or Mancozeb (DithaneM-45)/Bavistin @ 0.2%
WiltBacterial Wilt (Psedomonas solancearum)•The characteristic symptoms of thedisease are wilting of the foliage followedby collapse of the entire plant.•Wilting is characterized by gradual,sometimes sudden, yellowing, witheringand drying of the entire plant or some of itsbranches. Verticillium Wilt (Verticilium dahliae) : •Infected young plants show dwarfing and stunting with no flower and fruit. •Infection after the flowering stage results in distorted floral buds and fruits. Affected fruits finally drop off. •infected leaves show irregular, scattered necrotic pale yellow spots over the leaf lamina. Later on, these spots coalesce resulting in complete wilting of leaves. •Roots are split open longitudinally, a characteristic dark brown discoloration in the xylem vessels is observed.
• How to Mange Bacterial wilt?1. Clean and well drained land.2. Grafting with resistant Solanum root stock.3. Cultivate moderaterly tolerant variety like BARI Begun-6,7&94. Dip seedlings into streptrocycline (1gm/40 L water) for 30 minutes.5. Other solanaceous crops to be avoided in crop rotation.6. The field should be cleaned as soon as the disease is detected in the field i.e. the diseased fruits should be plucked and burnt. How Can You Control V. wilt? •Crop rotation with bhendi, tomato, potato should be avoided. •Soil application and foliar application with Benlate (0.1%) is effective in reducing the wilt disease.
Little LeafTransmission- leaf hopper Cestius phycitis •leaves in early stages are light yellow in color•Leaves show a reduction in size and are malformedplant are shorter, bearing a large number ofbranches, roots and leaves.•Give the plants a bushy appearance.•No fruit or hard and tough fruit and fails to mature Control Measures i. The disease affected plants should be destroyed, ii. Spray Dimethoate (Rogor-30 EC)/Oxydemiton methyl (Metasystox-25 EG) or Monocrotophos (Monocil)/ Malathion@ 1 ml per litre of water to check the spread of this disease, iii. Disease resistant variety such as Pusa purple Cluster should be cultivated
Leaf Curl•Transmission-whitefly Bemisia tabaci•Abaxial and adaxial curling of leavesaccompanied by puckering and blisteringof interveinal areas and thickening andswelling of veins • Cover nursery beds with nylon net or straw to • Protect the seedlings from viral infections. • Raise barrier crops such as maize, sorghum, pearl millet or snap bean around chillies in two to three rows • Remove infected plant as soon as they are noticed. • Spray metasystox or rogar at 0.1% at 10 days interval. • Spraying should be stopped 15-20 days before harvest of the crop.
MOSAICCharacteristic symptoms are appearanceof dark green and yellow areas on theleaf surface. These may be sunken or raised (puckering). Sometimes the leaves are greatly reduced in size and filamentous or shoe string like. Control 1.Rogue out the affected plants. Transmission 2.Collect the seeds from virus Contact &aphids free plants. 3.Avoid unnecessary touching of plants. 4.Use virus free seedlingsSpray with Malathion 50 EC @0.1% at 15 Days interval
ANTHRACNOSE, DIE BACK AND RIPE FRUT ROTDie back.•Necrosis of the tender twigs from the tipbackwards.•Entire branch or the entire top of the plantmay wither away.•Twigs are water soaked to brown,becoming greyish white or straw colored inadvance stage.•Large number of black dots called acervuliare formed on the affected twigs. Ripe fruit rot. •The disease usually occur on mature fruits as circular to elliptical sunken spots with black margins and marked with concentric rings . •Badly diseased fruits turn straw colored from normal red. On this discolored area, numerous black dots (acervuli) are present. The diseased fruit may drop off prematurely
Cercospora leafspot in chilli • Leaf spot can be controlled by spraying Mancozeb 2 g/lit or Copper oxychloride 2.5 g/lit.Symptoms :•Roughly circular, cherry red to dark red spots, variable in sizeare formed by C. canescens.•In case of C. cruenta black mats due to mouldy growth of thefungus are caused.•Defoliation occurs in both the cases. At maturity, infected podsshow black sporulation of the fungus.
CucurbitPowdery Mildew Erysiphe cichoracearumAppear first as a pale yellow spotsThe fungus soon sporulates yielding acharacteristic powdery-white appearance.This powdery appearance can involve theentire leaf which eventually turns yellowthen brown and dries to the point that itcrumbles when crushed. Use resistant varieties. good drainage and allow for maximum air circulation Apply protectant fungicides, such as wettable sulfur, to susceptible plants before or in the earliest stages of disease development. Spray Karathane/ chlorothalonil (e.g. Daconil 2787 10 day intervals.
Downy Mildew Pseudoperonospora cubensis Angular, chlorotic lesions on the foliage. Lesions appear angular because they are bound by leaf veins.This is the sporulation of the pathogen. Eventually,leaves will turn necrotic and curl upwards. In humid conditions, inspectionThe disease is sometimes called “wildfire” because of of the underside of the leafhow rapidly it progresses, as if burned by fire. reveals gray-brown to purplish- black ‘down’.
Control1.Plant varieties that are resistant to downymildew.2.Wide spacing between plants, choosingplanting sites with good soil and air drainageand exposure to all-day sun,3.Maintain ample but not excessive nitrogenfertility,4. Control weeds 5. Avoiding overhead Fig. When moisture and temperature are conducive, downyirrigation, 6. Apply contact fungicides mildew will quickly spread within a field chlorothalonil /maneb or systemic and to other fields. Leaf lesions will become numerous, cymoxanil/famoxadone, dimethomorph coalesce, and turn brown. Leaf edges may turn up, making the plants appear cymoxanil, Pamocarb scorched.
Disease: Leaf spot of betel vineCausal organism: Colletotrichum piperisSymptoms•The round to oval shaped spots are palebrown color at early stage and dirty black atlater stage which appear initially as watersoaked lesions on the leaves.•These lesions enlarge irregularly towardsthe center of the leaves. The mature spotshave ashy center, dork brown distinctmargin surrounded by yellow halo. Spray 1 per cent Bordeaux mixture or copper oxychloride 3 g/1 at 15 days interval.
Disease: Leaf rot of betel vineCausal organism: Phytophthora parasiticavar. piperinaSymptoms•The infected area of tile leaves turn brownto dark brown and later dirty black•Often starting from the edge or tip of theleaves and progress towards the centre ofthe leaves without a well defined margin.•The lesions enlarge rapidly to cover a partor whole leaf which later starts rotting.
Disease: Frog eye leaf spot of tobaccoCausal organism: Cercospora nicotianaeSymptomsNumerous, small reddish spots develop onthe leaves especially on the older leaves.The mature spots become roughly circularin shape. The centers of the spots turnwhile brown/ash colored with a greycircular layer surrounded by dark brownmargin. The spots look like the eye of thefrog, hence the disease so called.
Disease: Brown spot of tobaccoCausal organism: Alternaria longipes/A.tenuisSymptomsThe large, circular and brown colored spotspresent on the leaves which appear initiallyas pin pointed to large (5-10 mm diameter)spots. The mature spots have dark brownconcentric rings which is the mostimportant diagnostic character of thedisease. Several spots near the tip maycoalesce together causing death anddrying of leaves.
Thanks to allK. M. Golam DastogeerLecturerDepartment of Plant PathologyBangladesh Agricultural universityMmensingh-2202