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STUDIES ON PHYTOPHTHORA LEAF BLIGHT OF TARO (Colocasia esculenta (L.) Schott.)

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Title STUDIES ON PHYTOPHTHORA LEAF BLIGHT OF TARO (Colocasia esculenta (L.) Schott.)
 
Creator PADMAJA, G
 
Contributor UMA DEVI, G
 
Subject fungi, diseases, colocasia, vegetables, biological phenomena, biological development, fungicides, planting, pathogens, polysaccharides
 
Description Taro (Colocasia esculenta (L.) Schott.) a member of the Araceae family is also called as
colocasia, cocoyam and dasheen, has its origin in South East Asia. Taro is one of the major
tropical tuber crop. The tubers are rich in starch and used almost everywhere as vegetable, leaves
and petiole are also cooked and eaten as vegetable. Besides, this crop is of great medicinal value
and is included in many ayurvedic preparations. Taro tubers contain more protein, minerals,
phosphorus and iron compared to other tuber crops. In India, two taro types viz., Colocasia
esculenta var. esculenta Plucknett (Dasheen type) and Colocasia esculenta var. antiquorum
Plucknett (Eddoe type) are commonly cultivated throughout the country in an area of 80,000 ha
with a production of about 0.8 million tones. In Andhra Pradesh it is predominantly grown in
coastal areas especially East and West Godavari, Krishna, Prakasam, Guntur districts as well as
in Telangana regions of Ranga Reddy, Nizamabad, Nalgonda and Medak in an area of 2000 ha
and 8.29 thousand tonnes production (AICRP, 2011).
Taro production is highly affected by many biotic and abiotic factors. Among the fungal
diseases Phytophthora leaf blight caused by Phytophthora colocasiae has become major
constraint resulting in yield losses year after year. A detailed survey was carried out to isolate the
pathogen from different taro growing areas of Andhra Pradesh to study the variation in
morphological and cultural characteristics, to screen available germplasm for disease resistance
against P. colocasiae, to isolate phylloplane micro flora and identify potential antagonists against
the pathogen and to test the sensitivity of bioagents against fungicides was screened under
laboratory conditions at recommended and half the recommended dosage and to manage the leaf
blight disease of Taro under field conditions.
Leaf blight affected diseased samples were collected from Ranga Reddy, Hyderabad,
Kovvuru and Kerala and the pathogen was isolated, purified by single hyphal tip method and
were designated from PC 1 to PC 4 and their pathogenic nature was determined by proving
Koch’s postulates.
Among the different media tested, maximum growth of the pathogen was recorded on
Carrot Agar (86 mm), followed by Carrot Potato Agar (CPA) medium (79 mm), whereas
minimum growth of pathogen was recorded on PDA medium (22 mm) and CMA (29 mm).
Hence, the pathogen was maintained on carrot agar medium to carry out further studies.
Studies on morphological characters of different isolates of Phytophthora colocasiae
revealed that the mycelium of Phytophthora colocasiae was aseptate, hyaline with hyphal width
of 1 μm and hyphal swellings were absent. The sporangiophore of isolate PC 1 and PC 3 were
distinct from isolate PC 2 and PC 4 with simple sympodial branching while in isolate PC 2 and
PC 4 branched sympodium was produced which is a characteristic feature of Phytophthora. The
sporangium were semipapillate and globose in PC 1, PC 2, PC 3 but ovoid in PC 4.
Variation in cultural characters such as colony colour, texture, abundance of mycelium,
colony diameter, growth rate per day, mycelial dry weight was observed. The colour of the
colony in isolate PC 1 and PC 4 was white, while the other two isolates PC 2 and PC 3 produced
dull white colonies.
The texture of the mycelium was slightly fluffy and sparse in three isolates PC 1, PC 3 and
PC 4 whereas profuse abundant and fluffy mycelium was found in isolate PC 2. Differences
were observed among the isolates with respect to colony diameter and growth rate per day. The
isolate PC 1 from Hyderabad district showed maximum (88.00 mm) radial growth with
maximum growth rate per day (12.6 mm) and the isolate PC 2 from Ranga Reddy district
showed the minimum (72.00 mm) radial growth with 11.4 mm per day growth rate of mycelium.
Mycelial dry weight (282 mg) was maximum in the isolate PC 1, while it was minimum (152
mg) in the isolate PC 2.
Among the sporangial characters, difference was observed in size of sporangium, length
and width of sporangium and their ratio, size of oospore and zoospore in different isolates of
Phythophthora colocasiae was observed. Maximum size of the sporangium (417 μm2) was
observed in isolate PC 3 with highest length and width (24.3 μm × 17.2 μm) and minimum size
of the sporangium (312 μm2) with (21.2 μm × 14.9 μm) length and width was observed in isolate
PC 2. All the isolates was observed with 1.4:1 length and breadth ratio but isolate PC 4 was
showed highest length and breadth ratio (1.5:1). Maximum size of oospore was observed in
isolate PC 1 (772.5 μm2) with highest mean diameter (27.8 μm2) and minimum size of oospore
(486.7 μm2) was observed in isolate PC 3 with lowest (19.2 μm2) mean diameter. Highest size of
zoospore was observed in the isolate PC 4 (52 μm2) and minimum size of zoospore was recorded
in the isolate PC 1.
Twelve varieties viz, Jagtial local, RNCA-1, Muktakeshi, KCS-3, NDC-1, C-16, Tenali,
Hyderabad local, Kadma local, Kovvuru local, Satamukhi, Nellore were screened with four
isolates viz., PC 1, PC 2, PC 3, PC 4 under laboratory conditions by detached leaf method.
The disease reaction of 12 varieties showed differences in resistance to isolates of
Phytophthora colocasiae. Variety RNCA-1 showed highly resistant reaction to isolate PC 1,
resistant to PC 2 and moderately resistant to PC 3 and PC 4. Variety KCS-3 showed resistant
reaction to all the isolates of Phytophthora colocasiae and Muktakeshi also showed similar
reaction except to isolate PC 2. Moderately resistant reaction was recorded by variety Kovvuru
local to isolate PC 1, PC 2 and PC 3. Variety NDC-1 showed susceptible reaction to three
isolates viz, PC 2, PC 3 and PC 4 while Tenali local was susceptible to PC 2 and PC 3. Similarly
C-16 was susceptible to isolate PC 1 and PC 3. Hyderabad local was susceptible to PC 1 and PC
2 while Jagtial local was susceptible PC 2 and PC 4. Satamukhi was highly susceptible to PC 1,
PC 2, PC 3 and susceptible to PC 4 where as Kadma local was highly susceptible to PC 2, PC 3
and PC 4. Variety Tenali was also highly susceptible to PC 1 and PC 4, similarly Hyderabad
local was highly susceptible to isolates PC 3 and PC 4 while variety Nellore to isolates PC 2 and
PC 3.
All phylloplane microflora were tested for their antagonistic activity against leaf blight
pathogen (Phytophthora colocasiae) under in vitro condition using dual culture technique on
Carrot Agar medium. The fungus Trichoderma sp.1 inhibited the radial growth of the pathogen
P. colocasiae to the maximum extent 93.4 per cent followed by Trichoderma sp. 2 (79.9 per
cent). Among the phylloplane bacteria Phylloplane bacteria 1 showed maximum inhibition of
72.7 per cent followed by Phylloplane bacteria 3 (67.8 per cent), Phylloplane bacteria 4 (64.1 per
cent) and Phylloplane bacteria 2 (61.6 per cent) by inhibiting the growth of Phytophthora
colocasiae over control. Fungal antagonists Trichoderma sp.1 and Trichoderma sp. 2 were
further used for compatibility studies.
In vitro screening of fungicides was conducted to determine the sensitivity of
Phytophthora colocasiae by poisoned food technique at recommended and half the
recommended doses.
Complete inhibition in growth of mycelium of Phytophthora colocasiae was recorded in
Mancozeb, Pyrachlostrobin + Metiram and Tebuconazole at recommended concentration.
Fungicides cymoxanil, metalaxyl, copper oxy chloride significantly reduced the growth of
mycelium by 98.0, 92.9 and 91.0 per cent respectively, whereas dimethomorph (89.5 per cent),
thiophanate methyl (74.6 per cent), azoxystrobin (72.5 per cent) could also inhibit the pathogen.
Minimum per cent inhibition was recorded in Bordeaux mixture (70.3 per cent).
Similarly Pyrachlostrobin + Metiram, Tebuconazole showed 100 per cent inhibition of the
pathogen at half the recommended concentration. Whereas copper oxy chloride and cymoxanil
reduced the mycelial growth by 88.4 and 87.1 per cent respectively followed by dimethomorph
(85.47) and metalaxyl (84.53). Though 100 per cent inhibition was observed with mancozeb at
recommended dose it could inhibit only by 83.9 per cent at half the recommended concentration
when compared to control. Thiophanate methyl showed an inhibition of 62.2 per cent followed
by Bordeaux mixture (61.4 per cent), and azoxystrobin was less effective in inhibiting the
pathogen by 58.5 per cent at half the recommended dose when compared to other fungicides.
Fungicides mancozeb, metalaxyl, tebuconazole, cymoxanil, pyrachlostrobin + metiram
were used for testing the compatability of fungicides with bioagents Trichoderma sp.1 and
Trichoderma sp. 2.
Compatibility of two potential bio control agents Trichoderma sp.1 and Trichoderma sp.
2 with the recommended fungicides Metalaxyl, Mancozeb, Tebuconazole, Cymoxanil,
Pyrachlostrobin + metiram at recommended concentration against leaf blight pathogen
Phytophthora colocasiae of Taro revealed that maximum growth of Trichoderma sp. 1 was
found in metalaxyl (13.7 mm) followed by mancozeb (8.5 mm) and tebuconazole (6.0 mm).
Pyrachlostrobin + metiram showed complete inhibition (100 per cent) of Trichoderma sp. 1 and
Trichoderma sp. 2. Metalaxyl showed maximum growth of 10.2 mm followed by tebuconazole
(7.5 mm) and mancozeb (6.7 mm). However fungicide cymoxanil completely inhibited
Trichoderma sp.2.
From the above results it can be inferred that bio agents Trichoderma sp. 1 and
Trichoderma sp. 2 were compatible with metalaxyl, mancozeb and tebuconazole but not
compatible with pyrachlostrobin + metiram and cymoxanil.
Results of field experiment during Kharif, 2012 indicated that all the treatments were
effective in reducing the disease incidence and increasing the yield except T2 (Seed treatment
and soil application of Pseudomonas fluorescens (commercial) at the time of planting) which
was not significant.
Treatment T5 (T1 - Seed treatment and soil application of Trichoderma viride
(commertial ) at the time of planting + T4 Foliar application of mancozeb) was highly significant
in reducing the disease incidence by 50 per cent over control followed by T7 (T3 - Seed
treatment and soil application with potential bio agent (Trichoderma sp. 1 ) at the time of
planting + T4 - Foliar application of mancozeb) which reduced the disease by 42.5 per cent.
Treatment T2 (Seed treatment and soil application of Pseudomonas fluorescens (commercial) at
the time of planting) could reduce the disease incidence by 7.3 per cent and was non significant
when compared to other treatments.
Similarly all the treatments were significant in increasing the yield except T3 and T2
which were not significant. Highest significant yield was obtained in treatment T5 with 28.3 t/ha
followed by T7 (25.1%), T6 (24.4 t ha-1) and T4 (23.9 t ha-1) which were almost on par with each
other. Treatment T2 (19.6 t ha-1) though non significant, recorded lowest yield when compared
to rest of the treatments.
The data indicated that with the decrease in per cent disease incidence there was an increase in
yield. The treatment T5 recorded per cent disease incidence of 36.8 with significant increase in
yield of 28.1 t ha-1 when compared to control.
 
Date 2016-06-22T15:11:41Z
2016-06-22T15:11:41Z
2013
 
Type Thesis
 
Identifier http://krishikosh.egranth.ac.in/handle/1/67746
 
Language en
 
Relation D9437;
 
Format application/pdf
 
Publisher ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY