The role of Phytophthora on Cassava tuber rot in India

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The role of Phytophthora on Cassava tuber rot in
India
R. Radhakrishnan Nair, M.L.Jeeva and T.
Makeshkumar Central Tuber Crops Research
Institute Sreekariyam, Trivandrum, Kerala, India
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Cassava in India

• Area 2.35 m ha
• Production 5.3 m tonnes
• Tamil Nadu 85983 ha
• Salem 43 Area Production
• Productivity 41.2 t/ha
• Products Sago Starch
• Limiting Factor Tuber Rot

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The present study..

• Nature and Extent of spread
• Crop loss
• Pathogen
• Symptomatology
• Isolation of Pathogen from soil
• Effect of biocontrol agents
• Varietal reactions

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Survey

• Block level survey (1999 2000)
• Pethanaickanpalayam
• Attur
• Gangavally
• Thalaivasal
• Ayothiyapattinam
• Vazhapaddy
• Kadayampatty

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Extent of Spread and Crop Loss caused by Cassava
Tuber Rot in Salem district
Taluk H 226 Burma Mean
Disease Yield Disease Yield
Disease Yield incidence loss
incidence loss incidence loss
Attur 36.80 45.66 40.24 49.12
38.52 47.39 Rasipuram 33.56 41.40
39.80 44.54 36.68 42.97 Namakkal 22.60
18.32 18.78 21.30 20.69
19.81 Mean 30.98 35.12 32.94
38.32 31.56 36.72 CD (0.05) -
- - - 1.84 2.32
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Predisposing Factors

• Rainfall
• Soil moisture
• Poor drainage
• Excess irrigation
• Rotten tubers
• Black soils

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Pathogen

• Phytophthora palmivora
• Colony Uniform
• Mycelium Coenocytic, hyaline (4?)
• Sporangium Apical, Pear shaped, Papillate
  36 58 X 22 36 ?
• Stalk length 1 5 ?
• L B ratio 1.60
• Antheridia Amphigynous

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Effect of baiting techniques on isolation of
P. palmivora from infected soil
Bait Per cent isolation 48 hr 72
hr 96 hr Apple 0 17 0 Cocoa 17 33 50 Ca
rrot 0 33 17 Cassava 0 17 17 Pine
apple 0 17 17 Potato 0 17 0
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Selective isolation of P. palmivora from
infected soil
Medium Mean No. of colonies_at_ No.of 48
hr 72 hr 96 hr Propagules /g Soil
PVP 3 8 11 156 BNPRA
HM1 7 10 16 227
_at_ 20mg soil
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Effect of native antagonists on the growth of
P. palmivora
Antagonist Time of inoculation of the
pathogen Mean Same day
Before inoculation After inoculation
inhibitiion Colony inhib- Colony
inhib- Colony inhib- diameter
tion diameter tion diameter
tion Trichoderma sp 34 52.7 44
40.5 23 67.1
53.4 T.viridae 51 29.2 60
18.9 46 34.3 27.5 T.
harzianum 58 19.4 67
9.5 52 25.7 18.2 T. koningii
44 38.9 52 29.7 38
45.7 38.1 Control 72 0
74 0 70 0
0
Mean of 6 replications
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Effect of cell free culture filtrates of
antagonists on the growth of P. palmivora
Antagonist Radial growth (mm) Percent
No. of 96hrs after inoculation inhibiti
on propagules / g soil Trichoderma
sp 12 83 52 T.viridae
55 21 125 T. harzianum 67
4 172 T. koningii 22
68 96 Control 70
0 215
Mean of 6 replications
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Effect of Cassava varieties against infection by
P. palmivora
Variety Mean lesion size (mm) after
Starch 48 hr 72 hr 96 hr
120 hr H-226 10 22 34
48 29 M-4 9 16 29 41
26 H-97 6 11 18 28
29 Sree Sahya 6 12 20 32
30 Sree Vishakham 8 15 24 38
26 Sree Vijaya 6 10 16 26
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Mean of 6 replications
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ThanQ