variation in phytophthora palmivora on cocoa in papua new guinea

VARIATION IN
PHYTOPHTHORA
PALMIVORA ON COCOA
IN PAPUA NEW GUINEA
J Saul Maora, EYC Liew and D
Guest

Proportion of Merchandise exports
for 2008 <strong>in</strong> Millions of K<strong>in</strong>a
Total = K15,442 million K<strong>in</strong>a*
M<strong>in</strong>eral
Crude oil
Agric. Mar<strong>in</strong>e & non
m<strong>in</strong>eral
Forestry Products
Ref<strong>in</strong>ed Oil
Logs
*K1 = $0.40

Proportion of export values for
Agric. and Mar<strong>in</strong>e Products for
2008
Total Exports = K2,558.6 million K<strong>in</strong>a*
Palm Oil
Coffee
Cocoa
Copra Oil
Mar<strong>in</strong>e Prod
Copra
Rubber
Tea
K1 = $A0.40*

Cocoa

Cocoa
Dry<strong>in</strong>g Cocoa Beans
Bagged PNG Cocoa for Export

P. Palmivora Diseases
Stem Canker
Black Pod
Leaf Blight

Breed<strong>in</strong>g Program Location

Hypotheses
• P. <strong>palmivora</strong> is the sole species caus<strong>in</strong>g
disease on cocoa <strong>in</strong> PNG.
• There is <strong>variation</strong> between P. <strong>palmivora</strong>
populations on cocoa from different
locations <strong>in</strong> PNG.

Methods

Morphology
• Colony morphology
• Sporangiophore branch<strong>in</strong>g
• Sporangia morphology

Stellate/Striate colony morphology
at 4 days

Sporangiophore Branch<strong>in</strong>g

Sporangia Morphology

Physiological & Biological Tests
• Physiological
• Growth Rates on Carrot Agar
• Biological
• Compatibility Test on Kidney Bean Agar

Colony measurements on 4-dayold
cultures

Variation <strong>in</strong> lesions on pods, colony
morphology and growth rate
ENB 42
ENB 45

Variation <strong>in</strong> sporangia morphology
ENB 42
ENB 45

Compatibility Studies

Mycelial Growth
DNA Extraction
RAMS Analysis

Mycelial Growth & Storage

Frequency
Frequency of sporanagium length (µm) of
P. <strong>palmivora</strong> isolates from PNG cocoa.
80
60
40
20
0
25-
30
31-
35
36-
40
41-
45
46-
50
51-
55
56-
60
61-
65
66-
70
71-
75
76-
80
Sporangia Length (um)

Frequency
Frequency distribution of sporangia
breadth (µm) for P. <strong>palmivora</strong> isolates
from PNG cocoa.
60
50
40
30
20
10
0
17-
18
19-
20
21-
22
23-
24
25-
26
27-
28
29-
30
31-
32
33-
34
35-
36
36-
37
Sporangia breadth (um)

Frequency
Frequency distribution of sporangia
pedicel length (µm) of P. <strong>palmivora</strong>
isolates from PNG cocoa.
100
80
60
40
20
0
1.0-2.4 2.5-3.4 3.5-4.4 4.5-5.4 5.5-6.4 6.5-7.4
Sporangia Pedicel Length (um)

Frequency of Sporangia length/breadth
ratio of P. <strong>palmivora</strong> isolates from PNG
cocoa.
Frequency
30
25
20
15
10
5
0
1.26-1.30
1.36-1.40
1.46-1.50
1.61-1.65
1.71-1.75
1.81-1.85
1.91-1.95
2.01-2.05
2.11-2.15
2.21-2.25
2.31-2.35
Sporangia Length/Breadth Ratio

Comparison of Phytophthora species
implicated to cause disease on cocoa <strong>in</strong>
PNG
Species
Colony
Morphology
Sphorangiophore
Branch<strong>in</strong>g
Caducity
Sporangia
pedicel length
(µm)
P. arecae (=
<strong>palmivora</strong>)
Radiant, abundant
aerial mycelia
Simple sympodium Yes 1 – 6
P. <strong>palmivora</strong> Stellate, striate Simple sympodium Yes < 5
P. megakarya Cottony aerial
mycelia
Simple sympodium Yes 10 – 30
P. nicotianae Stoloniferous/
web-like
Loose sympodium
Unbranched
No -
P. citrophthora Petaloid Irregular branch<strong>in</strong>g
Loose sympodium
No -
Isolates from
current study
Radiant., stellate,
striate
Simple sympodium Yes 1 – 7

Mat<strong>in</strong>g Types (A1:A2)
0:1
0.1
1:9
0.1
0:1

Randomly Amplified Microsatellite
Primer CA
1 2 3 4 5 6
7 8 9 10 11 12 13 14
15 16 17 18 19 20

Randomly Amplified Microsatellite
primer CGA
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

UPGMA dendogram of P.
<strong>palmivora</strong> isolates on cocoa from
PNG

Conclusion
• Phytophthora <strong>palmivora</strong> is the sole Phytophthora
species caus<strong>in</strong>g disease on cocoa <strong>in</strong> PNG.
• Variation <strong>in</strong> sporangia morphology between
isolates with<strong>in</strong> a farm is very high.
• There is genetic <strong>variation</strong> between isolates <strong>in</strong>
PNG.

Implications of Disease Control
• P. <strong>palmivora</strong> population <strong>in</strong> PNG has a
potential to evolve and adapt to changes.
• Presence of one large cont<strong>in</strong>uous
population therefore breed<strong>in</strong>g <strong>in</strong> one
location acceptable.
• Deploy mixed cocoa cultivars and promote
Integrated Disease Management.

Future Studies
• Pathogenicity tests us<strong>in</strong>g representative
isolates on a range of cocoa clones.
• Genetic <strong>variation</strong> studies us<strong>in</strong>g other
RAMS primers.

Acknowledgements
• AusAid for the Scholarship & mak<strong>in</strong>g it
possible to attend 2009 APPS conference.
• The Cocoa Coconut Institute (CCI) PNG.
• Supervisors: Prof. Guest & Dr. Liew.
• Dr. Rose Daniel
• Extension, Pathology & Agronomy Staff of
CCI PNG for their assistance <strong>in</strong> isolate
collection.