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Infection of apples by Colletotrichum acutatum in New Zealand is limited by
temperature
K.R. Everett{ XE "Everett, K.R." }, O.E. Timudo‐Torrevilla, I.P.S. Pushparajah, R.W.A. Scheper, P.W. Shaw, T.M. Spiers, A. Ah Chee, J.T.
Taylor, P. Wood, D.R. Wallis, M.A. Manning
The New Zealand Institute for Plant and Food Research Limited, P.B. 92169, Mt Albert, Auckland, New Zealand
INTRODUCTION
Colletotrichum acutatum infects the surface of apples in New
Zealand to cause small, 1–2 mm diameter dark spots, usually on
the side of the fruit exposed to the sun, which can enlarge to
cover the entire fruit surface with one or several orange,
sporulating lesions. Infection eventually results in fruit drop.
Symptoms express in summer. Little is known of the
epidemiology of C. acutatum infecting apples, either in New
Zealand or elsewhere (1). A study was conducted to investigate
the epidemiology of this fungus on apples in New Zealand, to
facilitate the design of strategies to achieve control with no
residues.
MATERIALS AND METHODS
Laboratory inoculations. ‘Royal Gala’ apples were harvested
monthly starting immediately after fruit set in November 2005
until harvest in 2006. At each time, apples were woundinoculated
with 10 6 spores/ml C. acutatum and placed at 5, 10,
15, 17.5, 20, 25 or 30°C in humid conditions for 7 days. Lesion
diameter was then measured.
Field inoculations. ‘Royal Gala’ apples in two orchards in each of
three major apple growing regions in New Zealand, viz. Waikato,
Hawke’s Bay and Nelson, were wound‐inoculated monthly with
10 6 spores/ml C. acutatum beginning in November 2005 until
harvest in February 2006. Lesion diameter was then measured.
Lesion diameter (mm)
30
25
20
15
10
5
0
November
December
January
February
5 10 15 20 25 30
Temperature o (C)
Figure 1. Mean lesion diameter (mm) of detached apple fruit inoculated
at harvest with 10 6 spores/ml Colletotrichum acutatum. A Boltzmann
plot was fitted.
RESULTS
Detached ‘Royal Gala’ apples were susceptible to infection by C.
acutatum when a temperature of c. 15°C was exceeded,
regardless of maturity (Fig. 1). A wetness period of 72 hours was
required for infections without wounding (results not shown). In
the field ‘Royal Gala’ apples were infected by C. acutatum after a
temperature of 15.2°C was exceeded (Fig. 2).
mean number of infected fruit (max. = 5)
5
4
3
2
1
0
Y = 3.1 + (0.02 - 3.1)/(1+exp ((x-15.2/0.01))
R 2 = 73%
12 13 14 15 16 17 18 19 20 21
mean daily temperature ( o C)
Figure 2. The mean number of infected apple fruit out of five inoculated
with 10 6 spores/ml of Colletotrichum acutatum plotted against the mean
daily temperature for 72 hours after inoculation. A Boltzmann plot was
fitted. The x0 value (inflection point) = 15.2°C.
DISCUSSION
In New Zealand mean daily temperatures of 15°C are exceeded
during December, January and February. Effective control
without residues may be able to be achieved by reducing
inoculum early in the season before temperatures are above
mean daily termperatures of c. 15°C, as was achieved for control
of B. dothidea (2). A biological control agent or a benign
chemical such as calcium chloride (3) could be used to protect
the fruit from infection during summer when temperature is not
limiting infections.
ACKNOWLEDGEMENTS
This work was funded by MAF Sustainable Farming Fund, Pipfruit
New Zealand, Waikato Fruitgrowers’ Association and Nelson
Group 8.
REFERENCES
1. Peres NA, Timmer LW, Adaskaveg JE, Correll JC (2005) Lifestyles of
Colletotrichum acutatum. Plant Disease 89, 784–96.
2. Everett KR, Timudo‐Torrevilla OE, Taylor JT and Yu J (2007)
Fungicide timing for control of summer rots of apples. New Zealand
Plant Protection 60, 15–20.
3. Boyd‐Wilson KSH and Walter M (2007) Effect of nutrients on the
biocontrol activity of yeasts on apple pathogens. IN: Conference
Handbook, 16th Biennial Conference of Australasian Plant
Pathology Society. P. 43.
Session 2C—Epidemiology
APPS 2009 | PLANT HEALTH MANAGEMENT: AN INTEGRATED APPROACH 45