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Bananas in Carnarvon—good news for growers in survey for quarantine plant pests
and pathogens
S.J. Collins{ XE "Collins, S.J." } A , A.E. Mackie A , J.H. Botha A , V.A.Vanstone A , J.M. Nobbs B and V.M. Lanoiselet A
A
Department of Agriculture and Food Western Australia, South Perth, 6151, Western Australia
B
SARDI Plant and Soil Health, GPO Box 397, Adelaide, 5001, South Australia
INTRODUCTION
The banana industry in Carnarvon, Western Australia, is unique
among other Australian banana growing areas. While bananas are
typically grown in tropical to sub‐tropical regions where rainfall is
abundant, Carnarvon has an arid‐desert climate and growers depend
on year round irrigation. Under these unique conditions, plant pests
and pathogens common to other Australian banana growing areas
may not be successful. However, pathogens and pests more suited
to local conditions could potentially thrive. A survey to identify
potential quarantine risks and exotic viruses, bacteria, fungi, insects
and nematodes was initiated by HortGuard® and the Carnarvon
Banana Producers Committee.
METHODS
From the approx. 55 banana growing properties in the Carnarvon
area, 15 were selected for assessment based on a range in
production and management practices, yields and years in
production. Survey activities comprised three main areas, each with
specific sampling methods.
Nematodes. From each property, soil and roots were collected from
ten trees using methods adapted from Pattison et al. (1). Sample
trees were chosen randomly within older blocks where nematode
numbers were likely to be higher. Roots were examined for
symptoms. Nematodes were extracted from roots and soil in a mist
chamber over 5 days, then quantified and identified.
Virus, bacteria and fungi. A minimum of 100 plants per property
were inspected. Leaves, pseudostems, suckers and bunches were
visually assessed for symptoms of disease, mechanical and
physiological damage. Symptoms were described in terms of type,
quantity and severity. The most severely infected leaves were
incubated in moist trays under natural light for 2–7 days. For
identification, fruiting bodies on leaves were examined
microscopically, on half strength Potato Dextrose Agar and on Water
Agar. As no symptoms were observed for viruses, further testing was
not conducted.
Invertebrates. At each property 2–4 blocks of different aged plants
were assessed using sweep netting and direct observation. Sweep
net samples were collected from approx. 200 sweeps of the main
canopy and from 100x10 minute sweeps near the plantation floor.
Direct observation (10x hand lens) focused on invertebrates found
on leaves, fruit, flowers and the plantation floor.
RESULTS AND DISCUSSION
Nematodes. No nematodes of quarantine significance were
identified. Root Knot Nematode (RKN, Meloidogyne sp.) and Spiral
Nematode (Helicotylenchus multicinctus) were identified from both
the roots and soil (Table 1). Spiral Nematode and RKN were present
in all samples. Root Lesion Nematode (Pratylenchus sp.) was
identified from the roots, but not the soil in only one sample (2.7/g
dry root). Root symptoms of both RKN and Spiral Nematode were
observed. Typical symptoms of Burrowing Nematode (Radopholus
similis) were absent, and this species was not identified from any
sample.
These nematode levels would not be regarded as a production
constraint in tropical areas. In Carnarvon, where plants did not have
well developed root systems, it is possible that Spiral and Root Knot
Nematodes may have a greater impact (T. Pattison, pers. comm.,
2009). In tropical areas, Spiral Nematode is of secondary importance
to Burrowing Nematode. However, in areas where temperature and
rainfall conditions are limiting, R. similis is rare, and H. multicinctus is
the major nematode problem which can cause severe damage and
decline in bananas.
Table 1. Spiral and Root Knot Nematode (RKN) densities extracted from
roots and soil.
Nematodes/g dry root Nematodes/200g dry soil
Property Spiral RKN Spiral RKN
1 473.0 25.9 533.1 58.2
2 0 56.6 8.5 357.6
3 162.2 67.4 183.7 164.4
4 142.9 32.0 1418.9 54.2
5 638.9 9.7 892.4 29.6
6 530.4 83.1 236.5 19.4
7 254.8 22.8 245.6 18.9
8 149.5 39.0 571.6 89.1
9 458.1 21.7 577.2 25.5
10 344.5 22.1 1141.9 26.8
11 38.4 279.9 59.4 80.2
12 675.5 1.3 640.6 7.7
13 415.0 188.3 404.7 11.4
14 433.8 3.8 450.1 8.4
15 12.5 200.9 0 167.3
Virus, bacteria and fungi. No diseases of quarantine significance
were identified. From the 20 samples collected, secondary fungal
pathogens were identified from 14, including Alternaria sp.,
Stemphyllium sp., Penicillium sp. and Aspergillus sp. Colletotrichum
sp. was identified from leaf spots on one sample. Pleospora
herbarum was identified from one sample of a leaf spot with dark
margin and bleached centre. P. herbarum is a cosmopolitan fungus
that is occasionally a weak parasite known to cause leaf spots.
Invertebrates. No pests of quarantine significance were identified.
Pest levels were low over the entire area. Seventy per cent of the
surveyed properties use biocontrol agents, which may account for
the low pest numbers. Large numbers of spiders, which are
beneficial in reducing pest invertebrates, were found on all
properties. These included typical wheel‐web spiders (Araneidae)
such as Eriophora spp. as well as Sparassidae, Lycosidae and
Salticidae.
CONCLUSION
No exotic pests or diseases were identified. Only low levels of fungal
pathogens and invertebrate pests were detected. The unique
environmental conditions of Carnarvon, as well as its isolation from
other banana growing areas, may contribute to this finding.
Although Burrowing Nematode (R. similis) was not detected, Spiral
and Root Knot Nematodes may pose a potential production
constraint to bananas in this area.
ACKNOWLEDGEMENTS
Thanks to the Carnarvon Banana HortGuard ® Committee and the
APC Carnarvon Banana Producers Committee for supporting and
funding this work. D. Parr and S. Lawson assisted with sample
collection. H. Hunter, X. Zhang, L. De Brincat, C. Wang, M. You and N.
Eyres processed, and identified samples in the laboratory.
REFERENCES
1. Pattison T, Stanton J, Treverrow N, Lindsay S, Campagnolo D (2000)
Managing Banana Nematodes. 2nd ed. Qld Horticulture Institute,
DPIQ.
Session 1B—Disease surveys
APPS 2009 | PLANT HEALTH MANAGEMENT: AN INTEGRATED APPROACH 27