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| Mikania project leader Annastasia Kawi conducting laboratory studies on rust fungus, Puccinia spegazzini, in the NARI post-entry quarantine (PEQ) constant temperature room at NARI Kerevat, |
An alien is any species that is found out of its historically normal range.
Often the species will not survive as may not adapt to its new locale due to the locale having slightly different temperatures, seasonal variation, humidity, wind, predators, pests or diseases.
However, in a minority of cases, a plant will be able to survive.
Even more rarely, perhaps in 10% of cases, an alien will thrive in its new location better than in its original location.
This is often because of the absence of a predator or pest that would normally keep the species in check, and because of a biological trait that predisposes it to fast colonisation, such as a fast growth rate and the production of many seeds.
When this happens, the species can spread quickly to become very common and dominant in its new habitat, and is known as ‘invasive’.
A regional workshop on bio control heard that in the Pacific, 300–500 plant species could be regarded as invaders, with about 150 species classified as aggressive.
Mikania micrantha is one such aggressive and invasive weed species.
Often called “mile-a-minute weed”, it can grow as fast as one metre per month.
Mikania is a very destructive invasive weed which spreads far and wide and smothers other plants.
It is found in 17 Pacific Island countries and territories including Papua New Guinea.
Mile-a-minute is thought to have arrived in the Pacific islands in the early 1900s as contaminants of various imported products and is suspected to be a relatively new addition to the flora of PNG.
It has spread rapidly in most islands and coastal plains of mainland New Guinea.
Mikania has been suppressing forest regeneration or has changed the ecology of areas.
Analysis from a socio-economic survey conducted on Mikania indicated that 80% of the respondents in 15 lowland provinces consider mikania as a problematic weed.
Approximately 44% of farmers of subsistence mixed cropping control M. micrantha at least once a fortnight and implies that a lot of their time is spent on clearing this weed from their land.
The fight against mile-a-minute as an invasive weed in the Pacific’s agricultural sector and food security areas has been picking up in the past years with the release in Fiji and PNG of a pathogen rust fungus, to control mikania.
The rust fungus, scientifically known as Puccinia spegazzini, was imported to Fiji by the Secretariat of the Pacific Community (SPC) and the ministry of agriculture as part of their Mikania bio-control project.
The Fiji government gave the permission to import Puccinia following host specificity testing conducted on behalf of Fiji and PNG by the world-renowned Commonwealth Agriculture Bureau International (CABI), based in England.
Some plants, important to PNG and Fiji, were tested by CABI Europe-UK during the whole of 2006 against this rust fungus to make sure it did not attack any of our useful plants or native flora in the Pacific.
Host specificity testing confirmed that the rust fungus was host-specific and restricted to mikania only.
This biological control agent would help reduce unnecessary weeding costs such as labour and herbicide.
Preliminary results from Laboratory studies and field monitoring observations conducted at National Agriculture Research Institute (NARI) Kerevat suggests that mikania growth can be suppressed or reduced when the rust fungus is present on the bio-mass.
In November2008, the rust fungus was imported into PNG as part of an Australian Centre for International Agriculture Research (ACIAR)-funded project to control the Mikania weed.
CABI Europe-UK infected mikania plants grown from stock plants obtained from PNG early in November 2008.
Later that month, the plants were hand-carried to PNG NARI Kerevat by SPC project coordinator Warea Orapa.
Upon arrival, the UK-infected plants were transplanted into sterilised soil with water and placed in an inoculation chamber in the NARI post entry quarantine (PEQ) constant temperature room.
This rust fungus is the first of its kind to be introduced in PNG.
At NARI Kerevat, the rust is maintained and mass propagated for field distribution and monitoring.
Inoculation procedures and culturing, impact assessment, field release and monitoring of the rust are work undertaken to assess the progress of the rust and prevent contamination or pest outbreak.
The monitoring activities were jointly conducted by Mikania project staff from PNG Cocoa and Coconut Institute (PNGCCI), PNG Oil Palm Research Association (PNGOPRA) and NARI who are major collaborators of the ACIAR project in PNG.
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| Field release on rust fungus to the Oil Palm Research Association (OPRA) staff at Hoskins in 2009 |
The rust fungus controls mikania by developing many swollen lumps on leaves, stems and petioles forming copper-colored lumps on the surface of the dead plant parts.
High infection densities of these will reduce the ability of the weed to grow and become aggressive and death can be possible in conditions favourable to the fungus.
During the preliminary field release and monitoring strategy observation done in early 2009 at NARI Kerevat, infected plants were placed in amongst mikania-growing under cocoa and monitored for establishment.
Pustules were observed on mikania growing around the infected plants after three weeks.
Field release techniques used in different microhabitats, found that irrespective of the number of pustules, size of infected pots and time of releases, the rust establishes more easily on young growth stages of mikania compared to mature dense infestations.
Mikania project leader, Annastasia Kawi said: “The results of the average number of leaves infected and average number of pustules present on young mikania three weeks after field release suggests that the rust, when released in conducive environmental conditions, can survive.”
She added that the rust fungus had been released in 46 sites in East New Britain since January 2009 and monitoring of sites was conducted to confirm host specificity of the rust in natural environment.
At NARI Kerevat, the rust had been found growing on mikania near many different plant species and to date no inoculation has been observed on cultivated or wild species of any plant other than mikania.
Mikania has been recorded to be present in 1,052 sites in 15 provinces (excluding Eastern Highlands, Chimbu, Western Highlands, Enga and Southern Highlands province) in PNG.
The bio-control control agent (rust fungus) has been released in 454 sites in those 15 provinces to date.
A total of 80 sites have established in eight provinces and natural spread has been monitored up to 37km after one year.
Since the rust fungus was field established in 2009 in East New Britain and other provinces, monitoring of field establishment have been an important activity of the project.
It is observed that initial establishment is conducive in total or partial shade and near waterways, hence, once established it does well in wetter and cooler environment.
Kawi cautioned farmers to be observant of the biological control agent as it was environmental-friendly, acted as an alternate control option and sustainable in rural farming communities.
More information on the mikania weed can be obtained from NARI Islands regional centre in Keravat on 983 9145/9200.
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