As technology improves, the ability to more accurately identify pests such as pathogenic nematodes is crucial to minimising potential crop losses. 

Nematodes are often described as micro-worms and there are tens of thousands known to exist. Many are beneficial to soil health, but pathogenic nematodes such as Guava Root Knot Nematode and cyst nematodes are serious pests in vegetable crops. 

Identification of nematodes has been ongoing for decades, but with advancements in technology it is becoming easier to identify previously unknown nematodes, and confirm existing identifications.  

With the discovery of Guava Root Knot Nematode (GRKN) in the Northern Territory in 2022 and later in Queensland in 2023, the impetus to determine whether the nematode is a new incursion, or one that has been on our shores far longer, will influence the management practice for the pest. 

Guava root knot nematode is a devastating plant parasite causing significant crop losses on a global scale. This nematode has a broad host range spanning 30 plant families, including many important food crops. Notably, guava root knot nematode is a resistance-breaking species, causing severe damage to crops with genetic resistance to other root-knot nematode species. 

Consequently, this nematode is a significant biosecurity risk for multiple crops in Australia and is rated in the high to extreme risk categories on the biosecurity plans for multiple industries, including onions, potatoes, sweetpotatoes, and other vegetables. The wide host range and resistance-breaking characteristics of GRKN facilitates rapid spread, and this species is very difficult to control. Preventing establishment of this species in production areas where it was previously not present is thus critically important.  

The project Industry preparedness for exotic root knot nematode (MT22012), undertaken by CSIRO’s National Research Collections Australia, aims to use the latest advancements in molecular screening to provide a better understanding of the historic distribution of root-knot nematodes occurring in Australia and develop an identification tool for these nematodes that will be more cost effective than methods presently available. 

Dr Daniel Huston is part of the CSIRO team investigating identification systems for root knot nematodes.

“It is possible that Guava Root Knot Nematode has been around for a while and had only been identified recently with the use of molecular diagnosis techniques,” said Dr Daniel Huston, Research Scientist with the Australian National Insect Collection (ANIC-CSIRO). 

“In the past, identification was often based on what plant and the location where it was found to give a name to the nematode.” 

Dr Huston explained that by looking through historic specimens, the project aims to determine whether GRKN is truly a recent arrival or if it’s actually been present in Australia for some time. 

“Having this information before the nematode was first detected could have given us an idea of whether eradication was feasible or not,” he said. 

“But we didn’t know we needed that information at the time! The NT government has moved to management, but understanding the timing of arrival of GRKN will still be useful for future management plans, and the methods will be useful for future incursions.” 

The project therefore needs to develop a means of identifying nematodes, and review historical samples to diagnose the species that may have been incorrectly identified. 

The female root knot nematode has a distinctive ‘fingerprint’ that may identify its species.

Root knot nematodes have intricate, fingerprint-like patterns on the female body, but at half a millimetre in diameter, identification can be subject to human interpretive error.  

Dr Huston and colleagues at CSIRO are developing an AI approach to identify nematodes via high resolution images taken with a light microscope to capture the unique fingerprint each species presents. 

“Each nematode image is constructed from a stack of images compiled together to give the best possible resolution. From there, AI software will be given the images and ‘taught’ how to recognise different nematode species,” said Dr Huston. 

“From there, we can potentially identify any root knot nematode around the world as we expand our image database to more species, providing a quick way to identify these species and screen historic specimens from collections.” 

Another issue which makes working with historic specimens difficult is that many of them have been preserved in formalin, a formaldehyde solution. 

Formalin causes DNA to fragment, making it extremely difficult to analyse, however a recent methodology developed by CSIRO to extract DNA from formalin preserved samples will give Dr Huston a means of cross checking the fingerprint images with molecular identification of nematodes. 

“With GRKN, we anticipate that the two-pronged approach will enable us to correctly identify the nematode in current and historical samples so that we confidently say whether it is a new incursion, or if it has been in Australia for some time,” he said. 

“These identification systems can potentially be extended to other pest species so that we can pre-screen specimen collections for historic pest distributions to inform how we deal with an incursion more quickly to reduce the impact on Australian crops.”