John Fosu-Nyarko

Australia has a well-developed system for the regulation of genetically manipulated (GM) and gene-edited (GEd) organisms, including grains and horticultural crop plants. The aim is to protect the health and safety of people and the environment by identifying any risks posed by gene technology. It is based on two Commonwealth legislative acts, the Gene Technology (GT) Act 2000 and the Gene Technology Regulations 2001, with corresponding State and Territory laws. The GT Act included establishing the Office of the Gene Technology Regulator (OGTR), which is overseen by the Gene Technology Regulator, who takes advice and consults with a range of bodies, and is responsible for ensuring the monitoring and compliance of the GT legislation. There have been a series of reviews of the National Gene Technology Scheme to modernize and future-proof it in response to new scientific developments. Following a consultative review process (2016–2019), to address national policy on the products of various new GEd technologies (including site-directed nucleases: SDN-1, SDN-2, SDN-3 and olignucleotide-directed mutagenesis—ODM), in October 2019 the decision was released to deregulate SDN-1 products not generated via transgenic approaches, but not those which used SDN-2, ODM or SDN-3 technologies, which remain captured as GMOs. Thus only products of SDN-1 technology which do not contain any externally introduced DNA bases can be grown in the same way as products of conventional breeding activities.

In New Zealand, GM and GEd organisms are regulated by the Hazardous Substances and New Organisms (HSNO) Act 1996 administered by the Environmental Protection Agency (EPA). In an initial determination in 2012, the EPA determined that organisms produced using GEd methods, where no foreign DNA remained in the edited plant, were not GMOs. However, in 2014, following an appeal to this decision by the Sustainability Council of New Zealand Trust (Sustainability Council) in the High Court, the determination of the presiding judge was to overturn the EPA’s decision. Thus the current status of all GEd products in New Zealand is that they are regulated as GMOs.

Nonliving food products of GM or GEd technology are overseen by Food Standards Australia New Zealand (FSANZ); the Australia New Zealand Food Standards Code applies to GM and GEd foods. FSANZ is currently reviewing its position on GEd foods, and at present considers applications for GEd food on a case-by-case basis.

Plant-parasitic nematodes are found in most places in the world. The most prevalent ones have a broad host range, so wherever they are located, whether in a backyard garden or on a commercial farm, they are likely to be pests. For this reason, readily accessible, relatively inexpensive, and environmentally friendly methods of control have been sought and applied to control many species of these pests. One such control strategy is organic amendments, of which many types have been demonstrated as a potentially successful method for controlling different types of plant nematodes. This chapter discusses the biochemical and molecular mechanisms underlying the efficacy of organic amendments, the direct effects of active compounds, and the indirect adverse impact on various aspects of the life cycle of different plant-parasitic nematodes. Caveats in interpreting data on the applications of organic amendments to control nematodes and other factors that may dictate their efficacy are also discussed.

The biology of migratory plant parasitic nematodes has been less studied than that of the sedentary endoparasites. The damage they cause is less obvious, their presence and number are more difficult to quantify and they are difficult organisms to study. Nevertheless, they are economically serious pests of many crops, from wheat and barley grown in low rainfall areas to horticultural crops (e.g. Lilium longiflorum) and tropical crops such as coffee, banana and sugarcane. The most studied migratory nematodes are the root lesion nematodes, Pratylenchus spp., the burrowing nematode Radopholus similis and the rice root nematode Hirschmanniella oryzae. In the life cycle of migratory nematodes apart from the egg, all stages of juveniles and adults are motile and can enter and leave host roots. They do not induce the formation of a permanent feeding site, but feed from individual host cells. They create pathways for entry of other root pathogens, often resulting in lesions, stunted roots, yellowing of leaves and plants showing symptoms of water stress, leading to yield loss and decreased quality of produce. In terms of genetic plant defences, no major genes for resistance to migratory nematodes have been found, and resistance breeding is usually based on QTL analysis and marker-assisted selection to combine the best minor resistance genes. Feeding damage reduces root function, and root damage and necrotic lesions the nematodes cause can then make them leave the root and seek others to parasitise. Infestation induces classical plant defence responses and changes in host metabolism which reflects the damage they cause, although detailed studies are lacking. New genomic resources are becoming available to study migratory endoparasites, and the knowledge gained can contribute to improved understanding of their interactions with hosts. Notably transcriptomes of Pratylenchus coffeae, Pratylenchus thornei, Pratylenchus zeae, R. similis and H. oryzae and the first genomic sequence, for P. coffeae, are now available. From these data, some candidate effector genes required for parasitism have been identified: many effectors similar to those found in sedentary endoparasites are present, with the exception of those thought to be involved in formation of feeding sites induced by the sedentary parasites. Belowground defence, in the form of enhanced resistance to migratory parasites, may also be achieved by transgenic expression of modified cysteine protease inhibitors (cystatins), anti-root invasion peptides and host-induced gene silencing (RNAi) strategies, demonstrating that migratory nematodes are amenable to control by these technologies. New more environmentally friendly nematicides, combined with better biological control agents, can be applied or used in seed coatings in integrated pest management approaches to defend roots from attack by migratory nematodes.

Research is in progress to use biotechnological tools to aid development of new forms of diagnostics and resistance to nematodes in wheat. For diagnostics, protein profiling by MALDI-TOF mass spectroscopy has been used to identify a range of nematode species, including seed gall, root-lesion and stem nematodes. Nematode species, and in some cases, races, can be identified and differentiated on the basis of characteristic protein biomarkers. A reproducible assay system for compounds that affect root-lesion nematode replication, based on carrot mini-discs, has been developed. Genomic studies have also been initiated to generate eDNA libraries and genomic sequences of root lesion and cereal cyst-nematodes. For new forms of genetic resistance to nematode pests of cereals, molecular approaches are in progress to identify new gene targets, generation of potential resistance-conferring gene constructs and their introduction into wheat by particle bombardment followed by regeneration and challenge to identify nematode resistant wheat plants.

SCMoV has isometric particles, about 25 nm in diameter, which contain one genomic ssRNA molecule (4,258 nucleotides). Most naturally occurring isolates also contain either one or both of two ssRNA satellite molecules. The virus is readily mechanically transmissible. It is transmitted naturally from plant to plant by contact, mainly through trampling by stock and on the wheels of vehicles. SCMoV has a narrow host range among dicotyledonous plants. Its known geographical incidence is limited to the southern parts of Australia where infection is widespread in annual legume-based pastures. It causes significant economic losses in such pastures, especially in those dominated by Trifolium subterraneum.