Rhys G. R. Copeland

Root-lesion nematodes (Pratylenchus spp.) reduce the yield and quality of cereal crops in Australia. Eleven of the ~90 species characterised are present in Aus-tralia, with those determined as economic pests of broadacre agriculture costing an estimated AUD 250 million annually. Two species, P. curvicauda and P. quasitereoides, recently re-described, were isolated from fields located in the grainbelt of Western Australia, but little is known about their distribution in the region surveyed in this study. To investigate this and possible co-infestations with other Pratylenchus spp., we surveyed seven commercial wheat, barley, and oat farms near Katanning, Cancanning, Kenmare, Duranillin, Darkan, and a barley seed-bulk nursery near Manjimup, all in the southwest grainbelt of Western Australia. Morphological and molecular charac-terisation of Pratylenchus spp. extracted from soil and plant roots indicated all fields surveyed were infested. Both P. quasitereoides and P. curvicauda were present as single or mixed populations with P. penetrans and/or P. neglectus, although they were not found in the same field. Analyses of the D2–D3 sequences of the identified nematodes indicated that the species found in Australia were distinct, particularly P. quasitereoides and P. curvicauda. This work suggests P. curvicauda is likely to be present more widely in the WA grainbelt. Expanding molecular diagnostic testing for Pratylenchus species in the region to account for both nematodes is urgently needed so effective management can be implemented.

As global climate change intensifies, the occurrence and severity of various abiotic stresses will significantly threaten plant health and productivity. Drought stress (DS) is a formidable obstacle, disrupting normal plant functions through specific morphological, physiological, biochemical, and molecular mechanisms. Understanding how plants navigate DS is paramount to mitigating its adverse effects. In response to DS, plants synthesize or accumulate various plant growth regulators (PGRs), including phytohormones, neurotransmitters, gasotransmitters, and polyamines, which present promising sustainable green chemical strategies to adapt or tolerate stress conditions. These PGRs orchestrate crucial plant structure and function adjustments, activating defense systems and modulating cellular‐level responses, transcript levels, transcription factors, metabolic genes, and stress‐responsive candidate proteins. However, the efficacy of these molecules in mitigating DS depends on the plant species, applied PGR dose, treatment type, duration of DS exposure, and growth stages. Thus, exploring the integrated impact of PGRs on enhancing plant fitness and DS tolerance is crucial for global food security and sustainable agriculture. This review investigates plant responses to DS, explains the potential of exogenously applied diverse PGRs, dissects the complex chemistry among PGRs, and sheds light on omics approaches for harnessing the molecular basis of DS tolerance. This updated review delivers comprehensive mechanistic insights for leveraging various PGRs to enhance overall plant fitness under DS conditions.

Root lesion nematode (RLN; Pratylenchus spp.) infestations cause over $250 million in economic damage to Australian grain production annually. Two new species, P. quasitereoides and P. curvicauda, have been described recently in Western Australia (WA). After P. neglectus, P. quasitereoides is considered one of the most economically important Pratylenchus spp. in WA in terms of damage caused to cereal crops. The extent of economic losses caused by P. curvicauda has not yet been determined, but its ability to multiply on many cereal crops and other crop hosts makes it a potentially serious pest. Recent studies suggest that there could be mixed infestations by the two nematodes in the WA grainbelt, such infestations could be more damaging to cereal production than when only one species is present. One major aim of this research was to investigate how widespread the two species are in the southwest grainbelt of WA. A second major aim was to understand how RLNs find appropriate host roots.

Of the seven cereal fields sampled from a relatively wide area, morphological and molecular diagnostics indicated that P. quasitereoides was present in four fields, whereas P. curvicauda was present in two. They also existed as single or mixed infestations with P. penetrans and/or P. neglectus. However, the two species were not found co-infesting plants in the same field. The work confirmed the presence of P. curvicauda, which may be more widespread than previously thought, and indicates that commercial soil testing (‘Predicta B’) should be re-assessed to identify the presence of P. curvicauda in farmers’ fields, since management protocols need to be species-specific.

Metabolite profiles of root exudates of the wheat cv. Calingiri (susceptible to Pratylenchus neglectus) and triticale cv. 342 (resistant to P. neglectus) were used to evaluate if metabolites influence susceptibility or resistance to P. neglectus infection. GC-MS profiles of the two cultivars revealed that the concentrations of 51 metabolites differed between control plants and plants exposed to P. neglectus, 24, 48 and 72 hours after nematode exposure, suggesting that some metabolites may play a role in the response of the plants to nematode infection. Of these metabolites, eight were identified as potential attractants and thirteen as potential repellents. When the potential roles of five metabolites were assessed using chemotaxis assays, the concentrations used showed maltose and propanoic acid attracted the nematodes, but glycerol and fructose were potential repellents. Lower ribose concentrations repelled nematodes during the first two hours of the assay, but higher concentrations had the opposite effect.

To investigate how Pratylenchus spp. perceive host signals, such as the metabolites identified in this study, the response of homologues of chemosensory genes of C. elegans to specific metabolites were studied in P. neglectus. Transcripts of 24 of these genes were identified from a PacBio SMRT long-read transcriptome of P. neglectus. Using cellular localisation studies, four of the genes (arr-1, deg-3, klp-11 and gcy-7) were shown to express predominantly in regions associated with sensory organs; in the anterior and posterior regions of the nematode (arr-1 and deg-3), at the base of the stylet (gcy-7), and the region posterior to the nerve ring (klp-11). Following knockdown of the four genes using dsRNA in vitro, the nematodes’ attraction to root exudates and responses to propanoic acid and maltose were significantly reduced, suggesting the four genes were involved in the nematodes’ perception of root exudates, propanoic acid and maltose.

A minor aim, describing the neurons involved in metabolite perception by RLNs, was initiated, but time was lacking to complete this aspect.

The research findings broaden current knowledge on Pratylenchus spp. and their distribution in fields in the southwest grainbelt of WA, with implications on how the newly described species, P. quasitereoides and P. curvicauda should be identified and managed. The results of the metabolomics study highlight possible mechanisms by which susceptible and resistant cultivars interact with RLNs. RNA interference can be used to study genes that may be important to nematode-host interaction. This research contributes new information of value to plant breeders and helps contribute to understanding underlying RLN-crop interactions, so contributing to improving crop productivity.

The adverse effects of mounting environmental challenges, including extreme temperatures, threaten the global food supply due to their impact on plant growth and productivity. Temperature extremes disrupt plant genetics, leading to significant growth issues and eventually damaging phenotypes. Plants have developed complex signaling networks to respond and tolerate temperature stimuli, including genetic, physiological, biochemical, and molecular adaptations. In recent decades, omics tools and other molecular strategies have rapidly advanced, offering crucial insights and a wealth of information about how plants respond and adapt to stress. This review explores the potential of an integrated omics-driven approach to understanding how plants adapt and tolerate extreme temperatures. By leveraging cutting-edge omics methods, including genomics, transcriptomics, proteomics, metabolomics, miRNAomics, epigenomics, phenomics, and ionomics, alongside the power of machine learning and speed breeding data, we can revolutionize plant breeding practices. These advanced techniques offer a promising pathway to developing climate-proof plant varieties that can withstand temperature fluctuations, addressing the increasing global demand for high-quality food in the face of a changing climate.

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.