Most Australian vegetable growers apply fumigants or nematicides as a precautionary nematode control measure when crops susceptible to root-knot nematode (RKN, Meloidogyne spp.) are grown in soils and environmental conditions suitable for the nematode. The only way growers can make rational decisions on whether these expensive and environmentally disruptive chemicals are required is to regularly monitor RKN populations and decide whether numbers prior to planting are high enough to cause economic damage. However, such monitoring programs are difficult to implement because nematode quantification methods vary in efficiency and the damage threshold for RKN on highly susceptible vegetable crops is often < 10 root-knot nematodes /200 mL soil. Consequently, five nematode quantification methods were tested to see whether they could reliably detect these very low population densities of RKN. Two novel methods produced consistent results: 1) extracting nematodes from 2 L soil samples using Whitehead trays, quantifying the RKN DNA in the nematode suspension using molecular methods, and generating a standard curve so that the molecular results provided an estimate of the total number of RKN individuals in the sample, and 2) a bioassay in which two tomato seedlings were planted in pots containing 2 L soil and the number of galls produced on roots were counted after 21-25 days. Both methods could be used to quantify low populations of RKN, but bioassays are more practical because expensive equipment and facilities are not required and they can be done at a local level by people lacking nematological or molecular skills.

Considerable losses are inflicted by plant-parasitic nematodes (PPNs) due to their obligate parasitism; serious damage occurs in many susceptible crops, and the parasites have a broad distribution worldwide. As most PPNs have a subterranean nature, the complexity of soils in the plant rhizosphere and the structures and functions of the soil food webs necessitate a grasp of the relevant biotic/abiotic factors in order to ensure their effective control. Such factors frequently lead to the inconsistent performance and untapped activity of applied bionematicides, hindering efforts to develop reliable ones. Research efforts that take these factors into account to back the usage of these bionematicides by combining the disease-suppressive activities of two or more agricultural inputs are highlighted herein. These combinations should be designed to boost useful colonization in the rhizosphere, persistent expression of desirable traits under a wide range of soil settings, and/or antagonism to a larger number of plant pests/pathogens relative to individual applications. Relevant ecological/biological bases with specific settings for effective PPN management are exemplified. Determining the relative sensitivity or incompatibility of some biologicals entails studying their combinations and reactions. Such studies, as suggested herein, should be conducted on a case-by-case basis to avoid unsatisfactory outputs. These studies will enable us to accurately define certain outputs, namely, the synergistic, additive, neutral, and antagonistic interactions among the inputs. In optimizing the efficiencies of these inputs, researchers should consider their multi-functionality and metabolic complementarity. Despite previous research, the market currently lacks these types of safe and effective products. Hence, further explorations of novel integrated pest management plans that boost synergy and coverage to control multiple pathogens/pests on a single crop are required. Also, setting economic incentives and utilizing a standardized regulation that examines the authentic risks of biopesticides are still called for in order to ease cost-effective formulation, registration, farmer awareness, and usage worldwide. On the other hand, tank mixing that ensures legality and avoids physical and chemical agro-input-based incompatibilities can also provide superior merits. The end in view is the unraveling of the complexities of interactions engaged with in applying multiple inputs to develop soundly formulated, safe, and effective pesticides. Sophisticated techniques should be incorporated to overcome such complexities/limitations. These techniques would engage microencapsulation, nanopesticides, volatile organic compounds as signals for soil inhabitants, bioinformatics, and RNA-Seq in pesticide development.

The root-knot nematode (RKN) causes significant yield loss in tomatoes. Understanding the interaction of biocontrol agents (BCAs)-nematicides-soil microbiomes and RKNs is essential for enhancing the efficacy of biocontrol agents and nematicides to curb RKN damage to crops. The present study aimed to evaluate the in vitro effectiveness of BACa and nematicide against RKN and to apply the amplicon sequencing to assess the interaction of Bacillus velezensis (VB7) and Trichoderma koningiopsis (TK) against RKNs. Metagenomic analysis revealed the relative abundance of three phyla such as Proteobacteria (42.16%), Firmicutes (19.57%), and Actinobacteria (17.69%) in tomato rhizospheres. Those tomato rhizospheres treated with the combined application of B. velezensis VB7 + T. koningiopsis TK and RKN had a greater frequency of diversity and richness than the control. RKN-infested tomato rhizosphere drenched with bacterial and fungal antagonists had the maximum diversity index of bacterial communities. A strong correlation with a maximum number of interconnection edges in the phyla Proteobacteria, Firmicutes, and Actinobacteria was evident in soils treated with both B. velezensis VB7 and T. koningiopsis TK challenged against RKN in infected soil. The present study determined a much greater diversity of bacterial taxa observed in tomato rhizosphere soils treated with B. velezensis VB7 and T. koningiopsis TK than in untreated soil. It is suggested that the increased diversity and abundance of bacterial communities might be responsible for increased nematicidal properties in tomato plants. Hence, the combined applications of B. velezensis VB7 and T. koningiopsis TK can enhance the nematicidal action to curb RKN infecting tomatoes.