Plant parasitic nematodes (PPNs) are important pests of crop plants. Root-knot (Meloidogyne spp) and cyst nematodes (Heterodera, Globodera spp) are the two most damaging genera. They are difficult to control using crop rotation, chemical nematicides or biological control, and many nematicides have now been banned. RNA interference (gene silencing) technology is a potential alternative genetic approach for nematode control. A challenge of an RNAi-based transgene approach (‘Host-Induced Gene Silencing’) is to generate plants that express nematode control transgenes stably over many generations. Various factors can influence transgene stability (e.g., the target selected, transgene copy number, promoter methylation, sequence similarity). The aim of this research is to study the inheritance of RNAi in plants conferring resistance to PPNs to underpin knowledge of the application of RNAi as a strategy to confer nematode resistance in crop plants.
T2 seeds of different transgenic events expressing RNAi for 12 target genes are being studied to determine the segregation patterns in subsequent generations and the stability of nematode resistance. Replicated nematode challenges of transgenic events have been undertaken for populations of T2 and T3 plants, in which there was a signficant reduction in nematode reproduction. In a reciprocal study, infection assays evaluating progeny nematodes for maintenance of reproductive suppression will be done with control plants. A major question is whether knockdown of target genes is stably heritable between generations, and qRT-PCR will be used to characterise this. Next generation sequencing will be used to compare characteristics of small interfering RNAs processed by different generations of transgenic plants as part of the RNAi process. The outcomes of this study will help optimise and support an RNAi-based nematode control strategy over multiple generations: stability in RNAi- based traits is vital for this strategy to be used to reduce the economic losses caused by plant nematodes.