The Interactions of Root-Knot Nematodes and Coffee

Coffee is a major crop that supports the economy of over 60 countries, many of which are developing nations. A major detriment to coffee production is damage caused by plant parasitic nematodes. The most damaging species is the root-knot nematode, Meloidogyne spp. Many conventional methods to control plant parasitic nematodes can be inefficient and costly. This study aimed to characterise the molecular mechanisms that drive interactions of plant parasitic nematodes and Robusta coffee (Coffea canephora), including immune and defence responses of coffee to root-knot nematodes, and behavioural response of the nematode to root exudate of coffee, with a view to the longer-term development of improved nematode control strategies and technologies. The Robusta coffee varieties tested showed a differential physiological response to the infection of root-knot nematodes, as well as showing subtle differences in susceptibility to attack by nematodes. Contrasting varieties in susceptibility and tolerance to nematode attack were then used to compare the transcriptomic changes induced in root and leaf tissue following infection by root-knot nematodes. Genes involved in pathogen recognition, general defence and hypersensitive responses were revealed as key mediators of the Robusta immune response to plant parasitic nematodes. Cell-wall-regulation in coffee was identified as a mechanism that could provide protection against root knot nematode infection. Genes and gene pathways that have been identified could be utilised to develop coffee varieties that have improved protection against plant parasitic nematodes. They may also be used as molecular identifiers of innate tolerance against plant parasitic nematodes. An alternative to identifying and manipulating genetic components of coffee for nematode control would be to disrupt parasitic behaviours of root-knot nematodes to inhibit invasion and reproduction within the crop. Serotonin was immunolocalised within infective stages of root-knot nematodes and established as a key neurotransmitter mediating behaviours essential for root-knot nematode pathogenicity, including chemosensation and stylet function for invasion and feeding. Disrupting serotonin biosynthesis, using established serotonergic chemical inhibitors, also decreased the infective capability of root-knot nematodes. Serotonergic molecular components are suggested that could be targets for root-knot nematode control. Integrating novel genomic controls discussed in this project would provide crop protection against plant parasitic nematodes in coffee and reduce yield losses caused by the pathogen.