The host range paradox of Meloidogyne incognita : a physiological and transcriptomic analysis of nine susceptible interactions across six plant orders

Summary The plant–parasitic nematode Meloidogyne incognita is the pathogen with the broadest host range among all known biotrophic interactions. This species is also the single most damaging of a group of agriculturally important plant parasites, which together are estimated to contribute to losses in excess of $170 billion yr −1 to world agriculture. Understanding how M . incognita is able to infect representatives from most orders of flowering plants, covering more than 3000 species, addresses a fundamentally important question of how pathogens adapt to their host‐environment, and may inform control of a pathogen, which threatens global food security. Here, we analyse the plant‐nematode infection phenotype and cross‐kingdom transcriptome of nine interactions across six orders of flowering plants at 25 d post infection. Our data show that the phylogenetic distribution of hosts does not explain the phenotypic distribution of parasitism. Three distinct nematode ‘transcriptional programmes’ are evident, and we find that effectors are neither uniformly deployed across hosts nor across groups of hosts. Nevertheless, this differential deployment of effectors can determine host specificity. Finally, we show that there is no widespread core gall transcriptome at 25 d post infection, prompting the proposal of a model best described as ‘all roads lead to Rome’.