Characterisation of the Rk1 resistance to Meloidogyne in tobacco by RNA-Seq analysis
The root-knot nematode (Meloidogyne spp.) is a major pest causing severe damages in many tobacco growing areas such as Europe, Brazil or Africa. The use of nematicides to fumigate soils is not compatible with efforts to reduce agrochemical residues on tobacco. With crop rotation, the most efficient alternative is to develop resistant cultivars adapted to the repartition of the different species of Meloidogyne: M. incognita, M. arenaria, M. javanica.
The Rk1 dominant gene in tobacco conditions resistance to races 1 and 3 of the root-knot nematode Meloidogyne incognita. This resistance coming from Nicotiana tomentosa has been widely used for controlling nematodes in modern commercial cultivars such as K326 or NC95, with the help of RAPD markers to pilot the transfer.
In order to identify the Rk1 gene responsible for nematode resistance, RNA-Seq analysis of a panel of 30 tobaccos was used to compare differentially expressed genes between resistant and susceptible flue-cured cultivars. Candidate contigs have been identified, including sequences having high homology with late blight resistance homolog protein of tomato and potato.
Two contigs belonging to the same gene were validated, by confirming the N. tomentosa origin of these sequences, and also by testing on a F2 segregating population characterised for the presence of Rk with a SCAR marker developed from RAPD. Finally, this gene was also validated on 800 cultivars of the Imperial Tobacco collection.