Population and molecular genetics of root-knot nematodes

This thesis describes studies of root-knot nematodes Meloidogyne spp. - an economically important pest in agriculture - using population and molecular genetics. Variability in virulence to Mi bearing tomato genotypes is shown for Meloidogyne spp . isolates and their impact of implementation of proper management systems is discussed. Genetic polymorphisms in Meloidogyne spp. were assessed using molecular techniques that reveal nuclear and mitochondrial DNA divergence on different hierarchical levels. cDNA library constructed from the pre-parasitic second stage juveniles of Meloidogyne incognita was screened by single pass 5'-end sequencing to investigate genes expressed at the onset of parasitism. One expressed sequence tag homologous to an endoxylanase was used to identify a novel cell wall degrading enzyme - xylanase. Several lines of evidence support the endogenous origin of the nematode xylanase. The amino acid sequence revealed a high similarity with bacterial xylanases indicating that nematode xylanase may have been acquired from bacteria by horizontal gene transfer.