Effect of host plant on the genetic diversity of Tetranychus urticae Koch populations and their susceptibility to fungal infection

Abstract We studied the effect of host plant on the genetic population structure of Tetranychus urticae Koch populations and their susceptibility to fungal infection. We sampled adult T. urticae from ten locations, comprising six Rubus ulmifolius Schoot (blackberry) orchards and four R. idaeus L. (raspberry) orchards. Using sequence information from a fragment of the mitochondrial cytochrome oxidase subunit I (COI), phylogenetic relationships and genetic population structure of each group were determined using haplotype network analyses and an analysis of molecular variance (AMOVA). Based on these results, four populations were selected to compare their susceptibility to isolates of Beauveria bassiana (Bals.-Criv.) Vuill., Metarhizium anisopliae (Metschn.) Sorokīn, Lecanicillium lecanii (Zimm.) Zare & W. Gams and Isaria fumosorosea Wise. Two populations from raspberry (var. ‘7-UDV’ and var. ‘8-UDV’) and two from blackberry (var. ‘Tupy’ and var. ‘2-UDV’) were studied. Haplotype network analysis identified eight haplotypes. The greatest genetic diversity was found in the ‘7-UDV’ raspberry population which had five haplotypes; the remaining populations had one or two haplotypes each. The AMOVA analysis showed that neither host plant nor geographical origin explained all the genetic variation. The ‘2-UDV’ population was the most susceptible to fungal infection, followed by ‘Tupy’, both of which were from blackberry. The fungal isolates that caused greatest mortality in T. urticae were M. anisopliae and B. bassiana . In the least susceptible populations (‘7-UDV’ and ‘8-UDV’, both from raspberry), all isolates still caused some mortality, but there were no differences amongst the isolates. Our results suggest that host plant plays a role in the susceptibility of T. urticae to fungal infection, but not in their genetic population structure.