Are there variants to Mesocriconema xenoplax in California?

SYSTEMATICS OF MESOCRICONEMA XENOPLAX REVISITED: COMBINED ANALYSIS OF MORPHOLOGICAL AND MOLECULAR MARKERS.

Irma Tandingan De Ley,¹ Qi Li,¹ Joaquín Abolafia-Cobaleda,² Michael McKenry,¹ Isgouhi Kaloshian¹ & Paul De Ley.¹ ¹Department of Nematology, University of California, Riverside CA 92521, USA; ²Departamento de Biología Animal, Biología Vegetal y Ecología, Universidad de Jaén, Jaén, 23071, Spain

Abstract

The ring nematode Mesocriconema xenoplax is a widespread species whose systematics is complicated by numerous taxonomic and diagnostic problems. Field data suggest that California isolates of M. xenoplax respond differently on identical grape rootstock varieties. Microplots were therefore established to test the interaction of 5 isolates (three inland isolates Parlier, Belmont, and Livingston; and coastal isolates Los Alamos and Mendocino) in 2 different rootstocks and with or without their associated soil biota. Vines that grew the greatest biomass provided highest nematode build-up. The less vigorous 420A rootstock supported vines that yielded least or were in decline by the fifth year. Generally, the Parlier isolate had the highest reproductive potential in the presence or absence of suspected suppressive soils and regardless of host genotype.

In order to determine whether differences in reproduction between these populations correspond to detectable morphological and/or molecular differences, we analyzed individual nematodes with Video Capture and Editing followed by Polymerase Chain Reaction of the rDNA Internal Transcribed Spacer region (ITS) and large subunit D2D3 domain. Sequence analysis revealed the existence of two prevalent variants, differing from one another by eight substitutions in ITS and corresponding to a coastal haplotype versus a Central Valley haplotype. The latter included a population from the type locality of M. xenoplax. A few of the analyzed individuals exhibited single nucleotide polymorphisms matching the character state of either haplotype for the corresponding nucleotide positions. Both ITS and D2D3 phylogenetic analyses suggested that the 2 coastal populations formed a cluster within a clade that also included the 3 central valley populations. Observed genetic differences corresponded with a phenotypic difference in stylet length, with the coastal populations possessing smaller stylets compared to the Central Valley populations.

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