First report of Melodogyne fallax hosted by Trifolium repens (white clover): implications for pasture and crop rotations in New Zealand

Abstract

The root-knot nematode Meloidogyne fallax is reported for the first time from white clover roots in New Zealand. Identity of the nematodes from single egg mass culture was confirmed by DNA sequencing along with morphological characters of the juveniles and relative gall size. The implications of this and previous host records on the ability of farmers and growers to devise effective rotations to manage this nematode are discussed.Keywords False Columbia Root-knot nematode . Fodder beet . Invasion potential . Host range Meloidogyne fallax was first recorded in New Zealand in 1998 from potato (Solanum tuberosa) tubers, and infected cotula (Lepinella spp.) roots from lawn-bowling greens (Marshall et al. 2001). In July 2011 a sample of fodder beet (Beta vulgaris) was received at the AgResearch Nematology lab, Ruakura. The sample was from a crop which had been reported to have poor yield of uncertain cause. Many fine roots of the beet tubers were affected by root-knot nematode galls ( Fig. 1). DNA extraction (Shah et al. 2009) and ITS sequencing (Shah et al. 2010) of single juvenile (ie J2) nematodes from some of these galls confirmed morphological observations that they were M. fallax. Further putative M. fallax eggs and J2s were extracted from beet crop fine roots and inoculated onto tomato plants (cv. Rutgers) to establish a culture of these nematodes. This culture was maintained in the Ruakura nematology glasshouse and subsequent DNA sequencing again confirmed these as M. fallax.The first indication that white clover may host M. fallax was in April 2012 when a soil sample was taken below a patch of white clover in an unused stock access way at Ruakura. Upon extraction from the soil, nematodes morphologically and molecularly matching M. fallax were observed. In an attempt to confirm this, nematodes from the putative M. fallax tomato culture were inoculated into two pots of white clover seedlings in June 2012. One month post inoculation, all the white clover roots contained small galls with adult female egg masses.To confirm the identity of the putative M. fallax from tomato culture, and its ability to be hosted by white clover, twelve white clover seedlings were each grown in a 10 ml Eppendorf pipette-tip filled with 1:4 sand: potting mix. Two weeks after sowing, plants were inoculated with single egg masses of the putative M. fallax. Inoculated plants were maintained in a controlled environment room for 8 weeks at 20°C, transferred to a 10 cm diameter pot filled with potting mix and maintained in the controlled environment room for a further 2 weeks. Subsequently, the pots were transferred to a glasshouse and maintained for 2 weeks, after which the roots were evaluated for galling. All inoculated plants produced galled roots. Egg masses with females were picked from root galls, cleaned thoroughly with distilled water and allowed to hatch in water at ambient temperature. Morphology of the second stage juveniles was observed through a microscope and single J2s picked for DNA extraction and subsequent ITS s...

Quantifying the economic cost of invertebrate pests to New Zealand’s pastoral industry

“…Bell pers obs). M. fallax is a species with a wide host range (Rohan et al 2016) which has only been described from New Zealand since 2001 (Marshall et al 2001) but Figure 10. Populations of Heterodera and Meloidogyne nematodes in soil beneath white or Caucasian clover plots sown in September 1994 into a Bay of Plenty field with a continuous 15 year history of maize growing, and adjacent long-term pasture (data from a study described in Watson et al (1996).…”

“…This situation may now be changed with the expanded occurrence of M. fallax (NL Bell pers obs) which is hosted by Italian ryegrass (Den Nijs et al 2004) enabling it to endure such a sequence in greater numbers than the more cloverspecific species previously considered. M. fallax is also hosted by fodder beet and white clover (Rohan et al 2016) so is clearly an increased risk to successful pasture renewal, over and above those species previously considered.…”

Detection of Invertebrate Suppressive Soils, and Identification of a Possible Biological Control Agent for Meloidogyne Nematodes Using High Resolution Rhizosphere Microbial Community Analysis

“…White clover is a very good host for the resident M. trifoliophila in soil 3 (Mercer and Miller, 1997), as illustrated in this case by the relatively large amount of galling observed on plant roots from the control treatment. The M. fallax observed in soil 4 prior to sowing is also hosted by white clover (Rohan et al, 2016) but in this case appears to have been present in too few numbers initially to be able to establish a population causing noticeable galling in the control treatment, as was also the case for the putative M. trifoliophila in soil 2.…”

“…Meloidogyne hapla stock populations [confirmed as such by ITS sequencing (555 bp sequence 99% match to M. hapla (GenBank reference: LC030360), query coverage 100%, see Rohan et al, 2016 for PCR methodology)] were established and maintained on tomato plants ( Solanum lycopersicum cv. ‘Rutgers’) under glass house conditions.…”

Commodity risk assessment of Acer spp. plants from New Zealand

“…According to EPPO (online_c), Marshall et al (2001) and Rohan et al (2016), the pest was detected in the North and the South Island.…”