First Report of Mesocriconema xenoplax from Apricots (Prunus armeniaca) in Ontario, Canada.

Abstract

Plant-parasitic nematodes have been causing more economic losses and related damages to fruit crops in the Province of Ontario than previous estimates. We have been conducting surveys since 2019 for the presence of plant-parasitic nematodes in different orchards in the Niagara region. Collected soil samples were extracted for nematodes following Jenkins (1964). Among the plant-parasitic nematodes identified, we detected ring nematodes (Mesocriconema species) in 87% of the soil samples collected from different apricots fields, ranging from 20 to 200 ring nematode per kg of soil. The apricot cultivar was Haroblush and did not show any symptoms of nematode infestation. The morphometric measurements (mean in μm ± standard deviation, range) of the ring nematodes (adult females), n = 27), body length = (605 +/- 23, 550 - 650), stylet = (75 +/- 8, 65 - 79), a (total body length divided by maximum body diameter = 12 +/- 1.5, 10.2 - 13.9), b (total body length divided by pharyngeal length = 3.6 +/- 0.5, 3.2 - 3.9), c = 20, V (percentage of length from anterior end to vulva position in total body length) = 92 +/- 1.3,91 - 93), R (total body annules = 105 +/- 5, 100 - 110), Rvan (total annules between vulva and anus = 2), and Ran (total annules between anus and tail terminus = 5). Lips sclerotized, with conspicuous and elevated labial disc surrounding the oral aperture, sub-lateral lobes also conspicuous. The stylet was long and robust. Excretory pore was located between 30-31 annuli from the anterior end. The vulva located either between 6 and 7, but mostly between 7 and 8 annuli from the posterior end. The juveniles were similar to the females in body shape with: sub-lateral lobes present, stylet 55-60 µm long, total annuls 80-90, and fine longitudinal lines were observed. Based on the morphology (Figure 1) and morphometric characteristics, the nematode species was identified as Mesocriconema xenoplax, which was consistent with the description by Raski (1952). To further confirm, DNA was extracted from a total of 20 nematodes (females and juveniles), the D2-D3 expansion segment of 28S rDNA amplified using the primer pair: D2A: 5´-ACAAGTACCGTGAGGGAAAGT TG-3', D3B: 5'-TCCTCGGAAGGAACCAGCTACTA-3' (Nunn, 1992). The PCR product was purified and sequenced. The resulting sequence was deposited into the GenBank database and assigned with accession number ON130754. A BLAST search in the NCBI database revealed 99% similarity to sequences of M. xenoplax with accession numbers MH819082.1 and FN433854.1 from South Africa and California, respectively. Eight Haroblush plants were each inoculated with 100 ring nematodes/kg in 5-gallon pots. Haroblush without nematode were maintained as control. The nematode reproduction and symptoms were assessed after 6 and 24 months. The plants did not show below or aboveground symptoms after 6 months. However, root growth reduction, necrosis and death of feeder roots were observed after 24 months when compared to the control. Nematodes extracted from the soil had a mean of 512±48 and 1593±162 ring nematode/kg after 6 and 24 months, respectively, an indication of susceptibility. Mesocriconema xenoplax can cause 85% reduction in root biomass, and yield losses can occur at higher infestations (Pinkerton et al., 2004). Regardless, the potential impact and distribution of this nematode on apricots growth and yield in Ontario are not documented yet. To the best of our knowledge, this is the first report of the ring nematode M. xenoplax on apricots from Ontario, Canada.