Root-lesion nematodes (Pratylenchus spp.) are significant plant parasites, causing substantial crop damage worldwide. This study aimed to characterize Pratylenchus spp. in New Zealand maize fields using molecular techniques and map their prevalence. Soil sampling from 24 maize fields across the North and South Islands provided 381 composite samples. Root-lesion nematodes were extracted using the sieving-centrifugal-sugar flotation method and differentiated into five morphospecies. Molecular characterization involved direct partial sequencing of the D2/D3 28S rDNA, ITS rDNA, and COX1 mtDNA regions using Sanger technology from a single nematode. Five Pratylenchus species were identified: P. neglectus, P. crenatus, P. thornei, P. penetrans, and P. pratensis, confirmed by phylogenetic analysis. Prevalence mapping showed P. neglectus and P. crenatus in all sampled fields, while P. thornei, P. penetrans, and P. pratensis were more localized. This study is the first to report these Pratylenchus species on maize in New Zealand and provides the first partial sequences of the D2/D3, COX1, and ITS regions for these species on maize in New Zealand. The findings highlight the diversity of Pratylenchus populations in New Zealand maize fields and emphasize the need for region-specific management strategies to mitigate crop damage.

The root-lesion nematode, Pratylenchus penetrans, is a ubiquitous parasite of roots of temperate fruit trees. It affects early growth of trees replanted into former orchard sites where populations have built up and may contribute to decline complexes of older trees. Most British Columbia, Canada, apple acreage is planted with M.9 rootstock, but growers are increasingly considering Geneva-series rootstocks such as G.41 and G.935. Among these rootstocks, responses to P. penetrans, specifically, are poorly known. To compare the resistance and tolerance to P. penetrans of G.41, G.935, and M.9 rootstocks ('Ambrosia' scion), a field microplot experiment was established in spring of 2020 at the Summerland Research and Development Centre. The experimental design was a two by three factorial combination of: P. penetrans inoculation (+/-) and rootstock (G.41, G.935, and M.9), with 20 replicate microplots of each of the six treatment combinations arranged in a randomized complete block design. The P. penetrans inoculum was 5,400 nematodes per microplot (54 P. penetrans liter-1 soil), which is below commonly accepted damage thresholds. Though P. penetrans population densities were lower for the G.41 rootstock by the end of the 2021 growing season, the effects of P. penetrans were similar among rootstocks. In the establishment year (2020), P. penetrans caused significant reductions in aboveground growth. In 2021, shoot growth and root weight were reduced by P. penetrans. The nematode also reduced rates of leaf gas exchange and stem water potential. These data suggest that while G.41 and G.935 may have other horticultural benefits over M.9, they are equally susceptible to P. penetrans at the early stages of tree growth.

In California, the expanding pistachio crop has been considered free of serious nematode diseases based on surveys in the 1980s with nematode- resistant rootstocks. During the 1980s, Verticillium wilt started to occur more frequently in pistachio orchards on susceptible rootstocks. This led to the selection and shift to Verticillium wilt-resistant rootstocks of crosses of P. atlantica and P. integerrima, , propagated as seedling or clonal 'UCB1'. In prior research, seedling populations of UCB1 had exhibited differences in nematode susceptibility, leading to the here described testing of commercial UCB1 clones for susceptibility to Pratylenchus vulnus and Meloidogyne incognita. . In field inoculation experiments at the end of the first vegetation period, P. vulnus population densities were lower under pistachio than under Prunus or Juglans but there were numerical trends among UCB1 clones. The UCB1 clone with the lowest (UCB1 D71) and the one with numerically the highest (UCB1 D90) population densities of P. vulnus were chosen for microplot experiments in sand and sandy loam soil where they were exposed to different population densities of P. vulnus. . In the fifth year of the field inoculation experiments, P. vulnus population densities surged to levels comparable to those under other nut crops illustrating the principal susceptibility of Pistacia spp. In the sand and sandy loam soil microplots, UCB1 D71 grew more vigorously than UCB1 D90, but both grew less at increasing P. vulnus population densities. In a repeat of this experiment, higher population densities of P. vulnus at planting resulted in thinner plants at the end of the second growing season. A population density of 13.3 to 13.6 P. vulnus 250 cm-3 was determined as the tolerance limit for damage by P. vulnus on UCB1. Low initial population densities of P. vulnus developed slowly on pistachio but medium population densities at planting damaged UCB1 rootstocks when planted to P. vulnus- infested soil. This called for caution when pistachio are planted into soil known to have remedial population densities of P. vulnus from previous crops.