Nigel L. Bell

Transportation of nonindigenous species via soil on international aircraft passengers’ footwear

The potential for transported soil to harbour and spread nonindigenous species (NIS) is widely recognised and many National Plant Protection Organisations (NPPOs) restrict or prohibit its movement. However, surprisingly few studies have surveyed soil while it is in transit to provide direct support for its role in accidental introductions of NIS. Moreover, there are few border interception records for soil organisms because they are neither easily detected nor routinely isolated and identified. Better data would improve evaluations of risks from soil transported via different pathways, enable targeting of management resources at the riskiest pathways, and support development of new risk management methods. We surveyed organisms present in soil that had been removed from footwear being carried in the baggage of international aircraft passengers arriving in New Zealand and recorded high incidences, counts and diversities of viable bacteria, fungi, nematodes and seeds, as well as several live arthropods. These included taxa that have not been recorded in New Zealand and were therefore almost certainly nonindigenous to this country. In each gram of soil, there was an estimated 52–84% incidence of genera that contain species regulated by New Zealand’s NPPO, which suggests many were potentially harmful. Variation in the incidences and counts of soil organisms with sample weight, footwear type and season at the port of departure indicated it may be possible to develop methods for targeting management resources at the riskiest footwear. Comparisons with previously published data supported the hypothesis that survival of soil organisms is greater when they are transported in protected (e.g. in luggage) rather than unprotected environments (e.g. external surfaces of sea containers); this offers opportunities to develop methods for targeting management resources at the most hazardous soil pathways.

Optimising the Whitehead and Hemming tray method to extract plant parasitic and other nematodes from two soils under pasture

Three variations of the Whitehead and Hemming tray method for extracting vermiform nematodes from soil samples, and the decant and sieve method, were compared using a silt loam and a clay loam soil under long-term pasture. Comparisons showed that greatest nematode recovery was achieved when 50 g of soil was placed in a tray lined with two-ply paper tissue and extracted for 48 h with 500 ml water. Recovery of the total nematode fauna and of plant parasitic nematodes from the tray extract was significantly better (P ≤ 0.001) after allowing nematodes to sediment in a 1 l straight-sided beaker than in a 15 cm diam. filter funnel. After 48 h extraction on trays, this method recovered 77% of the total numbers of all nematodes (72.5% of the plant parasites) extracted over 144 h with daily collection from the trays. The optimum extraction duration was different for Paratylenchus nanus compared to Pratylenchus sp., apparently related to differences in their mode of parasitism, with root-dwelling stages of Pratylenchus being recovered at longer times. There was a significant treatment × soil interaction for Meloidogyne sp., recovery of which was improved by beaker sedimentation in silt loam but not clay loam soil, compared to funnel sedimentation. A significant treatment × soil interaction was also observed for H. trifolii, the beaker method being better at recovering this nematode in clay loam than silt loam soil, compared to the decant and sieve method.

Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the central North Island of New Zealand II. Nematodes

Abstract Soil samples were taken from around the base of tussock plants and paired areas of inter‐tussock vegetation at four native tussock grassland sites across New Zealand, in three consecutive summers. Seventy nematode taxa were identified with the plant associated nematode trophic group being the most abundant at three of the four sites. Of the plant parasitic nematodes, Criconema, Pratylenchus, and Helicotylenchus spp. were found at all sites, with Hemicycliophora, Longidorus, a putative Punctodera, and Rotylenchus found at only one site each. The observation of mermithid nematodes at three of the four sites, coupled with absence of insect parasitic Steinernema or Heterorhabditis sp. from microscopic observations and soil baiting suggests that the insect parasitism niche is occupied largely by mermithids in the tussock grassland habitats studied. A range of community indices were calculated, with Shannon‐Weiner (2.10–2.39), Simpson dominance (0.129–0.205), Maturity Index (2.67–2.92), and Structure Index (67.7–87.5) being significantly different among sites. Total nematode abundance was significantly greater beneath tussock than inter‐tussock vegetation, but the number of nematode taxa and species richness were significantly greater from inter‐tussock samples. This suggests that tussocks may provide a more productive habitat but that the increased diversity of the vegetation in inter‐tussock areas is reflected in some measures of nematode diversity. Comparisons are made and discussed with other studies of native grassland nematodes in New Zealand and worldwide.

Impact of clover root weevil Sitona lepidus (Coleoptera: Curculionidae) larvae on herbage yield and species composition in a ryegrass‐white clover sward

Abstract The effects of root herbivory at five densities of Sitona lepidus larvae (overall means between 4 and 333 larvae m‐2) were assessed over 2 years on newly established perennial ryegrass‐white clover swards in a small plot trial. Initial larval establishment in autumn 2003 was positively related to clover content in plots, and there was no significant impact on clover herbage yield in the first year. Nodule damage in winter 2003 increased with larval density, and results suggested an overcompensatory response in nodule production. A 34–35% reduction in clover yield between highest and lowest S. lepidus densities was recorded for both cultivars in the second year, with greatest losses in spring 2004. This coincided with reductions in clover root and stolon weights. Plant parasitic nematodes and grass grub larvae were most abundant in the plots with lowest weevil numbers. These results confirm field observations that S. lepidus is a major pest of pastures.

Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the central North Island of New Zealand I. The macro‐invertebrate fauna

Abstract This contribution introduces a short series of papers on biodiversity of indigenous tussock grassland at four sites in New Zealand. A survey of invertebrates of tussock grassland sites was carried out in summer of 3 successive years, 2001–03. The sites included two in Otago in snow tussock grassland at Deep Stream and Mt Benger, a site at Cass in inland Canterbury, and one at Tukino in the central North Island. Sampling was carried out by taking turf samples from each site, and extracting the invertebrates with heat extractors. The invertebrates were divided into 30 major groups. This quantitative sampling method allowed the densities of invertebrate groups to be calculated. Total macro‐invertebrate density for all sites ranged between c. 1600 and 5600 m–2. Total invertebrate abundance was highest at the central North Island site, but this was very much dominated by Formicidae. Across all sites, Formicidae, Coleoptera, and Pseudococcidae were consistently the most abundant groups represented.

Effects of plant-parasitic nematodes and rhizosphere microorganisms on the growth of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.)

A pot trial was carried out to study the effects of plant-parasitic nematodes and rhizosphere microorganisms on the growth of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Plants were grown together in Horotiu sandy loam (Vitric Hapludand). The treatments consisted of: untreated field soil (UT); soil frozen to −20°C to reduce nematodes (FR); soil fumigated with chloroform to kill most soil organisms (FU); and fumigated soil inoculated with a layer of frozen soil to reintroduce organisms present in frozen soil (FUI). The mean wet weights of white clover and ryegrass grown in UT soil for 6–9 weeks were only 10 and 60%, respectively, of those grown in FR soil and 5.8 and 56%, respectively, of those grown in FU soil. The severe growth reduction of white clover in UT was attributed to early invasion of roots by two nematode species, Heterodera trifolii and Meloidogyne hapla, which were detected in stunted 7-day-old seedlings. In the FR and FUI treatments, the freeze-thaw process appeared to have killed the second stage juveniles but not the eggs, which hatched to release more juveniles to invade white clover roots. Plant growth in FR, and to a lesser extent in FUI treatments, was reduced in comparison with FU, where there was no nematode invasion. The bacterial numbers in surface-sterilized roots were unaffected by any of the treatments. This suggests that the entry of bacteria into root tissues is independent of the wounding caused by nematodes. The mean bacterial numbers of the medians (means of log cfus across treatments and plant species of the median numbers across replicates) for “total” bacteria, fluorescent pseudomonads, Gram-negative bacteria and Gram-positive bacteria from surface-sterilized roots were 4.26, < 2, 2.94 and 3.08 for the four treatments, respectively. The most common bacterial genera identified were Pseudomonas and Bacillus. Fungi isolated from surface-sterilized roots included Fusarium oxysporum, Codinaea fertilis and many sterile fungi, with F. oxysporum being the most common identified fungus in FU and FUI treatments. C. fertilis was killed by the soil freezing process. F. oxysporum did not appear to be associated with a decrease in dry matter production of either white clover or ryegrass, but C. fertilis may have adversely affected the ryegrass dry matter production in the treatment UT.

Botanical survey of perennial ryegrass-based dairy pastures in three regions of New Zealand: implications for ryegrass persistence

A botanical survey of 24 commercial dairy pastures ranging in post-sowing age and perennial ryegrass type (mid-season diploid, late-season diploid, tetraploid) was undertaken in each of Waikato-Bay of Plenty (BoP), Taranaki and Canterbury during autumn/winter. The mean perennial ryegrass proportion (85% of total DM) and tiller density (3252 m−2) was greatest in Canterbury and the broadleaved weed proportion lowest (2%). Conversely, Waikato–BoP had the lowest ryegrass proportion (59%), tiller density (1817 m−2) and greatest proportion of broadleaved weeds (15%), with Taranaki intermediate. Tiller density was greater in pastures sown with diploid rather than tetraploids (averaging 3033 vs. 1784 m−2). Grass grub (Costelytra zealandica, 11 m−2) populations were lowest in the youngest age category pastures where nematode populations were highest (80 g−1 dry soil). The soil seedbank was dominated by unsown species (with total species emergence averaging 4594 seeds m−2), with negligible ryegrass emergence.

Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the Central North Island of New Zealand VI. Coleoptera biodiversity, community structure, exotic species invasion, and the effect of disturbance by agricultural development

Abstract The diversity of Coleoptera communities in tussock grassland at two sites in Otago, one in Canterbury and one in the central North Island, was compared. The impact of agricultural disturbance on the communities was compared between native tussock, tussock oversown with exotic pasture species and cultivated sown pasture. Coleoptera were heat-extracted from turf samples taken in summer in two consecutive years. In native and oversown treatments, Staphylinidae and Curculionidae predominated in abundance at three of the four sites, and in species richness at all sites and treatments. Carabidae were more species-rich than Curculionidae in cultivated treatments at most sites. The mean density of Coleoptera in native tussock treatments ranged between 654/m2 and 97/m2. Carnivores were the predominant trophic group followed by herbivores. Species diversity was higher in the native or oversown treatments and the Otago sites were the most diverse overall, and the least disturbed. A total of 19 exotic species were found but there was no relationship with treatment, although their density was higher in cultivated treatments. There was no evidence to suggest that modified vegetation provides a source of exotic Coleoptera species to invade native tussock.

Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the central North Island of New Zealand III. Soil microorganisms

Abstract Bacterial and fungal communities in indigenous tussock grassland soils were studied at four locations, Mt Benger and Deep Stream (Otago), Cass (Canterbury) and Tukino (central North Island). Soil samples collected from inter‐tussock and tussock areas were used to enumerate total culturable bacteria (colony forming units (CFU)) as well as a number of specific groups of bacteria, fungal types and diversity, and soil microbial functional diversity. Soil microbial biomass carbon (C) and nitrogen (N) as well as extractable C and N were also determined. Fungal populations were lowest at Mt Benger while fluorescent Pseudomonas was lowest at Cass. In these indigenous soils, bacterial CFU were c. 30 times lower and fungal populations c. 10 times greater than in developed New Zealand pastoral soils. CFU of bacteria in complex media (r‐strategists) were similar in magnitude to bacteria growing on weak CA medium (K‐strategists). The microbial biomass C in indigenous grassland soils were also significantly greater than that found in developed pastoral soils, possibly due to dominance of fungi in indigenous soils. Microbial C and N were lower in Cass and Tukino sites compared to Mt Benger and Deep Stream sites. Microbial nitrogen was also significantly greater (P < 0.001) in inter‐tussock than under tussock samples. The functional diversity of soil microbes, was significantly greater (P< 0.01) in inter‐tussock samples compared to tussock samples at all sites except Mt Benger. The total microbial activity, as measured by the colour development in Biolog plates (Average Well Colour Development (AWCD)), was low in Cass soil compared to others. Eighty‐three types of fungi belonging to 30 genera were recovered from the four sites. The diversity of fungi found in Otago sites was greater than in the other two sites (P < 0.001). Fusarium spp. that are often common in pastoral soils were conspicuous by their rarity in indigenous soils.

Plant-parasitic nematodes on pasture in New Zealand

White clover (Trifolium repens) fixes nitrogen and provides high-quality feed and is, therefore, a key contributor to New Zealand’s grazed pasture systems. However, its productive potential is rarely reached due to abiotic factors (e.g. drought) and various biotic constraints, including nematodes. In a recurrent selection program based in the greenhouse, resistance to Meloidogyne trifoliophila and Heterodera trifolii has been improved and resistant lines have been crossed to cultivars to improve field performance. Tolerance to root-infecting nematodes and other factors has been improved in a field-based program in which the best performing plants were selected and crossed. In grazed field trials, lines from both programs performed as well or better than cultivar controls. Counts of nematodes in roots showed that resistance reduced numbers, but results varied among sites and years. This paper summarises progress made in white clover breeding programs in New Zealand and also examines advances in genetic mapping and introgression as they affect resistance to nematodes. The nematodes associated with pasture grasses are reported, together with observations which suggest that root-feeding nematodes have little impact on yield and that the animal toxicity associated with Anguina seed galls in Australia is absent from New Zealand. The effects of infection by endophytic fungi on nematodes parasitising grasses are also reviewed.