Kerrie A. Davies

Suppressive Impact of Glucosinolates in Brassica Vegetative Tissues on Root Lesion Nematode Pratylenchus neglectus

The potential of tissue amendments from a variety of wild and cultivated Brassica spp. to kill the root lesion nematode (Pratylenchus neglectus) in soil was assessed in laboratory experiments. Soil amended with leaf tissues was highly nematicidal, killing 56.2–95.2% of exposed nematodes. Amendment with root tissues was less effective, causing 0–48.3% mortality. Little of the suppressive impact by leaf tissues could be related to either total contents or any individual glucosinolate as determined by HPLC analysis. While the levels of total glucosinolates within root amendments had a nonsignificant relationship to nematode mortality, levels of 2-phenylethyl glucosinolate within root amendments significantly correlated with nematode suppression (P < 0.001). Amendment of soils with equimolar levels of purified 2-phenylethyl isothiocyanate resulted in comparable levels of nematode mortality, suggesting that 2-phenylethyl glucosinolate has a role in the suppressive impact of Brassica spp. root tissues.

Morphological and molecular analysis of six aphelenchoidoids from Australian conifers and their relationship to Bursaphelenchus (Fuchs, 1937)

Six isolates of Australian Aphelenchoidoidea, viz., Laimaphelenchus preissii from native coniferous Callitris preissii trees, L. australis from the common pine plantation trees of Pinus radiata and P. pinaster and L. heidelbergi and two morphospecies of Aphelenchoides (H1 and K1) and Cryptaphelenchus sp. (K2) from diseased P. radiata trees, were studied using light microscopy, scanning electron microscopy and phylogenetic analyses of nearly full length sequences of SSU, D2/D3 expansion segments of LSU rDNA and a fragment of cytochrome oxidase subunit I (COI). Bayesian phylogenetic analyses of SSU, LSU and COI of the six nematode species revealed that none of these Australian aphelenchoidoids was inferred to be closely related to Bursaphelenchus. The selected isolates of Aphelenchoides and Laimaphelenchus used in this study were paraphyletic in all molecular analyses. Cryptaphelenchus sp. (K2) was inferred to be sister to Seinura with SSU sequences.

Chemical and biological induction of resistance to the clover cyst nematode (Heterodera trifolii) in white clover (Trifolium repens)

Possible induction of resistance to the clover cyst nematode, Heterodera trifolii, in white clover, Trifolium repens, by application of two chemical inducers and of soil-borne Pseudomonas-like spp. and Bacillus cereus was investigated. Salicylic acid and benzo(1,2,3)thiadiazole-7-carbothioic acid-S-methyl ester, applied as a root drench in growth cabinet soil bioassays, affected development of H. trifolii in cvs Haifa and Grasslands Huia. Treatments reduced fecundity of the nematodes, increasing the proportions of distorted females and of females with fewer eggs compared to water-treated controls. Application of pectinolytic fluorescent pseudomonad strains P29 and P80, and B. cereus strain B1, induced a response similar to that resulting from the chemical induction. Both live and dead cells of P29, but not cell-free culture filtrate, induced these effects on H. trifolii. A non-pectinolytic, fluorescent pseudomonad, strain P37, had no effect. From the nature of the responses, it is concluded that the effects of both the chemical and bacterial agents have similarities to resistance. From the timing of applications and known properties of both agents, these effects seem similar to induced systemic resistance.

Phylogenetic Relationships, Species Limits, and Host Specificity of Gall-Forming Fergusonina Flies (Diptera: Fergusoninidae) Feeding on Melaleuca (Myrtaceae)

Abstract Phylogenetic analysis of recently described gall-forming Fergusonina Malloch flies was performed using DNA sequence data from the mitochondrial cytochrome oxidase I gene. Fifty-three flies reared from nine species of Melaleuca L. were sequenced. Species boundaries delimited by mitochondrial data confirm recent morphological investigation with one exception. Fergusonina turneri Taylor, believed to feed on both Melaleuca quinquenervia (Cav.) S. T. Blake and Melaleuca fluviatilis Barlow, seems to be comprised of two cryptic species, each specialized on one of the two hosts. Because F. turneri is under consideration as a potential biological control agent for invasive M. quinquenervia in the Florida Everglades, understanding cryptic variation and the degree of dietary specialization of this species is critical.

Pseudaphelenchus yukiae n. gen., n. sp. (Tylenchina: Aphelenchoididae) associated with Cylindrotermes macrognathus (Termitidae: Termitinae) in La Selva, Costa Rica

A species of aphelenchoidid nematode was isolated from a subterranean termite, Cylindrotermes macrognathus, during a survey of termite-associated nematodes in a conserved forest in La Selva, Costa Rica. The nematode was morphologically intermediate between the families Aphelenchidae and Aphelenchoididae, i.e., the nematode had a true bursa supported by bursal limb-like genital papillae but lacked a clear pharyngeal isthmus. The molecular phylogenetic status of the new nematode among tylenchid, cephalobid, panagrolaimid, aphelenchid and aphelenchoidid genera was analysed based on ca 1.2 kb of SSU ribosomal DNA sequence and the inferred position was basal to the family Aphelenchoididae. It was clearly not part of the clade containing the genus Aphelenchus (=Aphelenchidae). This nematode is described herein as Pseudaphelenchus yukiae n. gen., n. sp., and the family definition of Aphelenchoididae is emended to include the unique morphological characters of this new genus. The molecular phylogenetic analysis supported the paraphyly of the three Aphelenchoidinae genera Aphelenchoides, Laimaphelenchus and Schistonchus and the monophyly of Ektaphelenchinae, Seinura (Seinurinae) and Noctuidonema (Acugutturinae). However, many more representatives are needed to resolve the family-genus level phylogeny of Aphelenchoididae.

First record of Fergusonina (Diptera: Fergusoninidae) and associated Fergusobia (Tylenchida: Neotylenchidae) forming galls on Metrosideros (Myrtaceae) from New Zealand.

Abstract A new species of fly, Fergusonina metrosiderosi Taylor sp.n. (Diptera: Fergusoninidae) [and its associated nematode, Fergusobia pohutukawa Davies sp.n. (Tylenchida: Neotylenchidae)], is described from unilocular basal shoot‐bud galls on Pohutukawa (New Zealand Christmas Tree), Metrosideros excelsa Banks ex Gaertn. (Myrtaceae). The fly is characterized by the short, sclerotized postabdomen of the female, distinctly grey wings, reduction in length of the reclinate orbital, postocellar and vertical setae, undifferentiation of the ocellar setae, supernumerary setation of the genae, and three pairs of scutellar setae rather than two. The dorsal shield is restricted to a few raised sclerotized spicules on the first to third thoracic segments of the larva and epidermis of the puparium. The nematode is characterized by the combinations of arcuate shape, small ‘a’ ratio, swollen cuticle, small cephalic region with elevated circum‐oral area with a flat tip, coarse annulation and relatively slender conical tail of the parthenogenetic female, and coarse annulation, long bursa and angular spicule with short, broad, offset manubrium of the male. Fergusonina metrosiderosi sp.n. and Fergusobia pohutukawa sp.n. represent the first record of the fly‐nematode association from the host genus Metrosideros, and the first record from New Zealand. Aspects of the biology and biogeography of the fly‐nematode association are discussed.

New plant-parasitic nematode from the mostly mycophagous genus Bursaphelenchus discovered inside figs in Japan.

A new nematode species, Bursaphelenchus sycophilus n. sp. is described. The species was found in syconia of a fig species, Ficus variegata during a field survey of fig-associated nematodes in Japan. Because it has a well-developed stylet and pharyngeal glands, the species is considered an obligate plant parasite, and is easily distinguished from all other fungal-feeding species in the genus based upon these characters. Although B. sycophilus n. sp. shares an important typological character, male spicule possessing a strongly recurved condylus, with the “B. eremus group” and the “B. leoni group” of the genus, it was inferred to be monophyletic with the “B. fungivorus group”. The uniquely shaped stylet and well-developed pharyngeal glands is reminiscent of the fig-floret parasitic but paraphyletic assemblage of “Schistonchus”. Thus, these morphological characters appear to be an extreme example of convergent evolution in the nematode family, Aphelenchoididae, inside figs. Other characters shared by the new species and its close relatives, i.e., lack of ventral P1 male genital papilla, female vulval flap, and papilla-shaped P4 genital papillae in males, corroborate the molecular phylogenetic inference. The unique biological character of obligate plant parasitism and highly derived appearance of the ingestive organs of Bursaphelenchus sycophilus n. sp. expands our knowledge of the potential morphological, physiological and developmental plasticity of the genus Bursaphelenchus.

A review of the taxonomy, phylogeny, distribution and co-evolution of SchistonchusCobb, 1927 with proposal of Ficophagusn. gen. and Martinineman. gen. (Nematoda: Aphelenchoididae)

The purposes of this paper are to clarify the taxonomic status of the fig-pollinating wasp associate Schistonchus sensu lato(Nematoda: Aphelenchoididae) and to suggest directions for future research on the systematics, life history and ecology of the group. Molecular phylogenetic analyses suggest that Schistonchus s.l.is polyphyletic, and the composition of the three major clades is outlined, together with information on nematode morphology, plant host species, associated pollinating wasp species, and distribution. Biological information and collection data is presented for Schistonchus s.l.from Ficussycones (Moracea) in Africa, Australia, Asia and Central America, and its putative phylogeny is discussed based on molecular and morphological evidence. Both wasps and figs are millions of years old and have worldwide distribution in tropical areas, i.e., opportunities for Schistonchus s.l.-like nematodes to have evolved could have occurred more than once. In addition, figs and their pollinating wasps have variable life histories, which could have provided opportunities for Schistonchus s.l.to also develop different life histories. However, these histories occur inside fig sycones and in association with wasps, which has apparently led to evolutionary convergence and extreme morphological conservatism. Diagnostic characters and their states, derived from examination of described species and morphospecies of Schistonchus s.l.and informed by molecular phylogenetic inferences, are discussed and illustrated. Schistonchus sensu strictois redefined, and Ficophagusn. gen. and Martinineman. gen. are proposed. Schistonchus s.s.is morphologically characterised by having the excretory pore opening in the region of, or posterior to, the metacorpus; Ficophagusn. gen. by having the excretory pore opening very near the cephalic region; and Martinineman. gen. by having it opening at the anterior end of the metacorpus. Several species of Schistonchus s.s.have a labial disc, but there is no evidence of this in either Ficophagusn. gen. or Martinineman. gen.

Distribution and Diversity of Soil Microfauna from East Antarctica: Assessing the Link between Biotic and Abiotic Factors

Terrestrial life in Antarctica has been described as some of the simplest on the planet, and mainly confined to soil microfaunal communities. Studies have suggested that the lack of diversity is due to extreme environmental conditions and thought to be driven by abiotic factors. In this study we investigated soil microfauna composition, abundance, and distribution in East Antarctica, and assessed correlations with soil geochemistry and environmental variables. We examined 109 soil samples from a wide range of ice-free habitats, spanning 2000 km from Framnes Mountains to Bailey Peninsula. Microfauna across all samples were patchily distributed, from complete absence of invertebrates to over 1600 specimens/gram of dry weight of soil (gdw), with highest microfauna abundance observed in samples with visible vegetation. Bdelloid rotifers were on average the most widespread found in 87% of sampled sites and the most abundant (44 specimens/gdw). Tardigrades occurred in 57% of the sampled sites with an abundance of 12 specimens/gdw. Nematodes occurred in 71% of samples with a total abundance of 3 specimens/gdw. Ciliates and mites were rarely found in soil samples, with an average abundance of 1.3 and 0.04 specimens/gdw, respectively. We found that microfaunal composition and abundance were mostly correlated with the soil geochemical parameters; phosphorus, NO3 − and salinity, and likely to be the result of soil properties and historic landscape formation and alteration, rather than the geographic region they were sampled from. Studies focusing on Antarctic biodiversity must take into account soil geochemical and environmental factors that influence population and species heterogeneity.

Schistonchus (Aphelenchoididae) from Ficus (Moraceae) in Australia, with description of S. aculeata sp. n.

A checklist of Schistonchus collected from Ficus spp. in Australia and stored in the Waite Nematode Collection at the University of Adelaide is presented. Within Australia, Schistonchus contains 12 morphospecies and four nominal species, based on a combination of the following characters: body shape when heat-relaxed, position of excretory pore, length of post-uterine sac, spicule form, and number and position of caudal papillae. Up to four morphospecies of Schistonchus have been collected from one species of Ficus and, in several cases, one morphospecies of Schistonchus has been collected from more than one host fig species. A phylogenetic tree based on D2/D3 sequences showed that Australian collections of Schistonchus fall into two clades, suggestive of endemic and introduced lineages with host switching. Schistonchus aculeata sp. n. is described from F. aculeata and F. opposita and differentiated from other species of Schistonchus by having the excretory pore opening near the lips, a short post-uterine sac, rosethorn-shaped spicules, arcuate gubernaculum or thickening of dorsal wall, amoeboid sperm, and three pairs of caudal papillae (one pair adcloacal, one just posterior to mid-tail, and one near the tail tip), association with Kradibia spp. pollinating wasps and apparent biogeographical range. A key to the known species and morphospecies of Schistonchus from Australia is presented.