Occurrence, taxonomy, biology and pathogenicity of aphelenchid nematodes associated with conifers in south-eastern Australia

Abstract

Australia has large plantations of exotic Pinus radiata conifers. This species is highly susceptible to Bursaphelenchus xylophilus, the pine wilt nematode, which is not found in Australia. Potentially pathogenic nematodes were isolated from several dead Pinus trees in Williamstown, Heidelberg and Knoxfield, suburbs of Melbourne, Victoria in 2000-2002. A survey of the above-ground nematode fauna of Pinus and other conifers in south--eastern Australia was undertaken. Stands of Pinus were surveyed in the Kuipto Forest and the South-East Region of SA; the south-west and the Gippsland region of Victoria; and the Hume region in NSW; and native Callitris preissii was sampled in the Murray Mallee. A total of 1140 samples from P. radiata, 50 from P. pinaster and 40 from C. preissii were examined. No nematodes were found in wood or young shoots of conifers except in the wood samples from diseased trees at Knoxfield and Heidelberg in Victoria. In contrast, nematodes were common in the bark samples of healthy trees. Morphologically, extracted nematodes were classified into five trophic groups, including: aphelenchida (plant, fungal and lichen feeders), rhabditids and areolaimids (bacterial feeding), Macrolaimus spp. (saprophagus), tylenchids (plant feeding), and dorylaimids (bacterial and algal feeders). Aphelenchids were the most commonly found trophic group. Three genera and twelve morphospecies of aphelenchids were identified. Eight species of Laimaphelenchus and one putative species of Acugutturus appear to be new records for Australia. Descriptions of two new species, L. preissii and L. australis have been published. Three species of Aphelenchoides were also found. No Bursaphelenchus spp. were found. Molecular studies included sequencing of the ITS region of Laimaphelenchus preissii, morphospecies Aphelenchid K1, and Aphelenchid H1; D2D3 fragments of 28S and 18S of L. preissii, morphospecies Aphelenchid K1, Aphelenchid K2, and Aphelenchid H1, Laimaphelenchus australis, and Laimaphelenchus Heidelberg; and COI of three aphelenchid morphospecies L. preissii, Laimaphelenchus Heidelberg and Aphelenchid K1. Phylogenetic analyses confirmed that Laimaphelenchus spp. are new species and that the unknown aphelenchids are close to Aphelenchoides. None of the six isolates studied from Australia was close to Bursaphelenchus. Population growth and mean doubling time of L. preissii, Aphelenchid K1 and Aphelenchid H1 were studied at different temperatures and on different food resources. The different species had markedly different population growth rates, which were significantly affected by temperature and food. A study on desiccation was carried out with L. preissii and morphospecies Aphelenchid K1, Aphelenchid K2, Aphelenchid H1 and Laimaphelenchus Heidelberg. Ability to survive desiccation varied between species, and the recovery rate of the different species was significantly different. A pathogenicity study was performed using young P. radiata trees in a shadehouse. No symptoms were observed following inoculation with Aphelenchid K1, Aphelenchid K2, Aphelenchid H1 and Laimaphelenchus Heidelberg isolated from diseased P. radiata in Victoria, or L. preissii from native Callitris in South Australia.