The taxonomic status of Aphelenchoides besseyi Christie, 1942 (Nematoda: Aphelenchoididae) populations from the southeastern USA, and description of Aphelenchoides pseudobesseyi sp. n.

Abstract

Summary Populations reviously identified as Aphelenchoides besseyi were studied. Using an integrated approach, the A. besseyi species complex contains several cryptic species: A. besseyi sensu stricto, A. oryzae, A. pseudobesseyi sp. n. and other putative undescribed species. A population from Florida strawberry morphologically fits the A. besseyi of both Christie and Allen and is considered the only representative of this species. A Louisiana rice population fitted the descriptions of A. oryzae of both Yokoo and Fortuner; PUS length was consistently less than one-third of VA. Aphelenchoides oryzae, parasitising rice and other monocots, was re-established based on morphological and molecular datasets. Three populations from Florida ornamental plants (Dryopteris erythrosora, Echinacea sp. and Farfugium japonicum) differed from those of the two above-mentioned species and are described as A. pseudobesseyi sp. n. Populations previously identified as ‘A. besseyi’ from several countries were considered representatives of this new species, which usually had a large and conspicuous PUS, 8-14 μm wide and with a length greater than one-third of VA in 40-70% of studied specimens. Morphological variability made separation of A. pseudobesseyi sp. n. from A. oryzae and A. besseyi unreliable without the examination of numerous specimens and molecular analysis.

TheAphelenchoidesgenomes reveal substantial horizontal gene transfers in the last common ancestor of free-living and major plant parasitic nematodes

“…5 ). Together these results emphasised that relationships among species in the A. besseyi species complex were highly diversified at the genome level despite being challenging to differentiate based solely on morphology 17 .…”

“…The A. besseyi strains were clustered into two groups based on their hosts, suggesting that relationships in these species within the A. besseyi species complex can be unambiguously resolved based on their different lifestyles and host preferences. Combined with the previous 28S phylogeny of the A. besseyi species complex 17 ( supplementary fig. S3 ), we further designated these two groups as A. oryzae and A. pseudobesseyi groups isolated from rice or other plants (land grass and bird’s-nest fern).…”

“…Despite their almost overlapping morphological features, we previously identified copy number variations of genes encoding cell-wall-degrading enzymes including glycosyl hydrolase family 5 (GH5) and GH45 cellulases between A. besseyi of different host origins 23 . An 18S phylogeny separated the strains isolated from rice and fern unambiguously, suggesting that A. besseyi might be a species complex, with literatures also identifying variations in different molecular markers in different hosts that are original to A. besseyi 18,24 17 to reclassify foliar nematodes into three separated clades: the A. besseyi isolated mainly from strawberries, the A. oryzae mainly isolated from rice and A. pseudobesseyi from wood fern suggesting this species complex may be well differentiated at the genome level. From an evolutionary perspective, A. besseyi is also interesting because its primitive plant parasitism was a relatively recent evolutionary adaptation 25 .…”

“…Subbotin et al . recently used a combination of molecule makers (28S, ITS and mitochondria COI gene) 17 to reclassify foliar nematodes into three separated clades: the A. besseyi isolated mainly from strawberries, the A. oryzae mainly isolated from rice and A. pseudobesseyi from wood fern suggesting this species complex may be well differentiated at the genome level. From an evolutionary perspective, A. besseyi is also interesting because its primitive plant parasitism was a relatively recent evolutionary adaptation 25 .…”

“…This nematode is 0.4-0.8 mm in body size, has a life cycle around 10 to 12 days and it can reproduce in extreme environments, making it hard to eliminate. Better known as the rice white tip, A. besseyi infects important agronomic crops such as rice, soybeans and strawberries (Oliveira et al, 2019; Subbotin et al, 2020), causing necrosis and distortion of its host’s leaves (Jen et al, 2012; Oliveira et al, 2019; Wang et al, 2014). The nematode has reportedly been responsible for up to a 60% crop loss in some cases (Koenning et al, 1999; Lilley, Kyndt, & Gheysen, 2011) and was listed among the top ten plant parasitic nematodes in a 2013 review (Jones et al, 2013).…”