An emergent plant‐parasitic nematode in Brazil: Aphelenchoides besseyi. Current status and research perspectives

Abstract

Aphelenchoides besseyi is an emerging and yet overlooked plant parasite of many economically important crops, including cotton, soybean and common bean. It presents an economic risk to these crops in several countries, notably in Brazil. Although first reported infecting strawberries in the United States as early as 1942, it was only identified to be the causal agent of green stem and foliar retention (GSFR) disease in Brazil in 2017. Currently, there are no chemical nematicides registered in Brazil against A. besseyi, and no known sources of genetic resistance. Here, we review the biology of A. besseyi, its spread across Brazil, its relevance to the country's current and future agriculture and the limited control measures. We describe control measures that have been successfully used to manage infestations of other plant‐parasitic nematodes and could potentially be extended to use in the control of A. besseyi. We also review and discuss potential future control measures, such as RNA interference and genome editing, for the development of crops with enhanced resistance to A. besseyi.

Discovery and Characterization of Four Aphelenchid Species from Cultivated Regions of Southern Alberta, Canada

“…The new species can be distinguished from A. angusticaudatus [39] by the presence of males vs. absence; a longer body length of females, 728.0 (564.0-978.0) µm vs. (550-610) µm; a lower b value of females, 9.0 (8.0-10.0) vs. (11-13); a higher c value of females 17.0 (15.0-21.0) vs. (12)(13)(14)(15)(16)(17)(18); and a lower c ′ value of females, 3.4 (2.8-4.0) vs. 5.1. From A. cyrtus, by having an almost straight body habitus of females vs. arc-shaped; swelling type stylet knobs vs. distinctly knobbed; spicule shape (condylus elongated rounded, rostrum small, blunt conical, lamina less wide, gradually tapers towards the rounded distal end vs. (after drawings) condylus and rostrum appear pointed, lamina is wider, distal end appears pointed); the position of the tail mucro (central vs. appears ventrally located); habitat (post-harvest potato field vs. lichens, mushroom amended with flax and straw additives); longer body lengths of females, 728.0 (564.0-978.0) µm vs. (500-570) µm, and males, 720.0 (624.0-859.0) µm vs. (500-510) µm; a higher a value of females, 34.0 (31.0-38.0) vs. (24-28), and males, 33.5 (30.0-36.5) vs. (26)(27).…”

“…These methods constitute the basis for the development of posterior species-specific molecular probes, for example, the diagnostic recombinase polymerase amplification (RPA) assays and lateral flow dipsticks (LF), developed by Subbotin [ 12 ] for the separation of the strawberry foliar nematode Aphelenchoides fragariae from other important foliar pathogens, such as the summer crimp nematode of strawberry Aphelenchoides besseyi or the rice white tip nematode Aphelenchoides oryzae [ 12 ]. Control measures that have been successfully used to manage infestations of aphelenchid species, particularly Aphelenchoides spp., on key crops have been recently reviewed by de Souza et al [ 13 ] and included the application of chemical nematicides, cultural practices, crop rotation with nonhost plants, biological control agents, induced resistance (silicon or endophytic microorganisms), and blocking parasitism genes (i.e., using RNA interference (RNAi) or genome editing (typically CRISPR/Cas) to disrupt the targets of the effectors in the plant). Here, we investigated both new and known species of Aphelenchus Bastian [ 14 ], Aphelenchoides , and Robustodorus (Goodey [ 15 ]) Andrássy [ 16 ], recovered from southern Alberta’s arable regions.…”

“…Consequently, when we discovered these species during our soil nematode inventory survey, we performed detailed characterization and identified them to the species level. Our thorough morphological and molecular analyses revealed their identities as Aphelenchus avenae Bastian [ 13 ], Aphelenchoides limberi Steiner [ 24 ], and two unique species of Aphelenchoides and Robustodorus , each displaying distinctive traits. Upon comparison with related species, it appeared that these species have a novel status.…”