Angular leaf spot inAcmella oleraceacaused by a foliar nematode

Abstract

Jambu plants (Acmella oleracea) exhibiting necrotic angular leaf spots were collected in Belém - Pará, Brazil. After previous analysis, the presence of nematodes fromAphelenchoidesgenus was observed. These nematodes were cultured onFusariumsp. and subsequently morphologically and molecularly characterized for species-level identification.Aphelenchoidessp. associated with jambu exhibited morphological and morphometric characteristics very similar to those of species within theA. besseyicomplex (A. besseyi,A. oryzaeandA. pseudobesseyi), but these characteristics were not sufficient to separate them into a unique species. The Bayesian inference analysis, utilizing the expansion segment of the large subunit (D2-D3 LSU) of nuclear ribosomal DNA, yielded results with a high posterior probability, indicating that theAphelenchoidessp. associated with jambu belongs to theA. pseudobesseyispecies. Under controlled conditions, the reproduction of the nematode in the leaf tissues (FR > 1) was observed, resulting in disease symptoms. The highest reproduction rate ofA. pseudobesseyi(FR = 2.6) was observed from inoculation with 100 nematodes per leaf. It is concluded thatA. pseudobesseyiis the etiological agent of jambu angular leaf spot. For future research, like evaluating the resistance of jambu to this nematode, it is recommended to inoculate a maximum of 100 nematodes per leaf.