Occurrence and pathogenicity of the stem and bulb nematode in onion crops in Rio Grande do Sul State, Brazil

Resumen

The stem and bulb nematode (SBN)  Ditylenchus dipsaci is one of the major problems affecting alliaceous crops in different cultivated areas in Brazil. However, reports on the occurrence of this phytonematode in onions are scarce. Recently, SBN was detected in onion crops in São José do Norte, city localized at the southern end of the coast of the state of Rio Grande do Sul (RS), Brazil, where parasitized plants showed reduced size and soft rot in the bulbs. Therefore, this study reported the occurrence of D. dipsaci in onion crops in Rio Grande do Sul State and characterized the nematode population morphologically, morphometrically, and molecularly through amplification of the 28S rDNA region. Pathogenicity was also evaluated under greenhouse conditions using ‘Bola Precoce’ onion plants inoculated with 500 specimens of D. dipsaci (initial population) and uninoculated controls. Morphological, morphometric, and molecular analyses confirmed the identity of the population as D. dipsaci. In both trials, inoculation reduced root fresh mass, bulb diameter, and bulb fresh mass. The mean reproduction factor (RF = final population/initial population) was 5.18.