Occurrence of Globisporangium sylvaticum Causing Lettuce Bottom Rot and Associated to Onion and Common Bean Roots in Brazil

Abstract

Globisporangium sylvaticum is a soil‐borne oomycete associated with diseases in a wide range of plant species. Here, we report the first occurrence of G. sylvaticum causing bottom rot in lettuce and its association with rotted roots of onion and common bean in two geographic regions of Brazil. Three isolates were recovered from symptomatic plants and characterized based on morphological features and, primarily, phylogenetic analyses of the ITS and COX II regions. To assess pathogenicity, the onion and common bean isolates were initially inoculated onto seedlings of their respective hosts under greenhouse conditions. The onion and common bean isolates were not pathogenic to their original hosts. Subsequently, all three isolates were inoculated onto detached lettuce leaves under laboratory conditions, where they induced typical leaf rot symptoms. Koch's postulates were fulfilled only for lettuce. These results demonstrate that G. sylvaticum is the causal agent of lettuce bottom rot, whereas its occurrence in onion and common bean was limited to its isolation from rotted roots under the conditions evaluated. This study constitutes the first report of G. sylvaticum causing bottom rot in lettuce in the Federal District, Brazil. In addition, we document its occurrence in association with rotted roots of onion and common bean in the state of Paraná, an important Brazilian producer of grain and vegetable crops, highlighting its potential relevance for plant disease surveillance and further investigations of its host range.