Guava decline: updating its etiology from ‘Fusarium solani’ to Neocosmospora falciformis

Abstract

Since the early 2000s, over 5000 hectares of guava orchards have been decimated in Brazil by guava decline. The disease has caused tens of millions of dollars in yield losses, the loss of thousands of jobs, and the closing of many fruit pulp-processing plants. Guava decline has been described as a synergistic interaction between the nematode Meloidogyne enterolobii and the fungus Fusarium solani. Nonetheless, the etiology of the disease has had to be reappraised because recent molecular studies have reassigned the whole ‘F. solani species complex’ to the genus Neocosmospora, with several plant-parasitic species being reclassified or synonymized. Hence, from a collection of ‘F. solani’ isolates associated with guava decline, we chose four of the most aggressive isolates, from which we sequenced RNA polymerase II subunit 1 (RPB1), RNA polymerase II subunit 2 (RPB2), and translation elongation factor 1-alpha (TEF1) genes. A GenBank® BLASTn search showed that the isolates belonged to Neocosmospora sp. Phylogenetic analyses using the maximum likelihood (ML) and Bayesian inference (BI) methods, with individual and combined datasets for TEF1, RPB1 and RPB2 genes, clustered all isolates within the N. falciformis clade, with maximum support in the ML and BI multilocus analyses. This and previous studies show that N. falciformis is the causal agent of guava decline and soybean sudden death syndrome, as well as of crown and root rots in other annual and perennial crops.