Characterization of <i>Neocosmospora falciformis</i> associated with root rot of guava in the United States

The root-knot nematode, Meloidogyne enterolobii Yang & Eisenback, has been reported to cause root galling in guava orchards in Homestead, Florida. In this study, infected roots exhibiting root rot collected from M. enterolobii-infected guava orchards were examined for fungal associates isolated from M. enterolobii egg masses. Morphological and molecular analyses of isolated fungi confirmed the presence of Neocosmospora falciformis Lombard & Crous in the orchards. To our knowledge, this is the first report of N. falciformis incidence in guava orchards in the United States. Two pathogenicity experiments were conducted using four N. falciformis isolates and two guava cultivars ('Homestead' and 'Barbie') under screenhouse conditions with ambient temperatures similar to outdoor conditions. Plant growth responses and disease severity differed between the cultivars and experiments. In an experiment conducted during winter, inoculation with N. falciformis had minimal effects on growth and disease development in both cultivars, with no significant differences between infected plants and the control. In an experiment conducted during the summer, 'Homestead' guava exhibited significant reductions in root and shoot growth and increased disease severity following fungal inoculation, with responses varying among isolates. In 'Barbie' guava, fungal inoculation affected plant growth and disease expression. Greater fungal populations in soil correlated with increased disease severity, suggesting isolate-specific aggressiveness under warm conditions. Overall, results suggest that 'Barbie' is likely more tolerant of N. falciformis infection than the 'Homestead' cultivar. The association of this fungus with M. enterolobii may exacerbate disease severity and contribute to guava decline, warranting further investigation to develop effective management strategies.