Novel Harzia ixtarensis fungus on Annona cherimola fruit in Mexico and its synergistic relationship with Colletotrichum fragariae

Abstract

Since 2005 in Íxtaro, Michoacán, signs of Harzia have been observed on immature Annona cherimola fruit with Colletotrichum fragariae-induced anthracnose lesions and mummified fruit. This study aimed to identify the Harzia species and evaluate its pathogenicity. Four isolates were obtained from fruit exhibiting symptoms, cultured in four types of agar under various conditions, and characterized based on concatenated ITS+LSU and ITS+SSU sequences. Additionally, the isolates were compared to two CBS species (two-type strains and two isolates) of H. patula and H. tenella under the same conditions as the Harzia isolates, and all known Harzia species in culture were included in two phylogenetic analyses. H. ixtarensis sp. nov. was proposed. Compared to H. patula CBS isolate 121524, which was the most closely phylogenetically related species, H. ixtarensis was characterized by slower colony growth (white to salmonish-beige), different percentages of two forms of conidia (elongated and globose; unicellular and hyaline to subhyaline), and smaller conidia. The conidia mainly germinated with two hyaline tubes without an appressorium. In situ inoculations (1×106 mL-1 conidia suspension) of fruit showed that fruit with wounds developed larger lesions than those without wounds. Harzia inoculation on anthracnose lesions (induced by prior inoculation with C. fragariae) produced larger anthracnose lesions than C. fragariae alone. When C. fragariae or H. ixtarensis was inoculated alone the lesion size was 51% and 99% smaller, respectively, indicating synergy between C. fragariae and H. ixtarensis. Thus, H. ixtarensis may have a parasitic-synergistic and necrotrophic lifestyle, and exhibited signs on anthracnose lesions.