Yeasts associated with aerial parts of Theobroma cacao L. in southern Bahia, Brazil, as prospective biocontrol agents against Moniliophthora perniciosa

Abstract

The cacao tree surface is a substrate for various microorganisms. However, the species which live on the surface have hardly been described. The aims of this study were to evaluate the diversity of native cacao yeasts and to investigate their possible interaction with Moniliophthora perniciosa. A total of 225 yeast strains were isolated from the surface of leaves, fruits, and flowers of 20 cacao genotypes selected as carriers of resistance genes to M. perniciosa and M. roreri, which are the causal agents of witches’ broom (WB) and frosty pod rot diseases (FPR), respectively. The yeast isolates were molecularly identified based on sequences of the D1/D2 and ITS1/ITS4 regions of the rDNA. A total of 20 taxa distributed into 11 genera was found: Hannaella (23), Cryptococcus (9), Candida (11), Hanseniaspora (4), Kwoniella (1), Occultifur (3), Rhodotorula (17), Pichia (2), Sporobolomyces (1), Wicherhamomyces (1), and Yamadazyma (1). Phylloplane tissues showed the greatest richness: 55% of species and 81.82% of identified genera. Six yeast strains (Candida orthopsilosis—LEV 225; Hanseniaspora uvarum—LEV 162, 210, 211; and Rhodotorula paludigena—LEV 166, 168) exhibited the desired traits for a BCA agent: antibiosis in cocultivation, antibiosis by volatile compounds, germination inhibition, and production of killer toxins. This study is the first to show the great diversity of yeasts found in the cocoa phytobiome and the discovery of at least six microorganisms with excellent potential as BCA against cocoa witches’ broom disease.