Inhibitory effects of epiphytic Kluyveromyces marxianus from Indian senna (Cassia angustifolia Vahl.) on growth and aflatoxin production of Aspergillus flavus

Aspergillus flavus infection and subsequent aflatoxin contamination are considered the major constraints in senna (Cassia angustifolia Vahl.) export. Using native epiphytic yeast to control phytopathogens is a successful strategy for managing plant diseases. In the present investigation, we exploited the antagonistic potential of epiphytic yeast isolates obtained from senna against A. flavus growth and aflatoxin B1 (AFB1) production. Four Kluyveromyces marxianus strains (YSL3, YSL16, YSP12, and YSF9) exhibited vigorous antagonistic activity with a maximum inhibition of 64 %. In vivo evaluation of senna pods showed that K. marxianus strains effectively reduced A. flavus colonization with a population range of 5.87 to 7.08 log10 CFU/g. In contrast, the untreated senna pods were found to have severe fungal colonization with a population of 7.84 log10 CFU/g. In addition, HPLC analysis showed that aflatoxin B1 in senna pods was drastically reduced upon yeast treatment up to 14 DAI. Furthermore, we demonstrated the antifungal action mechanisms of K. marxianus, such as surface colonizing ability on pods, production of antifungal volatiles (VOCs), siderophores, extracellular lytic enzymes, and cell wall binding ability to AFB1. All four strains of K. marxianus showed rapid colonization on the senna pod, and YSP12 reached the maximum population of 7.18 log10 CFU/pod at 9 days after inoculation (DAI). The exposure of A. flavus to K. marxianus VOCs significantly reduced the growth by up to 99 and 93.2 % at 7 and 14 DAI, respectively. Scanning electron microscopic images demonstrated severe mycelial damage and hyphal deformities of A. flavus. In addition, yeast VOCs can reduce aflatoxin biosynthesis in A. flavus by up to 99 and 93.2 % at 7 and 14 DAI, respectively. Gas chromatography–mass spectrometry analysis confirmed the presence of antimicrobial compounds such as dimethyl trisulfide, ethyl acetate, ethanol, 3-methyl butanal, 2-methyl-1-butanol, and 3-methyl-1-butanol in the volatiles. K. marxianus strains produced siderophores and hydrolytic enzymes such as chitinase and β-1,3-glucanase. A higher AFB1 binding ability was observed in the heat-killed cells (47.5 to 70.65 %) than in the viable cells (43.16 to 60.98 %) of K. marxianus. The current study demonstrated that epiphytic K. marxianus isolated from senna could be a successful biocontrol source to reduce aflatoxin contamination in senna pods. •Epiphytic yeast isolates showed effective antagonism against Asperg