In this research, the biosynthetic and biocontrol potential of endophytic yeast to improve the growth and development of tobacco has been elucidated. Three yeast strains were enriched and isolated from different plant tissues. Partial sequence analysis of ITS5-5.8-ITS4 region of the nuclear ribosomal DNA with universal primers identified YD5, YE1, and YSW1 as Saccharomyces cerevisiae (S. cerevisiae), Zygosaccharomyces bailii (Z. bailii), and Saccharomyces kudriavzevii (S. kudriavzevii), respectively. When cultivated in a medium supplemented with 0.1% L-tryptophan, isolated yeast strains produced indole-3-acetic acid (IAA). The capacities of those strains to improve the mobility of phosphorus and synthesize siderophores has been proven. Their antimicrobial activities against several Solanaceae plant pathogenic fungi (Alternaria solani pathovar. tobacco, Rhizoctonia solani, and Fusarium solani pathovar. phaseoli) were determined. S. cerevisiae YD5, Z. bailii YE1, and S. kudriavzevii YSW1 inhibited the growth of all tested pathogens. Yeast strains were tested for endophytic colonization of tobacco by two different inoculation methods: soil drench (SD) and leaf spraying (LS). To establish colonization in the various tissues of tested tobacco (Nicotiana tabaccum L.) plants, samples were taken on the seventh, fourteenth, and twenty-first days after treatment (DAT), and explants were inoculated on yeast malt agar (YMA). Both techniques of inoculation showed a high frequency of colonization from 83.33% to 100%. To determine the effectiveness of the microbial endophytes, their effect on some physiological processes in the plant were analyzed, such as photosynthesis, stomatal conductivity, and transpiration intensity. The effect of single and double treatment with yeast inoculum on the development and biochemical parameters of tobacco was reported. Plants have the ability of structural and functional adaptation to stress effects of different natures. All treated plants had a higher content of photosynthetic pigments compared to the control. Photosynthesis is probably more intense, and growth stimulation has been observed. The chlorophyll a/b ratio remained similar, and the total chlorophyll/carotenoid ratio slightly increased as a result of elevated chlorophyll levels. The most significant stimulating effect was recorded in tobacco plants treated by foliar spraying with Z. bailii YE1 and S. cerevisiae YD5. In contrast, S. kudriavzevii YSW1 had a better effect when applied as a soil drench. Thus, S. cerevisiae YD5, Z. bailii YE1, and S. kudriavzevii YSW1 have a high potential to be used as a biocontrol agents in organic agriculture.
Keywords: antimicrobial activity; endophytic yeast; indole-3-acetic acid; phosphate-solubilization; physiological parameters; siderophore; tobacco.