Bacillus spp. strain-induced modulation of stomatal density in parsnip (Pastinaca sativa L.) and associated soil microbiological responses

Reducing chemical pesticide use and adopting biological alternatives are key priorities in sustainable horticulture. This study compared the effects of chemical and biological treatments on stomatal density in parsnip (Pastinaca sativa L.) and evaluated associated soil microbiological changes. Field trials near Skopje included a control (untreated) plot and three treatments: (T1) foliar application of Ridomil Gold MZ 68 WG (40 g/kg metalaxyl-M + 640 g/kg mancozeb), (T2) Bacillus velezensis strain B-98, and (T3) Bacillus amyloliquefaciens strain B-62. Stomatal density was determined microscopically on both leaf surfaces, and soil microbial communities were quantified before and after the growing season. ANOVA revealed highly significant differences (p < 0.001) in lower epidermal stomatal density between the control and all treatments, with T3 exhibiting the highest value (1552 stomata/mm²). Biological treatments also increased beneficial soil microorganisms, including nitrogen-fixing and cellulolytic bacteria. The results highlight B. amyloliquefaciens strain B-62 as a promising biopreparation for enhancing physiological traits and soil health in sustainable parsnip production.