The Influence of Microbial Fertilizers on the Rhizospheric and Epiphytic Microbiota, as Well as the Foliar Feeding Impact on Apple Leaf Mineral Contents

Analysis of the apple tree rhizosphere and phylloplane microbiota revealed the presence of pathogenic and conditionally pathogenic micromycetes: <i>Penicillium</i>, <i>Cladosporium</i>, <i>Fusarium</i>, <i>Mucor</i>, <i>Trichotecium</i>, <i>Alternaria</i>. The application of microbial fertilizers (MFs)-Azafok, Enzymocid, and Nitragin-reduced their abundance in the soil. This occurred due to the beneficial bacteria contained in the biopreparations (<i>Bacillus</i> spp., <i>Bacillus aryabhattai</i>, <i>Pseudomonas fluorescens</i>, <i>Bradyrhizobium japonicum</i>), which possess fungicidal activity and the ability to improve the mineral nutrition of plants, thereby enhancing their immune status. Nitragin also reduced the colonization of leaves by pathogenic fungi. The greatest reduction in contamination was achieved by the combined application of MFs with foliar feeding using mineral substances, particularly when using Azafok. The influence of MFs on the state of the epiphytic microbiota is associated with their indirect action through the activation of the host plant's functional activity and the stimulation of its defense mechanisms. The MFs introduced into the soil stimulated an increase in the content of nitrogen, phosphorus, potassium, and calcium in the leaves. We also noted the influence of MFs on modifying the effect of foliar feeding on the nutrient content in the leaves. The leaf nitrogen content with the combined application of soil-applied Azafok and FF was lower than with soil application alone. Furthermore, the use of foliar fertilizing reduced the phosphorus and potassium content in the leaves against the background of Azafok and Enzymocid, although the relative level of these nutrient contents remained very high. Only the application of foliar fertilizing against the background of Nitragin stimulated an increase in the phosphorus and potassium content in the leaves. Further research is needed to clarify the nature of this modification.