Biostimulants research in some horticultural plant species-A review

Different substances from the natural origin which have beneficial effects on plant growth and development, stress resistance, and crop yield and quality can be called biostimulants or biostimulators. Their physiological effects depend on their composition as they contain various organic and mineral compounds which plants can use as metabolites, growth regulators, and nutrients; however, biostimulants cannot be considered biofertilizers. Biostimulants applied in plant production have been widely considered as an environment-friendly agricultural practice-and so are now among tools used in sustainable agriculture. Here, we discuss the results of the biostimulants' effect investigations performed in Croatia, focused on horticultural crops, with edible plant species, such as tomato, garlic, bell pepper, lettuce, strawberry, garden cress, and basil, as well as ornamentals, such as wild rose, wax begonia, Mexican and French marigold, moss rose, everlasting flower, common zinnia, English primrose, and scarlet sage. The investigated biostimulants were applied at all plant growth stages, from germination to full plant and fruit or flower commercial maturity, using the seed treatment, foliar application, or irrigation. To evaluate biostimulant effectiveness, various morphological, physiological, and quality traits were analyzed. In this wide array of studies, the evaluated biostimulants mostly enhanced seed and transplant vigor, stimulated vegetative growth, improved nutrient acquisition and distribution within the plant, increased antioxidative capacity of plant tissues, contributing to higher stress tolerance, and improved plant yield and fruit/flower quality. In general, the research reviewed here implies possible benefits of biostimulant application in horticultural production, especially in stressful growth conditions, such as the transplant stage, reduced fertilization, or incidence of other abiotic stress. Considering possible interactions among the contained physiologically active compounds, the effects on plants may depend on dose, time of treatment, growth conditions, and plant species. Therefore, further research of biostimulant applications in horticultural production is suggested.