Drought and heat are severe environmental stresses that constantly affect plant growth and development. Maize (Zea mays L.) is known for its sensitivity to abiotic stresses, which often causes significant yield losses. With plant growth-promoting rhizobacteria (PGPR), the harmful effects of drought and heat stress on plants can be alleviated. The aim of the present study was to investigate the physiological traits of plants affected by drought stress in a treatment including four PGPR bacteria, two regimes of irrigation and two stages of phenophases, and the analysis of the influence of the individual factors and their combined effects, respectively. In addition, the investigations covered the testing of the nutrient acquisition ability and nutrient use efficiency, the plant growth stimulating effect of PGPR bacteria, and the analysis of the performance trials. The largest amount of soluble orthophosphate was produced by Pseudomonas putida (51.636 µg/cm3). This is significantly more than the amount of phosphate solubilized by Bacillus pumilus (15.601 µg/cm3), Pseudomonas fluorescens (14.817 µg/cm3) and Bacillus megaterium (14.621 µg/cm3). The germination vigour of the seedlings in the treatment with Pseudomonas putida was 55% higher, represented by the value of 15,237.125, in comparison with the control, with the value of 9792.188. The Pseudomonas putida treatment resulted in the most outstanding fresh/dry weight ratio (7.312) compared to the control (7.780), when the interaction between all factors was taken into account under stressed conditions at 50% female flowering stage. The highest dry matter content of the plants (18.344%) compared to the control (17.344%) was measured in the case of the Pseudomonas putida treatment during the milk stage of development under stressed conditions. In the field trial, the plants treated with KD2 (Bacillus pumilus and Pseudomonas putida) presented significantly higher results in the aspect of grain yield (6.278 t/ha) compared to the control (5.468 t/ha).

The aim of this paper is to present the results of the field trial carried out to collect and assess data on the interaction of maize (Zea mays L) genotypes and beneficial microorganisms. The small plot field trial consisting of untreated control plots and plots treated with biostimulants was conducted in three consecutive years (2019, 2020 and 2021). Yield is a particularly important trait from the aspect of maize breeding as well as maize production; therefore, the present study focused more closely on how it was influenced by the biostimulant treatments. The level of grain yield, grain moisture content at harvest and grain dry-matter content were observed and recorded as the components of yield. The nutritional value of kernels was also tested, and protein, oil and starch contents were analysed as the most important components of this trait. The results reflected that the treatment with biostimulants constituted from beneficial microorganisms can be listed among the factors influencing the grain yield, in addition to the seasonal effect, the genotype and the nutrient supply of the soil. The treatment with biostimulants, even on its own among the factors, had an impact on the quantity and components of yield, and on the characteristics determining the kernel nutritional value. The interaction between the genotypes and the interacting microorganisms is of specific importance. The most spectacular result was attained with the application of one of the biostimulants leading to elevated grain yield in 75% of the maize genotypes in the study, along with a kernel nutritive value equal to the control group over all of the three years of the trial.