Biocontrol potential of Trichoderma harzianum and Bacillus subtilis against Phytophthora infestans in two potato varieties.

The potato is one of the most important crops in the world, due to its nutritional properties. However, Phytophthora infestans causes a significant reduction in potato growth and productivity. The use of chemical fungicides is the main control, consequently, the virulence and aggressiveness of the phytopathogen increases, and the use of biological agents with antagonistic activity is necessary. The objective was to determine the biocontrol effect of Trichoderma harzianum and Bacillus subtilis in a commercial and an improved potato variety as a sustainable strategy for the control of Phytophthora infestans in the highlands of Peru. The experiment was carried out in the field during two production seasons (2022-2023 and 2023-2024), with a 2x2x2 factorial scheme, referring to the variety (commercial variety Yungay and improved variety CIP 302295.32), two biological agents (T. harzianum and B. subtilis at a dose of 1 kg ha-1 and without application). The results revealed that plants subjected to P. infestans show a significant reduction in potato growth and productivity. However, the combined use of soil-applied T. harzianum and foliar-applied B. subtilis on the improved variety CIP 302295.32 reduced disease severity by 80.78 and 83.78% compared to the control in the two seasons, yielding more than 80% control efficiency of P. infestans. Likewise, this combination produced a significant effect on plant height (59.27 and 60.34%) in both seasons, significant increase in the number of commercial tubers per plant (84.66 and 88.89%), notable improvement in commercial weight per plant (84.88 and 90.11%) and the commercial yield exceeded the control by 85.45 and 90.12% in both seasons. Therefore, this study has clearly demonstrated the antagonistic effect of P. infestans with the combined use of the fungus "T. harzianum" applied to the soil and the endophytic bacterium "B. subtilis" applied via foliar and this effect was more significant in the improved variety CIP 302295.32, in addition, this combination produces a significant effect on the growth and productivity of the potato.