Biological characteristics of Fusarium verticillioides and optimization of methods for assessing pepper resistance to Fusarium wilt.

Relevance. Improving the efficiency of the pepper breeding process for resistance to fusarium wilt, caused by Fusarium verticillioides , requires studying the biological characteristics of the pathogen and the conditions for pathogenesis development according to the concept of the classical disease triangle. Taking these relationships into account is essential for developing reproducible and informative methods for evaluating breeding material. Purpose. To study the effect of temperature regime and nutrient medium composition on the vegetative growth of F. verticillioides , as well as to optimize key elements of the artificial inoculation protocol for accelerated evaluation of resistance in pepper breeding lines. Materials and methods. The study examined three F. verticillioides isolates with contrasting aggressiveness. The radial growth rate was assessed in vitro on PDA, OA, Czapek, and SNA media in the temperature range of 10-40 °C. Pathogenicity was tested in vivo on seedlings of five pepper lines at 25, 28, and 30°C. Additionally, two inoculation methods were compared: with mechanical stirring (orbital shaker, 100 rpm) and under static conditions. Results. Within the F. verticillioide s population, contrasting classes of pathogenicity were identified: highly aggressive (HA, 46%), moderately aggressive (MA, 27%), and weakly aggressive (WA, 27%). A direct correlation was established between the radial growth rate (VR) and aggressiveness: HA isolates grew 1,7-1,9 times faster than WA isolates (VR 13,0 vs. 7,6 mm/day). The temperature optimum for the growth of the highly aggressive isolate in vitro (VR 12,8 mm/day) and pathogenesis in vivo (I=3,4 points) coincided and was 28 °C. However, at 30°C, despite maintaining high growth in vitro (VR 10,3-11,8 mm/day), pathogenesis in vivo significantly decreased to 1,9 points. Two-way ANOVA showed that on day 7, the inoculation method (with shaker) accounted for 31,6% of the variance, while by day 14, the genotype dominated (40,6%). The use of an orbital shaker allowed accelerating pathogenesis and symptom manifestation, reducing the period of reliable evaluation from 14 to 7 days, which provided the opportunity for accelerated screening.
Conclusion. Integration of knowledge about the biological characteristics of the pathogen into the experimental methodology allowed improving the elements of the artificial infection protocol. The use of these elements made it possible to significantly reduce screening time and increase the reliability of evaluating pepper resistance to fusarium wilt, which is important for accelerating the breeding process. 

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