Influence of UV-B Radiation on Initial Development and Control of Pathogens in Soybean Seeds

Abstract

Ultraviolet-B (UV-B) irradiation is being explored as a non-chemical approach for seed sanitation with potential effects on early vigor. In soybean (Glycine max (L.) Merr.), preserving both physiological and sanitary seed quality is critical for stand establishment. We evaluated UV-B at a fixed irradiance (1.5 W m⁻²) across five durations (0, 10, 20, 30, 40 min), delivering cumulative doses of 0.9, 1.8, 2.7, and 3.6 kJ m⁻² (0.009, 0.018, 0.027, 0.036 J cm⁻²). Endpoints included viability (germination, dead seeds), vigor (first count, dry mass), seedling performance (shoot and root length, fresh mass), and sanitary status (blotter test). Responses were dose-dependent with hormetic features: prolonged exposures (30–40 min) markedly reduced germination (78% in the control vs. 46% and 28%), and the observed increases in shoot and root length at 30 min occurred only among surviving seedlings, providing no agronomic advantage due to the concomitant loss of viability. Total pathogen incidence (seeds with ≥1 detectable pathogen) decreased from 98% (control) to 55% at 40 min, with the largest reductions in Rhizopus spp. and visible bacterial colonies. Given the trade-off between sanitation and viability, 10–20 min (0.9–1.8 kJ m⁻²) emerges as a practical operational window that maintains acceptable germination while beginning to reduce pathogen load. Because blotter tests cannot resolve bacterial identity, bacterial results are reported as visible colonies only. UV-B should be considered a complementary, sustainable tool within integrated seed-borne disease management rather than a stand-alone replacement.