Abstract
Root diseases of red clover (Trifolium pratense L.) contribute to reduced persistence and production of sown red clover stands; however, the potential of biological control of these diseases has not yet been investigated. Our objectives were to determine the effect of application of Pythium oligandrum and poly-beta-hydroxy butyric acid on (i) plant density and root morphology development, (ii) relationships between root branching and plant root disease score and (iii) forage yield and yield components of red clover in a three-year field experiment. Two red clover varieties (Start and Callisto) were established and managed under cutting (3 cuts per year) with four treatments: untreated control; spraying of poly-beta-hydroxy butyric acid (Albit); or application of P. oligandrum (Polyversum) at two intensities. Each autumn, plants were evaluated for root morphology traits and scored for root diseases. Forage dry matter yield, compressed stand height and stem density were evaluated in each cut. Effects on root discoloration were visible only in the last year of the experiment where significantly lower disease score was detected for both Polyversum treatments (4.58) compared with untreated control (4.94). In that year, Polyversum application at the higher intensity promoted increased tap-root diameter (+4%), root branching (+27%), stand height (+13%) and forage yield (+18%) in comparison with the control treatment. Improved forage yield was associated with plant growth stimulation more than from protection against Fusarium. Relationships among root traits and aboveground biomass highlight the need for evaluation of the effects of biological control of forage legumes considering root disease occurrence, together with root morphology traits and forage yield. This study demonstrated a potential of P. oligandrum for improving red clover yield, but optimization of application timing is necessary for determination of practical recommendations and economic efficiency.
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