Resumen de Effects of post-emergence herbicides on in vitro growth of fusarium oxysporum isolated from red clover root rot
In Chile, Fusarium root rot reduces red clover (Trifolium pretense L.) pasture yield and persistence. Fusarium oxysporum (Schlect.) is the most prevalent pathogen in diseased red clover plant roots. Agronomic management of red clover includes applying herbicides such as MCPA, 2,4-DB, flumetsulam, bentazon, and haloxyfop-methyl. In addition to weed control, herbicides can modify disease development, generally as a result of the interaction between direct effects on the pathogen and indirect effects via plant-mediated responses. The objective of this study was to evaluate the influence of these herbicides on in vitro growth of F. oxysporum at four application rates 0, 50, 100, and 200% at the field-recommended active ingredient rate. Herbicides were amended on Petri dishes containing potato dextrose agar (PDA) and buffer MUB (tris-hydroxymethyl-aminomethane). Fusarium oxysporum was cultivated at 22°C for 25 days and colony area was measured every 5 days. The herbicides MCPA and Flumetsulam had no effect on fungal growth. 2,4-DB showing an inverse dose effect on fungal growth varying between 16 and 35% at the end of the experimental period. The contact herbicide Bentazon exhibited the strongest inhibitory effect on F. oxysporum development by the application of the field recommended rate, with a 54% decrease with regard to the control at the end of the experiment. Haloxyfop-methyl showed the highest colony stimulation since 15 days after of the application, increasing 29% the colony area respect to the control at the end of the experiment. These results suggest that applying some herbicides to red clover could affect soil pathogens such as Fusarium oxysporum, increasing or inhibiting its development.
