Ulvan enhances seedling emergence and controls Fusarium oxysporum f. sp. phaseoli on common bean (Phaseolus vulgaris L.)

This study aimed to evaluate the potential of ulvan to control the bean Fusarium wilt caused by Fusarium oxysporum f. sp. phaseoli (Fop) as well as their effect on seedling emergence. Seed soaking was carried out for 4 h before sowing, whereas soil irrigation or foliar spraying were performed at 12 days after sowing. Ulvan reduced the disease severity when sprayed onto leaves but did not show significant effect when applied via seed soaking or soil irrigation. However, when soaked in seeds, ulvan enhanced seedling emergence by 55%, 30% and 44% on Fop-infested, non-infested and sterilized substrate, respectively. The effect of ulvan spray frequency on Fusarium wilt progress and fungal colonization was analyzed in follow-up assays. Our results revealed that one, two or three applications of ulvan similarly protected bean plants by reducing Fop-colonization at earlier, but not at later phenological stages. As a consequence, ulvan significantly decreased the area under disease progress curve by 27%. Possible reasons why this protective effect can be obtained in certain circumstances are discussed.