Potassium deficiency and root exudates reduce root growth and increase Fusarium oxysporum growth and disease incidence in continuously cultivated strawberry

Strawberry fruits are increasingly produced under continuous cultivation and K deficiency, but the response of strawberry to this combination of stresses has not been extensively studied. Pot and tissue culture grown strawberry (Fragaria ananassa Duch.) plants were used to determine the effect of strawberry root exudates on the growth of strawberry plants and Fusarium oxysporum under continuous cultivation and potassium (K) deficiency. The pot experimental results showed that the Fusarium wilt disease rating and index were very high (62% and 86, respectively), and the lateral roots of strawberry plants were significantly restricted under the continuous cultivation and K deficiency treatment. The growth of tissue culture plantlets was inhibited by a high concentration (4%) and promoted by a low concentration (1%) of root exudates from the replanted pot strawberries. The number of lateral roots of tissue culture plantlets was significantly lower in the 4% root exudate treatment. Growth of F. oxysporum was promoted by the relatively high concentration of root exudates of the replanted pot strawberry under continuous cultivation and K deficiency. Total phenolics and three individual phenolics (ferulic acid, p-coumaric acid and cinnamic acid) were detected in the rhizosphere soil of replanted pot strawberries and were higher in the K-deficiency treatments. Fusarium oxysporum growth was promoted by the addition of exogenously added phenolic acids. A positive relationship was observed between the growth of F. oxysporum and the higher concentration ranges of ferulic acid and p-coumaric acid.