Composition of root exudates from cucumber cultivars differing in resistance to Fusarium wilt

Seedlings of cucumber cultivars differing in their degree of resistance to Fusarium oxysporum. f. sp. cucumerinum J.H. Owen were inoculated with a fungal spore suspension (1 ×107/ml) or deionized water, thereafter the root exudates were collected. Amino acids in the root exudates were analyzed with an Automatic Amino Acid Analyzer and the other compounds in the exudates were detected by gas chromatography-mass spectrometry (GC-MS). The number of amino acid types and the overall proportion of amino acids in the resistant cultivars were higher than susceptible cultivars. Phenylalanine, valine, methionine, glycine and cystine were found in the root exudates of all cultivars in both treated and untreated seedlings. However, the total percentage of these five amino acids in root exudates from uninoculated seedlings was higher than inoculated seedlings. The total percentage of these amino acids in root exudates from susceptible cultivars was higher than resistant cultivars. Besides the soluble amino acids, 85 other compounds were detected by GC-MS in the root exudates. Regarding the uninoculated seedlings, the number and abundance of all compounds were higher in the root exudates of susceptible cultivars than in resistant cultivars. Furthermore, the number and abundance compounds were higher in the root exudates from inoculated seedlings than in uninoculated seedlings. A possible relationship between the content of organic acids (acetic acid and benzoic acid) in the root exudates and resistance to Fusarium wilt by the cucumber cultivar was indicated.