| Narcissus pseudonarcissus (daffodil) is a kind of bulbous crops with high value of flowers having a variety of fantastic forms. It is a popular plant in China, while the bulbs have been being imported from Holland. Because of the influence of climate and geography, daffodils were easily infected, especially by the pathogen of Fusarium oxysporum f. sp. narcissi (FON). In order to find out the relation of host and pathogen, the deeper studies on pathogen characteristics and on plant protective enzyme system were carried out. The results as follows:Firstly, four distinct strains F40, BO, GO, and ZO were purified from different cultivars of Narcissus pseudonarcissus, including Marieke, Mount hood, Giant star and Pinza. These isolates were assigned with different biological strains to Fusarium oxysporum f. sp. narcissi (FON) by means of morphological characteristics under light microscope.Secondly, four strains'physiological characteristics were identified by carbohydrates metabolism analysis. In the experiments of carbohydrate metabolism, the results showed that the rates of carbohydrate utilization among strains were obviously different, and the types of carbohydrate that strains could use also were different. Generally speaking, for all catabolism F40 had the weakest capability followed by ZO, and BO had the best performance.As results of fermentation of soluble starch, glucose and sucrose in Durhan tube, they were acid producing and aerogenesis. In fermentation of D-galactose, L-rhamnose and D-xylose the results were acid producing. However, in fermentation of maltose, D-fructose, lactose, trehalose and cellobiose, four strains showed difference.In experiments of assimilation, as compared with most sugars, all tested isolates had no appreciable reaction with alcohols except for the sugars L-rhamnose and lactose as shown in their assimilation metabolism, although there were positive reactions.Thirdly, two pairs of primers for detecting FON were designed through molecular approaches, and they were useful in detecting the presence of FON. During the first amplification of Nested-PCR, the sequence obtained with the outer primers was approximately 750 bp in length which agreed with expectation. During the second amplification, a clear belt obtained with the internal primers was approximately 400 bp in length which was also accordance with assumption. The partial sequences of the 28S ribosomal RNA gene of tested strains were analyzed. By BLAST search and phylogenetic tree analyses, four strains belonging to FON were further determined, and the results also showed that F40 was an original strain, followed by ZO, and BO were the latest one, in terms of the order of strains evolution.Fourthly, with the expectation of finding out the influence of pathogen on activity of daffodil protective enzyme system, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities of infected leafs of Mount hood were measured and compared. The result revealed that POD and CAT activity of healthy leaves in infected plant were lower than those of totally healthy plant leafs, while SOD activity was stable comparatively. With the development of infected conditions of leafs, enzymes activities rose quickly, especially 3.0 and 3.5 times of SOD activities were observed in severer and the severest infected areas compared with those in healthy plant leaf, while 1.3 and 2.0 times of POD activities along with 1.5 and 1.8 times of CAT activities were observed respectively.Fifthly, the enzyme activities also were compared in healthy plant leaves among daffodil cultivars. Among these early-flowering cultivars of Delibes, Shangnong Zaochun and Pinza, the lowest enzyme activities were in Pinza. The late-flowering cultivars Sovereign and Mount hood, enzyme activities of Mount hood were lower.
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