ABSTRACT
During the process of pathogens penetrating the plant cell, pathogens often secret some chemicals into plant cells, at the same time, they also produce mechanical signal by physical pressure on the plant cell. Here the pressure is used as the stress signal, to study its effect on phytoalexin accumulation and the induction of plant resistance in cucumber seedling. It is found that stress can induce the resistance in cucumber seedling significantly. When breaking the plant cell wall and plasma membrane adhesion by RGD peptides, the resistance induction is almost eliminated. Results from TLC and HPLC showed that stress stimulation could increase phytoalexin accumulation in cucumber seedling. This suggests that the accumulation of phytoalexin is one possible reason of the increased resistance after stress stimulation. When the adhesion between plant cell wall and plasma membrane was block by RGD, there is only small amount of phytoalexin accumulation compared with the control, suggesting that the stress induced phytoalexin accumulation and resistance is relying on the adhesion of plant cell wall and plasma membrane.
ABSTRACT
A black scab disease occurred on sword bean (Canavalia gladiata) in plastic film houses around Chinju area during the spring season of 1999. The disease started from flower bud, then moved to flower stalk, pod, petiole, cirrus, stem and leaves. The lesions started with small dark brown spots then were gradually expanded. Severely infected plants reached 37.4% of whole plant covered with scab. Numerous conidia were produced on the diseased flower disk, pod, floral axis, stem and leaves. Most of the conidia were appeared to be readily dispersed in the air, but the mycelia were not suggested causing of sooty mold by ectoparasitism. A fungus was isolated from the diseased stem, and inoculated to healthy plants to satisfy the Koch's postulates and proved the fungus was the causal agent of the disease. The isolated fungus grew on potato dextrose agar, forming greenish black to pale brown colonies. Conidia were ellipsoidal, fusiform or subspherical, mostly one-celled but occasionally septated. The conidia were 3.9~34.1x2.7~5.1microm in size and formed in long branched chains on the erected conidiophores which were pale olivaceous brown and variable in length between 7.2~210.7microm in size. Ramoconidia were 7.6~29.2x3.2~14.4microm in size. The fungus was identified as Cladosporium cucumerinum based on the above morphological characteristics. The optimum temperature for mycelial growth and conidial formation was about 15 to 25degrees C. Cladosporium scab of sword bean caused by the fungi has not been reported in Korea previously.