EFFECT OF LIGHT-INTENSITY ON ABNORMAL SWELLING OF PEDUNCLE IN MUSCAT OF ALEXANDRIA GRAPE

'Muscat of Alexandria' grapevines, grown under heated greenhouses, sho w abnormal swelling on the peduncles and rachises during an early stag e of berry growth. The cause of this abnormality was investigated by c ontrolling the light intensity to the clusters. Complete shading bf th e peduncular nodes for 4 weeks after full bloom caused a noticeable sw elling in all the treated peduncles. Fifty % shading caused swelling i n half the number of the treated peduncles. The rate and the degree of swelling were reduced by the exposure of clusters to sunlight or by u sing a sunlight reflector film. In vitro culture of excised disks from swollen peduncles revealed active division of callus cells even on ho rmone-free MS medium. The division was stimulated when the cultures we re kept in the dark. These results suggest that accumulation of some l ight-decomposable factors at the peduncular nodes causes this abnormal ity.