1989 Volume 1 Pages 32-40
In natural infection of bacterial blossom blight of kiwifruit, symptoms of infected buds and flowers are classified into five types. Initial infection of flower buds occurs on burst sepals of young buds. In this case, pathogenic bacteria invade through the wound of sepals causing a necrotic symptom on the sepals (S type). However, interior organs of the flower buds showed no symptom at this stage. After 3-4 days of rainfall, swelled buds showed most severe symptoms, all interior organs being rotted with dark brown rot color. Swelled buds were highly susceptible to the disease, and all the infected buds exhibited the most severe symptoms such as dark brown rot of stamens, stigmata and styles, and yellowish browning of petals (F-I and F-II types). If the infection had occurred in open or opening flower buds at the blossom stages, symptoms were mild and only limited number of anthers, and some of the stigma became faint brown color. Generally, infection of swelled buds resulted in remarkable infection of stigmata. When efflorescence followed soon after infection, light-symptoms were observed of the flowers. The stigma infection is related directly to falling of buds and fruits (Fr-I and II), and the production of various deformed fruits (Fr-III-A, B and C) of no commercial value. High concentration of the inoculum is essential for the occurrence of severe symptom of swelling buds. When high concentration of bacterial suspension that had been prepared from colonies of the pathogenic bacteria on nutrient agar medium were inoculated by spraying on the surface of swelling buds, necrosis of the bud were not observed for 3-4 days. When the same suspension was injected into interior of buds, however, the typical severe symptom appeared 2-3 days after injection. These results indicate that the bacteria cannot invade directly into buds from the outside in a short period of time. Even if many bacteria were spread from infected leaves and stems, they are most likely unable to invade quickly into swelled buds to cause severe infection. Infection of the interior organs of floral buds seems to occur in such a way that the bacterial ooze effused on inner surface of infected sepals are directly carried into interior organs with rainwater through interspace between the sepals and petals of swelled buds.
