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Studies on citrus melanose and citrus stem-end rot by Diaporthe citri (Faw.) Wolf. Part 9. Effect of light and temperature on the self-defense reaction of citrus plants.

1988; Phytopathological Society of Japan; Volume: 54; Issue: 3 Linguagem: Inglês

10.3186/jjphytopath.54.282

1882-0484

Yutaka ARIMOTO, Yasuo Homma,

Plant Parasitism and Resistance

Light and temperature were both very important for the induction of a self-defense reaction of citrus plants against penetration by Diaporthe citri (Faw.) Wolf or against mechanical injury. Under light (5, 000 lux, 25C), melanose spots or scars made up of brown cells and a cork-like layer were produced on leaves inoculated with the pathogen or injured mechanically. Scoparone, a phytoalexin, was produced in these leaves, and the infecting pathogen was found to be arrested within the melanose spots. Under dark (<0.5 lux, 25C), however, neither melanose spots nor scars were produced when the leaves were inoculated or injured, nor was any scoparone detected in the leaves. The infected pathogen spread in the leaves without being impeded by any barricade, and pycnidia and pycnospore developed on the leaves 2 weeks after inoculation. The cell browning and cell division in inoculated leaves or the incised part of the shoot were most severe at 25C. The degree of cell browning and division decreased as the temperature became lower. At 15C, the infected epidermal cells or the cells in the incised part granulated and only slightly turned brown, but no adjacent cells divided. At 10 and 5C, neither cell browning nor cell division occurred even in citrus plants kept under light (5, 000 lux) after the treatment. Scoparone production was also affected by temperature. The largest quantity was produced in the melanose spots or scars at 25C. The amount decreased at the temperature became lower, until no scoparone was detected at 10 or 5C. These results mean that the self-defence reaction, which can effectively impede pathogen invasion, in citrus plants depends strongly on light and temperature.