1962 Volume 27 Issue 3 Pages 102-108
In this paper, results of experiments on the relationship between the lodging of rice plants caused by stem rot (causal fungi: Leptosphaeria salvinii Catt. and Helminthosporium sigmoideum Cavara var. irregulare Cralley et Tullis) and disintegration of infected tissues are described.
1. Lodging of diseased plants occurs generally after earing. At this growth stage, in the stem lesion, parenchymatous tissues are disorganized and lignified tissues such as vascular bundles become separated from the epidermal layer.
2. The pectic substances in the middle lamella showed a change in staining reaction, and sometimes were observed to have been digested. Results of viscosity-tests and observations under a polarizing microscope, indicated that the structure of cellulose changed and the specific viscosity decreased.
3. These results indicate that the alteration of the infected tissue was caused by enzymic actions of the pathogenes.
4. Pectic enzymes and cellulases were produced on synthetic medium by the above mentioned fungi, but type of action of enzymes were different between them. More pectic enzymes which dissolve the pectic acid and Cx type cellulase, were secreted by the former than by the latter, while by the latter more pectic enzymes which decompose pectic acid and C1 type cellulase were secreted.
5. Resistance of diseased plants to the lodging was determined in terms of Young modulus of the stem, Young modulus was found closely related with the degree of alteration of cell walls and the separation of lignified tissues in the lesion.
6. From the present experiments, decrease of Young modulus of the stem resulting from chemical and physical changes of the stem tissue infected by the pathogen, was considered to be the main cause of the lodging of diseased rice plants.