1959 Volume 28 Issue 4 Pages 241-256
Since 1953, laboratory studies on the pathogens causing the rot disease of lotus rhizome and field survey on the prevalence of the disease in relation to the environmental conditions were carried out, and control measures have been established basing on the field experiments. The results obtained are summarized as follows.
1. The rot disease of lotus rhizome was classified into three types basing on the prevailing pathogens.
Type 1. Brown rot disease caused by Fusarium spp.
Type 2. Light-dark purple rot disease caused by Pythium sp.
Type 3. Complex rot disease caused by mixed infection of Fusarium and Pythium.
2. It was found that the disease was transmitted through seed rhizome, water, and diseased leaves and rhizomes ploughed into the soil. The pathogens invaded into the rhizome mainely through the ab-sorbing roots or directly through the diseased por-tions of the seed rhizome, and sometimes through the wounds on the rhizome or soft tissues of the growing point.
3. The pathogenetic Fusaria could not survive 20cm or deeper in the soil under the drained condition, and 25cm or deeper under the waterlodged condition. Pythium was never perished under the above men-tioned conditions, though it could not survive on the soil or water surface.
The brown rot disease caused by Fusaria is pre-valent mainely in the paddy-fields irrigated with shallow depth of water and with shallow ploughed layer of soil. On the contrary, the light-dark purple disease caused by Pythium is mainely prevalent in the lotusmoats filled with deep water or in the low and constantly wet paddy fields.
4. The temperature and pH ranges for the grow-th of the pathogens were as follows.
Temperature Range Optimum Lethal
Fusarium spp. 1033°C 27_??_30°C 54°C(lOmin.)
Pythium sp. 10_??_45 30 50 (5min.)
pH Range Optimum
Fusarium spp. 2.2_??_11.7 7.2
Pythium sp. 3.2_??_9.4 6.2
The rot disease was more prevalent and proleptic when soil or water temperature was high. There-fore, deep irrigation or waterfilling for long period was more effective for the control of the rot disease.
5. Keeping the field filled with water during winter was an effective control measure of the brown rot disease. Draining or cultivating the field in winter made the field favorable for the prevalence of the brown rot disease.
For the light-dark purple rot disease, those measures had an entirely contrary effect.
6. Soil disinfection by applying calcium cyana-mide at soil preparation was found to be an effective measure for controlling the disease. Application of lime sulfur in the period from soil preparation to early May was also effective.
Application of wettable Captan to the soil in the period from soil preparation to early May was prov-ed to be surprisingly effective for the disinfection of soil.
7. Resistance of the lotus varieties to the diseases was tested by inoculating cultivated pathogens to the cross sections of lotus rhizomes. The results showed that Shina-shu was most resistant, Kobasu and Tenno were most susceptible, and Bitchu, Ka-zusa and Chukan-shu were intermediate to Fusaria. Field experiments showed the same results on the varietal difference in resistance to the brown rot.
Significant differences were hardly found in the susceptibility to Pythium among lotus varieties.