FUNGI ASSOCIATED WITH DIE-BACK OF SISSOO

G. Manandhar and S. K. Shrestha
Plant Pathology Division, Nepal Agricultural Research Council, Khumaltar, Nepal

1. INTRODUCTION

Sissoo (Dalbergia sissoo Roxb. Ex DC.), is an important timber plant, grown in terai region of Nepal. During the last decade, the public have been encouraged to start sissoo plantations. As a result, large areas in terai and inner terai were covered with pure sissoo plantations. But in recent years, die-back of the trees has caused concern among growers and new plantations have been stopped.

2. OBSERVATIONS AND CONCLUSIONS

The symptom expressed by dying trees was suspected to be similar to that of the wilt caused by Fusarium oxysporum, reported in India under the similar environments (Ivory 1985). Root decay is a major problem associated with fungi including Ganoderma sp., Polyporus sp., and Fusarium sp. – these were collected in the terai belt in association with sissoo die back in 1999.

Five root samples of sissoo were received from the Department of Forest Research & Survey for further investigation in April 25, 1999. Each sample was thoroughly examined, visually and under microscope. From each root, a number of samples were cultured on different media including water agar, Potato Dextrose Agar, Carnation Leaf Agar, Nash and Snyder Agar.

Brown discoloration of wood tissue was observed in some parts of 2 samples. In one part of the sample, black stroma, consisting of groups of pycnidia of Botryodiplodia sp. Was identified. The brown discoloured tissue of another sample also produced the pycnidia and spores of Botryodiplodia sp. In culture. Three samples including 2 from Sapahi, were observed infected by Fusarium solani. Occurrence of paired chlamydospores of the fungus was also observed in 11-24 days old culture at room temperature. One of the 5 samples was also observed infested by termites.

In the past year (1998) sissoo samples infected with Fusarium sp. On one root of a young seedling in a nursery in Kathmandu was recorded. F. solani was isolated from a piece of stem of the affected tree, grown in Chitwan district.

One seed sample, provided by the Department of Forest Research & Survey, sample no 1913 of seed source Kamdi, Banke, was tested for seed borne infection by Fusarium species on June 4, 1999. For this purpose, 50 seeds/pod, each surface sterilised and non-surface sterilised were planted on a selective medium of Fusarium and incubated at 22-28°C under 12 hours darkness and 12 hours NUV for 5 days. The seeds were found free from infection by species of Fusarium. Other fungi associated with the seeds were Aspergillus spp., Cladosporium sp., and Alternaria sp. Also on seeds/pods the infection percent observed as low as 4% and 3% in surface sterilised seed and seed with pod, compared to 44% and 100% in non-surface sterilised seed and seed with pod, respectively.

The leaf blight disease was also observed on leaves of some seedlings of Makawanpur caused by Phoma species. Rust was also detected on leaves of some seedlings, and was caused by Uredo sissoo

Pathogenicity test was carried out on sissoo seedlings received from the Department of Forest Research & Survey in June 1999. Three seedlings were inoculated by dipping them in suspension of the F. solani, after cutting some of their roots to enhance the infection easily and then transplanted on sterilised soil, 1 plant per pot. Similarly, 3 seedlings without injury were also transplanted and spore suspension, was poured over the soil. No effect could be detected on me seedlings, irrespective of the treatment. The reason is not clear.

F. solani was recorded in the list of wilt in sissoo (Mukherji & Bhasin 1986). It was also considered a facultative parasite associated more with the wounds/injuries and on hosts weakened by unfavourable conditions (CMI 29).

Concerning other fungal diseases of sissoo, 2 Rusts by Uredo sissoo and Maravalia achora; a Leaf Spot by Phyllachora dalbergiae; Powdery Mildew by Phyllactinia dalbergiae were recorded in the country (Jackson 1987).

The list of fungi isolated from sissoo is given in Table 1. In general, Fusarium solani was frequently isolated from the samples. However, seed-borne infection by Fusarium species was not observed, and can be ruled out.

Table 1. Fungi isolated from different parts of sissoo samples, 2000

Hence, a detailed study on this problem needs to be carried out in order to identify the problem, which would be needed if the plantations are to be expanded in the country.

3. REFERENCES

CMI. 1964. Description of Pathogenic Fungi and Bacteria The Commonwealth Mycological Institute Issue No. 29. Ferry Lane, Kew, Surrey, England.

Ivory, M. H. 1985. SRP visit of Forest Pathologist March (unpublished report).

Jackson, J. K. 1987. Manual of Afforestation in Nepal. Nepal-U.K. Forest Research Project, Forest Survey and Research Office, Department of Forest, Kathmandu, Nepal.

Nelson, P. E., Toussoun, T. A. & Marasas, W.F.O. 1983. Fusarium species, An Illustrated Manual for Identification. The Pennsylvania State University Press, University Park and London.