R.B. Joshi and S.R.
Department of Forest Research and Survey, Babarmahal, Kathmandu, Nepal
Dalbergia sissoo (sissoo in Nepal) is one of the most valuable tree species of the sub- Himalayan area from Assam to Afghanistan. The species occurs naturally on the reverine forests mostly in association with Acacia catechu. Hence, the most suitable site for its growth is sandy and alluvial soils on the banks of rivers and streams. It is found growing throughout Nepal from Terai plains (ca 100 m) to inner valleys. For the last 30 years or so, this species has become the most widely planted tree in Nepal. Unfortunately, the recent die-back symptoms observed in the plantations have caused much concern amongst the sissoo planters. Such die-back of sissoo is perhaps due to some fungi such as Fusarium sp. And Ganoderma lucidium, along with stem borer insects (see FORESC 1997, Parajuli et al. 1999). However, an unidentified root nematode was also implicated in the die-back of sissoo (FORESC 1997). Similar problems have been observed in the neighbouring countries, India and Pakistan. Tewari (1994) provides comprehensive report on it. Sissoo root rot was carefully documented previously, prominently by Bakshi (1954) and Bakshi and Singh (1959).
Before describing the sissoo die-back, it would be valuable to briefly introduce the history of tree plantation in Nepal which started with the plantation of Pinus roxburghii in and around Kathmandu Valley in the early 1950s. The large scale plantation in the mountain and the lowlands (Terai and inner Terai), however, began only in the mid 1970s.
Various organisations such as the district level forestry offices of the Department of Forest, the Terai Community Forestry Project, the Sagarnath, Ratuamai and Nepalgung Forestry Development Projects, etc. were involved in tree plantations in the lowland. With the growing awareness of tree plantations coupled with the decreasing supply of fuelwood and timber form public forests, a large number of private entrepreneurs also started tree plantations in private lands. The plantations were also set up in degraded public forestland, canal-sides, roadsides, on crop fields and on marginal lands.
The popularity of sissoo as a plantation tree in Nepal could be attributed to: a) fast growth and multipurpose use; b) easy to propagate; c) provides high economic return d) high demand; d) nitrogen fixing ability; and e) deciduous habit, making it possible to plant other agricultural crops during the early years. For these reasons sissoo has become the most preferred species for afforestation in the Terai (Joshi 1994) and is estimated to cover about 90% of the plantation area here (Gautam 1996). The other tree species such as Eucalyptus camaldulensis, Tectona grandis, Melia azadirach and Albizzia procera make up the rest.
Baral (1995) traced the first report of sissoo die-back in the plantations of Nepal to 1993. However, the official reports, from the district forest offices to the Department of Forests (DoF), and the Department of Forest Research and Survey (DFRS) were received only from the year 1996/97. Realising the critical nature of the problem, the DFRS immediately organised a meeting with the Community and Private Forestry Division of the DoF to jointly undertake a preliminary investigation. A team of researchers, including personnel from DoF, Tree Improvement and Silvicultural Component, and DFRS were sent to the five Terai districts (Sarlahi, Dhanusha, Siraha, Sunsari, Morang) of eastern and central development regions to quickly report on the disease incidence in the sissoo plantations. This was the first preliminary investigation of sissoo die-back in Nepal. Following the visits, the team submitted a brief report (see FORESC 1997), the conclusion of which is reproduced below:
"Field visit at various sites revealed that a serious threat has occurred to the sissoo plantation in the Nepal's Terai. Sissoo trees of varying ages, especially those planted on/or along rice fields, are dying. Of the major reasons for such death of trees, neither the fungal attack on leaves nor the defoliating insects have much significance. It seems, it is either due to stem and root borers, and/or fungal attack in sissoo roots. Almost every dying (or dead) tree has revealed root decay at its cortical layer followed by the attack of stem borer. It is interesting to note that most of the dead trees were from such sites which have compact soil where there is possibility of water logging, at least, for a season.
A number of insects were also reported. Pinhole larvae of the family Buprestidae and Curculinidae (beetles) were reported to be one of the various reasons of the top-dying (FORESC 1997)."
The limitation of the above study was that it was carried out in a very short time and covered only a few districts. Also, detailed investigation of the pathogens was not in the agenda. However, possible attack of Fusarium solani, a facultative fungus in sissoo roots was indicated. Similarly, detailed studies on the physico-chemical parameters of the soil where the trees were growing were not carried out. Thus the possibility of root-rot as the primary cause could not be confirmed.
Following the recommendations made by the first general survey, the next investigation was carried out during 1998/99, by a team as well (foresters – DFRS and Churia Forest Development Project; Pathologist – Department Plant Resources; Entomologist – National Agricultural Research Centre). This team studied sissoo plantations in seven districts (Dhanusa, Siraha, Saptri, Udaypur, Sunsari, Morang and Jhapa). The conclusion of the report is reproduced below:
"The investigation collected many species of fungi prevailing in the region. They are Xyleria sp, Schizophyllum communi, Uredo sissoo, Phyllactinia dalbargiae, Ganoderma lucilium, Coriolus versicolor, C. tephroleucus and Polyporus sp. Maravalia achroa and Phyllactinia coryle parasitic to the same host also do occur in the same region which needs further investigation.
The cultures made from the sissoo roots and stems of the study area revealed that the trees of Sissoo has been seriously attacked by the fungus Ganoderma lucidium, Fusarium sp. (probably F. solani) and bacteria. The rots were due to bacteria while the whitish patch in the rings and scattered patches were due to the fungus. The fermentation in the roots and some portion of the trunk were due to the bacteria, which appeared to be a secondary infection. However, it is necessary to ascertain the role of bacteria also."
There are many species of Ganoderma that are similar to G. lucidum prevailing in the tropical region, extending from Japan to the Indian sub-continent. So, more has to be found out about their presence, virulence and susceptibility.
Several fungal pathogens and insect pests and including bacteria were recorded during this study. However, only a few of them pose a serious threat to the sissoo trees and other tree plantations. The species of concern are the fungi G. lucidium, Fusarium sp, and Polyporus spongiosum, and the insect borers belonging to the families Scolytidae, Buprestidae, Cerambycidae of the Order Coleoptera (beetles). However, to some extent the role of termites has also to be considered.
The role of insects and fungi in damaging the sissoo trees has to be studied so as to ascertain which are the primary and secondary agents.
The above study also had some limitations, which are listed below:
The Department of Forest Research and Survey is carrying out a detailed survey at 25 Terai districts of the country during the year. The objective of the study is:
The field work on the general survey in the 25 districts is about to be completed. The data will be analysed, and more detailed work will be carried out thereafter (including pathological, entomological and soil-site interactions) in 7 of the 25 districts.
The Department of Forests and Survey will also review the work undertaken by other agencies in Nepal as well as on-going studies in the neighbouring countries. In fact, the organisation of the present seminar is one such step. Through such networking at a regional or sub-regional level, it is hoped that more scientists would be able to share their experiences, tackle the problem jointly, and solve the problem more speedily.
The Department of Forests and Survey is planning to work on the sissoo die-back for at least two more years. The Department also aims to disseminate the research results to a varied audience in a quickest possible way. In order to support the implementing agencies such as DoF and other private entrepreneurs to reduce the problem of sissoo die-back, DFRS has opted the following dissemination mechanisms:
The following recommendations are suggested:
Baral, S. R. 1995. Disease in sissoo. Ban-Upaban, 1(1): Forest Produce Development Board, Kathmandu, 24p (in Nepali).
Baral, S. R. 1999a. Problem of sissoo in the Terai (in Nepali). Kantipur Daily (26th May 1998).
Baral, S. R. 1999b. Problem of sissoo and its mitigation (in Nepali). Kalpabriksha, a monthly extension bulletin of the Ministry of Forests and Soil Conservation, Singhadurbar.
Bakshi B. K. 1954. Wilt disease of sisham (Dalbergia sissoo) due to Fusarium solani Sensu Synder and Hansen. Nature 174: 278.
Baksi, B. K. & Singh, S. 1959. Root disease of sisham (Dalbergia sissoo Roxb.) VIII. Inoculation studies on wilt. Indian Forester 85:415.
FORESC. 1997. A report on field investigation of top-dying of Dalbergia sissoo growing at some districts of the central and eastern Terai. Forest Research and Survey Centre and Department of Forests, Kathmandu.
Gautam, K. H. 1996. Growth of multiple-stems in a two-year old Dalbergia sissoo plantation in Nepal Terai. Banko Janakari 6(2):82-84. Forest Research and Survey Centre, Kathmandu.
Joshi, R. B. 1994. Growth performance of Dalbergia sissoo as fuelwood species in the lowlands of Nepal. Banko Janakari 4(2): 154-156. Forest Research and Survey Centre, Kathmandu.
Parajuli, A.V., Bhatta, B., Adhikari, M. K., Tuladhar, J. R. Thapa, H. B. & Uuwa, G. B. 1999. Investigation on the causal agents responsible for the die-back of Dalbergia sissoo in eastern Terai belt of Nepal. Department of Forest Research and Survey, Kathmandu, Nepal.
Tewari, D. N. 1994. A Monograph on Dalbergia sissoo Roxb. Indian Council of Forestry Research and Education. International Book distributors, Dehra Dun – 248001.pp. 1-202.