SISSOO DIE-BACK: IS TREE IMPROVEMENT A PROBABLE SOLUTION?

L. P. Dhakal
HMG/DANIDA Tree Improvement and Silviculture Component/Natural Resource Management Sector Assistance Programme, Hattisar, Naxal, Kathmandu, Nepal

1. INTRODUCTION

Dalbergia sissoo (sissoo) is an important species for rural as well as industrial plantations. It is popular for plantations due to its fast growth and multiple use properties. Sissoo prefers well drained, alluvial soils near rivers and streams. The trees is distributed from Bhutan in the East to Afghanistan in the west (Fig. 1). In Nepal it is distributed from the terai up to 1400 m (Napier & Robbins 1989). Sissoo has a unique property in that it hardly regenerates under the old mother trees. It is pioneer in nature and often grows in clumps in new well-drained alluvial sites near river/stream beds.

The natural D. sissoo populations have come under considerable pressure from human disturbance. Very few remnant populations still exist in the riverine plains of the Terai and Siwaliks. East Nepal had considerable populations until late 1980s, but now they are confined (except in Protected Area Systems, PAS) to a few natural patches in Far- western Nepal, in a very threatened state.

Tree improvement aims at improving the quality of production and services from the operational plantations. Nepal's ninth five-year plan emphasises development of large-scale tree plantations (30,000 ha) through participatory planning and implementation. Tree improvement should have an important role to play in such a process, especially when diseases and pests are affecting one of the major plantation species of the country. Here, I wish to review the probable causes of the sissoo die- back and mitigating measures to be introduced.

2. CAUSES OF SISSOO DIE-BACK

Recent studies (Baral et al. 1997, Anon. 1999) suggest that sissoo die-back in Nepal may have been avoided or minimised if: I) appropriate matching of seed sources to planting sites was done; and ii) genetically superior planting material was used. Other factors that made the problem more severe include inappropriate or non-existent management and silvicultural regime, and pathological and entomological incidences.

Fig. 1. Natural Distribution Range of Dalbergia sissoo

The shaded portion indicates Dalbergia sissoo natural distribution range
Source: (Roshetko & Yadava 1994)

Selection of seed source and site for plantation are the most important decisions made in artificial regeneration. The species chosen should be suitable to the soil, climate and biotic environment. As far as possible a monoculture in operational plantations should be avoided. The desired gains from plantings would be available when site matching is appropriate. Seeds used in plantations rarely come from a broad genetic pool. This narrow genetic base, often one or few clones (trees), has contributed to inferior progeny (higher chance of inbreeding) which are prone to pest and disease attack.

Selection of improved genetic material is a crucial decision for the success of the plantation programme, as it will have impact on the amount and quality of the product, the economic output, and the buffering capacity against pests and disease (Hansen & Kjaer 1999). Until recently, planting programs in Nepal gave little heed to growing seedlings from the best seeds (Thomson 1995). Recent market survey conducted by Tree Improvement and Silviculture Component of IUCN (TISC) (1999a) indicates that the users (HMG/Private/Forest User Groups) acquire tree seeds from wherever possible with complete disregard to genetic suitability.

Cultural techniques and management of the trees from the nursery to the plantation stage ensure best performance of the trees. In Nepal hardly any systematic management prescriptions are applied in the sissoo plantations. Due to lack of silviculture and management inputs the majority of the plantations are without thinning and pruning, and hence are vulnerable to the disease and pest infection.

Pathological and entomological problems are evident from the studies conducted in the die-back sites in the eastern and central Nepal (Anon. 1999, Baral et al. 1997). Ganoderma lucidium and Fusarium spp. Are major fungi contributing to the death of sissoo in Eastern Nepal (Anon. 1999). Site preparation before the planting is important to reduce the pathological problems.

3. TREE IMPROVEMENT FOR DISEASE RESISTANCE

Tree Improvement and Silvicultural Component (TISC) has initiated two-fold activities for D. sissoo improvement – basic and advanced programs. Basic activities include identification of natural stands from where best mother trees are selected. These trees are used for seed collection. Domestication of such plants is promoted. Results show that using these seeds for plantations will significantly increase the volume and yield during final harvest. Besides, TISC, under its advanced tree improvement programme has established Breeding Seedling Orchards (BSO's¹).

3.1. The Breeding Programme

The breeding programme for sissoo started in 1993. For this purpose HMG/Danida Tree Improvement Programme (TIP) conducted a countrywide survey to identify superior phenotypes of D. sissoo. Seeds from these superior phenotypes, from 10 Terai districts (see Fig. 2), were used as the base breeding population for the establishment of BSO. 94 superior phenotypes were available for collection of seeds out of 103 identified trees. TISC in total has established 4 BSOs (one in each region – Eastern, Central, Western and Mid-western Development Regions). Similarly, in 1995 progeny trials were established at Teelkane, Chitwan, and Central Development Regions from 35 families from Kailali, Far-western Development Region.

Fig. 2. Dalbergia sissoo Base Breeding Population Selected Sites

Map indicates Development regions of Nepal and the sites/Districts from where base-breeding population of D. sissoo was selected. Noticeable is the far lesser representation of eastern provenances compared to western and central development regions

3.2. Selection of Plus Trees

For any breeding programme selection of best possible genetic material is very important. The criteria for selection were (Thomson 1994): I) vigour and health; ii) dominance; iii) straight, cylindrical bole of superior diameter; iv) strong apical dominance; v) no ramicom branching habit; vi) light branches growing more or less at 90° to the stem; and vii) a tendency to self prune. The selection criteria have emphasised on the vigour and health, as reflected in the scoring system (Table 1).

Table 1. Dalbergia sissoo scoring system for the Plus tree selection to be represented in the BSOs

Source: Thomson (1994)

This scoring system was used to arrive at an index value for each candidate tree. These candidates were assessed with the surrounding (comparison) trees (total of 5). The candidate trees were on average 50 % better than the comparison trees.

Tables 2 and 3 indicate the selection of base breeding population of D. sissoo, from 5 development regions, to be used in the establishment of BSOs. The seeds for the Progeny Trial came from 35 families in 5 populations of Kailali in the Far Western Development Region.

Table 2. Base breeding populations for BSOs of Dalbergia sissoo

Source: Thomson (1994)

Table 3. Dalbergia sissoo Base Population of the Progeny Trial at Teel Kane, Chitwan from 5 sites

Source: Thomson (1993)

3.3. Establishment of BSO

The seeds collected in 1994 were used for establishing 4 intermediate level BSOs. A randomised complete block design of several blocks where each family is represented in a block by 16 seedlings, at 1.5 x 1.5m spacing was used. Similarly, the seeds collected in 1993 were used for the Progeny Trial, which was established as a single tree plot with 35 families, 96 replications, at 2.5 x 2.5m spacing.

Table 4. Details of intermediate level BSOs of Dalbergia sissoo and progeny trial

RCBD: Randomized Complete Block Design, STP: Single Tree Plot.
Sources: Thomson (1993),Rimal et al. (1995), Jha et .al. (1996), Aryal (1998)

3.4. Performance of BSO and Progeny Trial

General performance of all the intermediate BSOs appeared to be good in terms of growth and survival, except the BSO in Dharan, Sunsari District. This BSO was under severe attack by stem borers and had high mortality. The reason may be due to the heavy clay content of the site, making it not unsuitable for sissoo plantation. Continued management of this site would be of importance to select for those few families (if any of the progenies survive) which will be capable of withstanding the disease. These families could be used for breeding the disease resistant varieties in the future.

The Progeny Trial at Teel Kane, Chitwan District was measured and analysed (1998 and 1999) and genetic parameters were estimated (TISC 1999c, in press). The estimates suggest that high genetic variation exists for both vigour and stem form, thus contributing to >25 % gain in stem volume, >20 % gain in branch weight, and >15 % gain in stem form, when compared with best available unimproved seed (otherwise good), at moderate selection intensity.

Preliminary investigation (TISC, 1999c, unpublished) suggests that sissoo BSO will improve stem volume by 20-25%. Disease/pest resistance is also expected to improve since pest resistance was one of the important selection criteria. Evaluation of the pest resistance qualities needs some more years (probably 10-15). Likewise, gain in disease and pest resistance is also difficult to estimate until the BSO's begin producing offspring.

4. FUTURE INVESTIGATIONS

With respect to the present level of understanding in D. sissoo, there are four issues that need further investigations:

1. Does sissoo show localised adaptation from East to West?; 
2. Are foreign seed sources inferior to indigenous sources?;
3. Are there distinct provenances differentiated with distribution along river systems and soils?; and
4. The need for in-situ conservation² of D. sissoo gene resource.

4.1. Local Adaptability of Sissoo

Neil (1989) and Joshi and Thapa (1997) have indicated some local adaptations, in terms of growth and development of D. sissoo. Indigenous provenances of Nepal were compared with Pakistan provenances in different sites (Neil 1989- at Adhabar; Bara et al. 1997- at Tarahara, Sunsari and Shankhar Nagar, Rupandehi). The Nepali provenances were significantly better than the Pakistani ones. In both cases, the local provenances (nearer to the research sites) out-performed other indigenous and Pakistani provenances. This suggests that there may be some adaptation to local sites in D. sissoo, which needs to be tested. Systematic testing of provenances throughout Nepal is needed, and provenance testing with larger representation of Eastern and Central provenances is needed.

4.2. Seed Sources

Very limited research results are available from provenance testing. Pakistani provenances were significantly inferior to Nepali provenances (Joshi & Thapa 1997). Exotic seeds of sissoo until now have performed very badly in each of the trials conducted in Nepal. Although none from India have been tested, but the seeds from India are openly traded in Nepal (TISC 1999a). Use of these unknown seed sources of exotic origin should be immediately stopped. Untill comprehensive provenance tests of sissoo from various exotic sources are tested extensively, it is advisable to use seeds from trees already growing in Nepal.

4.3. Provenance Testing

Large phenotypic variation is a general feature of all natural D. sissoo populations (Thomson 1994). The degree of relatedness among different natural patches in not known to Nepal. This has created difficulty in defining provenances (ecotypes). Presently major watersheds are accepted as provenance regions for sissoo (White et al. 1990). This is supported by the findings of Hansen (1998) where allozyme markers have found significant differentiation between the distinct populations, and have revealed a geographic pattern of isolation by distance.

There is disproportionate representation of progenies from East to West Nepal (see Table 2) in the BSOs established by the TISC. Western Nepal has higher representation whereas East is poorly (or not at all in some BSOs) represented. The main reason for favouring high number of plus trees from the western part of Nepal seems to be due to the available provenance results at that time (see White 1990) and the visible evidence in the field (phenotypes of the far-western Nepal are apparently superior). Whether this is due to superior genotype or the environmental condition or less exploitation, is not known (Thomson 1994)). TISC should immediately plan and initiate the national and international provenance testing. Nation-wide tests should consider major watersheds and each should be adequately (at least 30 from each) represented (Fig. 3).

4.4. In-situ Conservation

It is important to conserve natural populations of sissoo since they constitute the base for future domestication (Hansen & Kjaer 1999). These conservation efforts should be replicated in all the four major watersheds. Conservation activities are relatively easier to execute, if carefully planned in the four protected area systems (PAS) (Fig. 4) of Terai of Nepal which follows more or less with the major watershed patterns.

Fig 3. Major Watersheds and River Systems of Nepal

Map indicates 4 major watersheds and drainage system of Nepal. It is believed that provenance (ecotypes) differences of D. sissoo are present along the major watersheds

Fig 4. Protected Area Systems of Terai of Nepal

Legend: SPWR: Shukla Phanta Wildlife Reserve; RBNP: Royal Bardia National Park; RCNP: Royal Chitawan National Park; PWR: Parsa Wildlife Reserve; KTWR: Koshi Tappu Wildlife Reserve. These PAS are potential sites of in-situ D. sissoo conservation

Sufficient care should be taken to protect the natural populations inside the PAS, such that outside sissoo populations do not pollute (since private holdings may have Indian Sissoo plantations) the natural population (down stream).

It is difficult to protect the natural populations of sissoo in private lands or land under Department of Forests/HMG tenure. However, such protection provisions in HMG land have been spelled out in Forestry Acts of Nepal. Some conservation work has already been undertaken by Kanchanpur District forest office (pers. Comm.), Far-western development Region. This process should be supported technically with systematic planning and implementation

In situ conservation of sissoo has international importance since occurrence of this highly exploited sub-Himalayan species is widely believed to be among the very few populations of Hindu-kush Himalayan region. Hence this species can be regarded as an asset of international importance (Graudael 1996).

5. IMPROVING THE PRESENT SITUATION

In this paper, solutions for sissoo die-back are observed purely from the tree improvement perspective only. The following considerations would be useful:

5.1. Decentralized Seed Distribution

D. sissoo is an important species for rural community. This is the reason for its large- scale domestication by the farmers. Identified problem from seed delivering agencies (as TISC (TISC 1999b)) is the lack of supply channels to meet these individual, but highly scattered, farmers developing small wood lots. Increasingly farmers are key players in tree plantations. With improved seeds, improved seeds would be realised by the farmers. Central or even regional (in some instances) seed supplying channels have not been effective in reaching the target groups (farmers) (Lillesoe et al. 2000). There is a need to channel the improved germplasm to the local farmers through cooperatives or other means. Additionally, private seed dealers/merchants (see Table 5) should be supported through technical information support.

Besides, there is a need to improve identify and improve the quality of seed collection channels, and link the district level producers with other tree seed users. Associations or networks (co-operatives) of tree seed producers at local level are already in place (one each in Kavre and Kaski, supported by TISC).

A recent seed market study (Lillesoe et al. 2000) indicates that nearly two thirds of seedlings produced (Table 5) come from seed collected by the Nursery Naikes (with limited knowledge of appropriate genetic information) and hardly any documentation is made. This situation calls for outreach support by responsible agencies, thorough decentralised channels, with basic technical training and assisting them with simple tree domestication tools.

Table 5. Seedling production in different category of Nursery in 15 Districts of Nepal (Average production of 1997-1998)

Source: TISC 1999b

5.2. Improved Management and Silviculture

Sissoo plantations are hardly managed. Likelihood is that most of the government established plantations have no silvicultural tendings. Private sissoo plantations are to some extent managed (Baral et al. 1997), but this too is not adequate to meet that of operational plantations. Baral et al. (1977) have indicated fairly large private plantations plot (>10 ha) of central and eastern Nepal have been affected by die-back. Simple silvicultural inputs (cultural practices- thinning, pruning, culling) in sissoo plantations can significantly decrease the risk from pest and disease, and increase the returns from the plantations.

5.3. Use of TISC-Developed Potential Vegetation Map

TISC-developed vegetation maps are based on the original natural vegetation types of Nepal. This map is an elaboration of field work carried out mainly by Dr. J. F. Dobremez and the field botanists of the HMG (for details, see TISC 1999d). This vegetation map covers all Nepal and depicts natural environment of any particular place indicated by the component vegetation types. Vegetation types are referred through forest types and the associates of all 59 major forest types indicated in the map are elaborated. TISC is finalising the map with species specific seed zonation details.

Vegetation map can be effective tool for: I) country-wide planning of sissoo plantations; ii) appropriate site selection with sissoo provenances (therefore matching seed sources); iii) identification of sissoo provenance range in the four major watersheds of Nepal.

This map is available in digitised form, and so GIS tools can be used to analyse, update, and collate new any new information. They can be used for planning very efficiently.

6. REFERENCES

AgriBrief, HMG Ministry of Agriculture/Winrock International Policy Analysis in Agriculture and Related Resource Management, Winrock, Kathamandu, Nepal.

Aryal, H. L. 1998. Breeding Seed Orchard Establishment, D. sissoo at Kohalpur, Nepalgunj, Banke District. HMG/Danida Tree Improvement Programme, Kathmandu, Nepal.

Aryal, H. L. & Thomson, W. 1994. Breeding Seed Orchard Establishment, Dalbergia sissoo at Sauraha, Chitwan District. HMG/Danida Tree Improvement Programme, Kathmandu, Nepal.

Baral, S. R., Mishra, B., Tuladhar, J.J. & Sharma, R. K. 1997. A report on field investigation of top dyeing of Dalbergia sissoo growing in some districts of the central and eastern terai. Forest Research and Survey Centre, TISC Archive, Hattisar, Kathmandu, Nepal.

Frankel, O. H. 1976. Natural variation and its conservation. In.A.Muhammed, R. Aksel and I. Bostel (Eds): Genetic Diversity in Plants. (pp. 21-44). Plenum Press, New York, USA.

Graudel, L. 1996. Tree Improvement and Gene Conservation at TIP, Status and Recommendation, Technical Backstopping Report. TIP. Hattisar, Naxal. Nepal.

Hansen, L. N. 1995. Genetic population study of Dalbergia sissoo in Nepal. Status report No.3 Report to DFSC and TIP. Dept. of Genetics and Ecology, Institute of Biological Science, University of Aarhus, Denmark.

Hansen C. P. & Kjaer. E. D. 1999: Appropriate Planting Material in Tree Plantings: Opportunities and Critical Factors. Paper presented at International Expert Meeting on the Role of Planted Forest Management 6-10, April 1999, Santiago, Chile. Published by: DFSC, Denmark.

Hilbert, P. 1998. Project Completion Report. Internal Document. TISC Archive.

Jha, P. K. & Kjoller, P. 1996. Breeding Seed Orchard Establishment, Dalbergia sissoo at Dharan, Sunsari District. HMG/Danida Tree Improvement Programme, Kathmandu, Nepal.

Joshi, R. B. & Thapa, H. B. 1997. Growth Performance of Dalbergia sissoo Provenances of Nepal and Pakistan, Banko Janakari 7(2): 27-31.

Lillesoe, J. P. B., Dhakal, L. P, Jha, P. K. & Aryal, H. L. (unpub). Analysis and Strategy Proposal for addressing small holders demand for propagation material of woody species. Tree Improvement and Silviculture Component, Hattisar, Naxal, Nepal.

Napier, I & Robbins,M. 1989. Forest Seed and Nursery Practice in Nepal, Nepal-UK Forestry Research Project, Department of Forestry and Plant Research, Babarmahal, Kathmandu, Nepal.

Neil, P. E. 1989. Preliminary provenance testing of Dalbergia sissoo. Banko Janakari 2(2): 113-114.

Rimal, S. K. & Frederiksen, S. 1995. Breeding Seed Orchard Establishment, Dalbergia sissoo at Hattiausha, Kapil Bastu District. HMG/Danida Tree Improvement Programme, Kathmandu, Nepal.

Roshetko, J. M. and Yadava, J. N. 1994. Botany and Ecology. In: Roshetko,J. M. and Westley, S. B. (eds)1994: Dalbergia sissoo Production and Use, A Field Manual. Nitrogen Fixing Tree Association.

Spurr, S. H. & Bames B. V. 1973. Forest Ecology Second Ed. Pp370. The Ronald Press Company NY, USA.

Thomson, W. 1993. Progeny trial establishment report. "35 families form Kailali", Dalbergia sissoo. HMG/Danida Tree Improvement Programme, Kathamandu, Nepal.

Thomson, W. 1994. The selection of Base Breeding population of Dalbergia sissoo to be used in the establishment of Regional Breeding Seed Orchards. HMG/Danida Tree Improvement Programme, Kathmandu, Nepal.

Thomson, W. 1995. Using and Protecting Nepal's forest genetic resources, HMG/Danida Tree Improvement, Programme. TISC Archive Hattisar, Naxal, Kathamandu, Nepal.

TISC. 1999a. Seed Market survey of 15 district of Nepal, Internal Report, TISC Archive Hattisar, Naxal, Kathmandu, Nepal (in press).

TISC. 1999b. Seedling Production Survey of Nepal, Internal Report. TISC Archive, Hattisar, Naxal, Kathmandu, Nepal (in press).

TISC. 1999c. The potential of genetic improvement of Dalbergia sissoo to the benefit of small scale tree planters in Nepal: Lessons learned and ideas for the future: TISC Archive Hattisar, Naxal, Kathmandu, Nepal (in press). 

TISC. 1999d. Iso potential Forest Type/Ecological zone map of Nepal, HMG/DANIDA Tree Improvement and Silvicuture Component/IUCN. TISC Archive., Hattisar, Naxal, Kathmandu, Nepal (in press).

White, K. 1990. An Improvement Plan for Dalbergia sissoo in Nepal. Banko Janakari 2 (4): 382-384.

White, K., Gautam, I. & Dahl, M. 1990. Six Nepal Provenances of Dalbergia sissoo Banko Janakari 2(4): 363-376.

1 BSO: This is an alternative (or complementary) approach to traditional tree breeding. The purpose of BSO is to save time and resources by combining testing of mother trees and seed production in one planting.

2 in-situ conservation is the continuing maintenance of population within the community of which it forms a part, in the environment to which it is adopted (Frankel 1976)