Irum Mukhtar?R.Bajwa?G.Nasim
Major constraints on shisham(Dalbergia sissoo)plantations and pathological debate on dieback disease in Punjab,Pakistan
Irum Mukhtar1?R.Bajwa1?G.Nasim1
Today,shisham plantations in Punjab,Pakistan face major constraints,especially dieback disease.This article reviews the multidisciplinary team work by forest and plant pathologists and economists to resolve the confusions in the pathology of dieback disease.It is intended to be of practicaluse to the foresters and plant pathologists reporting on this issue.
Shisham·Dieback disease·Plantations· Forest
Forests play a vital role in the social,architectural,climatic,ecological,and economical status of a country. Globally,forest resources cover 33%or 4 billion hectares (ha)of Earth landmass and are a vital constituent of the economy and ecology worldwide(Sabine et al.2004;FAO 2006).In Pakistan,the totalarea of forest cover constitutes 4.2 million ha that represent only 4.8%of the total land area of 79.6 million ha(Anonymous 2006).This forest area percentage is low compared to other Asian countries like India(24%),Japan(36%),Sri Lanka(42%),the Philippines(43%),South Korea(49%),Bhutan(50%), and Brunei(90%).
Pakistan is basically a forest-deficient country with only 0.0265 ha of forest per capita(Pakistan Economic Survey 2004–2005)compared to the world average of 1 ha.The forests provide only 3.5 million m3of industrial wood each year.Due to population growth of 2.66%annually,the forest resources per capita decline is increasing(Anonymous 2003).The direct contribution of the forestry sector in GDP of 0.2%is nominal,which is not satisfactory,but this does not include the intangible and indirect benefits (Anonymous 2007).
The total forested area is distributed in different provinces and territories of Pakistan viz.Sindh(0.92), Baluchistan(0.33),Punjab(0.69),Khyber Pukhtunkhwa (1.21),Azad Kashmir(0.42)and Northern areas(0.66) (Anonymous 2005).In Punjab,approximately 200 million trees are found in farmlands,of which 90%are in irrigated areas.Shisham(D.sissoo),is one of the important timber tree in the Punjab region along with other species like Phulai(Acacia modesta),Kikar(Acacia nilotica),Bakain (Melia azadirachta)and Ber(Zizypus muritiana)(Qurashi 2004).
The genus Dalbergia commemorates a Swedish Botanist Nicholas Dalberg.It is a pantropical genus with approximately 100 species in different regions of tropical Asia,North America and Australia(Thothathn 1987). Approximately,27 Dalbergia species are represented in the Indo-Pakistan subcontinent,of which 15 are native.Shisham(Dalbergia sissoo Roxburgi)is an important and established forest species of this genus found in Pakistan, Bangladesh,Nepal,Bhutan,India,and Afghanistan.This species is also distributed in tropical to subtropical regions of Africa and Asia.However,it is most likely to found in Java,Nigeria,Mauritius,Srilanka,Kenya,Northern Zimbabwe,Palestine,and South Africa(Tewari 1994).Shisham is one of the important deciduous forest trees inPakistan(Khan and Khan 2000).Due to its great socioeconomic value,this tree has been extensively planted along roadsides,canalbanks,and sometimes on vacantand along boundaries of agriculture lands.
Shisham is cultivated in tropical regions worldwide due to high timber quality of the timber.The geographic distribution of shisham spans a broad region in the Indian subcontinent,generally at a height of 900–1500 m from sea level(Southon 1994).However,this precious tree is facing many devastating challenges over the last six decades that is dragging it toward disappearance from the subcontinent. The three leading causes of shisham deforestation in subcontinent are mismanagement and poor planning for shisham distribution,diseases affecting this species,and Illegal cutting and smuggling.
In last two decades,shisham has faced high mortality at an epidemic rate.This massive mortality caused billions of dollars lost to the forest economy in different countries of subcontinent(Dayaram et al.2003).The main reason of this high shisham decline is mismanaged and overexploited forest planning throughout subcontinent.
Rich germplasm,suitable agro-climate,and cultural practices are important in the sustainable forestry.In early forest planning,the seeds used rarely came from a broad genetic pool.Monoculture practice was adopted without considering sustainable productivity in various areas of subcontinent.Itis one of the reasons behind rapid spread of the diseases in plants.In dense monoculture plantations, the root system of healthy plants easily makes contactwith the infected roots of diseased plants and thereby transferring the infection from one plant to another.
Monoculturing has been one of the factors involved in the high mortality,causing wilting in all trees irrespective of age in Bangladesh.In Nepal,shisham seeds of unknown source and origin have been openly imported for use in various shisham trials(TISC 1999a;Dhakhal 2000).Until preset,there is no specific shisham germplasm distribution system in forest department in sub continent.
Abiotic stresses and management constraints are the behind the reduction in plantation area,low growth,and disease development in forest cover.Several species of fungi and insects have been reported in shisham from nurseries,plantations and natural forests throughout subcontinent(Beeson and Bhatia 1937;Indian Forest Record 1938;Beeson 1941;Browne 1968;Bakshi 1976;Joshi and Kumar 1986;Sharma and Bhardwaj 1988;Sheikh 1989; Sharma et al.2000,2011).However,there is no hostspecific biological control mentioned in the research literature.Fungal dieback,wilt,and canker have been extensively recorded on shisham in this region(Bagchee 1958;Bakshi 1963,1976;Browne 1968;Khan and Khan 2000;Bajwa et al.2003a).
Shisham dieback disease has characteristic symptoms that progress from top to bottom,like thinning of leaves and crown,drying up of crown branches followed by stag headedness in extreme cases(Khan 2000;Bajwa et al. 2003b).In wilting,the key symptoms are chlorosis,leaf thinning,progressive defoliation,and death(Bakshi 1963, 1976).Wilt disease progresses from the bottom to the top and trees show susceptibility for wilting,regardless of age and may die within few weeks(Bajwa et al.2003a).
Due to the high wood quality of shisham,many(timber mafia and habitual forest offender)groups are involved in Illegal cutting and smuggling of trees,have led to the reduction of shisham cover in subcontinent.These groups,in various constellations,include local timber smugglers, Guzara owners,former harvesting contractors,local timber-traders;sawmill owners and attimes,forestry staff and local politicians.Hundreds of shisham trees have been felled illegally with help of some forest officials and influential political agents in Pakistan and caused millions of dollars loss.The timber mafia is also exploiting the government-administered fixed-price and net-sale systems for this valuable tree.As a result,local stakeholders are being disenfranched,the profits for the concessionaires are falling,and ultimately the unsustainable harvesting of shisham resources.In present situation,this high cutting rate of trees will turn the forest into bare lands very soon.
Forest decline is interpreted as deforestation and forest degradation or a combination of both.However,in general terms,the gradual but slow reduction of growth and vigor in a plant is called decline.Whereas,dieback means the progressive death of twigs and branches that starts at the tips.Generally,trees and shrubs may die within 3–5 years from dieback disease after the symptoms first appear;in some cases,trees can survive indefinitely.
Since the turn of the twentieth century,dieback and wilting have been prevalent in the subcontinent.Over the lasttwo decades,these two diseases have changed the forest situation in subcontinent altogether.Dieback usually occurs in fairly old trees of 25 or more years in age.Trees appear to lose vitality,become sparsely foliated,gradual reduction in growth and branches begin to die back from the top eventually as stag headedness appearance is evident.
Dieback disease has caused up to 55%mortality of the shisham population in various regions of subcontinent (Webb and Hossain 2005).In Pakistan,It has caused 5% mortality during 1990–1991,25%during 1999–2000 and43%in 2001 in various districts of Punjab province(Gill etal.2001).However in another detailed survey of Punjab, shisham mortality was recorded 70–80%along the canal sides,20–40%along the roadsides and highways.While dieback and wilting are clearly the main reasons for shisham mortality,the underlying causes are numerous and interrelated.The following major causes of shisham dieback in subcontinent are discussed;
The selection of germplasm and the amount of land for the plantation are the two mostimportant criteria in plantation forestry.The narrow genetic bases,often one or few clones (trees),contribute to inferior progeny(higher chance of inbreeding)that are prone to pest and disease attack.The tree improvementand silviculture component(TISC)of the IUCN market survey shows that the user(forest department,private growers)obtain seeds from different sources without complete genetic suitability(TISC 1999a,b).In early shisham plantations(Troup 1921)seeds rarely came from a broad genetic pool in Pakistan and other South Asian countries.The plantations were promoted without considering the risks involved in monocultures and site selection.Around 90%of the plantation trees in Nepal were thought to come from monoculture that caused serious dieback(Parajuli et al.1999;FORESC 1997).Therefore,distribution of susceptible germplasm stock by the Nepalese forestry department and other agencies in past, caused a severe dieback and wilt outbreak starting in 19982005 all over south Asia.
In the recent past,phenotypically different varieties of shisham have been grouped on the basis of their relative resistance to dieback disease(Javaid et al.2003,2004). Moreover,Dhakaletal.(2005)studied genetic variation in mortality by comparing the survival rate of shisham progenies,originating from differentparts of Nepal,and found a significant difference in mortality percentage between shisham biotypes.
Selection of improved germplasm is crucial for success of plantation programmes.The thriving of healthy shisham directly or indirectly will impacton the amountand quality of the forest outputs,economic productivity,and sustainable forest cover(Hansen and Kjaer 1999).Shisham dieback in Pakistan could be avoided or minimized if: appropriate matching of seed sources to planting sites was properly done and genetically superior planting material was used.According to the current scenario,the forestry department is giving no attention in shisham planting programs to grow seedlings from the best germplasm in Pakistan and like wise in other South Asian countries.
An effective disease management strategy depends on knowledge of disease and pathogen.The lack of adequate disease information and non-linear interactions between biotic and abiotic factors thatinduce disturbance in a forest ecosystem that can cause widespread of tree mortality.In pervious studies,various factors have been discussed as causes of shisham dieback disease.Abiotic factors such as drought,flooding,or soil conditions have thought to contribute to shisham dieback(Sharma et al.2000;Sah et al. 2003;Dahiya et al.2004).
Fungi have been predominantly claimed as causative agents of dieback,including Fusarium solani,which was reported in 1954 from India as the putative agentof wilting on shisham,similar to dieback(Bakshi 1954).However, shisham dieback and wilting mortality has confused by foresters and researchers for long time(Gill et al.2001). Therefore,an actual loss due to dieback or wilting cannot be estimated.Several fungalpathogens including F.solani, insects,and bacteria are recorded during dieback disease investigations in Nepal(Joshi and Baral 2000;Manadhar and Shrestha 2000;Shakya and Lakhey 2007)and Bangladesh(Baksha and Basak 2000;Tantau et al.2005). However,Shakya and Lakhey(2007)claimed that F. solani is the primary causative pathogen of shisham dieback in Nepal.
In the Punjab province(Pakistan),shisham dieback and wilt has been of serious concern to foresters and farmers since its proliferation over the past several decades.According to Khan and Bokhari(1970),the primary cause of shisham dieback is F.oxysporum and Ganoderma lucidum, whereas secondary causes are pinhole beetles.Khan and Khan(2000)concluded that the root rot fungus, Ganoderma lucidum,is a primary pathogen of dieback. Several fungal isolates like Phytophthora cinnamomi,F. dimerum,F.solani,and species of Pestalotia,Spergillus, Botrytrichum,Botrytis,Phoma,Drechslera,Botryodiploia sp.,Alternaria and Rhizoctonia were also isolated from samples of root and bark of dieback infected trees.P. cinnamomi was also declared a dieback pathogen in Punjab (Gill et al.2001;Zakaullah 1999).Whereas,Gul(2001) believed root,and stem rotting fungal pathogens are the main cause of Shisham dieback in Punjab,Pakistan.
In recent studies,F.solani,along with F.oxysporum (Bajwa and Mukhtar 2006),were isolated as dominant fungal species in various agroecological zones and Botryodiplodia theobromae was reported as causal organism of shisham dieback during 2003–2005 in Punjab (Idrees et al.2006).Pathan et al.(2007)and Rajput et al. (2008)isolated F.solani,Rhizoctonia solani,and Curvularia lunata as prominent fungal species from dieback-infected shisham trees samples.Recently Ceratocystis fimbiata along with F.solani,has been claimed as shisham pathogens of and the cause of shisham decline disorder in Pakistan(Poussio et al.2010).
Despite many national and even regional forestmonitoring efforts,there is an absence of adequate and accurate data on shisham dieback in Pakistan and other shisham growing countries.Currently,the provincial forest departments and national and provincial research institutes are conducting mega research projects on this problem in collaboration with national institutions and agricultural universities.There is a clear need to create linkages between studies that will help evaluate trends in shisham mortality and forecast about future disease outbreaks. Inappropriate or non-existentmanagementand silvicultural regimes have made the problem more severe in the form of pathological and entomological incidences.
Previous contradictions in shisham dieback studies clearly indicate that there are two schools of thought, which make shisham dieback a complex issue in Punjab. According to one group,quite a large number of pathogens are shown to be involved in shisham dieback,without any link with pervious studies(Khan and Bokhari 1970;Khan and Khan 2000;Gul 2001;Gill et al.2001;Zakaullah 1999;Idrees et al.2006).The second group strongly supports the involvement of only one or two pathogens,in support of earlier literature(Joshi and Baral 2000; Manadhar and Shrestha 2000;Bajwa and Mukhtar 2006; Shakya and Lakhey 2007;Poussio et al.2010).
Therefore,additional monitoring of shisham health and result-oriented research is needed to improve scientific certainty regarding shisham dieback.A research agenda like this will be helpful for accurate input into policy decisions and forest management in Pakistan.
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28 September 2013/Accepted:6 January 2014/Published online:7 May 2015
?Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2015
The online version is available at http://www.springerlink.com
Corresponding editor:Chai Ruihai
?Irum Mukhtar erumm21@yahoo.com
1Institute of Agricultural Sciences,University of the Punjab, Quiad-E-Azam Campus,Lahore 54590,Pakistan
Journal of Forestry Research2015年2期