Ashok Kumar?K.S.Sangha?G.P.S.Dhillon

Screening of 19 genotypes of Eucalyptus spp.against gall wasp (Leptocybe invasa)in North-western India

Ashok Kumar1?K.S.Sangha1?G.P.S.Dhillon1

The present study was carried out at Punjab AgriculturalUniversity,Ludhiana,India.Nineteen clones of Eucalyptus spp.were evaluated for tolerance to gall wasp. The totalnumberofgalls perplantwere recorded at1 month after planting(MAP)and the number of galls per branch were recorded at4 and 7 MAP.Gallwasp incidence(number of galls)was recorded on a whole plant basis during the seedling stage and the number of galls were recorded from the upper,middle and lower crown places at4 and 7 MAP. Categorization was done on the basis of relative gall-wasp damage by keeping in view the totalnumberofgalls perplant and branch(leaves and petiole).No clone was found free from gall damage.Clones C-526,P-23 and P-103 were the least attacked by the gall wasp.Incidence as indicated by number of galls caused by Leptocybe invasa on eucalypts was higher in March than in December.

Eucalyptus·Clones·Gall wasp·Leptocybe invasa·Damage index

Introduction

Eucalyptus originated in Australia and is now grown in more than 120 countries(Yao and Chen 2009).The genus comprises about 700 species(Eldridge et al.1993)and hasbeen planted extensively owing to its fast growth and short rotation for various end uses including pulp,paper,sawn timber,pole and extraction of aromatic oils(Lal 2000). These evergreen trees readily adapt to different environments,have a short rotation and a good economic value. Eucalyptus is extensively grown in tropical and subtropical areas in India.The plantations established from genetically uniform materials are highly vulnerable to climatic factors particularly for insects and diseases due to the narrow genetic base(Aradhya and Phillips 1993).Since 2000,a new invasive pest(Leptocybe invasa Fisher&La Salle,sp.n.)is wreaking havoc on Eucalyptus plantations throughout the world.

The invasive gall wasp,L.invasa(Hymenoptera:Eulophidae),was firstdescribed in 2004(Mendel etal.2004). As a new pest of eucalyptus,L.invasa was firstrecorded in the Middle East and Mediterranean region in 2000(Fatih 2006)and has become established in Mediterranean countries over the last decade(Aytar 2003;Mendel et al. 2004;Dooanlar 2005;Protasov et al.2007).In India,L. invasa was first noticed in 2001 in the Mandya district of Karnataka and later at Marakkanam in Villupuram district of Tamil Nadu(Jhala et al.2010).In Punjab,it was first reported in 2009(Sangha et al.2011).Eucalyptus occupies 8 million ha in India and spread of the gall wasp is of huge economic concern to the country(Jacob et al.2007).More than 20,000 ha of young Eucalyptus trees have already been affected in southern states of India(Anonymous 2007).

L.invasa induces hyperplasia of leaf midribs,petioles, and twigs of seedlings and trees of Eucalyptus up to 2 years of age have been found more prone to the pest and the hyperplasia results in bump-shaped galls(Fig.1).Gall formation by L.invasa on growing shoot tips and leaves of Eucalyptus result in quicker abscission of leaves anddrying up of shoots.A heavy infestation of the wasp results in loss of vigor and growth subsequently results in twig dieback.With the increasing pest threats,there is urgent need for screening the existing germplasm and making new selections that are tolerant to L.invasa.The future thrustof genetic improvement should be for productivity and tolerance against this severe pest.Another area for improvement is better management practices for insect-pests.

Fig.1 Incidence of gall wasp (Leptocybe invasa)on leaf and petiole among the 19 clones of Eucalyptus spp

Materials and methods

The study was conducted atthe Departmentof Forestry and Natural Resources at Punjab Agricultural University, Ludhiana,Punjab,India,(30°58′N latitude 75°44′E longitude,247 m altitude)in the central-plain region of Punjab (India).The site is characterized by a sub-tropical,semiarid climate with three distinct seasons including hot and dry summers(Aprilto June),hotand humid monsoon(July to September)and cold winters(November to January).On an average,the site receives 500 mm to 750 mm rainfall and 75–80%of the rainfall occurs during 3 months(July to September).Clonal planting stock of Eucalyptus was procured from Prakirti Biotechnology Pvt.Ltd.India. Nineteen clones(316,411,413,526,2013,2034,2070, 2136,2188,3011,3020,3021,P-7,P-13,P-14,P-23,P-46, P-48,P-103)were planted in August 2012 following in complete randomized block design(CRBD)at 3×1 m spacing with four replications and a plot size of 10 plants. The degree of gall infestation was recorded at three different time periods:September,2012(1 MAP); December,2012(4 MAP);and March,2013(7 MAP).The total number of galls per plant were recorded at stage I when plants were at the seedling stage.Plants become tall and vigorous at stages II and III,when counting the total number of galls on whole plant basis was difficult.For this purpose,three plants from each clone in each replication were selected for recording L.invasa induced galls;three branches were then selected from the lower,middle and upper crown level;and then the totalnumbers of galls were recorded(on leaves as well as petioles).Thereafter,clones were selected on the basis the criteria given in Table 1.

Statistical analysis was done as per the procedure laid down for completely randomized block design(CRBD). Analysis of variance,criticaldifference(CD),and variance components were calculated for interpretation of results of the study following Panse and Sukhatme(1989).The various data were statistically analyzed using Proc GLM(SAS Software 9.3,SAS Institute Ltd.U.S.A.).Allpossible pairs of treatments means were compared with Duncan’s multiple range test(DMRT)at 1%probability level(Duncan 1955).The DMRT is similar to that of lsd test.DMRT involves the computation of numerical boundaries that allow the classification of the difference between any two treatment means as significant or non-significant.DMRT attempts to control family-wise error rate atαew=1-（1-αpc）k-1 when comparing k,where k is the number of groups viz.,a,b,c,d,e,as shown in Table 2 and Fig.2.

Clones were categorized into six categories on the basis of rating points assuming the rating 0 to 5 with 0 for minimum and 5 for maximum gall damage as the method demonstrated by Ahmad(1993)given below:

Table 1 Categorization of Eucalyptus genotypes on the basis of range based on number of galls at different time period

Table 2 Number of galls/branch on 19 genotypes of Eucalyptus at different time periods

where,x(A)is mean number of galls for each clone,X is overall mean of the number of galls for all the 19 genotypes,σis standard deviation.

Weightage percentage of the resistance(WPR)was calculated by considering minimum and maximum values of number of gall damage as 0 and 100 and applying the following formula:

where,WPR is weightage%of resistance,MaLAF the maximum number of galls,LAFCC the number of galls of the concerned genotypes,and MiLAF in minimum number of galls.

Results and discussion

The results are based on the total number of galls produced by Eucalyptus gall insect(Leptocybe invasa)from August, 2012 to March,2013.The number of galls per plant was highly significantly at the stage I and number of galls per branch also was significant at stages II and III.Our results showed thatno clones were free from the gall insect attack. At the stage I(1 MAP),C-411,P-103 and C-413 were registered as free from gall damage which was statistically at par with all other clones,with the following exceptions: C-3011,C-2013,C-316,P-13 and P-14,which were severely attacked(Fig.2).At the stage II(4 MAP)minimum gall damage was observed in C-526 and P-23,which were at par with that of P-103,C-413,C-411,C-3020, C-2188,P-7 and C-2136,whereas,the highest gall damage was recorded in C-2013,which was statistically similar to C-316(Table 2).At the stage III(7 MAP)minimum gall damage was recorded in C-2188 which was on par with all other clones studies except C-2013,C-316,P-14,C-3011, P-48 and C-3020.

The current study documents substantial differences in L.invasa infestation and damage among clones of Eucalyptus spp.These differences may be due to factors including differences in host physical and nutritional characteristics,and to differences in host biochemical defenses(Bentur and Kaslode 1996).Some clones such as P-13,P-46,C-2013 and C-2034 have found less few gallsduring March than December.This was due to initial formation of corky tissues(ovipositor)that did take place, however they did not develop into full galls.Similarly, significant difference was reported in clonal Eucalyptus by Krishnakumar and Jacob(2010).

Fig.2 Variation in number of galls/plant among the Eucalyptus genotypes at1 MAP

Our results also suggested,however,that the impact of L.invasa on eucalypts was greater in stage III(March),and we therefore suspect that climate may affect the susceptibility of eucalypt to L.invasa attack.Gall intensity was higher in March than December:similarly,gall attack was higher from March to October and at a minimum during November to February because of very low temperature in Northern India.However,the trend was opposite to the trend in Centraland Southern India(Kulkarni 2010)where the attack was higher during September to April.Similarly, leaf damage in Eucalyptus clones was higher during May to June in E.camaldulensis and E.citrodora(Rajpoot 2012).The findings of the Patel(2010),based on correlation of the weather factors with damage of gall insect in Eucalyptus seedlings revealed that gall incidence increased with increase in temperature,relative humidity and wind velocity.More branches were observed in E.camaldulensis indicating higher gall infestation as compared to E.citriodora and also observed that impact of weather factors on gall incidence was found significant and positive with respect to temperature,while it was significant and negative with rainy days.Similar,results had been reported by Krishnakumar and Jacob(2010).

In terms of rating scale(Table 1),the clones that fall under the category of 0 rating were C-411,P-103,P-23 and C-413 during September,and C-526,P-103 and P-23 during December and March,indicating minimum gall damage.Maximum(6 clones)were categorized in rating 1 during September and 4 clones during December and March.Clones C-2013,C-316,P-14 and P-13 during September,and C-2013 and C-316 fall in rating scale 5 during December to March,indicating maximum gall damage.

Results indicate that prevailing climatic conditions affects the degree of incidence of L.invasa.For example,P-13 was found rating 5 during September but it was categorized in rating 2 during December and March, similarly,P-7 had got rating 3 and it was categorized in rating 2 during Decemberand March.Few clones viz.,P-46, C-2070 and C-3020 were observed in rating 1 at nursery stage butwere categorized in rating 3 during December and March.The results are in agreementof Kulkarni(2010).He reported that C-411 and C-413 was found free from galls in South Indian conditions,whereas,they had gall wasp incidence in prevailing condition in North India.Weightage percentage of resistance(WPR)varied from 0 to 100 atthe resistance end(Table 3).The results revealed that clonesC-526,P-103,P-23,C-413 and C-411 were relatively resistantto L.invasa incidence.This may be due to variation in leaf toughness or nutritional composition of the leaves among the genotypes.These clones may be further evaluated for the mechanism of resistance.

Table 3 Relative gall insect performance on different Eucalyptus genotypes at the different age,under no choice test condition

Prevailing climatic conditions also affects the susceptibility of eucalypts germplasm to L.invasa.For example,E. camaldulensis was relatively resistant to L.invasa in China and Kenya,but was relatively susceptible in Vietnam and Uganda(Pham et al.2009;Nyeko et al.2010)and Israel (Mendel et al.2004;Philip et al.2007).The susceptibility of E.robusta and E.tereticornis to the L.invasa also appears to vary among regions(Pham et al.2009;Nyeko et al.2010).Why host susceptibility to L.invasa might differ among regions is unclear but climate and the time since the initial wasp invasion might be important.

In conclusion,our study suggests thatsusceptibility to L. invasa and the population dynamics(number of galls) differ among Eucalyptus species and clones.It is also possible that differences in the damage caused by L.invasa resulted from differences among genotypes.Definitive determination of how tree genotype and other factors affect susceptibility to L.invasa will require controlled experimentation.As practically no clones are free from wasp attack,insecticidal management of gall wasps of Eucalyptus is pretty much inevitable.Presently,only preliminary information is available regarding screening of available clones and the management of the gall wasp in Punjab.Detailed bioecology,symptomology,seasonal history and bioassays for management are needed for establishing the host range(alternate or collateral hosts), number of generations,insect morphology and integrated pest management strategies for the holistic management of L.invasa in Northern India.

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4 October 2013/Accepted:9 January 2014/Published online:24 April 2015

?Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2015

The online version is available at http://www.springerlink.com

Corresponding editor:Chai Ruihai

?Ashok Kumar ashok.dhaked1987@gmail.com

1Department of Forestry and Natural Resources,Punjab Agricultural University,Ludhiana 141004,Punjab,India