Selection for drought tolerance and wood quality traits from selected accessions of Tectona grandis linn f.

Abstract

Teak (Tectona grandis Linn. f.) is an important hardwood timber in the tropic. Most teak-growing countries are now performing tree improvement programs. It mainly aimed at achieving superior growth characteristics. These may have indirect effect on wood properties. So it is essential to include wood quality traits in breeding of teak. As teak requires long nursery period which extends to almost one year and any decline in moisture during this period may cause decline in initial growth and may eventually lead to death of teak.Asstated,mostofthebreedingactivitiesthathavebeendoneonteakinvolvedselecting plustreesbasedonlyonquantitativeandqualitativetraits.Tillnow,veryfewworkwasdone on screening teak for drought tolerance. The study is being conducted at the teak provenance trial plantation established in Livestockresearchstation,Thiruvizhamkunnu.30accessionsofteakwereplantedincompact family block design with 3 progenies each, replicated five times. Out of 30 accessions, eight were completely absent in the field. From the remaining 22 accessions, three were discarded due to the lack of enough number of progenies (minimum 2) per accession. So the 19 accessions were used for the further studies. Growth characters and wood quality traits were observed among these accessions from thefield. Growth parameters like height and girth showed significant variations among 19 provenances.Variationofheightwasintherangeof9.57m(A5)to17.97m(A2).Thevariation in the girth at breast height was in the range of 31.75cm (A5) to 86.07(A29). PPD and SWV showedsignificantvariationsamong19provenances.AccessionsA2,A29,A21,A20,A1,A3 andA22showedbettergrowthparameters.ThevalueforPPDrangefrom20.25mm(A1,A23) to 24.25mm (A20). The value for SWV ranged from 3535 ms-1 (A29) to 4360 ms-1(A30). Specific gravity for the different accessions was calculated from the regression equation using PPD. Specific gravity range from 0.32 (A20) to 0.44 (A1, A23). Among the accessions, A23, A17, A28, A19, A18, A21 and A22 showed better wood qualitytraits. Eighteen trees belonging to eighteen accessions were then selected using comparison method. These trees were then vegetatively propagated through stem cuttings for further studies. These accessions were then screened for drought tolerance by studying physiological changes in response to imposed drought stress in three stages viz. normal, stress and regain. Kruskal Wallis test showed significant variation among physiological parameters during these three stages of drought. A significant reduction in stomatal conductance, transpirationrate, photosynthetic rate, relative water content, chlorophyll a and chlorophyll b content, total chlorophyll content, membrane stability index, chlorophyll stability index as compared to normal growing conditions among the accessions of teak. A significant increase was observed in the canopy air temperature difference among the accession. A hierarchical cluster analysis was carried out for physiological parameters of the accessionsduringdrought.Theaccessionswhichperformedwellduringdroughtweregrouped in cluster IV. The accessions belonging to this cluster was A21, A6 and A24. During drought, higher values for chlorophyll stability index, membrane stability index, chlorophyll a and chlorophyll b content, total chlorophyll content, relative water content and the photosynthetic rate was observed for A21. In addition to that highest value for stomatal conductance and transpiration was recorded in A21 and A6. Chlorophyll fluorescence was observed highest in A21, A24, A5 and A6. Among the accessions, the lowest value for the canopy air temperature difference was observed inA21. Duringregainrecoveryinphysiologicalcharacterswasobservedamongtheaccessions. A21 showed higher values for physiological parameters like chlorophyll stability index, membrane stability index, chlorophyll a and b content, total chlorophyll content, chlorophyll fluorescence, relative water conductance, transpiration and stomatal conductance. The photosynthetic rate was observed highest in A21, A6, A5 and A24. A13 and A17 found to be least recovered during drought because of prolonged damage to physiological process after imposeddrought.Itcanbeconcludedfromtheaboveresultsthatconsiderablevariationexisted among the teak accessions for wood properties and growth characters. In drought tolerance studies significant variation among the accessions were also observed. A21 is found to be drought tolerant compared with other accessions.