Culling phenotypically inferior trees in seed production area enhances seed and seedling quality of Acacia auriculiformis

Improvement in seed and seedling quality of Acacia auriculiformis after culling phenotypically inferior trees was studied in a 6-year old seed production area （SPA）. A 5-ha plantation was identified, of which 2.3 ha was converted into SPA. The initial stocking, 1 612 trees·ha^-1, was thinned down to 982 trees·ha^-1 based on growth characteristics. The following fruiting season, seeds were collected from 10 randomly selected trees in culled and non-culled stands, and seed physical characters, germination and seedling traits were assessed. Seed weight, seed thickness and percentage germination increased by 32.1%, 4.43% and 22.37%, respectively in the culled stand compared to the non-culled stand. Culling also increased the speed of germination, seedling dry weight and seedling vigor index. Heritability values were high for seed weight （0.974） and seed thickness （0.948） while medium values were observed for percentage germination （0.577） and total dry weight （0.534）. Predicted genetic gain was 11.13% and 11.22% for seed weight and percentage germination, respectively. The actual gain was 32.1, 51.9 and 22.9% for seed weight, percentage germination and total dry matter, respectively. In conclusion, SPAs established by culling inferior trees could serve as sources of good quality seeds for reforestation programs until genetically improved seeds are made available.

DNA polymorphisms and genetic relationship among populations of Acacia leucophloea using RAPD markers

RAPD （randomly amplified polymorphic DNA） markers were employed to characterize polymorphisms among 5 provenances of Acacia leucophloea and to detect genetic relatedness of the species with 6 other acacias （A. holosericea, A. auriculiformis, A. mangium, A. dealbata, A. ferruginea, and A. nilotica） widely grown in India. Of 194 markers scored for the provenances, 29.38% exhibited polymorphism. Also, 326 markers were generated among 7 species of Acacia, accounting for 55.82% of the polymorphisms. The fifteen 10-mer primers employed were capable of producing 1-8 polymorphic bands for the provenances, and 6-17 for all seven species of Acacia. The genetic similarity coefficient based on Jaccard＇ s coefficient revealed that provenances Thirumangalam and Dharmapuri were closely related. The dendrogram based on a sequential agglomerative hierarchical non-overlapping （SAHN） clustering analysis grouped 4 provenances of A. leucophloea （Dharapuram, Thirumangalam, Pudukottai and Dharmapuri） into one cluster and the other provenance, Sendurai, into a separate cluster. The genetic similarity matrix for 7 Acacia species showed that A. nilotica and A. dealbata were distantly related, while A. holosericea and A. ferruginea were very closely related. Cluster analysis grouped the species of Acacias into 3 major groups of which A. dealbata alone formed a separate group. The RAPD markers generated 36 provenance-specific markers and 162 species-specific markers that could have strong applications for species identification and tree breeding programs for A. leucophloea and for other Acacia species included in this study.

Discrimination of Acacia seeds at species and subspecies levels using an image analyzer

Seeds of Acacia species and subspecies were characterized using an image analyzer and discriminated for the purpose of identification of species, using their seeds. The species considered in the study were Acacia nilotica subsp. indica, A. nilotica subsp. cupressiformis, A. nilotica subsp. tomentosa, A. tortilis subsp. raddiana, A. tortilis subsp. spirocarpa, A. raddiana, A. senegal, A. auriculiformis, A. farnesiana, A. leucophloea, A. mearnsii, A. melanoxylon, A. planifrons and A. mangium. Eight samples each consisting of 25 seeds per species were studied using the image analyzer for physical characteristics of seeds, such as 2D surface area, length, width, perimeter, roundness, aspect ratio and fullness ratio. Discriminant analysis showed that acacias can be discriminated at species and subspecies levels, with 96% accuracy. Exceptions were A. nilotica subsp. tomentosa(75.0%), A. tortilis subsp. spirocarpa(75.0%) and A. raddiana(87.5%) which had relatively low discrimination accuracy. However, discriminant analysis within selected species showed complete recognition of these species except for A. tortilis subsp. spirocarpa, that had still a large overlap with A. leucophloea. The study also revealed that both seed size and shape characteristics were responsible for species discrimination. It can be concluded that rapid analysis of seed size and shape characteristics using image analysis techniques can be used as primary and secondary keys for identification of acacias.

Growth response of Pterocarpus santalinus seedlings to native microbial symbionts(arbuscular mycorrhizal fungi and Rhizobium aegyptiacum)under nursery conditions

The objective of this research was to improve the growth and biomass of Pterocarpus santalinus L.f.(an endangered leguminous tree)using native microbial symbionts such as arbuscular mycorrhizal fungi and Rhizobium associated with native populations of P.santalinus.The native arbuscular mycorrhizal fungi isolated from P.santalinus soils were identifi ed as(1)Glomus fasciculatum;(2)Glomus geosporum;and Glomus aggregatum.A nitrogenfi xing microbial symbiont was isolated from the root nodules of P.santalinus and identifi ed as Rhizobium aegyptiacum by 16s rRNA gene sequencing.These microbial symbionts were inoculated individually and in combination into P.santalinus seedling roots.After 90 days,growth and biomass had improved compared with uninoculated controls.Shoot and root lengths,number of leaves,stem circumference,number of root nodules,biomass,nutrient uptake and seedling quality index were signifi cantly increased by a combined inoculation of arbuscular mycorrhizal fungi+Rhizobium aegyptiacum.It was concluded that native microbial symbionts positively infl uenced P.santalinus seedling growth which will be helpful for successful fi eld establishment.

Identification of diverse genotypes with high oil content in Madhuca latifolia for further use in tree improvement

Madhuca latifolia Macb.commonly known as Indian butter tree,is an open-pollinated plant.Improvement in seed and oil yields depends on the progress in the desired characters in the base material and the genetic variability available in the collected germplasm.We evaluated 23 genotypes of M.latifolia to understand genetic variability,character association and divergence in seed traits and oil content for use in breeding programs.Variation was recorded in seed length（27.3–38.6 mm）,seed breadth（15.6–19.1 mm）,two dimensional（2D） surface area（328.3–495.4 mm2）,100 seed weight（216.8–285.3 g）,acid value（13.4–25.8 mg KOH/g）,iodine number（62.4–78.6） and oil content（37.8–51.0 %）.High estimates of genotypic coefficient of variation,broad senseheritability and genetic gain were observed for seed oil content.Variability studies for seed traits revealed that genotype CPT-16 had the highest 100-seed weight（281.5 g） and oil content（51 %）.Highly significant genotypic and phenotypic correlations were observed.The100-seed weight was positively and significantly correlated with oil content at both phenotypic（r = 0.57） and genotypic（r = 0.60） levels.Cluster analysis of the scores of the first three principle components（80.83 %） resulted in four clusters,consisting of 4,7,3 and 9 genotypes in the first,second,third and fourth clusters,respectively.Cluster 3was distinguished from others based on significantly higher means for most seed traits except seed breadth,acid value,iodine number and oil content.Cluster 1 appeared more divergent as it had significantly higher means for acid value and iodine number.A comparative assessment of means of the four clusters for 100-seed weight and oil content suggested that cluster 3 would be useful for higher 100-seed weight and oil content.Hence these genotypes,CPT-3,CPT-6 and CPT-15 in cluster 3 can be used for direct selection and utilization in breeding programs.

Growth response of three plantation species of the tropics exposed to elevated CO_2 levels

The response of forest trees, the largest carbon sinks on the earth, to continuing rise in atmospheric carbon levels is unknown. Re- ports state that increasing levels of atmospheric CO2 will stimulate pho- tosynthesis and productivity in most ecosystems. However, the duration and magnitude of this stimulation, particularly in the tropics, remains a question. To investigate the effects of CO2 fertilization on plant growth, seedlings of three common plantation species, Casuarina equisetifolia, Ailanthus excelsa and Tectona grandis were grown in closed chambers enriched with CO2. After 180 days of treatment, morphological traits of seedling height, biomass of root and shoot and root-shoot allometric co-efficient were measured. The activity of carbonic anhydrase and con- tents of chlorophylls, total carbohydrates and soluble proteins were de- termined. In Tectona grandis, significant effects of CO2 supply were found on chlorophylls, root-shoot allometric ratio and seedling quality index. Ailanthus excelsa showed significant effect on only the shoot characteristics on exposure to elevated CO2 but the root characteristics and concentrations of chlorophylls were not significantly different. Ca- suarina equisetifolia also showed significant effects on exposure to ele- vated CO2 in terms of shoot characteristics and concentrations of chlo- rophylls. Total sugars, the major photosynthates, did not show any sig- nificant variation to elevated CO2 in any of the three species. Carbonic anhydrase, the key enzyme responsible for transfer of CO2 into the tis- sues significantly increased in all three species. Overall, all the variables responded to elevated CO2, reflecting the positive effects of one parame- ter of climate change conditions on seedling quality. A positive response of these three plantation species to elevated CO2 content is a good indi- cation for their future existence in potentially changed climatic eonditions.

Responses of Bruguiera sexangula propagules to beneficial microbes in the nursery

Bruguiera sexangula （Lout） Poir., a threatened mangrove tree, was inoculated with beneficial microbes in a nursery to assess any improvements in growth and bio- mass. From soil samples from the rhizosphere of B. sexangula in a mangrove forest in Panangadu of Kerala India, nitrogen-fixing bacteria Azotobacter chroococcum and Azospirillum brasilense were isolated. The phosphatesolubilising bacterium Bacillus megaterium and potassiummobilizing bacteria Frateruria aurantia were also isolated and cultured on suitable media. Later, ripe propagules of B. sexangula were collected from matured trees and raised in sterilized soil bags （13 × 25 cm） containing sterilized soil and sand （2：1 ratio）. The cultured beneficial microbes were propagated and used to inoculate the ripe propagules of B. sexangula and maintained in the nursery for 6 months. After 6 months, growth and biomass of the inoculated propagules were greater than for the uninoculated control propagules. Shoot length, number of leaves, stem girth and root length were also significantly greater than in the controls. This study showed that the mangrove-specific beneficial microbes influenced the growth of B. sexangula