PLOIDY EFFECTS ON REPRODUCTIVE BIOLOGY OF ACACIA MANGIUM

1. AA-2x AM-2x AM-4x pollen tubes polyad ovule penetrated 30 µm 45 m 60 m Type I Type III Type II 5 mm Normal seed Abnormal seed AM-2x x AM-4x Style stigma 50 m polyad AM-2x AM-4x AA-2x CP 3x seedlings 5 mm Type I Type II Type III Abnormal seed Normal seed AM-2x AM-4x AA-2x N. Q. Chi1,3, C. Harwood2, R. Griffin1, J. Harbard1, H. H. Thinh3,and A. Koutoulis1 1School of Plant Science, University of Tasmania, Hobart, TAS. 7001, Australia 2CSIRO Ecosystem Sciences, Hobart, TAS. 7001, Australia 3Research Centre for Forest Tree Improvement, Forest Science Institute of Vietnam, Hanoi, Vietnam 1. Introduction 3.2. Pollen tube growth and ovule penetration (72 h after pollination) An Acacia hybridizing seed orchard was established in southern Vietnam. Ramets of clones of colchicine-induced autotetraploid A. mangium (AM-4x) [1], diploid A. mangium (AM-2x) and diploid A. auriculiformis (AA-2x) were planted in alternate rows to promote inter-ploidy pollination. Despite heavy and largely synchronous flowering and seed production of all three species/ploidy types, the orchard produced very few open-pollinated triploid (3x) seeds. We examined possiblebarriers to fertilisation and/or successful development of triploids. 2. Methods • Hand pollination was conducted following [2] • Floral morphology and pollen tube growth was studied using light and fluorescence microscopy • Pollen tube growth was studied using a clear squash technique [3] • One ramet of each of 3 different clones of AM-2x, AM-4x, and AA-2x was selected for CP treatment • Treatment mean comparisons were performed by Tukey-Kramer’s multiple range test at α = 0.05 Note: ** = 0.001≤ P ≤ 0.01 and *** = P ≤ 0.001. Different letters denote significant (P < 0.05) differences among nine cross-types pollen tube pollen tube pt pt Pollen tubes grew well in the style Ovule development 5 weeks post-pollination Ovules penetrated in the ovary 3. Key results 3.3. Normal and abnormal seeds harvestedfrom different cross-combinations • 3.1 Floral morphology [4] • AM-4x flowers were intermediate between those of AM-2x and AA-2x Mature seed category Note: Different letters denote significant (P < 0.05) differences within species/ploidy combinations • Stigma cup width was greater than polyad diameter for all species/ploidy combinations 4. Conclusions • Differences in floral morphology were not sufficient to prevent interploidy pollination • No pre-zygotic reproductive barriers were detected for intra- and inter ploidy mating of A. mangium and A. auriculiformis • However, yields of pods and normal seeds from inter-ploidy crosses were extremely poor, compared to those from intra-ploidy crosses. • Post-fertilization genic imbalance may limit the production of viable triploid progeny. AM-2x x AM-4x References Mean diameter of stigma cups and polyads. Error bars show critical difference (P<0.05) between treatments. [1] Blakesley D, Allen A, Pellny TK, Roberts AV (2002) Natural and induced polyploidy in Acacia dealbata Link. and Acacia mangium Willd. Annals of Botany 90, 391-398. [2] Sedgley M, Harbard J, Smith RM, Wickneswari R (1992) Development of hybridisation techniques for Acacia mangium and Acacia auriculiformis. ACIAR Proceedings Series, 63-69 [3] Martin FW (1959) Staining and observing pollen tubes in the style by means of fluorescence. Stain Technology34, 125-128. [4] Nghiem CQ, Harwood CE, Harbard JL, Griffin AR, Ha TH, Koutoulis A. (2011). Floral phenology and morphology of colchicine-induced tetraploid Acacia mangium compared with diploid A. mangium and A. auriculiformis: implications for interploidy pollination. Australian Journal of Botany59, 582-592. Acknowledgements We thank FSIV and the Australian Centre for International Agricultural Research (ACIAR) collaboration projects (FST 2003/002 and FST 2008/007) for plant material, and Hong, Xuan and Dzung for field assistance. Funding and in-kind support for N.Q.Chi was provided by a John Allwright Fellowship from ACIAR. PLOIDY EFFECTS ON REPRODUCTIVE BIOLOGY OF ACACIA MANGIUM