Axillary Bud Behaviour in Macadamia Integrifolia and Its Hybrids
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Axillary bud behaviour in Macadamia integrifolia and its hybrids Janine Conway B. App. Sci., G.Dip. Env. Man. & Dev. M.Phil. Hort. Sci. A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2014 School of Agriculture and Food Sciences i Abstract Macadamia integrifolia and hybrids with M. tetraphylla are multiple flushing, subtropical trees which form the basis of the macadamia nut industry in Australia. However little is known about the process of inflorescence or new stem formation in these trees, including floral induction. Axillary buds form both new stems and inflorescences, so this thesis reports investigations into the effect of architectural position in the tree, and of temperature, on axillary bud release from dormancy and floral or vegetative identity. Location of inflorescence emergence and of new stem production over one year was mapped according to their locations within tree architecture. Bud location down to node level was related to proportion of nodes branching or flowering, and to number of inflorescences or stems per node. Nodes were mapped by position along the growth unit, by growth unit position along the axis, and node position along axes. Interactions of these positions with the size of axis and the size of growth units were also examined. Position of the node along the growth unit was the strongest factor influencing both proportion of nodes flowering and proportion of nodes branching. The proportion of nodes flowering increased with node proximity to the growth unit base. The proportion of nodes branching was highest by far on node two below the top of the growth unit. Pruning resulted in branching on the node or two immediately below the cut, whether the cut was at the top or base of a growth unit. However pruning did not increase numbers of new stems on the axis. Pruning did not change number or location of inflorescences on the growth unit pruned, but did increase inflorescences emerging from the growth unit below it, and significantly increased the number of inflorescences emerging from the axis by around 50%. Growth unit position along the axis also exerted a strong influence on location of inflorescences and new stems. Nodes on growth units closer to the base of an axis were more likely to flower than those on growth units towards the tip. Nodes of growth units closest to the tip were more likely to branch than those at the base. Axis size influenced the proportion of nodes flowering in five year old trees of variety 741, in which flowering was greatest on shorter axes, but not in twelve year old variety 741 trees or thirteen year old variety 842 trees in which flowering was also studied. The effect ii of growth unit size on proportions of nodes flowering was different in different varieties and ages. Axes extending were more likely to branch and less likely to flower than axes that did not extend. Branching as well as extension of an axis reduced the number of inflorescences emerging from that axis. Different applications of mineral nutrients varied the proportions of axes extending and branching in potted trees. Trees receiving moderate levels of fertiliser along with low levels of water extended more and branched less than other treatments, resulting in trees becoming more open in structure over one growth period. In varieties A4 and A36, temperature appeared to affect flowering in two stages. Warm night temperatures (19°C) followed by cool night temperatures (11.5°C) resulted in substantial inflorescence emergence, but cool night temperatures followed by warm resulted in almost no emergence. Only-warm or only-cool night temperatures each resulted in moderate emergence. Along with the work of previous researchers, this suggests that an early stage of flowering is promoted by warm night temperatures, and a later stage by cool night temperatures. As cool temperatures are known to promote emergence of minute dormant inflorescences, the early stage may be floral induction and subsequent meristem evocation and determination. Axillary buds were collected during months of warm night temperatures and several months following these. Microscopic examinations of buds showed morphological gradients in development along the growth unit, parallel to gradients in node likelihood of flowering. However no obvious morphological difference between the high branching node just under the growth unit tip and other nodes was detected. A small number of buds from growth units that had just finished elongation appeared to contain round, domed meristems, which are indicative of floral growth. Together with the finding that warm night temperatures promote an early stage of flowering, this prompts the suggestion that floral evocation in macadamias could occur predominantly during the summer flush growth period. One preformed node was found in most buds towards the base of growth units by the time this same flush period was ending. Two preformed nodes were found in most apical buds at this time. The findings of clear patterns in flowering and branching, and that these change with pruning, as well as the relationship between temperature and control of flowering, may iii assist orchardists in designing new orchard management programs that increase efficiency and sustainability of macadamia nut production. iv Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the General Award Rules of The University of Queensland, immediately made available for research and study in accordance with the Copyright Act 1968. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. v Publications during candidature None Publications included in the thesis None Contributions by others to the thesis Allan Lisle – interactions within multiple logistic regression analyses, and graphic representation of these Statement of parts of the thesis submitted to qualify for the award of another degree None vi Acknowledgements Thanks to my ancestors, for chicken sandwiches on the beach, and inspiration, and plain old fashioned love, and making me do my homework. Thank you to my Principle Advisor Dr. Jim Hanan, for your logic and new perspectives, and being a gem. Thanks also to Prof. Shu Fukai and Dr. Russell Stephenson for your attention to detail and sharing your wealth of experience. Thankyou heaps to Allan Lisle and Olena Kravchuk for biometric analyses, as well as much valued education in stats along the way. Thanks also to Jo-anne DeFaveri, Kerry Chandra, Bob Mayer and Trevor Olesen for biometric analyses in between times. And big thanks to the staff of Maroochy Research Facility for practical help, academic encouragement and good company. Thank you also to the kind orchardists who allowed me to muck about with their lovely trees; Lindsay Fullarton and David Bell. Thank you to the Australian Macadamia Society and, Horticulture Australia Limited for project funding. Thanks to my dear pet Hamster and chai walla, for grand adventures and all those shoulder massages And thanks special gals – Wani, Kylie, Rozzy, Laus and Cait - for keeping me sane enough xox! vii Keywords Axillary bud, branching, flowering, temperature, macadamia, plant architecture, sub- tropical tree, Proteaceae, pruning, nutrients Australian and New Zealand Standard Research Classifications (ANZSRC) 060703 Plant Developmental and Reproductive Biology 100% Fields of Research (FoR) Classification 0607 Plant Biology 100% viii Table of contents Chapter 1. Introduction .............................................................................................................. 1 Chapter 2. Literature review ...................................................................................................... 6 2.1. Macadamia structure and phenology .............................................................................. 6 2.2. Axillary bud formation and dormancy ............................................................................ 7 2.2.1. Internally regulated dormancy ................................................................................. 8 2.2.2. Environmentally regulated dormancy .................................................................... 10 2.3. Flowering ...................................................................................................................... 11 2.3.1. Floral transition