Progress 08/15/02 to 08/14/04
Outputs
Activities conducted under the project, "Competition among Reproductive and Vegetative Organs in Woody Plants," included sabbatical visits by the Principal Investigator, Dr. Yaffa Grossman, to study reproductive and vegetative growth in low yielding mango (Mangifera indica) systems in Australia and South Africa; presentation of nine seminars and two workshops in Australia, South Africa, and the U.S. on the response of the carbon budget of peach trees to global warming, environmental modeling, management of crop load on fruit trees; and participation in two international conferences on modeling plant growth. In collaboration with colleagues Dr. Alonso Gonzalez and Dr. Edelgard Pavel, Dr. Grossman converted her PEACH model (Grossman and DeJong, 1994, Tree Physiol. 14:329-345) into a mango growth model. This carbon budget model was used to examine factors that limit mango crop yield using field data from the Northern Territory, Australia, and Hoedspruit, South Africa. At
both locations, instantaneous leaf level carbon assimilation rates varied seasonally, from lows of 3-6 μmol CO2 m-2 s-1 to high values of 10-11 μmol CO2 m-2 s-1. Crop growth occurred when photosynthetic rates were in the lower half of this range, except near the time of fruit harvest in South Africa. Simulated gross carbon assimilation increased through the season from low values in June-August to high values in February-April. Simulated carbon availability limited crop growth during a portion of the fruit growth period at both locations. The effect of crop load on fruit growth was examined by simulating varying initial fruit set and final fruit number. For "Kensington Pride" mangoes in Australia, increasing final fruit number did not decrease final fruit size, but increasing both fruit set and final fruit number decreased final fruit size substantially. For "Kent" mangoes in South Africa, increasing final fruit number with low and high initial fruit set reduced final fruit
size to similar extents. These simulations were interpreted to mean that efforts to increase fruit set may not increase the numbers of marketable-sized fruits because of carbon limitations on fruit growth. Dr. Grossman and Dr. Gonzalez also studied the carbon balance of elongating mango shoots and determined that although vegetative shoots of mango import carbon for a relatively short period of time, comparable to the import period for apples, the period of time needed for the new shoots to recover their production costs is substantially longer than the recovery period for apples. This long recovery period has implications for optimal canopy management of mango trees. Dr. Grossman worked with Beloit College undergraduate students on several modeling projects. During the 2003-04 academic year, James Davis and Tim Morgan wrote a Java program based upon the PEACH model, with the help of visiting professor Peter Theron. The Java model version of the model is more portable than the
previous Visual Basic version. During the spring and summer of 2004, Jennifer Spangenberg began development of an L-system model for germinating peas as a system for exploring root and shoot growth potential.
Impacts
In many environments, mango trees produce large amounts of vegetative growth. Using the findings of this study, we will be able to suggest ways to divert this flow of carbon through the tree from vegetative to reproductive growth, enhancing crop yields. In addition, the specific results of the vegetative growth cost-benefit analysis will allow us to provide insights into optimal timing of pruning in order to maximize carbon gain by the tree.
Publications
- Pavel, E.W. Vanassche, F.M.G. and Y.L. Grossman. 2003. Optimization of irrigation management in mango trees by determination of water and carbon demands to improve water use efficiency and fruit quality. Final Report to the Water Research Commission, Pretoria, South Africa.
- Grossman, Y.L., Gonzalez, A. and Pavel, E.W. 2004. Modeling mango fruit and vegetative growth. Proceedings of the Seventh International Symposium on Computer Modelling in Fruit Research and Orchard Management. In press with Acta Horticulturae.
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Progress 08/15/02 to 08/14/03
Outputs
Yaffa Grossman spent a successful sabbatical year studying competition between reproductive and vegetative growth in low yielding mango systems in Australia and South Africa. With data from Dr. Alonso Gonzalez at CSIRO-Plant Industry in Darwin, Australia, and Dr. Edelgard Pavel of the University of Pretoria, South Africa, and their colleagues, she converted the PEACH model (Grossman and DeJong 1994) into a mango growth model. Photosynthetic, respiratory, and growth parameters were altered to represent mango. The similarities and differences between the deciduous peach and evergreen mango led to the development of new modules that track carbohydrate reserves, simulate flowering over a protracted time period, and simulate multiple vegetative growth periods during one calendar year. The results of an early revision of the model were presented by Dr. Grossman in a video-conference seminar to all of CSIRO-Plant Industry, which more than 45 people attended. MANGO is
currently being tested against field data from both Australia and South Africa and will be described in a manuscript for publication. Dr. Gonzalez and Dr. Grossman designed an experiment to address the absence of information about mango vegetative flush development. They determined that although vegetative shoots of mango import carbon for a relatively short period of time, comparable to the import period for apples, the period of time needed for the new shoots to recover their production costs is substantially longer than the recovery period for apples. This long recovery period has implications for optimal canopy management of mango trees. Before visiting Darwin, Dr. Grossman spent two weeks as a Visiting Scientist with the Victoria Department of Natural Resources and Environment. She gave three lectures on the simulated effects of global warming on peach tree growth and fruit production at Victoria Natural Resources and Environment offices, two three-hour workshops on modeling, and
one lecture on managing fruit growth to the annual meeting of the Victoria Peach and Apricot Growers Association. These lectures and workshops were attended by a total of more than 115 people. Her travel to Australia was funded by the Victoria Department of Natural Resources and a Fellowship from the Australian McMaster Foundation. In South Africa, Dr. Grossman gave two seminars on global warming and simulation modeling of tree fruit growth to students and faculty at the University of Pretoria. Dr. Pavel and Dr. Grossman collaborated on a manuscript about the mango model that became a chapter in a report to the Water Research Commission. Dr. Grossman has not conducted any experiments on root growth potential because she was fully engaged in the other project. She plans to proceed with this project, with the help of Beloit College students, beginning in September and expects to complete it at the end of the no-cost extension period. Literature cited Grossman, Y.L. and DeJong, T.M.
1994. PEACH: a simulation model of reproductive and vegetative growth in peach trees. Tree Physiology 14:329-345.
Impacts
In many environments, mango trees produce large amounts of vegetative growth. Using the findings of this study, we will be able to suggest ways to divert this flow of carbon through the tree from vegetative to reproductive growth, enhancing crop yields. In addition, the specific results of the vegetative growth cost-benefit analysis will allow us to provide insights into optimal timing of pruning in order to maximize carbon gain by the tree.
Publications
- Pavel, E.W., Vanassche, M.G. and Grossman, Y.L. 2003. Optimization of irrigation management in mango trees by determination of water and carbon demands to improve water use efficiency and fruit quality. Project No.: K5/1136. Water Research Commission, Pretoria, South Africa.
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