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HARPER ADAMS UNIVERSITY Minimising post-harvest losses in radishes through an understanding of pre and post-harvest factors that influence root splitting A thesis submitted in partial fulfilment of the requirements of Harper Adams University for the degree of Doctor of Philosophy by Rachel Anna Lockley BSc (hons) Biological Sciences at Harper Adams University, Newport, Shropshire, TF10 8NB June 2016 1. Declaration This thesis was composed by me and is a record of work carried out by me on an original line of research. All sources of information are shown in the text and listed in the references. None of this work has been presented/accepted for the award of any other degree or diploma at any University. Rachel Lockley June 2016 ii 2. Abstract Radish splitting reduces marketable yield and increases production costs. Minimising losses may be possible through identification of factors affecting splitting. Splitting occurs during growth (growth splits) and post-harvest (harvest splits). Growth splitting was shown to be affected by cultivar and periderm thickness, split radishes tended to have thicker periderms. Growth splitting was also affected by irrigation; greater volumetric water content resulted in more split radishes. This may have been due to increased turgor pressure from greater hypocotyl water uptake. Radishes were particularly sensitive to increased substrate VWC at Growth Stage 41, defined as the point when the periderm becomes the hypocotyl surface. Radish development stages were developed following the Biologische Bundesanstalt, Bundessortenamt and CHemical industry (BBCH) scale. This suggests irrigation management could reduce growth splits, however consistent control of soil moisture may be difficult in field-grown crops and manipulating post-harvest conditions may be more achievable. Radishes with different hypocotyl water content (WC) were tested for susceptibility to harvest splitting as a result of mechanical damage. Hypocotyl WC was negatively correlated with compression and puncture failure force and more radishes split as a result of impact at higher hypocotyl WC. Hypocotyl WC and relative WC were correlated with water pressure leading to the conclusion that greater turgor pressure within the hypocotyl resulted in the radishes being more susceptible to splitting. Radishes were also shown to be increasingly susceptible to splitting with decreasing temperature. Again, this was thought to be as a result of turgor pressure; the cytoplasm and cell wall may contract more than the vacuole at low temperatures resulting in increased pressure. The mode of failure was shown to be plasmoptysis, increasing turgor pressure increases susceptibility to plasmoptysis. In conclusion, susceptibility to splitting could be reduced by decreasing post-harvest hypocotyl turgor pressure. Therefore, using current commercial production methods it is more feasible to minimise harvest splitting than growth splitting. iii 3. Acknowledgements Firstly, I would like to thank my supervisor Jim Monaghan for his help, enthusiasm and patience especially through what has ended up being quite a lengthy write up period. I’d also like to thank Ivan Grove my second supervisor for his attention to detail and for his guidance on understanding and measuring soil moisture. I would like to thank everyone from G’s who helped me. I was extremely impressed with everyone I met and without their generosity this PhD would have been much poorer. I would also like to thank BADC and the Met Office for supplying weather data for RAF Marham. I’d like to thank AHDB Horticulture (HDC) for funding my PhD. I’ve found it an immensely enjoyable and rewarding process which has changed my life and for that I’ll always be grateful. I would also like to thank my line managers Debbie Wilson and Jon Knight at AHDB Horticulture for allowing me to take time off to write my thesis when I was concerned I would never finish. I’d like to thank the HAU staff in the laboratories, RFA and at CERC for their support in using equipment. In particular I’d like to thank Jan Haycrox for her company on long days in the glasshouse. Finally, on a personal level I’d like to thank my family and friends for their backing and encouragement. They have all been brilliantly supportive despite very few of them fully understanding why anyone would want to study for a PhD in radishes. They have kept me grounded and amused throughout and I’m hugely appreciative for that. Sam McGauley has given me constant backing and I can’t thank him enough. He moved with me to an area which he never liked and commuted for two hours a day for three years without moaning (much). In addition his cajoling and encouragement to write at weekends has been instrumental in my finishing. iv 4. Published work Lockley, R., Grove, I. and Monaghan, J. (2015) ‘Splitting in Radish – Does Preharvest Environment Influence the Response to Postharvest Handling?’, Proceedings of the Sixth International Conference on Managing Quality in Chains, 1(1), pp. 231– 237. Lockley, R., Grove, I. and Monaghan, J. (in press) ‘Minimising Losses in Radish (Raphanus sativus) at Harvest Due to Splitting by Manipulation of Water Availability During Growth’, Proceedings of the XXIX International Horticultural Congress: IHC2014. Lockley, R., Grove, I. and Monaghan, J. (in press) ‘Investigating Factors Affecting Post- Harvest Splitting in Radish (Raphanus sativus)’, Proceedings of the XXIX International Horticultural Congress: IHC2014. v 5. Contents 1. Declaration ................................................................................................................. ii 2. Abstract ..................................................................................................................... iii 3. Acknowledgements .................................................................................................... iv 4. Published work ........................................................................................................... v 6. List of tables .............................................................................................................. xi 7. List of figures ......................................................................................................... xxvi 8. List of equations ................................................................................................... xxxvi 9. List of abbreviations ............................................................................................. xxxvii 1. Literature review ......................................................................................................... 1 1.1 Introduction .......................................................................................................... 1 1.2 The radish crop .................................................................................................... 1 1.2.1 Taxonomy ..................................................................................................... 4 1.2.2 Morphology ................................................................................................... 4 1.2.3 Growth and development .............................................................................. 6 1.2.4 Commercial production ................................................................................. 8 1.3 Splitting.............................................................................................................. 23 1.3.1 Differences in splitting susceptibility between cultivars ............................... 25 1.3.2 Anisotropy .................................................................................................. 26 1.3.3 Growth splits ............................................................................................... 28 1.3.4 Harvest splits .............................................................................................. 35 1.4 Water ................................................................................................................. 40 1.4.1 Soil water content ....................................................................................... 40 1.4.2 Plants and water ......................................................................................... 44 1.5 Conclusions from the literature review ............................................................... 51 1.5.1 Objectives of the research .......................................................................... 52 1.6 Thesis map ........................................................................................................ 53 2. General materials and methods ...............................................................................