Improved potato (Solanum tuberosum L.) seed production through aeroponics By Steve Ndondji Tshisola Thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Agriculture (Agronomy) at the Faculty of AgriSciences at Stellenbosch University Supervisors: Mrs. Estelle Kempen Department of Agronomy Stellenbosch University Dr. Jacques Van Zyl Department of Agriculture Elsenberg March 2014 Stellenbosch University http://scholar.sun.ac.za Declaration By submitting this dissertation electronically, I declare that the entirely of the work contained therein is my own, original work, that I am the owner of the copyright thereof (unless to the extent explicitly otherwise stated) and that I have not previously in its entirety or in part submitted it for obtaining any qualification. Date: December 2013 Steve Ndondji Tshisola Copy right © 2014 Stellenbosch University All rights reserved i Stellenbosch University http://scholar.sun.ac.za Acknoledgements Thanks to God the Father, and our Lord Jesus Christ who gave himself for our sins. To whom be glory for ever and ever. Thank you to my family for the endless love, encouragement and financial support. Thank you to my friends that were there, especially those who helped me with my trials. A big thanks to my supervisors Estelle Kempen and Jaques Van Zyl, thank you for your precious time, patience, advise, wisedom and generosity toward me. It was a blessing and honour working with you. I am grateful to Dr. Pieterse, head of the department of Agronomy at Stellenbosch University and to Mr. La Grange for managing the technical part of this study. I am also grateful to Dr. N.J.J. Combrink for constructive suggestions during the initial stages of this study. ii Stellenbosch University http://scholar.sun.ac.za Abstract The potato can be considered as one of the most important food crops in many African countries. The potential of this crop is reflected in the large increase in area of production where Africa showed the highest rate of growth within the developing world over the past twenty years. The multiplication rate of potatoes is very low compared to other crops. Therefore it is essential to investigate methods of increasing the number of minitubers produced from disease free in-vitro plantlets. There is a number of potato propagation procedures that are currently being used worldwide to multiply seed potatoes. As aeroponics is still a relatively new technique that has not been researched extensively for the production of minitubers, a study relating to the production practises including the nutritional requirements of potato minitubers produced in a aeroponic system were undertaken. Potato plantlets, cv BP1, were grown aeroponically at two different densities (20 and 30 plants/m2) and four harvest intervals (7, 10, 14 and 18 days). The interaction between harvesting intervals and plant densities did not influence plant growth, minituber quality or yield. Best results were realised when harvesting every 7 days with a higher total tuber number over the growing period. Harvest interval also influenced the phosphorus and copper concentration in minitubers. To study the effect of Calcium (Ca) application rate, potato plantlets of cultivars Up- to-date, Mnandi, Buffelspoort and BP1 were grown at four different Ca levels (8.40, 6.75, 5.10 and 3.45 meq/L). The interaction between Ca application levels and cultivars significantly influenced the percentage stolon branching. BP1 had more stolons at the lowest Ca application level and Buffelspoort had more stolons at the full Ca application levels. However, low Ca treatments produced the highest yield. The minituber number and weight harvested were three times more for Mnandi. An aeroponic study on the irrigation frequency (20, 30, 40 and 50 minutes interval) was conducted on four potato cultivars (Up-to-date, Mnandi, Buffelsoort and BP1). Significant differences were noted in the interaction between irrigation frequencies and cultivars for the percentage tuberised plants and stolon and tuber dry mass. When irrigated every 40 minutes, 48% of the Buffelspoort plants produced tubers. Plant height was also significantly affected by the interaction between irrigation frequencies and potato cultivars, with Mnandi producing taller plants when irrigated iii Stellenbosch University http://scholar.sun.ac.za every 30 minutes. Total tuber number and tuber fresh and dry weight was higher at the irrigation frequency of 20 minutes. The interaction between irrigation frequencies and cultivars on the response to macro and trace elements was not significant for sodium and iron but was for phosphorus, potassium, calcium, zinc and aluminium. A field study was conducted in a greenhouse where potato seed of BP1 obtained from the first trial were graded into different sizes (Small: >20, medium: 20–40 and large: > 40 mm of diameter) and stored at 3 different temperatures (3, 16 and 25oC) for 2 supplementary months before being planted. Sprouting capacity was mostly influenced by temperature regardless of other factors applied to potato seed minitubers such as harvest intervals and sizes. The higher storage temperature of 25oC resulted in tubers with a higher number of sprouts, longer sprouts and with a higher sprouting capacity. Uittreksel Aartappels is een van die belangrikste voedselgewasse in baie lande in Afrika. Die potensiaal van die gewas word gereflekteer in die groot toename in produksie areas, met Afrika wat die vinnigste van al die ontwikkelende lande gegroei het die laaste 20. In vergelyking met ander gewasse is die tempo van planvermeerdering by aartappels baie stadig. Dit is dus essensieel om metodes te ondersoek wat sal help om die aantal miniknolle wat per in vitro plantjie verkry kan word te verhoog. Daar is heelparty plant vermeerderings prosedures wat tans wêreldwyd gebruik word om saad aartappels te vermeerder. Aangesien aeroponika nog steeds ʼn relatiewe nuwe tegniek is wat nog nie ekstensief ondersoek is vir die verbouing van miniknolle nie, is ‘n studie geloods om te kyk na die produksie praktyke, wat insluit die voedingsbehoeftes van aartappel miniknolle in ʼn aeroponika sisteem. Aartappel plantjies, kultivar, BP1, is aeroponies verbou by twee plant digthede (20 en 30 plante/m2) en vier oesintervalle (7, 10, 14 en 18 dae). Die interaksie tussen oesintervalle en plantdigtheid het geen effek gehad op plant groei, miniknol kwaliteit of opbrengs nie. Die beste resultate is verkry waar die knolle elke 7 dae geoes is met ‘n hoër totale aantal knolle oor die groeiseisoen. Die oesinterval het ook ‘n effek gehad op die fosfaat en koper konsentrasie van die miniknolle. iv Stellenbosch University http://scholar.sun.ac.za Om die effek van die Kalsium (Ca) toedieningspeil te ondersoek is aartappel plantjies; kultivars Up-to-date, Mnandi, Buffelspoort en BP1 gekweek by vier verskillende Ca peile (8.40, 6.75, 5.10 en 3.45 meq/L). Die interaksie tussen Ca toedienings peile en kultivars het ‘n beduidende effek gehad op die persentasie stolon vertakking. BP1 het meer stolons gehad by die laagste Ca toedieningspeil en Buffelspoort het meer stolons gehad by die volle Ca toedieningspeil. Die hoogste opbrengste is egter waargeneem by die laagste Ca toedieningspeil. Die aantal miniknolle en oes massa was drie keer meer vir Mnandi. ‘n Aeroponiese studie op die besproeiingsfrekwensie (20, 30, 40 en 50 minuut intervalle) is gedoen met vier aartappel kultivars (Up-to-date, Mnandi, Buffelsoort en BP1). Beduidende verskille is opgemerk in die interaksie tussen besproeiings frekwensie en kultivars vir die persentasie plante met knolle en stolon en knol droë massa. Met besproeiings elke 40 minute het 48% van die Buffelspoort plante knolle produseer. Plant hoogte is ook beduidend beïnvloed deur die interaksie tussen besproeiingsfrekwensie en aartappel kultivar met Mnandi plante wat hoër was wanneer dit elke 30 minute besproei is. Die totale aantal knolle en knol vars- en droë massa was hoër wanneer daar elke 20 minute besproei is. Die interaksie tussen besproeiings frekwensie en kultivars op die makro- en mikro element inhoud van die knolle was nie beduidend vir natrium en yster nie, maar wel vir fosfaat, kalium, kalsium, sink en aluminium. ‘n Potproef is gedoen in ‘n kweekhuis waar aartappel saad van BP1 verkry vanaf die eerste proef nadat knolle verdeel is in verskillende grootte klasse (klein: < 20mm, medium: 20-40mm en groot: >40mm) en gestoor is by drie verskillende temperature (3, 16 en 25oC) vir 2 addisionele maande voor plant. Spruit ontwikkelings kapasiteit was meestal beïnvloed deur temperatuur ten spyte van ander behandelings soos oes intervalle en knol grootte. Die hoër bergings temperatuur 25oC het aanleiding gegee tot knolle met ‘n hoër aantal spruite, langer spruite en ‘n hoër spruit ontwikkelings kapasiteit. v Stellenbosch University http://scholar.sun.ac.za Contents Chapter 1 .................................................................................................................... 1 Introduction and literature review............................................................................ 1 Introduction ............................................................................................................... 1 1. Potato plant developmental phases ..................................................................................... 3 1.1. Sprouting and plant establishment ............................................................................... 3 1.2. Tuber initiation .................................................................................................................... 4 1.3. Tuber bulking ...................................................................................................................... 5 1.4. Tuber maturation ................................................................................................................ 5 2. Aspects influencing growth, tuber initiation and yield.................................................... 6 2.1. Temperature ......................................................................................................................... 6 2.2. Photoperiod and light intensity ...................................................................................... 6 3. Factors influencing nutrition .................................................................................................. 7 3.1. Nutrient uptake ................................................................................................................... 7 3.2. Essential macroelements ................................................................................................. 8 3.3. Water quality and irrigation management ................................................................. 10 4. Tuberization enhancement.................................................................................................... 11 4.1. Tuber induction ................................................................................................................. 11 4.2. The tuberization signal ................................................................................................... 12 4.3. Plant growth regulators .................................................................................................. 12 5. Seed potato multiplication .................................................................................................... 13 5.1. Production systems ......................................................................................................... 13 5.2. Aeroponics in seed potato production ....................................................................... 13 6. Potato seed quality ................................................................................................................. 15 6.1. Dimension of seed ........................................................................................................... 15 6.2. Dormancy and physiological age ................................................................................ 15 6.3. Physiological disorders .................................................................................................. 16 7. Factors influencing potato tuber quality multiplications .............................................. 17 7.1. Storage conditions ........................................................................................................... 17 Objective and Conclusion ......................................................................................................... 18 References ..................................................................................................................................... 18 CHAPTER 2 .............................................................................................................. 31 The effect of harvest interval and plant density on plant growth, tuber size distribution and yield of potatoes (Solanum tuberosum L.) in aeroponics. ...... 31 vi Stellenbosch University http://scholar.sun.ac.za Abstract .......................................................................................................................................... 31 Introduction ................................................................................................................................... 32 Materials and methods ............................................................................................................... 33 Location and crop details .......................................................................................................... 33 Data collected ............................................................................................................................. 35 Treatments and experimental design ................................................................................. 37 Results and discussion .......................................................................................................... 37 Effects of harvesting interval and plant density on vegetative plant growth. .................... 37 Minituber quality and yield ........................................................................................................ 41 Conclusion ..................................................................................................................................... 50 References ..................................................................................................................................... 51 Chapter 3 .................................................................................................................. 57 The role of different calcium application rates on the growth, tuber size distribution and yield of potato (Solanum tuberosum L.) minitubers using aeroponics ............................................................................................................... 57 Abstract .......................................................................................................................................... 57 Introduction ................................................................................................................................... 58 Materials and methods ............................................................................................................... 60 Plant material .............................................................................................................................. 60 Aeroponic system ....................................................................................................................... 61 Measurements and Analysis ........................................................................................................ 62 Data collected ............................................................................................................................. 62 Treatments and experimental design ...................................................................................... 65 Results and Discussion ............................................................................................................. 65 Morphology and vegetative growth .......................................................................................... 65 Yield .............................................................................................................................................. 69 Conclusion ..................................................................................................................................... 78 References ..................................................................................................................................... 79 Chapter 4 .................................................................................................................. 86 The effect of irrigation frequency on the growth, tuber size distribution and final yield of potato (Solanum tuburosum L.) minitubers produced in aeroponics ............................................................................................................... 86 Abstract .......................................................................................................................................... 86 Introduction ................................................................................................................................... 87 Materials and methods ............................................................................................................... 88 vii Stellenbosch University http://scholar.sun.ac.za Plant material .............................................................................................................................. 88 Aeroponics system ..................................................................................................................... 89 Data collected ............................................................................................................................. 90 Results and discussion. ............................................................................................................. 93 Morphology .................................................................................................................................. 93 Yield .............................................................................................................................................. 98 Conclusion ................................................................................................................................... 110 References ................................................................................................................................... 111 Chapter 5 ................................................................................................................ 118 Post-harvest quality of potato minitubers (Solanum tuberosum L.) produced aeroponically ......................................................................................................... 118 Abstract ........................................................................................................................................ 118 Introduction ................................................................................................................................. 119 Materials and methods ............................................................................................................. 120 Plant material ............................................................................................................................ 120 Data collected ........................................................................................................................... 121 Treatment and experimental design ...................................................................................... 122 Results and discussion ............................................................................................................ 122 Conclusion ................................................................................................................................... 136 References ................................................................................................................................... 137 Chapter 6 ................................................................................................................ 142 Summary and General Conclusions .................................................................... 142 Harvest interval and plant density ......................................................................................... 143 Calcium rates .............................................................................................................................. 144 Irrigation frequency ................................................................................................................... 145 Postharvest in the field ............................................................................................................. 146 viii Stellenbosch University http://scholar.sun.ac.za The referencing style in this thesis for all chapters was written according to the requirements of the South African Journal of Plant and Soil. This thesis represents a compilation of manuscripts where each chapter stands as an individual unit. Repetition between chapters that may occur was thus unavoidable. ix