Water relations and sunburn in apple fruit

256 Pages·2017·12.19 MB·English

Water relations and sunburn in apple
fruit
By Giverson Mupambi
Dissertation presented for the degree of Doctor of Philosophy (Agric) in the Faculty of
AgriScience at Stellenbosch University
Promoter: Prof W.J. Steyn Department of Horticultural Science, Stellenbosch
University and HORTGRO Science, Stellenbosch
Co-promoter: Dr S. Dzikiti Council for Scientific and Industrial Research (CSIR)
Stellenbosch
Co-promoter: Dr M. Schmeisser Department of Horticultural Science, Stellenbosch
University
December 2017
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Declaration
By submitting this dissertation electronically, I declare that the entirety of the work contained
therein is my own original work, that I am the authorship owner 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.
Signature:
Date: December 2017
Copyright © 2017 Stellenbosch University
All rights reserved
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Abstract
Sunburn in apple is a major problem in South Africa with losses of up to 50% of total yield.
The primary objective of this study was to investigate the relationship between tree water
relations and sunburn development under South African conditions. Cultural practices that
may affect sunburn development through modification of plant water status and the effect of
microclimate on fruit peel anatomy was also studied.
Induced water stress increased sunburn necrosis and incidence in ‘Granny Smith’ and sunburn
severity in ‘Cripps’ Pink’ apple. Although not very pronounced, chlorophyll fluorescence
pointed to photochemical changes within the peel under water stress. Water stress influenced
ascorbic acid levels in peel, indicating the occurrence of oxidative stress. Leaf net carbon
assimilation was reduced due to lower stomatal conductance and possibly also
photoinhibition.
Pulsing irrigation reduced the incidence of sunburn in ‘Golden Delicious’ and ‘Granny Smith’
compared to an under irrigated control. The reduction in sunburn might be attributed to either
the improved plant water status, which reduced tree stress compared to the under irrigated
control, or the comparatively more vegetative growth resulting in shading of fruit. Canopy
ambient temperature was lower under pulsing irrigation and plant water status was improved.
Foliar S˗ABA (active form of abscisic acid) application had no effect on sunburn incidence
and severity under South African conditions over three growing seasons. The main apple
growing regions in South Africa (33-34º S latitude) experience high radiation, while
temperatures often exceed 40 ºC during the growing season. S-ABA application resulted in
lower stomatal conductance with a consequent decrease in gas exchange and reduction in fruit
size. Tree water status in terms of stem water potential was improved due to the reduction in
transpiration.
Fruit transpiration and water loss was higher in young compared to mature fruit, which
seemingly corresponds with increasing susceptibility of fruit to sunburn during fruit growth.
Stomata are present in young fruit and are under regulatory control, which makes them more
effective for transpiration. In mature fruit, the predominant lenticel type was partially open
and not effective for transpiration. Lenticel density and morphology varied considerably
within and between cultivars, between different canopy positions, and between production
areas. Although fruit transpiration and water loss decreased over the growing season, it did
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not always follow the same pattern as fruit surface morphology. In addition, the contribution
of transpiration and water loss to the fruit heat balance is negligible. Hence, differences in
fruit surface morphology may not explain differences in cultivar and fruit sunburn sensitivity.
In conclusion, this study provides insight into ecophysiological and biochemical changes that
occur under water stress and that might have a bearing on sunburn development in apple fruit.
The study provides further proof of the link between plant water status and sunburn
development and shows that good management of plant water status through irrigation is
instrumental to controlling sunburn in a warm production region.
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Opsomming
Sonbrand is ʼn ernstige probleem in Suid-Afrika met verliese van tot 50% van totale produksie
wat ondervind word. Die primêre doelwit van hierdie studie was om die verband tussen boom
waterverwantskappe en sonbrand onder Suid-Afrikaanse kondisies te ondersoek.
Verbouingspraktyke wat sonbrand ontwikkeling mag affekteer deur die modifikasie van die
plantwaterstatus asook die effek van makro- en mikroklimaat op die vrugskil anatomie is ook
ondersoek.
Geïnduseerde waterstres het die graad van sonbrand in ‘Granny Smith’ en ‘Cripps’ Pink’
appels vererger. Ten spyte van ʼn relatiewe klein effek, het chlorofiel fluoressensie gedui op
fotochemiese veranderinge in die skil vanweë waterstres. Waterstres het askorbiensuurvlakke
in die skil geaffekteer, wat dui op die voorkoms van oksidatiewe stres. Netto
koolstofassimilasie is verminder vanweë laer huidmondjiegeleiding en moontlik ook foto-
inhibisie.
Pulsbesproeiing het sonbrand in ‘Golden Delicious’ en ‘Granny Smith’ verminder in
vergelyking met ‘n onderbesproeide kontrole. Die vermindering in sonbrand kan moontlik
toegeskryf word aan enige van of beide verbeterde plant waterstatus wat stres verlaag het
vegeleke met die onderbesproeide kontrole, of the relatief verhoogde vegetatiewe groei en
gevolglike oorskaduwing van vrugte. Pulsbesproeiing het die temperatuur van die blaredak
verlaag asook die plantwaterstatus verbeter.
Blaartoediening van S-ABA (aktiewe vorm van absissiensuur) oor drie groeiseisoene het geen
effek op die voorkoms en graad van sonbrand onder Suid-Afrikaanse toestande gehad nie. Die
hoof produksie-areas in Suid-Afrika (33-34ºS breedtegraad) ondervind hoë straling terwyl
temperature dikwels 40 ºC oorskry. S-ABA toediening het huidmondjiegeleiding verlaag met
ʼn gevolglike verlaging in gaswisseling en vruggrootte. Boomwaterstatus, in terme van
stamwaterpotensiaal, is verbeter vanweë die verlaging in transpirasie.
Vrugtranspirasie en waterverlies was hoër in onvolwasse vergeleke met volwasse vrugte. Dit
stem oënskynlik ooreen met die toenemende vatbaarheid van vrugte vir sonbrand soos wat hul
groei. Huidmondjies is aanwesig in onvolwasse vrugte en is onder regulatoriese beheer. Dit
maak hul meer effektief vir evaporatiewe verkoeling. Gedeeltelik oop lentiselle was die mees
algemene lentisel tipe in volwasse vrugte. Hierdie lentiselle is oneffektief vir transpirasie.
Die digtheid van lentiselle asook hul morfologie het heelwat tussen en binne kultivars, tussen
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vrugposisies in die blaredak en tussen produksie-area verskil. Alhoewel vrugtranspirasie en
waterverlies gedurende die groeiseisoen afgeneem het, het dit nie altyd dieselfde patroon as
vrugskilmorfologie gevolg nie. Bowendien is die bydrae van transpirasie en waterverlies tot
die vrug hittebalans weglaatbaar klein. Gevolglik mag verskille in oppervlakmorfologie
waarskynlik nie verskille in kultivar en vrug sonbrand sensitiwiteit verklaar nie.
In gevolgtrekking; hierdie studie verskaf insig in ekofisiologiese en biochemiese veranderinge
wat tydens waterstres ervaar word en wat moontlik ʼn strekking mag hê op die ontwikkeling
van sonbrand in appels. Die studie verskaf verder ook bewyse van die skakel tussen
plantwaterstatus en die ontwikkeling van sonbrand en dui daarop dat goeie bestuur van die
plantwaterstatus deur besproeiing instrumentaal is tot die beheer van sonbrand in warm
produksiestreke.
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Publications and conference presentations from this thesis
Peer reviewed published conference proceedings
1. Mupambi G., Schmeisser M., Lötze E., Malan C., Dzikiti S. and Steyn, W.J. 2015.
Effect of supplementary irrigation at high ambient temperatures on sunburn, plant physiology,
soil and canopy environment of 'Granny Smith' apple. Acta Hort. 1150:239-244.
https://doi.org/10.17660/ActaHortic.2017.1150.33
2. Mupambi G., Reynolds J.S. and Steyn, W.J. 2014. Foliar S-ABA application does not
reduce sunburn in 'Granny Smith' apple. Acta Hort. 1042:303-309.
http://dx.doi.org/10.17660/ActaHortic.2014.1042.36
Conference presentations
1. Mupambi G., Schmeisser M., Lotze E., Malan C., Dzikiti S., and Steyn W.J. 2015.
Effect of supplementary irrigation at high ambient temperatures on sunburn, plant physiology,
soil and canopy environment of ‘Granny Smith’ apple. VIII International Symposium on
Irrigation of Horticultural Crops, Lleida, Spain, 8-11 June 2015. (Oral).
2. Mupambi G., Schmeisser M., Lotze E., Malan C., Dzikiti S., and Steyn W.J. 2015.
Additional irrigation at high air temperatures reduces sunburn in ‘Golden Delicious’ apple.
Combined Congress, Nelson Mandela Metropolitan University, George, 19-22, January 2015.
(Oral)
3. Mupambi G., Reynolds J.S. and Steyn, W.J. 2014. Foliar S-ABA application does not
reduce sunburn in 'Granny Smith' apple. Combined Congress, Rhodes University,
Grahamstown 20-23, January 2014. (Oral)
4. Mupambi G., Reynolds J.S. and Steyn, W.J. 2013. Foliar S-ABA application does not
reduce sunburn in 'Granny Smith' apple. XII International Symposium on Plant Bioregulators
in Fruit Production, Orlando, Florida, United States, 28 July-1 August. (Oral).
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Acknowledgements
I am gratefully indebted to the following people and institutions:

My promoter Prof. W.J. Steyn for his guidance and mentorship throughout my studies. Thank
you for all your help and support throughout the years. It was and still is, very much
appreciated.

My co-promoters, Drs S. Dzikiti and M. Schmeisser for their assistance, guidance and input
throughout my studies.

Prof. K. Theron for always maintaining an open door and her input throughout my studies.

The South African Apple and Pear Producers’ Association for funding my research.

Anton Muller for assistance with trial sites and his friendship.

Chris Malan, Leon Horn and Charles Cherry for help with the irrigation pulsing trial.

The following growers for providing trial sites and assistance: Albert Rust, Herbert Honnibal,
Carl van Lingen and Ian Macdonald.

Brian ‘Homeboy’ Makeredza for being my walking encyclopedia on everything apple related
and for his friendship.

Irene Idun for her friendship and kind encouragement throughout my studies.

My fellow PhD students that I shared the office with, many thanks for the laughter and good
memories: Tarryn De Beer, Simeon Hengari, Micheline Inamahoro and Tavagwiza ‘Doc’
Muziri.

Dianah Daniels, Carin Pienaar and Melissa Nel for administrative support and making sure
everything always ran smoothly.

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Gustav Lötze, Andre Swartz, Tikkie Groenewald, Revona Poole and Mishiela for technical
support.

Sandy Turketti for help with the lenticel work.

The various assistants I had over the years: Mario Ruiters, Simphiwe Tshoni, Anelle
Blankenberg, Asanda Matiso, Mark Kirstein, Mareli Grobbelaar and Priscilla Ramphaka.

Halalisiwe and Nolwandle ‘Nana’ Msimango for their support throughout my studies and
helping keep me sane.

Cuthbert and Pamela Chideme for their help to get where I am today.

My many friends from all walks of life who have come to be like my family: Munya
Mubazangi, Alex Kuhudzai, Joanna Mpofu, Aleck Kuhudzai, Nisbert Chimboza, Tendani
Chimboza, Hein Gerber, Hans Kelstrup, Becky Matter, Tendai Mariri, Stephen Danje and
Kudzai Chideme.

Oscar Whacha for being the best flatmate ever, made my life easier

Staff and interns at the Washington Tree Fruit Research Commission for my enjoyable stay in
Wenatchee.

Special thanks to Ensa and Jody Ceesay for setting me up with a home office so that I could
finish up my writing and making sure I experienced the American way of life!

Geraldo Garcia, Cindy Rojas and the Garcia family for making me feel at home in the US and
their hospitality. The Mexican food certainly helped☺.

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Dedications

This dissertation is dedicated to my grandmother Violet and my siblings Welly, Grace and
Petros. Sorry it took me so long for me to finish this.

Also dedicated to the memory of my late parents Gavin and Vaidah, and my late brother
Sebastian.

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