Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Potatoes is the fourth most important food source in the world. To provide in the ever
increasing demand by the growing world population for this staple food, alternative
ways will have to be found to produce a cheaper and a healthier end product. The
tubers mainly consist of carbohydrates and starch, although 9% of the dry weight of
the tubers consist of proteins. In its natural state the potato tuber is low in sodium and
high in potassium and vitamin C. These proteins can provide in all the amino-acid
requirements of humans and make it an outstanding balanced diet.
The most important factor by which the production and quality of potatoes can be
increased, is to provide better propagation material to producers. Minituber
production is a relatively new method of producing better quality propagation material
for producers. It is, however, very expensive because of the high capital investment
needed. By producing more tubers per plant, or more tubers per square meter, the unit
price per tuber may be lowered. The system commonly used for minituber production
is where in vitro plants are planted in a greenhouse, usually in a vermiculite/peat
mixture as medium. As in a hydroponic system, nutrients are added to the irrigation
water.
As possible strategy to increase the production of mini-tubers, the effect of nutrition
was investigated. No significant differences were found in tuber production with
small deviations in phosphorous and calcium nutrition. Researchers who reported
significant differences in tuber production with nutrition, either corrected extreme
shortages or induced it.
By subjecting the root and tuber medium of potato plants to a pH-shock (nutrient
solution with a pH of 3.5 for 10 hours), large amounts of tubers were initiated. A new
production technique was developed where plants were grown in a hydroponic way
without any root medium. In this way the right sized tubers could be removed without
damaging the plant. Potato plants do not initiate tubers easily where stolons are not
subjected to mechanical resistance. This problem was solved with the help of a pHshock,
where significantly more tubers were formed per plant. The action of the pH-shock could be explained by a temporary inaccessibility of
nutrients to the plant. Both calcium and magnesium absorpsion are hampered at a low
pH, but calcium is also poorly translocated in the plant. Considering that a nutrient
solution without calcium produced the same results as the pH-shock treatment in this
study, one may make the assumption that an induced calcium shortage may be
responsible for the low pH effect. The same effect may even be induced by giving the
plants clean water for some time. Such a treatment was, however, not tested but
should receive attention in further studies.
The correct timing for a low pH-shock may need more research. A precise number of
days after transplanting can not be prescribed since many factors such as light
intensity, daylength and cultivar difference affect plant growth and tuber initiation.
Environmental conditions, the physiological age and the biomass of the plant may
affect the timing of the shock. A low pH-shock could not at any stage induce tubers in
potato plants where unfavorable environmental conditions occurred. It seems as if the
plants need to be ready for tuber initiation before the pH-shock can be successfully
applied. By removing/harvesting the tubers at the required weight, the burden on the
plant may be relieved enabling more tubers to form.
It was experienced that the reproductive system of the potato plant is complex with a
number of factors affecting it. The new production system has potential, but more
developmental work is still needed. / AFRIKAANSE OPSOMMING: Aartappels is die vierde belangrikste voedelsoort in die wereld, Om te kan voorsien
aan die ewigdurende verhoogde vraag na hierdie stapelvoedel deur die groeiende
wereld-bevolking, sal daar maniere gevind moet word om die eindproduk goedkoper
en in 'n gesonder toestand op die mark te plaas. Die knolle bestaan hoofsaaklik uit
koolhidrate en stysel, alhoewel 9% van die droe gewig van knolle uit proteiene
bestaan. Die aartappelknol is in sy natuurlike toestand laag in natrium en hoog in
kalium en vitamien C. Hierdie protei'ene kan in al die aminosuur-behoeftes van
mense voorsien wat dit dus 'n uitstekende gebalanseerde dieet maak.
Die belangrikste faktor waarmee die produksie en kwaliteit van aartappels verhoog
kan word is om beter voortplantingsmateriaal aan produsente te verskaf.
Miniknolproduksie is 'n relatief nuwe manier om gesonde en groeikragtige
voortplantingsmateriaal vinnig by die produsente te kry. Dit is egter 'n duur metode
omdat die kapitaal-investering groot is. Deur meer knoUe per plant, of meer knolle per
vierkante meter te produseer kan die eenheidsprys per moer verlaag word. Die sisteem
wat algemeen vir miniknolproduksie gebruik word is om in vitro plantjies in 'n
kweekhuis, gewoonlik in 'n vermikulietldennebas mengsel te plant. Voedingstowwe
word dan soos in 'n hidrokultuurstelsel saam met die besproeiingswater toegedien.
As moontlike strategie om die produksie van miniknolle by aartappels te verhoog, is
die invloed van voeding daarop ondersoek. Daar is gevind dat daar nie groot verskille
in knolproduksie met klein afwykings in fosfaat- en kalsium-voeding veroorsaak is
nie. Navorsers wat wel betekenisvolle verskille III knolproduksie met
voedingsbehandelings verkry het, het ekstreme tekorte reggestel of gemduseer.
Deur die wortel- en knolmedium van aartappelplante aan 'n pH-skok
(voedingsoplossing met 'n pH van 3.5 vir 10 ure) bloot te stel, is daar gevind dat 'n
groot hoeveelheid knolle geinisieer word. Verder is 'n nuwe produksietegniek
ontwikkel waar die plante met 'n suiwer waterkultuur metode geproduseer word,
sodat knolle wat oesgereed is verwyder kan word. Aartappelplante inisieer nie maklik knolle onder hierdie omstandighede waar stolons geen meganiese weerstand ervaar
nie. Met behulp van die pH-skok het daar betekenisvol meer knolle per plant gevorm.
Die werking van die pH-skok kan moontlik aan 'n tydelike ontoeganklikheid van
voedingstowwe toegeskryf word. Beide kalsium en magnesium word moeilik by 'n
lae pH opgeneem maar kalsium word boonop moeilik deur die plant getranslokeer.
Aangesien 'n voedingsoplossing sonder enige kalsium dieselfde resultate as die pHskok
gelewer het, lyk dit asof 'n geinduseerde kalsium-gebrek vir die lae pH effek
verantwoordelik mag wees. Die skok kan makliker en veiliger toegepas word deur vir
'n tydperk net skoon water aan die plante te gee. So 'n behandeling is egter nie
beproef nie maar behoort in opvolgwerk aandag te ontvang.
Die optimum tyd waarop so 'n skok toegedien moet word is nog onduidelik. Daar kan
nie op 'n eksakte aantal dae na uitplant gewerk word nie, aangesien daar te veel
faktore soos ligintensieteit, daglengte en kultivar is wat plante se groei en
knolinisiasie kan beinvloed, Omgewingstoestande, die fisiologiese ouderdom van die
plant en die hoeveelheid biomassa wat gevorm het mag bepaal wanneer die plante
geskok moet word. Waar ongunstige omgewingstoestande geheers het, kon 'n lae-pHskok
op geen stadium knolinisiasie induseer nie. Dit wil voorkom asof die plant vir 'n
knolinisiasie fase gereed moet wees voordat 'n lae-pH-skok doeltreffend is. Dit
verhoog dan bloot die aantal knolle wat per plant ontwikkel. Deur die knolle op die
verlangde grootte te pluk kan die las op die plante verlig word sodat meer knolle mag
vorm.
Daar is ervaar dat die reproduktiewe stelsel van die aartappelplant kompleks is en dat
daar baie faktore is wat dit mag beinvloed. Die nuwe produksiestelsel toon potensiaal,
alhoewel verdere ontwikkelingswerk nog nodig is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52606 |
| Date | 12 1900 |
| Creators | Barnard, Ruben |
| Contributors | Combrink, N. J. J., Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | af_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 80 p. : ill. |
| Rights | Stellenbosch University |
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