The influence of light intensity, light quality and root zone temperature on patato minituber production

Kempen, E. (2007-12)

Thesis (MScAgric)--Stellenbosch University, 2007.

Thesis

ENGLISH ABSTRACT: In South Africa the production of minitubers, as starting material for seed potato production, is achieved by transplanting in vitro plantlets to a hydroponic growth medium in the greenhouse, but current yields for minituber production are relatively low. As commercial growers start to prefer earlier generation seed, minituber production systems need to be re-evaluated in order to maximize yields. The effect of light intensity, light quality and root zone temperature on the growth, tuberization, assimilate distribution, tuber size distribution and tuber dormancy of potato was investigated in a series of greenhouse and glasshouse experiments. The comparison of plants grown under different light intensities indicated that shading of 20% did not have a negative impact on the potato plants' growth, net assimilation or distribution of biomass within the plant. Higher shading levels of 40% and 50% resulted in most of the biomass being partitioned to the aboveground plant parts. The total number of tubers was not affected by light intensity but the dry matter percentage of the tubers was reduced by a decrease in the light intensity. The duration of dormancy was only determined by cultivar and tuber size. In the light quality trial, filtering some of the red light reaching the plants resulted in an increase in stem and stolon growth and a high leaf dry mass percentage, which can be associated with an increase in the photosynthetic efficiency associated with conditions favourable to tuberization. Tuber number and total tuber mass per plant also increased and a high percentage of the total biomass was allocated to the tubers. Under the blue light absorbing covers stem and stolon growth also increased but neither the tuber number nor the total tuber mass per plant was affected. The most distinctive effect the far-red filter had was a decrease in tuber number but an increase in the average fresh mass per tuber. Finally, a glasshouse study was conducted with different root zone temperatures. Cooling of the root zone to below 15°C resulted in plants with a reduced height, lower leaf-, stem- and stolon mass and reduced leaf areas. Final tuber number or yield was not affected, but plants were more efficient in partitioning dry matter to the tubers. The results indicated that cooling of the root medium may facilitate a decrease in stem growth without affecting tuber formation and final tuber yield. In conclusion, it can the recommended that in order to reduce excessive foliar growth due to a large percentage of assimilates being partitioned to the haulm, minituber producers should ensure high light intensities and cool growth medium temperatures in the greenhouse. In areas where low light intensities commonly prevail during the growing season, additional lighting with the incorporation of a red filter may for this reason help to increase minituber yields.

AFRIKAANSE OPSOMMING: In Suid-Afrika word miniknolle, verkry vanaf in vitro plantjies wat hidroponies in die kweekhuis verbou word, as begin materiaal vir saadaartappelproduksie gebruik. Miniknol-opbrengste wat sodanig verkry word is egter relatief laag. Omdat kommersiele produsente egter in 'n toenemende mate voorkeur toon vir vroee generasie saadaartappels, is dit nodig om die produksiestelsels van GO miniknolle in kweekhuise te herevalueer ten einde opbrengste te verhoog. In hierdie studie is die effek van ligintensiteit, ligkwaliteit en groeimedium temperatuur op die groei van plante, knolinisiasie, verdeling van assimilate, knolgrootte verspreiding en knoldormansie van aartappels ondersoek in 'n reeks glas/kweekhuis-eksperimente. Deur plante te vergelyk wat gekweek is ender skadunette wat verskillende lig persentasies deurlaat, is waargeneem dat 20% beskaduing nie die loofgroei van aartappelplante, totale biomassa of verspreiding van die biomassa benadeel nie. Hoer skaduvlakke (40% en 50%), het egter veroorsaak dat die grootste gedeelte van die biomassa na die bogrondse plantdele ge-allokeer is. Die aantal knolle geinisieer, is nie geaffekteer deur die ligintensiteit nie, maar droemateriaal persentasie van die knolle was laer by laer ligintensiteite. Die dormansie periode en aantal spruite wat gevorm is, was slegs afhanklik van kultivar en knolgrootte. In die ligkwaliteit proef het 'n vermindering van die rooi lig wat plante bereik, sowel stingel- en stolongroei as droemassa persentasie van die blare verhoog. Dit kan dui op 'n verbetering in die fotosintetiese effektiwiteit soos waargeneem wanneer toestande gunstig is vir knolinisiasie. Onder die rooi lig filter was die aantal knolle en knolmassa per plant ook hoer en is 'n groot gedeelte van die totale biomassa na die knolle geallokeer ge-allokeer. Plante ender die blou lig filter het ook 'n verhoging in stingel- en stolongroei getoon, maar die aantal knolle en knolmassa per plant was onveranderd. Die ver-rooi filter het 'n vermindering in die knolgetal, maar 'n toename in die gemiddelde knolmassa tot gevolg gehad. In die glashuisstudie met verskillende groeimedium temperature het 'n verlaging in temperatuur die planthoogte verminder en 'n afname in blaar-, stingel- en stolonmassa veroorsaak. Hoewel dit laer plantblaaroppervlaktes tot gevolg gehad het, is knolgetalle nie beYnvloed nie. Dit beteken dat die verkoeling van die groeimedium die effektiewe akkumulasie van droemateriaal in die knolle verhoog. Ten einde oormatige loofgroei te verminder word hoe ligintensiteite en lae groeimedium temperature dus aanbeveel. In produksiegebiede waar lae ligintensiteite in die kweekhuis dus 'n probleem is, kan addisionele beligting saam met 'n rooi lig filter moontlik help om miniknol opbrengste te verhoog.

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