Die invloed van boor, trosvibrasie en relatiewe humiditeit van die trosatmosfeer op die bestuiwing van kweekhuistamaties (Lycopersicon esculentum L.)

Smit, Johannes Nicolaas (2003-03)

Thesis (MScAgric)--University of Stellenbosch, 2003.

Thesis

ENGLISH ABSTRACT: In South Africa tomato production in greenhouses normally occurs out of season when conditions are unfavourable for production and for the pollination process. Pollination is of special importance and the backbone of production. High temperatures contribute to the formation of abnormalities in flower morphology such as splitting of the anther cone and style exsertion. Low temperatures inhibit growth of the anther cone and therefore the style is uncovered. The movement of pollen from the anther to the style is inhibited by the higher style position in relation to the anther cone. Under humid conditions the pollen tends to stick to the anther surface. Another factor contributing to the problem is the banning of European bumble bees in South Africa. Alternative methods of pollen transport have to be found. Truss vibration, honey bees and plant growth regulators (PGR) are the most popular alternatives. Truss vibration and the use of PGR's are labour intensive and honey bees tend to get disorientated inside a plastic greenhouse. During the first part of this study pollen from plants, grown at four different B-levels (0.02; 0.16; 0.32 and 0.64 mg rl) was germinated in vitro. It was kept at different temperatures and periods before incubating on different growth media. No proof was found that pollen from B-deficient plants germinated poorly. Germination of pollen decreased significantly after one week storage. Deterioration of pollen viability could be lowered by storage at 5°C. At least 10% sucrose is needed in the growth medium for in vitro germination but addition ofB had no positive effect. In a second phase of the study, the influence of the mentioned B application rates were tested. The experiment was done in a glasshouse where temperatures were mechanically regulated (22°C and 10°C day/night). Seedlings of the greenhouse tomato cultivar, Abigail, were planted in acid washed river sand. Plants were grown with the main stem trellised vertically and the side shoots removed weekly. Only the first, third and fourth cluster were used for this part of the study. The uptake of all the essential nutrient elements, fruit set, the relation of larger to smaller fruits, physical and chemical quality and fruit shelf life were evaluated. The application of B at higher rates increased the uptake of Ca and decreased K-uptake. Fruit set, fruit development, fruit color and shelf life were the best at a B-Ievel of 0.16 mg r'. At this rate the abortion of flowers was the least. The same plants were used for the second part of the study, using the third cluster. The influence of the same four B-Ievels, the relative humidity (RH) of the truss atmosphere and truss vibrations were tested. The second cluster was covered with a plastic bag. Dry {<I 0% relative humidity (RH)}, normal {60-7S% RH} and moist {8S-97% RH} air were constantly applied to the bags at ± 50 ml min-I. As a third factor, truss vibration was applied daily by means of an electric vibrator (polli-bee), The amount of flowers per cluster, fruits per cluster, fruit set, weight of the cluster (yield), fruit weight, seed production, fruit weight per amount of seeds formed and fruits with blossom-end-rot (BER) were evaluated. The application of higher B-Ievels, air with the normal RH and the vibration of the clusters positively affected fruit weight, weight of the cluster and fruit set. High RH increased the occurrence of BER, probably due to a lack of transpiration from the fruit surface and therefor a lack in Ca translocation.

AFRIKAANSE OPSOMMING: Die verbouing van kweekhuistamaties in Suid-Afrika geskied meestalonder toestande wat ongunstig is vir produksieprosesse en veral die bestuiwingsproses wat die basis van produksie is. Onder toestande van hoë temperature is die voorkoms van afwykings in die blommorfologie (gesplete meeldraadbuis en verlengde styl) algemeen. Net so, onder toestande van lae temperature, sal gebrekkige groei van die meeldraadkrans ook tot die blootstelling van die stempel lei. Die oordraging van die stuifmeel vanaf die helmknop na die stempel word hierdeur benadeel. Tydens humiede toestande mag vasklewing van stuifmeel aan die helmknoppe ook die beweging van stuifmeel belemmer. 'n Verdere faktor wat tot die probleem bydra is die verbod op die invoer van hommelbye uit Europa. Alternatiewe metodes vir oordraging van stuifmeel moet dus gevind word. Trosvibrasie, heuningbye en die gebruik van plantgroeireguleerders (PGR's) is die mees populêre alternatiewe. Trosvibrasie met 'n 'polli-bee' en die aanwending van PGR's is arbeidsintensief. Heuningbye ondervind navigasieprobleme in plastiek kweekhuise en is nie so effektief as hommelbye nie. Tydens die eerste fase van die ondersoek is stuifmeel vanaf plante, wat by vier verskillende Bvoedingspeile (0.02; 0.16; 0.32 en 0.64 mg rl) verbou is, versamel en in vitro ontkiem. Dit is by verskillende temperature en periodes opgeberg en op verskillende media vir ontkieming geïnkubeer. Geen bewyse kon gevind word dat stuifmeel vanaf B-gebrekkige plante swak ontkiem nie. Kiemkrag van stuifmeel het na sewe dae opberging betekenisvol verswak. Verswakking in kiemkrag kon beperk word deur die stuifmeel by SoC op te berg. 'n Ontkiemingsmedium met ten minste 10% sukrose is vir goeie in vitro ontkieming van stuifmeelkorrels nodig terwyl die byvoeging van B geen voordelige effek getoon het nie. Tydens die tweede gedeelte van hierdie ondersoek is die invloed van die genoemde vier B-voedingspeile ondersoek. Die ondersoek is in 'n glashuis, waarvan die temperature meganies beheer is (22°C en 10°C dag/nag), uitgevoer. Plantmateriaal van die kweekhuistamatiekultivar, Abigail, is in suurgewasde riviersand geplant. Hoofstamme is vertikaalopgelei en die sylote is een maal per week uitgebreek. Die eerste, derde en vierde bloeiwyses is vir die ondersoek gebruik. Die opname van al die essensiële voedingselemente (blaarontledings), vrugset, die verhouding van groot vrugte tot kleiner vrugte, fisiese en chemiese kwaliteite van die vrugte en die raklewe daarvan is ge-evalueer. Die toediening van B teen hoër peile het die opname van Ca ten koste van K bevoordeel. Die beste resultate ten opsigte van vrugset, vrugontwikkeling, vrugkleur en die houvermoë (raklewe) van die vrugte is verkry teen 'n B-toedieningspeil van 0.16 mg.l'. Vir die derde gedeelte van die ondersoek is die tweede tros van dieselfde aanplanting gebruik. Die invloed van die vier B-voedingspeile, relatiewe humiditeit (RH) van die omgewing rondom die tros en trosvibrasie is ondersoek. Die tweede bloeiwyse is met 'n deursigtige plastieksakkie bedek. Droë {dO% relatiewe humiditeit (RH)}, normale {60-75% RH} en vogtige {85-97% RH} lug is teen 50 ml min-1 oor die tros gestuur. Trosvibrasie is as derde faktor teen twee peile gebruik deur trosse daagliks met 'n elekriese vibreerder ("polli-bee') te vibreer. Die aantal blomme per tros, vrugte per tros, vrugset, trosmassa (opbrengs), vrugmassa, aantal sade, vrugmassa per saad en blom-end-verrotting (BER) is ge-evalueer. Die toediening van hoër B-voedingspeile, 60-75% RH lug en trosvibrasies het vrugmassa, trosmassa en vrugset bevoordeel. Hoë lugvog het die omvang van BER verhoog, waarskynlik weens 'n gebrek aan transpirasie vanaf die vrugoppervlakke wat aanleiding tot 'n beperking in translokasie van Ca kon gee.

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