| Summary: | Thesis (MScAgric)--University of Stellenbosch, 2003. === 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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