Greenhouse production of watermelon (Citrullus lanatus)

Kuvare, Uparura S. K. (Uparuru Silvanus Karl) (2005-03)

Thesis (MSc)--Stellenbosch University, 2005.

Thesis

ENGLISH ABSTRACT: Various researchers have determined that salinity causes several kinds of damage to plants such as germination inhibition, metabolic disturbances, yield reduction and quality losses. However, the severity of salt damage has been found to be dependent on the cultivar, level of salinity, period of exposure to salinity, and the growth stage of the plant. An understanding of the severity of salinity and its potential negative impacts on crops is essential to optimise production. Knowledge of seed vigour, expressed as germination percentage and germination rate at the optimum temperature for germination, would provide growers with valuable information to measure and compare the viability of seed lots. A study was done where fresh and aged seeds of two watermelon cultivars were investigated in germination tests under laboratory conditions at four salinity levels and five temperature regimes. The best germination was achieved at 4 mS cm-1 for both cultivars, Odem and Paladin. At 8 mS cm-I, the germination percentage for Paladin was 31% better than for Odem. The germination time for aged Odem seeds was significantly delayed at this EC 8 level but ageing of Paladin seeds had no detrimental effect at this EC level. Paladin germinated significantly better than Odem at the relatively low temperature range of I5-20°C, indicating that it is well-adapted for early planting. A new plant growing system, using vertical training of two shoots was tested in a greenhouse, aiming to optimise the growth regulating capabilities of this crop environment. Traditional watermelons are open-field planted in rows at low densities. Even with this plant spacing, by harvesting time the vines are spread in such a way that the foliage laterally covers the inter-row spacing, making cultivation practices such as spraying, weeding and harvesting difficult and almost impossible. The production of greenhouse crops is advantageous, but involves a number of cultural inputs and techniques for optimum yields. The effects of plant pruning systems and salinity levels on watermelon cultivars (Odem and Paladin) in a low-cost greenhouse were studied using a drain-to-waste fertigation system. Changing the nutrient solution from a low salinity level (EC 4 mS cm1) during vegetative growth to EC 4 mS cm-I after pollination, did not reduce fruit mass, but significantly increased the sugar yield of Odem, the icebox-type cultivar. Excessive pruning (less leaves per shoot) was more efficient with low salinity levels than at a high salinity level. Moderate pruning (more leaves per shoot) represented a good system, producing fruits of lesser weight and acceptable quality.

AFRIKAANSE OPSOMMING: Verskeie navorsers het reeds die skadelike gevolge van brak toestande op ontkieming, plant metabolisme, opbrengs en kwaliteit van gewas plante ondersoek. Die omvang van die skade kan deur kultivars, die konsentrasie soute, die periode van blootstelling asook plante se groeistadium bepaal word. 'n Goeie begrip van die potensiële skadelikheid van hoë sout konsentrasies op gewasse is nodig om produksie te optimaliseer. Inligting oor die kiemkragtigheid van saad, uitgedruk as die persentasie ontkieming asook die ontkiemingstempo, is vir kwekers nodig ten einde te verseker dat goeie saad gebruik kan word. 'n Ondersoek is gedoen waar vars asook verouderde saad van twee waatlemoen kultivars onder laboratorium toestande by vier sout peile en vyf temperature ontkiem is. Die beste ontkieming vir beide kultivars, Odem en Paladin, is gevind waar die elektriese geleiding (Eï,') 4 mS cm-1 was. Teen 8 mS cm-1 was die persentasie ontkieming vir Paladin 31% beter as vir Odem. Veroudering van Odem saad het 'n betekenisvol swakker ontkiemingstempo met'n Ee van 8 mS cm-1 getoon terwyl verouderde Paladin saad nie by hierdie Ee swakker vertoon het nie. Paladin het by die relatief lae temperatuur sone van 15-20oe betekenisvol beter as Odem saad ontkiem wat daarop dui dat dit vir vroeë aanplantings geskik is. 'n Nuwe produksiestelsel, waar twee lote per plant vertikaal in 'n V-vorm opgelei is, is in 'n kweekhuis getoets in 'n poging om die groeiregulerende potensiaal van so 'n omgewing te optimaliseer. Waatlemoene word tradisioneel in rye teen 'n lae plantdigtheid in veldaanplantings verbou. Met so 'n praktyk ontwikkel daar soveel ranke tussen die rye dat praktyke soos onkruid beheer, plaagbeheer en oes bemoeilik word. Die produksie van gewasse in kweekhuise hou voordele in maar 'n aantal insette en spesiale tegnieke is nodig vir optimum opbrengs. Die invloed van snoeipraktyke en soutpeile is met twee waatlemoen kultivars (Odem en Paladin) in 'n lae-koste kweekhuis ondersoek deur 'n sisteem te gebruik waar voedingsoplossings in vry dreinerende sakke met saagsels gedrup is. Waar die Ee van die voedingsoplossing voor vrugset 2 mS cm-1 was en toe vir die periode van vrugontwikkeling tot 4 mS cm-1 verhoog is, het geen vrugverkleining by Odem gevolg nie terwyl die suikeropbrengs wel verhoog het. Oormatige verwydering van blare was minder skadelik met 'n lae EC as waar die EC hoog was. 'n Matige snoeiproses met meer blare per loot, het 'n goeie produksie van aanvaarbare vruggrootte en 'n goeie kwaliteit verseker.

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