Nwogha, Jeremiah Sunday (2014-12)
ABSTRACT ENGLISH: Canola is increasingly becoming an important economic field crop in South Africa, because it can be used to produce high quality cooking oil and margarine, animal feed, biofuel and in crop rotation systems to break the disease cycle and improve weed management. Effect of temperature on phenological responses with respect to required number of days, growing degree days, photothermal units to specific growth stages, growth rate, as well as vegetative and reproductive growth of canola were studied under controlled conditions.
Seven canola cultivars selected from early and mid-maturing groups of canola cultivars, presently planted in the Western Cape canola production area, were grown in 3 litre plastic bags filled with a mixture of sand and compost at ratio of 1:1 and irrigated with fully balanced nutrient solution at EC=2.0 in two glasshouses at night/day temperature regimes of 10/15oC and 15/20oC. Number of days, growing degree days (GDD) and photothermal units (PTU) from planting to seedling emergence, first true leaf appearance, visible flower buds, first flower opening, seed ripening and seed physiological maturity were recorded. Plant heights were measured at 14 day intervals from 28 to 84 days after planting (DAP). Plants were sampled for leaf area (LA) and above ground dry mass (DM) at budding, flowering and seed physiological maturity. Plant growth rates (PGR) from planting to budding, from budding to flowering and from flowering to physiological maturity were calculated. Relative growth rates (RGR) and net assimilation rates (NAR) from budding to flowering and from flowering to physiological maturity were also calculated. Days after planting, GDD and PTU at budding, flowering and physiological maturity were correlated with leaf area, dry mass, number of pods plant-1 and pod dry mass plant-1 at budding, flowering and physiological maturity to determine whether there were relationships between the variables.
The study showed that by increasing night/day temperature from 10/15⁰C to 15/20⁰C plant height, number of leaves plant-1 at budding stage, leaf area at budding , plant growth rate (PGR) from planting to budding stage and relative growth rate (RGR) from budding to flowering stage were increased. However, PGR from budding to physiological maturity, RGR from flowering to physiological maturity, net assimilation rate (NAR) from budding to flowering stage, leaf area at flowering and physiological maturity stages , as well as number of flower stems, number of pods plant-1, above ground total dry mass at flowering and physiological maturity stages were decreased. Pod dry mass at physiological maturity decreased by 22.24% to 40.35% for different cultivars which clearly demonstrated the sensitivity of canola cultivars to increasing night/day temperatures.
By increasing the mean daily mean temperature from 12.5⁰C (10/15⁰C night/day) to 17.5⁰C (15/20 ⁰C night/day) the duration of the period from planting to seedling emergence as well as the vegetative and reproductive growth stages were decreased. With the exception of the vegetative growth stage, GDD and PTU requirements to reach specific growth stages increased with an increase in temperature. Plant growth parameters such as dry mass, leaf area, number of pods plant-1 and pod dry mass plant-1 at specific growth stages showed a positive correlation with the number of days needed to reach that growth stage, but not with GDD or PTU requirements. Although the responses of cultivars to increasing temperatures did differ for most parameters measured, responses did not always correlate with the maturity grouping of cultivars, suggesting that responses to temperature may to a large extent be determined by the genetic make-up (breeding company) of cultivars. These results indicate that number of days, GDD and PTU requirements to reach physiological maturity may be used to describe the cultivar maturity groupings, but because of the effect of temperature and day length, GDD and PTU should be more accurate.
AFRIKAANSE OPSOMMING: Canola se waarde as ekonomies belangrike akkerbou-gewas in Suid-Afrika het die afgelope aantal jare skerp toegeneem, omdat dit gebruik kan word om hoë kwaliteit kook-olie en margariene asook bio-brandstowwe en dierevoere, te vervaardig. In wisselboustelsels kan dit gebruik word om die siekte-ketting te breek en onkruidbeheer te vergemaklik. In hierdie studie is die invloed van temperatuur op die fenologiese reaksies van canola in terme van die aantal dae, gewasgroeidae en fototermiese eenhede, benodig om spesifieke groeistadiums te bereik, asook die invloed op groeitempo, vegetatiewe- en reproduktiewe groei onder gekontroleerde toestande nagevors.
Sewe canola cultivars vanuit die kort en mid-groeiseisoen volwassenheidsgroepe wat tans in die Weskaap verbou word is geplant in 3-liter plastiek houers gevul met „n 1:1 sand: kompos mengsel as groeimedium en besproei met „n volledig gebalanseerde voedingsoplossing met EC=2.0. Twee glashuise met nag/dag temperature van onderskeidelik 10/15oC en 15/20oC is vir hierdie doel gebruik. Die aantal dae, gewasgroeidae (GGD) en fototermiese eenhede (FTE) wat vanaf plant tot saailingverskyning; eerste volwasse blaarverskyning; eerste blomknop verskyning; eerste blom; saad verkleuring en fisiologies volwasse stadiums vereis word, is bepaal. Plant lengte is gemeet met 14-daagse tussenposes vanaf 28 tot 84 dae na plant. Plante is gemonster is tydens die eerste blomknopverskyning asook blom- en fisiologies volwasse stadiums om blaaroppervlakte (BO) en droëmassa (DM) te bepaal. Plant groeitempos (PGT) vanaf plant tot blomknopverskyning; blomknopverskyning tot blom en vanaf blom tot fisiologiese volwasse stadium is bereken. Relatiewe groeitempos (RGT) en netto-assimilasietempos (NAT), is bereken vanaf blomknopverskyning tot blom en vanaf blom tot fisiologiese volwasse stadium. Die aantal dae vanaf plant, asook GGD en FTE benodig om blomknopstadium, blomverskyning en fisiologies volwasse stadiums te bereik, is gekorreleer met BO en DM plant-1 asook die aantal peule en peulmassa plant-1 tydens genoemde groeistadia om moontlike verwantskappe te bepaal.
Die studie het getoon dat deur die nag/dag temperatuur te verhoog vanaf 10/15⁰C tot 15/20⁰C, plant lengte, aantal blare en BO plant-1 tydens blomknopverskyning, asook PGT vanaf plant tot blomknopverskyning en RGT van blomknopverskyning tot blomstadium, toeneem. Daarteenoor het PGT van blomknopverskyning tot fisiologies volwassenheid, RGT van blom tot fisiologies volwassenheid, asook NAT van blomknopverskyning tot blomstadium en BO tydens blom en fisiologies volwasse stadium, afgeneem. Reproduktiewe ontwikkeling soos gemeet aan die aantal bloeistele, peule plant-1 en peulmassa plant-1 is ook benadeel deur genoemde verhoging in temperatuur. Die afname in peulmassa het gewissel tussen 22.24% en 40.35% vir verskilende cultivars en is „n duidelike aanduiding van die verskillende canola cultivars se gevoeligheid teenoor toenemende nag/dag temperature.
Die toename in gemiddelde nag/dag temperatuur vanaf 12.5⁰C (10/15⁰C) tot 17.5⁰C (15/20 ⁰C) het die aantal dae vanaf plant tot saailing verskyning asook die vegetatiewe en reproduktiewe groei fases verkort. Met die uitsondering van die vegetatiewe groei fase, het die GGD and FTE vereistes om spesifieke groeistadiums te bereik toegeneem met „n toename in temperatuur. Plant komponente soos DM, BO, aantal peule plant-1 en peulmassa plant-1 tydens spesifieke groeistadia het „n positiewe verwantskap getoon met die aantal dae wat benodig is om spesifieke groeistadiums te bereik, maar sodanige verwantskap is nie bevestig met GGD en FTE vereistes. Hoewel die reaksie van verskillende cultivars teenoor „n toename in temperatuur vir die meeste gemete plantkomponente verskil het, het die reaksie nie altyd verband gehou met die volwassenheidsgroepering van die cultivars. Dit wil dus voorkom asof die reaksie teenoor temperatuur tot „n groot mate ook verband hou met die genetiese samestelling van die cultivar soos bepaal deur die telingsmaatskappy.
Hierdie resultate toon dat die aantal dae, GGD en FTE wat vereis word om fisiologiese volwassenheid te bereik gebruik kan word om die cultivar se volwassenheidsgroepering te beskryf maar dat GDD en FTE waarskynlik meer akuraat sal wees weens effek van temperatuur en daglengte op die ontwikkkeling van cultivars.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95883