Seed germination, tree growth and flowering responses of Moringa Oleifera lam. (horseradish tree) to temperature

Moringa oleifera Lam. is a tree with great potential as it is fast growing and drought tolerant. Amongst the tree’s multitude of benefits, it can also be used to produce a biodiesel fuel. However, prior to the establishment of commercial plantations, all cultivation aspects of this promising tree have to be understood. Temperature is a significant climatic factor influencing both geographical plant distribution and growth, and since M. oleifera trees are naturally found in tropical climates around the world, the extent of their adaptability to cooler climates was the main objective of this study. Trees were cultivated from seed and germinated in a controlled greenhouse environment at the Experimental Farm of the University of Pretoria. After germination, 50% of the seedlings were hardened-off by placing them outside under ambient growing temperatures, while the rest remained inside the greenhouse. With trial commencement, 132 of both the hardened and non-hardened seedlings were planted into 10 ℓ plastic bags and randomly placed into three temperature-controlled greenhouses, each with a different fluctuating night/day temperature regime namely; 10/20°C ± 2°C, 15/25°C ± 2°C and 20/30°C ± 2°C. In addition, half the trees within each temperature regime were treated with the growth regulator paclobutrazol to determine its effect on growth/flowering at different temperatures. During the 224-day trial period, biweekly measurements of tree height, stem diameter and leaf area estimates of each individual tree within all three temperature regimes were taken. Despite germination percentages being slightly higher at the low 10/20°C regime, the MGT, germination rate, uniformity and seedling growth were superior at the higher 20/30°C regime. The temperature induced seed dormancy at the 20/30°C regime, could be overcome by an incubation period at lower temperatures, as fewer instances of seed dormancy were observed at the 10/20°C regime. The increase in temperature resulted in significant (P≤0.05) growth rate increases of over 650% between the 10/20°C and 20/30°C and 250% between the 10/20°C and 15/25°C night/day temperature regimes. In addition, the 20/30°C temperature treatment, although fluctuative, consistently had the highest leaf area over the entire trial period. Hardening-off of trees during the seedling stage, significantly (P≤0.05) increased the final tree height by 3.09X, 1.44X and 1.23X, compared to their non hardened-off counterparts under the 10/20°C, 15/25°C and 20/30°C temperature regimes respectively. Leaf thickness decreased by a significant (P≤0.05) 43.1% with increase in temperature between the 10/20°C and 20/30°C regime, mostly due to a thinner mesophyll layer. The efficacy of paclobutrazol on M. oleifera growth was found to be temperature dependant, reducing growth at 10/20°C, while increasing growth at both the higher 15/25°C and 20/30°C regimes. Flowering however remained unaffected by paclobutrazol. The highest instances of flowering and pollen viability were observed at the 15/25°C regime. The absence of inflorescence induction at the 20/30°C regime was responsible for the reduced flowering, signifying the necessity of vernalization prior to flowering. Even though all the results confirm the preference of M. oleifera trees towards a tropical climate, satisfactory growth with possibly improved flowering during the hot summer months in certain sub-tropical climates is achievable. CopyrightDissertation (MSc(Agric))--University of Pretoria, 2010.Plant Production and Soil Scienceunrestricte

Flowering, fruit growth and intracellular storage component formation in developing Moringa Oleifera Lam. seed as influenced by irrigation

Moringa oleifera has become increasingly popular as an industrial crop in recent times due to its multitude of useful attributes as a water purifier, nutritional supplement and biofuel feedstock. Besides this, Moringa oleifera has also demonstrated high tolerance to sub-optimal growing conditions, particularly towards drought. As a result, the current and anticipated cultivation areas of this tree are in medium to low rainfall areas. To what extent this drought tolerance was at the expense of reproductive development remained unclear. This study therefore aimed to assess the effect of different irrigation rates on flowering, fruit growth and storage compound synthesis of Moringa oleifera. Established Moringa oleifera trees were subjected to three different irrigation treatments simulating total annual rainfall amounts of 900 mm/annum (900IT), 600 mm/annum (600IT) and 300 mm/annum (300IT). Irrigation was administered through surface drip irrigation, while semi-weekly soil water measurements using a neutron probe were performed at several depths to ascertain differences between treatments. After having exposed trees to the different irrigation rates for nine months, the treatment effects were assessed. Firstly, individual inflorescences from each treatment were tagged during floral initiation and monitored throughout until fruit set. Flower bud initiation was 65.3% higher at the 300IT and 4.6% higher at 600IT compared to the 900IT. Fruit set however, was 22.0% lower for the 300IT and 4.4% lower for 600IT, compared to the 900IT. Floral abortion, reduced pollen viability as well as moisture stress in the style were contributing factors to the reduction in fruiting/yield observed at the 300IT. Subsequently, microscopic studies of developing seed were performed to better comprehend storage compound biosynthesis and accumulation throughout seed growth. From these studies, the endosperm was found to be nuclear, becoming cellular at a fruit diameter of ±6 mm from the micropylar side towards the developing embryo. At a fruit diameter of ±8 mm the cellular endosperm had covered the entire inner integument, which coincides with the developing embryo reaching the globular stage. Cotyledon development commenced at a fruit diameter of ±12 mm and continued up until ±24 mm. At the end of this phase the cotyledons had filled the entire seed coat, while the unicellular epidermal layer of the inner integument remained distinctly visible between the cotyledons and the testa. Fruit growth measurements throughout the first 60 days after flowering (DAF), revealed a significant reduction in fruit growth rates and final fruit size with decrease in irrigation rate. The number of mature fruit, average seed count and time to maturity however, increased with the rate of irrigation. Average seed mass also increased from the 300IT to the 600IT, but decreased again between the 600IT and the 900IT. As photosynthesis is central to plant growth and development, the extent to which the irrigation treatments affected photosynthesis and ultimately tree performance had to be assessed. Photosynthesis measured during the vegetative, flowering and fruit development stages revealed not only a reduction in photosynthetic activity throughout the growing season, but also with reduction in irrigation rate. Lower photosynthetic rates were primarily as a result of stomatal (conductance and SI) and non-stomatal (possible RuBP regeneration, ATP synthesis and mesophyll conductance) limitations, while the decreases observed throughout the growing season were as a result of diminishing leaf chlorophyll concentrations. Harvested fruit were categorized according to their diameter (Ø0 mm - 28 mm) at 2 mm increments and the compositional changes monitored at each irrigation treatment. Starch was the first to accumulate during the initial histo-differentiation phase (Ø0 mm - 12 mm), while both oil and protein levels remained comparatively low. During the subsequent expansion phase (Ø12 mm - 24 mm) however, stored starch was remobilized and used in oil biosynthesis, thereby reducing the starch content percentage. Most of the oil and protein reserves were synthesized during this phase. As fruit reached their final maturation phase (Ø24 mm - 28 mm), the average oil content percentage was 24.8%, while the protein content percentage was 24.7% and the starch content percentage was 8.8%. The different irrigation treatments did not influence the final content percentage of the seed components as much as it did affect the time and rate of their synthesis throughout seed development. By using both light and electron microscopy in conjunction with histochemical staining techniques, the intracellular locality of storage compounds as well as the initiation of their synthesis could be determined. The storage compound detecting stains were; Sudan III (oil), Light Green SF (protein), Orange G (protein) and Periodic Acid-Schiff’s reagent (starch). During early seed development (fruits of 8 mm in diameter), starch was synthesized by the plastids and transiently stored in the cell periphery. Protein and oil bodies were synthesized in association with the endoplasmic reticulum and finally stored in the centre of cotyledonous cells. Protein and oil body formation only commenced in significant amounts inside cotyledons at a fruit diameter of ±14 mm. Intracellular protein bodies were largest at between ± 5 μm to 8 μm in diameter while oil bodies ranged from ± 0.2 μm to ± 1 μm in size. Identification of numerous intracellular compounds using histochemical staining proved very effective. This prompted further investigation into whether storage compound content could be quantified from stained sections using digital imaging software. The percentage stain coverage area calculated using Adobe® Photoshop® was compared to the content of the same compound determined analytically at the corresponding developmental stage. The best correlation between measured seed storage compound and stain coverage was observed for the protein and oil detecting stains, Orange G and Sudan III throughout seed growth. A stage specific factor based on seed mass was however necessary in order to estimate storage compound content (g) from image analysis results. Conclusively, results from this study suggest that moderate water stress prior to flower development encourages floral initiation. Irrigation should however be resumed once flowering has commenced to ensure good pollination, fruit set and yield. Between the fruit diameters of 12 - 24 mm, the majority of storage reserves were synthesized and as a result this stage of fruit development was found most susceptible to water stress. Increased irrigation rates not only shortened the time to storage compound synthesis initiation but also increased their synthesis rate. Reduced irrigation in contrast, delayed the onset of oil biosynthesis, and as a result starch levels continued to increase reaching much higher levels prior to its remobilization during oil biosynthesis. The highest oil content percentage and seed mass at maturity were measured at the intermediate irrigation treatment. Along with decent flowering and fruit set, 600 mm/annum appeared to be the most suitable irrigation/rainfall amount for Moringa oleifera. This irrigation amount was low enough to initiate floral initiation, but also sufficient to sustain the subsequent seed developmental processes. Digital image stain quantification proved reasonably effective for simple comparisons between storage compound contents at different developmental stages. Differences between storage compound contents of the same developmental stage from different irrigation treatments were however, not as clearly distinguishable using this method. Although the success of digital image analysis might be stain dependant, it certainly is a cost effective technique for compound content estimation. This study enabled the identification of sensitive stages throughout fruit/seed development, by providing detailed insight into oil, starch and protein biosynthesis. Ultimately these findings provide current and prospective Moringa growers with recommendations to ensure suitable site selection as well as irrigation management guidelines.Thesis (PhD)--University of Pretoria, 2014.Plant Production and Soil SciencePhDUnrestricte

Bud development, flowering and fruit set of Moringa oleifera Lam. (Horseradish Tree) as affected by various irrigation levels

Moringa oleifera is becoming increasingly popular as an industrial crop due to its multitude of useful attributes as water purifier, nutritional supplement and biofuel feedstock. Given its tolerance to sub-optimal growing conditions, most of the current and anticipated cultivation areas are in medium to low rainfall areas. This study aimed to assess the effect of various irrigation levels on floral initiation, flowering and fruit set. Three treatments namely, a 900 mm (900IT), 600 mm (600IT) and 300 mm (300IT) per annum irrigation treatment were administered through drip irrigation, simulating three total annual rainfall amounts. Individual inflorescences from each treatment were tagged during floral initiation and monitored throughout until fruit set. Flower bud initiation was highest at the 300IT and lowest at the 900IT for two consecutive growing seasons. Fruit set on the other hand, decreased with the decrease in irrigation treatment. Floral abortion, reduced pollen viability as well as moisture stress in the style were contributing factors to the reduction in fruiting/yield observed at the 300IT. Moderate water stress prior to floral initiation could stimulate flower initiation, however, this should be followed by sufficient irrigation to ensure good pollination, fruit set and yield

Irrigation amounts affect the compositional changes of Moringa oleifera seeds throughout different developmental stages

The compositional development of Moringa oleifera seed across a range of growth stages was monitored at three irrigation treatments, simulating total annual rainfall of 900 mm, 600 mm and 300 mm/annum over two consecutive growing seasons (24 months). Fruit developmental stages were categorized according to fruit diameter (0 mm – 28 mm) at 2 mm increments. Starch was the first to accumulate during the initial histo-differentiation phase (fruit diameters of 0 mm-12 mm), while oil levels remained comparatively low. During the subsequent expansion phase (fruit diameters of 12 mm – 24 mm) however, stored starch was mobilized and used in oil biosynthesis, reducing the starch content. The bulk of oil and protein were synthesised throughout this phase with their content increasing sigmoidally. As the seed moisture content decreased during the final maturation phase (fruit diameters of 24 mm – 28 mm), the average oil content reached 24.8%, while the protein contents were 24.8% and the starch contents were 8.7%. The different irrigation treatments had less of an effect on the final starch, oil and protein content than on the time and rate of their synthesis throughout seed development. Higher irrigation levels principally favoured oil biosynthesis. The highest final oil contents were measured at the intermediate irrigation treatment (600 mm/annum), suggesting that both lower and higher irrigation levels could possibly reduce final oil contents. The reduction in irrigation amount delayed the onset of oil biosynthesis and as a result the starch content reached higher levels prior to its remobilization during oil biosynthesis.© 2014 Friends Science Publishershttp://www.fspublishers.orgam201