Alfred Odindo

Salicylic acid and methyl jasmonate improve chilling tolerance in cold-stored lemon fruit (Citrus limon).

Chilling injury (CI) is associated with the degradation of membrane integrity which can be aligned to phenolic oxidation activated by polyphenol oxidase (PPO) and peroxidase (POD), enzymes responsible for tissue browning. Phenylalanine ammonia-lyase (PAL) is a further enzyme prominent in the phenolic metabolism that is involved in acclimation against chilling stress. It was hypothesized that treatment with methyl jasmonate (MJ) and salicylic acid (SA) may enhance chilling tolerance in lemon fruit by increasing the synthesis of total phenolics and PAL by activating the key enzyme regulating the shikimic acid pathway whilst inhibiting the activity of POD and PPO. Lemon fruit were treated with 10μM MJ, 2mM SA or 10μM MJ plus 2mM SA, waxed, stored at -0.5, 2 or 4.5°C for up to 28 days plus 7 days at 23°C. Membrane integrity was studied by investigating membrane permeability and the degree of membrane lipid peroxidation in lemon flavedo following cold storage. The 10μM MJ plus 2mM SA treatment was most effective in enhancing chilling tolerance of lemon fruit, significantly reducing chilling-induced membrane permeability and membrane lipid peroxidation of lemon flavedo tissue. This treatment also increased total phenolics and PAL activity in such tissue while inhibiting POD activity, the latter possibly contributing to the delay of CI manifestation. PPO activity was found to be a poor biochemical marker of CI. Treatment with 10μM MJ plus 2mM SA resulted in an alteration of the phenolic metabolism, enhancing chilling tolerance, possibly through increased production of total phenolics and the activation of PAL and inhibition of POD.

Genetic diversity of bottle gourd (Lagenaria siceraria (Molina) Standl.) landraces of South Africa assessed by morphological traits and simple sequence repeat markers

Bottle gourd (Lagenaria siceraria (Molina) Standl.) is an important crop in rural communities in South Africa but it remains under-researched. The objective of this study was to assess the genetic diversity present amongst bottle gourd landraces grown by smallholder farmers in South Africa using morphological traits and 11 selected polymorphic simple sequence repeat (SSR) markers. Marked phenotypic differences were observed amongst bottle gourd landraces. Principal component analysis on quantitative traits identified seven principal components, which accounted for 87% of the total variation. Number of alleles varied from 3 to 9 with a mean of 6 per SSR locus. Number of effective alleles ranged from 1.99 to 6.72 with a mean of 3.75. Shannons information index varied from 0.95 to 2.01 with a mean of 1.41. Expected heterozygosity values ranged from 0.5 to 0.87 with a mean of 0.71 with polymorphic information content values of 0.5 to 0.85 and a mean of 0.7. Morphological traits and SSR marker analyses showed a significant correlation in clustering the landraces. The present study demonstrated the presence of genetic diversity amongst bottle gourd landrace collections from South Africa useful for strategic improvement, direct production or conservation.

Yield-based selection indices for drought tolerance evaluation in selected bottle gourd [Lagenaria siceraria (Molina) Standl.] landraces

ABSTRACT Bottle gourd is an important crop in arid and semi-arid tropics where recurrent drought is the major constraint to crop production. Identification of drought-tolerant bottle gourd genotypes is fundamental to enhance productivity and for effective breeding and conservation. The objective of this study was to determine drought tolerance of a diverse set of bottle gourd landraces and to identify promising genotypes for direct production or breeding. A field study was conducted using a 12 × 2 factorial experiment involving 12 bottle gourd landraces under drought-stressed (DS) and non-stressed (NS) conditions. Significant differences were observed among bottle gourd landraces with respect to fruit yield under DS and NS conditions. The mean fruit yield under DS and NS conditions was 8.75 and 22.4 t ha−1, respectively. Drought stress reduced fruit yield by 62%. Correlation and principal component analyses revealed the significance of yield-based indices of drought tolerance, such as tolerance index, geometric mean productivity, stress tolerance, mean productivity, yield index and harmonic mean, which allowed discrimination of drought-tolerant bottle gourd landraces. Such landraces as BG-79, BG-31, BG-67, BG-52, BG-78 and GC were identified useful for drought tolerance breeding or rootstock development programs.

Estimating Swiss chard foliar macro- and micronutrient concentrations under different irrigation water sources using ground-based hyperspectral data and four partial least squares (PLS)-based (PLS1, PLS2, SPLS1 and SPLS2) regression algorithms

Swiss chard nutrients were estimated under trial conditions using hyperspectral data.Partial least squares (PLS1 and PLSR2) and sparse PLS1 and PLS2 regressions performance was compared.SPLS-based regression methods significantly reduced the dimensionality in hyperspectral data.Macronutrients estimation models were more accurate than micronutrients estimation ones. Timely information on crop foliar nutrient content provides a measure of crop nutritional and vitality status. Growers and farm managers use such information for precision crop management such as an appropriate fertilizer application to correct for any crop nutrient deficiencies at identified hotspots. Foliar heavy nutrient content could also be a direct indicator of crops having been polluted from the surroundings, which may be a result of heavy metals absorbed from, among others, contaminated soils and waste water. In the present study, we explored the potential use of four partial least squares (PLS)-based regression algorithms for estimating foliar Swiss chard macro- and micronutrient concentrations using ground-based hyperspectral data under three treatments; i.e. rainwater+fertilizer (R+F), tap water+fertilizer (T+F), and treated wastewater (W). Swiss chard canopy-level hyperspectral measurements under these three treatments were collected using a handheld spectroradiometer 2.5months after sowing. The reflectance spectra were normalized to their first-order derivatives. The concentrations of three Swiss chard foliar macronutrients (NPK) and three micronutrients (Zn, Cu and Fe) under the three treatments were determined. Regression models for estimating macro- and micronutrient concentrations were then derived using PLS1 and sparse PLS1 methods, while the potential simultaneous estimation of the macronutrient as well as micronutrient concentrations was explored using the PLS2 and SPLS2 regression approaches. Results showed that high variances in the macro- and micronutrient concentrations can be explained by the four regression models under the three treatments (R2train ranged between 0.73 and 0.99), except when P, Zn and Cu concentrations were estimated using the PLS2-based models under the three treatments (R2train ranged between 0.08 and 0.68) and Fe concentration using SPLSR1 under W treatment (R2train=0.64). Our results further showed that Swiss chard foliar N (RMSE=1.67%) concentration under R+F treatment and Fe (RMSE=7.83%) concentration under the T+F treatment most accurately estimated macro- and micronutrients. Our study also showed that the Swiss chard foliar macronutrient concentrations were more accurately estimated compared to micronutrient concentrations and PLS2 outperformed the PLS1 based regression model. The results of the current study pave the way for developing an effective foliar nutrient estimation routine suitable for monitoring Swiss chard nutrient status under different treatments.

Correlation and path coefficient analyses of qualitative and quantitative traits in selected bottle gourd landraces

ABSTRACT Knowledge on associations between yield and related traits is vital to improve selection efficiency in cultivar improvement. This study determined the relationships among qualitative and quantitative traits in bottle gourd landraces using simple correlation and path analyses. Results showed significant and positive correlations between the number of fruits per plant (NFPP) with number of male flowers (NMF), number of female flowers (NFF), plant height (PHT) and number of branches (NB). Number of seeds per fruit (NSPF) positively correlated with PHT, NMF, NFF, NB and fruit weight (FW). Fruit texture, degree of warts (DW), fruit shape (FS), and degree of neck bending, stem-end fruit shape and fruit neck length (FNL) had significant negative correlations with NFPP or NSPF. Path analysis revealed high direct path coefficient value (0.96) between FW and NSPF. Also, positive direct path coefficient value (0.92) was exhibited between NFF and NFPP. Relatively high direct path coefficient value (0.47) was exhibited between DW and NSPF. This study demonstrated that selection for increased FW and NFF may improve genetic gain in seed yield and fruit yield in bottle gourd breeding. Using the above analyses, the following landraces such as BG-06, BG-07, BG-09, BG-11, BG-13, BG-24 and BG-67 were selected for breeding.

The cost-effectiveness of using latrine dehydrated and pasteurization pellets and struvite: Experimental evidence from South Africa

Faecal sludge and urine can be recycled and processed into usable fertilizer products such as the latrine dehydrated and pasteurization (‘LaDePa’) pellets and struvite, respectively. To quantitatively determine the financial cost effectiveness of using LaDePa and struvite, a study was conducted using experimental data for maize, wheat and sugarcane production in KwaZulu-Natal, South Africa. The costs per hectare of using these potentially new human waste-based fertilizer products to meet crop nutrient requirements for the selected crops and achieve the optimum target yields were determined and compared with the costs per hectare of using recommended commercial fertilizers. The financial feasibility was determined using partial budgets. The results showed that both LaDePa and struvite are financially viable if used in place of the organic fertilizer studied. LaDePa is even more cost effective if it is used as a soil amendment to improve soil physical properties.

Physiological responses of irrigated wheat (Triticum aestivum L.) genotypes to water stress

ABSTRACT The recent drought in South Africa has reduced the production of both dryland and irrigated wheat. This study evaluated physiological traits of irrigated wheat genotypes in response to water stress (WS) imposed at different growth stages. A 8 × 2 × 3 [(genotypes) × (water treatmets; stresses and non-stressed) × (growth stages; tillering, flowering and grain filling)] factorial experiment based on a randomised complete block design with three replicates was conducetd. In general, the rate of photosynthesis was unaffected by WS except for genotypes LM43 at tillering and LM98 at grain filling. Stomatal conductance (SC) and transpiration rate (Tr) followed the same treand except for genotype LM35 which reduced its SC and Tr significantly at grain filling. Instantaneous waster use efficiency (IWUE) of genotype LM35 and LM57 was unaffected (p > 0.05) by WS at tillering but at flowering stage it was affected. However, at grain filling IWUE was affected (p < 0.05) in genotypes LM35, ML57, LM79 and LM 98. The relative water content was unaffected at tillering except for LM35 and LM47 genotypes whereas at flowering LM57, ML79, LM83 and LM98 were affected. These results indicate some degree of drought tolerance of these genotypes at different growth stages.

Leaf gas exchange and water-use efficiency of dry-land wheat genotypes under water stressed and non-stressed conditions

ABSTRACT The objective of this study was to determine drought tolerance characteristics of dryland wheat genotypes based on leaf gas exchange and water-use efficiency in order to identify promising genotypes for drought tolerance breeding. Physiological responses of ten genetically diverse wheat genotypes were studied under non-stressed (NS) and water stressed (WS) conditions using a 2 × 10 factorial experiment replicated 3 times. A highly significant water condition × genotype interaction (P < 0.001) was observed for photosynthetic rate (A), ratio of photosynthetic rate and internal CO2 concentration (A/Ci), ratio of internal and atmospheric CO2 (Ci/Ca), intrinsic (WUEi) and instantaneous (WUEinst) water-use efficiencies suggesting genotypic variability among wheat genotypes under both test conditions. Principal component analysis (PCA) identified three principal components (PC’s) under both test conditions accounting for 84% and 89% of total variation, respectively. Bi-plot analysis identified G339 and G344 as drought tolerant genotypes with higher values of A, T, gs, A/Ci, WUEi and WUEinst under WS condition. The current study detected significant genetic variation for drought tolerance among the tested wheat genotypes using physiological parameters. Genotypes G339 and G344 were identified to be drought tolerant with efficient A, T, gs, A/Ci and water-use under water stressed condition.

Characterisation of pigeon pea (Cajanus cajan) landraces grown in two climatic zones in KwaZulu-Natal province, South Africa

Pigeon pea is an important legume in arid and semi-arid areas of the Sub-Saharan Africa. Knowledge of adaptation characteristics of genotypes would significantly enhance its production in diverse environments of the region. Field experiments were conducted at two sites, namely Makhathini and Newlands Research Stations, both in KwaZulu-Natal province, South Africa, to assess the variation in agronomic characteristics among six local landraces obtained from smallholder farmers. The six landraces were categorised based on seed coat colour according to farmers’ perception. Significant differences were observed among landraces with respect to plant height and time to 50% flowering, indicating phenotypic variability. The Light Brown-seeded landrace planted at Newlands flowered earlier (106 d after planting). The Dark Brown-seeded landrace flowered within 150 d at Makhathini and reached physiological maturity in 185 d, earlier than other landraces. The results of principal component analysis suggested that yield of the Light Brown-seeded landrace was associated with two important agronomic parameters, namely harvest index (HI) and pod mass. The Light Brown-seeded and Cream with Brown-seeded landraces were associated with desirable yield traits including grain yield, HI and pod mass and can, therefore, be recommended as suitable parental lines in crop improvement programmes to improve pigeon pea grain yield.

Agro-morphological variation among two selected wheat varieties after ethylmethanesulphonate mutagenesis

The study was aimed at investigating variations in agro-morphological traits of two selected wheat varieties after chemical mutagenesis using ethylmethanesulphonate (EMS). Two varieties (SST 56 and SST 875) were subjected to EMS mutagenesis using 0.5% v/v EMS at 32.5°C for 1 h. Field trials were carried out at Ukulinga Research Farm of the University of KwaZulu-Natal using a randomized complete block design with two replications. Data on nine important agro-morphological traits were collected and analyzed using the analysis of variance (ANOVA), correlation and principal component analysis (PCA) procedures. Significant variations were found among the agro-morphological traits between M1 individuals of the varieties after the mutagenesis compared to untreated checks. EMS significantly reduced seed germination in the field at 40% in both the varieties and significantly delayed days to heading by eight days. The mutagen caused a shortening of the days to maturity by 13 days in both the varieties. EMS treatment also significantly reduced plant height to 18 and 21cm in SST 56 and SST 875, respectively. The spike length was also reduced by ∼2.5 cm in both the varieties compared to control. 100-seed weight, flag leaf length and seeds per spike significantly increased in the treated seeds of both the varieties. Plant height had positive and significant correlation with number of tillers, number of seeds per spike, flag leaf length and 100-seed weight. However, it had negative correlation with the number of days to maturity. PCA revealed that three principal components (PC 1, PC 2 and PC 3) accounted to 57% of the total variations among the agro-morphological traits in both the varieties. PC 1 alone contributed to 27.7% of the variation which was correlated well with plant height (0.767), tiller number (0.812), number of seeds per spike (0.599) and seed yield (0.720). PC 2 explained 15.6% of the variation and well-correlated with germination percentage (0.784), spike length (0.554) and flag leaf length (0.772). PC 3 accounted to 12.4% of the variation and had negative correlation with days to maturity (−0.730). The study found that EMS had the potential to increase agro-morphological variations in wheat. This could be useful in selecting novel mutants with desired phenotypic traits.