Samson Zeray Tesfay

Screening of Bread Wheat Genotypes for Drought Tolerance Using Phenotypic and Proline Analyses

Drought stress is one of the leading constraints to wheat (Triticum aestivum L.) production globally. Breeding for drought tolerance using novel genetic resources is an important mitigation strategy. This study aimed to determine the level of drought tolerance among diverse bread wheat genotypes using agronomic traits and proline analyses and to establish correlation of proline content and agronomic traits under drought-stress conditions in order to select promising wheat lines for breeding. Ninety-six diverse genotypes including 88 lines from the International Maize and Wheat Improvement Center (CIMMYT)s heat and drought nurseries, and eight local checks were evaluated under greenhouse and field conditions during 2014/15 and 2015/16 making four testing environments. The following phenotypic traits were collected after stress imposed during the heading to anthesis period: the number of days to heading (DTH), days to maturity (DTM), productive tiller number (TN), plant height (PH), spike length (SL), spikelet per spike (SPS), kernels per spike (KPS), thousand kernel weight (TKW) and grain yield (GY) and proline content (PC). Analysis of variance, Pearsons correlation coefficient, principal component and stress tolerance index were calculated. Genotypes with high yield performance under stressed and optimum conditions maintained high values for yield components. Proline content significantly increased under stress, but weakly correlated with agronomic traits under both optimal and water limited conditions. The positive correlation observed between grain yield and proline content under-drought stress conditions provides evidence that proline accumulation might ultimately be considered as a tool for effective selection of drought tolerant genotypes. The study selected 12 genotypes with high grain yields under drought stressed conditions and favorable adaptive traits useful for breeding.

Anti-oxidant levels in various tissues during the maturation of ‘Hass’ avocado (Persea americana Mill.)

Summary Avocado is a fruit high in polyunsaturated fatty acids, with a high mineral content. However, no reports are available on how valuable avocado fruit could be as a source of anti-oxidants, depending upon their stage of maturity. Such a feature might become an important marketing tool in future. To evaluate the presence of anti-oxidant systems throughout avocado fruit development, various tissues were analysed for both their total and specific anti-oxidant compositions.Total anti-oxidant levels were found to be higher in the exocarp and in seed tissues than in the mesocarp, a possible reason for the susceptibility of avocado to post-harvest mesocarp disorders. While seed tissues contained predominantly ascorbic acid (AsA) and total phenolics (TP), the anti-oxidant composition of the mesocarp was characterised by the presence of the C7 sugar, D-mannoheptulose. Among the anti-oxidant enzymes assayed, peroxidase (POX) and catalase (CAT) were present in higher concentrations than superoxide dismutase (SOD) in mesocarp tissue. The low concentration of anti-oxidants in the mesocarp could be a major reason for the susceptibility of avocado fruit to physiological disorders.

A Review of Destructive and Non-destructive Methods for Determining Avocado Fruit Maturity

Optimum harvest maturity is one of the important factors determining the quality of avocado fruit. Currently, avocado harvest maturity is mostly determined using markers or indices such as mesocarp oil, dry matter, or moisture content, all quantified destructively using representative samples of a batch in a consignment. Although useful, destructive techniques are time-consuming and results reflect properties of specific produce evaluated. High variation in maturity stages affect postharvest quality and the rate of ripening within a consignment, causing logistical difficulties. Emerging analytical techniques have particular advantages in non-destructive detection of food quality and safety. In this paper, destructive and non-destructive analytical methods and instruments for determining maturity parameters of avocado fruit are discussed. This review also looks at the trends in applying emerging optical and imaging techniques to the analysis of avocado fruit maturity and quality, in particular, visible to near infrared spectroscopy, ultrasonic system, ultrasound imaging, hyperspectral imaging, magnetic resonance imaging, and fluorescence imaging. On the basis of the observed trends, the technical challenges and future prospects for commercial application of these non-destructive techniques for maturity determination of individual avocado fruit are presented.

Growth responses of tropical onion cultivars to photoperiod and temperature based on growing degree days

Onions (Allium cepa L.) are widely produced within the tropics, but little is known about the Eritrean cultivars Hagaz Red 1 and 2 (HR 1, and HR 2) and Red Creole (RC). Responses of the onion cvs. HR 1, HR 2 and RC to photoperiod and temperature on bulbing were compared. Plants were grown in growth rooms under combinations of photoperiod (11.5, 12, and 12.5 h) and day/night temperatures (25/12, 30/15 and 35/18°C). Growth responses were determined by growing degree day (GDD) base and the broken-stick regression model. There were relationships between bulb initiation and rate of leaf area growth under 12 and 12.5 h. Under the 12 h photoperiod, cultivars needed 343, 482, and 597 GDD before bulb initiation and 405, 432, and 431 GDD to increase rate of leaf area development at 25/12, 30/15, and 35/18°C, respectively. Under a 12.5 h photoperiod, cultivars needed 344, 423, and 432.2 GDD to initiate bulbing and 140, 411, and 579 GDD to increase leaf growth rates at 25/12, 30/15, and 35/18°C, respectively. Temperature induces variations in leaf number, plant height, leaf area, and affect bulbing and these responses may be used in the development of superior cultivars for tropical conditions.

Ripening physiology and quality of ‘Hass’ avocado (Persea americana Mill.) after cold storage at 1ºC

Summary The export of avocado (Persea americana Mill.) fruit into foreign markets has become a high priority for the South African industry due to increased competition in the European market. Some of these countries require phytosanitary treatment before access is granted. Cold disinfestation is the only suitable phytosanitary treatment available for avocado, but the fruit are generally considered to be sensitive to temperatures below approx. 5ºC. Phytosanitary disinfestation of South African avocados of acceptable fruit quality has been achieved by maintaining the pulp temperature below 2ºC for 28 d, but the effect on ripening physiology has not been determined. The effect of cold storage at 1ºC (air delivery temperature) on ‘Hass’ avocados with or without modified humidity packaging (MHP) for 28 d was examined. Compared to a conventional storage temperature of 5.5ºC for 28 d, fruit stored at 1ºC had significantly reduced rates of respiration and ethylene production, less softening, water loss, fresh weight (FW) loss, and mannoheptulose consumption measured immediately after cold storage. The use of MHP resulted in similar reductions at the conventional temperature and, when MHP was used in combination with 1ºC storage, these reductions were enhanced. Cold storage at either temperature resulted in increased cellulase and polygalacturonase activities during ripening when compared to non-stored fruit (kept at 21ºC until ripe), but no significant differences were recorded between the four cold storage treatments (i.e., 1ºC and 5.5ºC, with or without MHP) in the activities of cellulase, polygalacturonase, and pectin methylesterase during ripening. The number of days to ripen increased slightly after storage at 1ºC, but the percentage of marketable fruit was not significantly reduced. Significantly reduced FW and water losses from fruit stored under MHP resulted in significant reductions in the severity of skin spotting. The ripening physiology and quality of South African ‘Hass’ avocados were not negatively affected when fruit were stored at 1ºC for 28 d. When considered with previous results, this treatment appears to be suitable for future use.

Physical, nutritional and antioxidant properties of Zimbabwean bambara groundnut and effects of processing methods on their chemical properties

This study examined the physical, nutritional and antioxidant properties of popular Zimbabwean bambara groundnut landraces and the effects of different processing methods on their chemical properties. The physical, nutritional and antioxidant properties of grains of the bambara landraces differed significantly with grain type, and the processing methods investigated had varying effects on the chemical properties of the grains. Bambara had significantly lower protein content than the reference common bean. Protein and carbohydrate content of the grains increased upon dehulling, while tannin (approx. 36%), total phenolic content (approx. 83%) and antioxidant activities (approx. 18%) decreased. Roasting alone seemed to have little or no effect on the nutrient content of the grains, while sifting significantly reduced the phenolic content and antioxidant activity of all the dehulled and roasted samples. The results indicate that roasting bambara grains would be a suitable method as it is relatively more conservative of nutrients and antioxidants than the other methods investigated.

Maize grain soluble sugar and protein contents in response to simulated hail damage

Production of grain of high nutritional quality is essential in maize (Zea mays L.) as a food grain crop. Grain quality may be influenced by environmental and management factors, such as hail, plant density and grain selection. A study was conducted to determine the effect of hail damage on maize grain contents of soluble sugars and total proteins in relation to grain position on the cob and planting density. Maize was grown at three planting densities (65 000 plants ha−1 [high], 46 000 plants ha−1 [moderate] and 28 000 plants ha−1 [low]) at two sites (Baynesfield and Swayimane) in KwaZulu-Natal, South Africa. Approximately 80% hail damage was simulated on the leaves at the seventh leaf (V7) and tasseling (VT) stages of development of three maize cultivars (‘SC701’, ‘Mac Medium Pearl’ and ‘Zama Star’), whereas undamaged plants served as the control. After harvest at maturity, grains from the proximal and distal portions of the cob were divided and analysed for grain nutritional quality, i.e. soluble sugars and proteins. Soluble sugar analysis focused on the predominant sugars, namely glucose, fructose and sucrose. Although not significant, hail damage typically at VT reduced grain soluble sugar and protein contents by at least 3.2% and 3.8%, respectively, and grains produced at Baynesfield were more resilient to damage compared with those produced at Swayimane. Selection of seeds from the distal cob portion, especially for ‘SC701’, and low plant density reduced the detrimental effect of hail damage on grain sugar and protein content. The present results indicate that in areas prone to hail ‘SC701’ is a cultivar of choice, and a low plant density and selection of grains from the distal cob portion can mitigate the detrimental effects of hail on grain nutritional quality.

Effect of ultraviolet irradiation on postharvest quality and composition of tomatoes: a review

Ultraviolet (UV) irradiation has recently emerged as a possible alternative to currently used postharvest phytosanitary treatments. Research has also highlighted other benefits associated with UV irradiation in postharvest technology. This review presents the effects of UV irradiation on postharvest and nutritional quality of tomatoes. The application of UV irradiation on tomatoes is discussed including its effect on biological (respiration rate, ethylene production and microbial growth), physico-chemical (firmness, colour, total soluble solids and titratable acidity) and nutritional (vitamins, carotenoids, phenolic and antioxidants) quality. UV-treated tomatoes have shown resistance to microbial growth and decay. Although UV irradiation reduces the loss of vitamin C during storage, the loss of vitamin E remains a concern. UV treatments lead to higher antioxidant capacity, flavonoids and phenolic content. UV irradiation significantly reduced carotenoids in certain cultivars. Based on the literature reviewed, the success of UV irradiation treatments is cultivar-dependent. While improved retention of phytochemicals has been reported in UV-C treated fruit, increased losses have been reported in certain cultivars. Research efforts on the development of cultivar-specific UV irradiation protocols are warranted. The effect of harvest maturity and seasonal differences in the efficacy of UV treatments is required to be investigated.

Antioxidant activity and soluble sugars of African ginger (Siphonochilus aethiopicus) in response to irrigation regimen and nitrogen levels

ABSTRACT African ginger (Siphonochilus aethiopicus), as a medicinal plant, is known for its medicinal properties, containing various antioxidant compounds and carbohydrates. Rhizome yield is improved by water regimens and fertilizers applied at plant phenological stages. However, the rhizomatous herb, which is traditionally used for the treatment of asthma, inflammation and malaria has limited information on water and nitrogen requirements for its production. This study assessed the effect of irrigation regimens (30%, 50% and 70% allowable depletion level (ADL) and nitrogen (N) levels (0, 50, 100, 150 and 200 kg ha−1) on antioxidant activity and carbohydrates on plant leaf, root and rhizome. The interaction treatment effect of severely stressed (70% ADL) with the N application of 100 kg ha−1 had significant effect on leaf phenolic concentration (87.02 ± 2.51 mg g−1 gallic acid equivalent). Interaction effect of moderately stressed (50% ADL) and severely stressed (70% ADL) treatment with N application rate of 0 kg ha−1 had significant effect on plant flavonoids and phenolics in all plant parts. In plant carbohydrates, root had high sucrose content (47.68 ± 9.0 mg g−1 dry weight) with the application of low N (0 kg ha−1) grown under severely stressed treatment. In conclusion, this implies that different S. aethiopicus parts can produce substantial amount of antioxidants and carbohydrates, as exhibited under low N and reduced water supply applied during the phenological cycle.