PhD, EngD and MSc by research theses (SWEE)
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Browsing PhD, EngD and MSc by research theses (SWEE) by Subject "abscisic acid"
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Item Open Access Discovering biomarkers of postharvest resilience and flavour life in imported citrus and table grapes.(Cranfield University, 2022-02) Navarro-Calderon, Angela; Alamar, M. Carmen; Terry, Leon A.Clementines and table grapes, which are the main fruit crops consumed in the UK after bananas and apples, are considered non-climacteric fruit, not showing an increase in respiration rate and ethylene production during ripening. Previous research has suggested that a different ripening hormone, abscisic acid (ABA), has a more crucial role in the ripening of this kind of produce. The study presented herein aimed to identify biomarkers of postharvest resilience and flavour life of imported clementines and table grapes. For these studies two experiments were designed with the common objectives of determining: 1) the pre- or postharvest factors influencing the postharvest produce quality – both physiological and biochemical, and 2) the role of ABA and ABA catabolites on fruit senescence. The main findings from these studies were that the canopy position of clementines significantly affected fruit postharvest quality and hormonal content. Fruit located on the inside canopy showed higher RR and lower sugar content than outside fruit at the end of postharvest storage, resulting in a shorter shelf- life. At the same time, inside fruit showed a higher content of ABA and ABA catabolites than outside fruit, coinciding with a lower consumer preference score for external appearance, aroma and flavour. This is the first study that determined the ABA and ABA catabolite contents in the pulp of clementines from different canopy positions during senescence, and related this to consumer acceptance. The use of an ethylene inhibitor, 1-methylcyclopropane (1-MCP), during the postharvest storage of table grapes was investigated. The treatment did not have a positive effect on their postharvest quality; in fact, grapes were significantly affected by mould incidence at the end of the shelf-life. The hormonal content in different berry sections was also evaluated; the distal section, which showed a higher mould incidence than the proximal, had three times more ABA and ABA catabolites than the proximal section. This is the first time that the spatial distribution of ABA during the senescence of table grapes was profiled. Despite being different products, similar novel results were observed for both clementines and table grapes. This study indicated that senescence processes in these non-climacteric produce was initiated after a significant increase in RR, and that ABA could be considered a biomarker for clementines and table grapes senescence since an ABA peak during postharvest storage preceded an increase in RR, mould incidence, organic acids, and sucrose hydrolysis. This coincided with a decrease in berry firmness. These findings are of significant importance for the industry. Understanding how ABA regulates senescence processes and the quality changes taking place during postharvest cold storage of clementines and tables grapes improves the consistency in fruit quality and reduces waste and consumer complaints. Although clear beneficial findings have been identified, the results of this study were limited by time, resources, climatic conditions, and other factors. Therefore, recommendations for future work are: to perform molecular studies on genes regulating the ABA pathway from field to postharvest storage; to investigate the crosstalk between ABA, ethylene, and sucrose from ripening to senescence; and to further investigate the use of shade nets and harvesting by canopy position on fruit quality consistency and consumer acceptance.Item Open Access Understanding the regulation of onion dormancy as influenced by deficit irrigation and postharvest storage regimes.(Cranfield University, 2019-02) Ohanenye, Ikenna Christian; Terry, Leon A.; Thompson, Andrew J.; Carmen Alamar, M.Onion (Allium cepa L.) is a biennial crop that produces a bulb in the first season only, but the demand for onion bulbs is all-year-round and to meet demand, they are stored for up to nine months. Consequently, this extended bulb storage causes premature sprouting, which impacts negatively on onion storage quality. Ethylene and 1-methylcyclopropene (1-MCP) were revealed to inhibit sprout growth in stored onion bulbs, whether applied independently or in combination. Also, higher abscisic acid (ABA) and fructans (especially, those at a higher degree of polymerisation) are reported to positively correlate with delayed sprouting. Moreover, the accumulation of ABA and fructans have previously been reported in other plants grown under water-stress. This study investigated (1) the the impact of deficit irrigation (DI) on sprouting; (2) the effects of DI on ABA and fructans contents, and redistribution, in relation to onion bulb dormancy and quality in store; and (3) the molecular mechanisms of fructans and sucrose metabolism in stored onion bulbs during onion dormancy break and sprouting. Across three seasons, onion cultivars ‘Red Baron’ sets, ‘Sherpa’ and double haploid (CUDH2107) seeds were grown and subjected to full irrigation (FI) (100% replacement of crop evapotranspiration) or deficit irrigation (DI) (50% of FI treatment) from bulb initiation to harvest. Bulbs were harvested at full maturity and stored at 1°C for five months and treated with or without 1-MCP (1 µL L⁻¹) for 24 h before storage under continuous ethylene supplementation (10 µL L⁻¹) or air. DI had no effect on dormancy- break, sprout emergence, total fructans and sugar content. Pre-harvest and end of curing ABA contents in the baseplate of DI bulbs was significantly higher compared to FI bulbs; however, no significant difference in sprouting between DI and FI bulbs was found. It was hypothesised that ABA accumulated under water-stress may not enhance onion dormancy. Ethylene and 1-MCP independently reduce the rate of ABA decline in stored onion bulbs. However, while ethylene was found to delay sprouting for both DI and FI bulbs, 1-MCP did not. This therefore questions the role of ABA in onion dormancy; nonetheless, bulbs treated with 1-MCP and stored under ethylene produced the shortest sprouts. Sucrose and fructans contents declined in sprouted bulbs while the expressions of the genes SPS (sucrose phosphate synthase), 1-SST (sucrose:sucrose 1- fructosyltranferase) and 6G-FFT (fructan:fructan 6G-fructosyltranferase) involved in sucrose and fructans biosynthesis were significantly upregulated. This suggested posttranslational regulations, or a higher catabolic rate compared to biosynthesis. The concentration of DP3-8 fructans were higher in top and bottom sections compared to the baseplate. Prior to sprouting, fructans of DPs 7-8 were no longer present in the top and bottom wedges, while they accumulated in the baseplate, irrespective of pre- or postharvest treatments. This redistribution of fructans within the bulb indicated a transition in dormancy state and could be used as a predictive marker for sprouting in stored onion bulbs. The application of this finding could significantly reduce onion bulb losses due to unpredictable sprouting during storage