The effects of boron sprays on fruit yield and fruit quality in guava (psidium guajava l.)
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- This thesis reports on field and laboratory investigations into the effects of boron sprayed directly onto leaves (foliar spray) on growth (yield), colour, texture and chemical composition of common guava (Psidium guavjava L.) fruit. The key areas of research included the use of different concentrations of boron (as boric acid) in two different growing seasons (2002 and 2003) with different climatic conditions. Physical parameters of fruit quality were measured such as size (diameter) and weight, and colour and texture, as well as detailed analysis of fruit chemical composition, including crude fibre, total soluble solids, pectin, acidity and vitamin C content. Time of fruit deterioration was monitored to assess shelf-life, and concentrations of boron taken up into the fruit and plant leaves were monitored for safety reasons. Finally, a panel of fruit experts was used to assess the sensory and eating quality of fruit with or without boron application, and a final assessment of fruit eating quality was determined. Results from the study clearly showed that boron sprays at or near the highest concentrations used in this study significantly improved fruit size and weight. There was a subtle colour change in the skin towards a more green fruit, and the physical texture of the fruit was harder with boron application. Almost all chemical analyses demonstrated that with boron application fruit had higher acidity, vitamin C content, total soluble solids, but crude fibre had decreased. Pectin levels in 2003 were low and could not be accurately quantified, but in 2002 boron also increased the levels of pectins. A significant result was that boron sprays decreased fruit deterioration over time, and shelf life of guava could be extended from 5-7 days with no boron spray to 14- 16 days with the highest boron concentration spray. A panel of fruit experts assessed the fruit from the highest boron sprayed trees to be overall the best fruit in taste, colour and texture, with fruit from trees without boron application being the poorest fruit in these aspects. This study, therefore, for the first time investigated the role of boron in post-harvest fruit physiology and composition in a tropical fruit, as distinct from other studies on temperate fruits. However, the results of this study are in agreement with other studies of boron application in temperate fruits, and the available broad literature is used to explain the effects observed. The data provided a consistent picture as to the benefits of boron application, in what tuned out to be very different tropical climatic conditions over the two seasons of this study. The results are discussed in relation to the effects of boron on tree physiology, biochemistry and fruit development; additionally economic and orchard management implications of the research are discussed. Finally, a brief discussion on possible negative environmental effects of boron accumulation in plants and soil are discussed as a result of boron spraying, with a brief review of possible human heath implications.
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