Influence of temperature on yield and quality of carrots (Daucus carota var.sativa)
Manosa, Nthabiseng Adelaide
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The influence of temperature on yield and quality of carrots were examined using two pot trials that were conducted in the glasshouse and growth chambers at the Department of Soil, Crop and Climate Sciences, on the Bloemfontein campus of the University of the Free State in 2009 and 2009/10. In the first trial the influence of four temperatures (10, 18, 26 and 32°C) on the growth, yield and quality of two pre-pack carrot cv’s. Nectar and Star 3002 were studied. Carrot seed were sown in 0.34 m x 0.34 m x 0.35 m pots, filled with topsoil of the sandy loam Bainsvlei form. Pots were kept in the glasshouse at 20°C (±1°C) for four weeks to allow the seedlings to establish and reach the first true leaf stage whereupon they were moved to the controlled environment chambers at different temperatures for 20 weeks. Growth parameters such as leaf number, plant height and leaf growth were significantly influenced by temperature and all these parameters performed the best at 10°C at the end of the growth season irrespective of cultivar. Root fresh and dry mass did not differ significantly between the two cultivars but the affect of temperature was significant. The highest root fresh mass for both cultivars was also obtained at 10°C, with “Star 3002” with the highest mass (39.12 g) followed by “Nectar” (34.26 g). Both cultivars exhibited the highest root dry mass at the lower temperature treatment (10°C) with “Star 3002” having a higher root dry mass (4.15 g) than “Nectar” (3.87 g). External quality parameters such as root length and diameter differed significantly between the temperature treatments and only the length of carrot roots did not differ significantly between the cultivars. Both “Nectar” and “Star 3002” exhibited the longest roots at 10°C and the shortest roots at 18°C. Root diameter for both cultivars was significantly greater at 10°C than at 18°C. The only defects observed were green shoulder and misshapen roots. Although not significant, the percentage green shoulders and misshapen roots were higher at 18°C than at 10°C. Carrots were significantly firmer at the low temperature (10°C) than at 18°C. The total soluble solid content of carrots however, grown at 18°C was significantly higher than those grown at 10°C. In the second pot trial the influence of four dual temperatures (15/5, 24/10, 28/20 and 35/25°C) on the growth, yield and quality of two pre-pack carrot cultivars “Nectar” and “CS 1006” was studied. Based on the results of this study, temperature influenced leaf number and plant height of both cultivars, although not always significantly, during the 32 weeks of growth. Leaf number and plant height of carrot plants were greater at 15/5°C treatment. Yield parameters and the external quality parameters such as root length; diameter and absence of defects were also influenced significantly by temperature. Carrot root length and diameter were significantly influenced positively by lower temperatures (15/5°C) and absence of defects such as green shoulder and hairiness were significantly influenced negatively by higher temperatures (28/20°C). Some of the internal quality parameters such as firmness, total soluble solids, carotene, β-pinene and caryophyllene were also significantly affected by temperature. Firmness, total soluble solids and carotene were significantly influenced by lower temperature (15/5°C) whereas β-pinene and caryophyllene were significantly influenced by higher temperatures (28/20°C). Free choice profiling (FCP) was carried out in order to investigate how semi-naïve panelists described and perceived carrot samples cultivated under different temperature conditions. This method allowed participants to use their own attributes to describe and quantify the food product. The FCP procedure generated six descriptors on the attribute taste and one on aftertaste. The two carrot cultivars grown at the higher temperatures (24/10 and 28/20°C) had descriptors like bitter, sour, bland and chemical, with a definite aftertaste while carrot cultivars grown at lower temperatures (15/5°C) had descriptors such as sweet and carrot taste.