Abstract
In carrot seed production, harvesting of the umbels is generally staggered, or sometimes the whole plant is harvested with the umbels at different stages of maturation; in that case, there is a risk of harvesting immature seeds and of losses due to natural dehiscent, or to physiological deterioration as a result of unfavourable environmental factors. The present study aimed to evaluate the physiological and biochemical changes related to the maturation of 'Planalto' carrot seeds from diferent umbels. The samples were collected 120 days after anthesis, with the primary, secondary and tertiary umbels being harvested separately. Seeds were analysed for germination, first count and germination rate, at temperatures of 25 °C (optimum) to 35 °C (adverse), as well as for emergence in the greenhouse and the emergence rate. Analyses were also carried out of the enzymes peroxidase (POX), ascorbate peroxidase (APX), catalase (CAT) and superoxide dismutase (SOD), and of the total protein. Seeds obtained from the primary and secondary umbels displayed a higher rate of germination than from the tertiary umbels, with the seeds from the primary umbels showing high activity for peroxidase, catalase and superoxide dismutase, and low activity for the enzyme ascorbate peroxidase.
Highlights
During flowering, the carrot plant (Daucus carota L.) emits a primary floral stem containing a central inflorescence at the apex, known as the primary umbel, which in turn branches into secondary, tertiary and quaternary umbels
It is known that with seed physiological maturity, there is a tendency towards a reduction in physiological quality, where the deterioration rate is influenced by environmental factors, especially those predominant during the final stage of maturation (PEDROSO et al, 2008)
When analysing the parameters of germination and vigour, seeds from the primary and secondary umbels showed superior physiological quality compared to seeds from the tertiary umbels at the two temperatures (Figures 1 and 2)
Summary
The carrot plant (Daucus carota L.) emits a primary floral stem containing a central inflorescence at the apex, known as the primary umbel, which in turn branches into secondary, tertiary and quaternary umbels. The seeds produced in the different orders of umbels differ in physiological quality due mainly to uneven maturation (GOMES et al, 2012; NASCIMENTO, 1991). For seed production, staggered harvesting of the umbels based on visual characteristics is generally adopted, it still being possible to harvest the whole plant when the tertiary umbel has matured (SOARES, 2009). It is necessary to determine at which point carrot seeds mature, in order to avoid quantitative losses from dehiscent, and qualitative losses due to a susceptibility to physiological deterioration as a consequence of adverse environmental factors. It is known that with seed physiological maturity, there is a tendency towards a reduction in physiological quality, where the deterioration rate is influenced by environmental factors, especially those predominant during the final stage of maturation (PEDROSO et al, 2008). As the membranes consist of a lipid bilayer, they are the primary site for the process of lipid peroxidation, which leads to the production of free radicals, with disorganisation of the membrane system and a decline in seed vigour (MCDONALD, 1999)
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