Abstract
ABSTRACT The adequate time for carrot seed harvest influences its physiological quality. The objective of this study was to evaluate physiological, anatomical and histochemical changes in carrot seeds harvested at different stages of development and to establish the most appropriate harvest time. Secondary umbels were harvested at 14, 21, 28, 35, 42, 49, 56 and 63 days after anthesis (DAA). For seed anatomical and histochemical characterization, sections were stained with Toluidine blue stain, Xylidine Ponceau, Lugol’s iodine, Sudan Black B and submitted to polarized light. Seed moisture content, seed dry matter, germination, first count, emergence percentage and emergence speed index of seedlings were evaluated. Cultivar Brasília carrot seeds at 14 DAA are in cell division and expansion. In addition, as lipids were identified in the endosperm, despite the seed low dry matter. At 21 DAA, reserve substances such as protein and starch were also identified. Along the seed development process, deposition of lignin occurs in the endocarp cells, and this collapsed lignified layer represents the resistance layer of the seeds. Physiological maturity, represented by the maximum dry matter accumulation, occurs at 35 DAA, with the endosperm occupying almost all volume of seeds, the embryo occupying a small cylindrical region and the integument showing a single layer of cells. At this time, the seeds presented 56% moisture content and the color of the pericarp is green-yellow. Maximum seed germination and vigor occurred at 30 DAA, just before physiological maturity was reached (35 DAA). Thus, the ideal time to harvest the seeds of cultivar Brasília is from 30 DAA, where the seeds have maximum physiological quality.
Highlights
Carrot (Daucus carota L.) is a vegetable of great economic importance, being among the ten most produced ones in Brazil
The objective of this research was to associate histochemical, physical and physiological changes occurring during the carrot seed maturation process in cultivar Brasília, and determine the most appropriate time for harvest aimed at the yield of high physiological quality seeds
The seeds in early development do not occupy the entire space defined by the pericarp (Figure 2A), the integument shows a single layer of cells (Figure 2A, arrow) and the endosperm is in the phase of cell division and expansion
Summary
Carrot (Daucus carota L.) is a vegetable of great economic importance, being among the ten most produced ones in Brazil. It belongs to the Apiaceae family and the plant has an indeterminate growth and a composed umbeltype inflorescence. The plant moves from the vegetative to the reproductive phases, giving a rod or floral tassel ending in an umbel-type inflorescence called central or primary umbel. From this one, there are branches ending in secondary umbels from which new branches or tertiary umbels rise. Flowering within each umbel is not uniform (Carvalho et al, 2014), resulting in seeds with different maturity levels at harvest. Nascimento (1991) has observed that germination and seed vigor decreased with the increase of the order of umbels
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