Response of seed carrot to various water regimes. II. Reproductive development, seed yield, and seed quality.

Seed yield and quality of carrot (Daucus carota var. sativa DC.) were influenced by a wide range of water application regimes and levels. Irrigation treatments were imposed beginning at the time of extension of the primary umbel and extending throughout the reproductive development period. The three application regimes used were: 1) a high-frequency, low water deficit treatment (100% of daily accumulated crop evapotranspiration (ET c)); 2) a series of five low-frequency (irrigated after 30 mm of accumulated ET,) application treatments with a range of water deficits from moderate to minimal (40% to 120% of ETC applied); and 3) a series of three treatments that had rapidly developing water deficits applied by terminating irrigation at 7, 5, and 2 weeks before harvest after being grown under low-stress conditions. Pure live seed (PLS) yield was optimized by different treatments within each of the three application regimes. Maximum yields were achieved with short-term (2-week) rapidly developing water deficits near harvest, moderate deficit irrigation with 60% to 80% of ET c applied after 30 mm of ET c, or with a low water deficit, high-frequency application. Seed germination percentage decreased as the amount of applied water increased. This effect was more pronounced in the later-developing umbel orders. However, seed quality measured as seedling root length was improved with increasing water application. The seed carrot plant grows in an indeterminate fashion, pro- ducing seed in umbels that arise from multi-rank ordered branches. This general growth form results in seed of different maturity stages being present on the plant at the same time. Therefore, when the seed of the primary umbel is mature and ready for harvest, seed from secondary and tertiary umbels may not be mature, and tertiary and quarternary umbels may still be in flower. As a result, there is a great deal of variability in the maturity of the seed at harvest. Since genetic efforts to improve the carrot plant have been directed primarily toward improved root production and quality, carrot reproductive development has remained much the same as that of undomesticated relatives (Braak and Kho, 1958). The effects of water management on carrot seed production and quality are not well-understood, with limited published in-