PR-101

Response of four carrot cultivars to light and Supraoptimal CO₂

D.G. Mortley, L. McCoy, C.K. Bonsi, W.A. Hill, and C.E. Morris
Center for Food and Environmental Systems for Human Exploration of Space and G.W.Carver Agricultural Experiment Station, Tuskegee University, Tuskegee AL 36088.
 
A series of studies were conducted to evaluate the response of four hydroponically-grown carrot cultivars (Kinko-4, Mignon, Nevis-F1, and Parmex) to irradiance and CO₂. Seeds were planted in moist arcillite and transplanted into growth channels (0.15 x 0.15 x 1.2 m) after 18 days in growth chambers with nutrients continuously supplied by a half-Hoagland solution. Irradiance was 150, 300, or 450µmol m^-2s^-1 and CO₂, 400 (ambient), 1200, or 4000 µmol mol^-1.  Additional growth chamber conditions included a 16/8 h photoperiod, a diurnal 22/16ºC thermoperiod, and relative humidity between 70% and 80%. Plants were harvested at about 80 days. Shoot height and root fresh yield were influenced by both irradiance level and CO₂ concentration. Root dry yield, fibrous root dry yield, and fibrous root fresh yield were influenced by irradiance but marginally by CO₂ levels, whereas root length, root diameter, core diameter and root fresh weight were not significantly affected by either treatment. Irradiance significantly influenced shoot dry weight, fibrous root dry weight, fibrous root fresh weight, and shoot diameter, while CO₂ concentration did not. CO₂ concentration significantly influenced shoot fresh weight, shoot fresh yield and shoot dry yield while irradiance did not. Varietal differences also contributed significantly to the growth responses of the plants. Betacarotene content was variable being greatest at 450 µmol m^-2s^-1 plus 2200 µmol mol^-1 for Mignon, followed by Kinko-4, Nevis F-1 and Parmex. These results indicate that dry root and fibrous root responses were influenced more by irradiance than CO₂, while fresh shoot responses were influenced more by CO₂ concentration.

PR-102

Hormonal and ecophysiology of bulking in cut and peel carrots

Rayirath U P., Lada R. R., Adams A and Veitch R. S
Department of Plant and Animal Sciences, Nova Scotia Agricultural College, Truro, NS, Canada, B2N5E3

Individually Quick Frozen (IQF) carrot industry is expanding in North America. Recently, IQF cut and peel carrots have been developed as a high-value product with a great market potential. Obtaining uniform and highest quality baby-grade roots is critical for optimizing root quality thereby favoring industry expansion. Root grades are under the control of the root bulking process, which is complex and modulated and signaled through endogenous hormonal levels in response to genetic and ecophysiological parameters. Current research on the bulking physiology of cut and peel carrots are limited. Understanding the interrelationships between the hormonal, physiological and environmental factors in the root bulking process would uncover bulking physiology and help to optimize the root grades. It is hypothesized that agro-ecosystem management practices alter endogenous ethylene and polyamine(s) and thereby the root bulking. Experiments were conducted to quantify endogenous levels of ethylene and polyamines in the roots and shoots as altered by genotypes, crop competition and nitrogen rates. The changes in the root grades as affected by changes in the canopy photosynthesis, ethylene and polyamine content in situ in response to these agro-ecological factors were determined and the relationship among these factors and root bulking affecting the final root grades are discussed.

Key words: Carrots, root bulking, hormones, ethylene, polyamine and ecophysiology.

PR-103

Nitrogen management in carrot rotations

Kevin Sanderson¹, Basil Dickson¹, Sherry Fillmore² and Sylvia Wyand^1
1 Agriculture and Agri-Food Canada, Crops and Livestock Research Center, 440 University Avenue, Charlottetown, Prince Edward Island, C1A 4N6, Canada
² Agriculture and Agri-Food Canada, Atlantic Horticulture and Research Centre, Kentville, Nova Scotia, B4N 1J5, Canada

A long term, carrot rotation study was established in 2005 to determine the effect of applied N to the carrot crop in the 3-yr crop rotation. Crop rotations consisted of: (1) barley under-seeded to Timothy/ Timothy/ carrot; (2) barley under-seeded to Timothy/ Timothy followed by pearl millet/ carrot and (3) barley/ pearl millet/ carrot. Within carrot plots, six combinations of pre-plant and top-dress N were applied at from 0 to 150 kg N ha^-1. Where no N was applied, pre-plant soil N averaged 16.2 and 2.6 mg kg^-1 compared to 2.8 and 0.5 mg kg^-1 post-harvest, for the 0-30 and 31-60 cm depths, respectively. Across N treatments, values of soil N after carrot harvest ranged from 2.5 to 3.3 mg kg^-1 and 0.4 to 2.8 mg kg^-1 for the 0-30 and 31-60 cm depths, respectively and were not affected by treatment. Bi-weekly soil N (0-15 cm) ranged from 2.8 to106 mg kg^-1 and increased with rate of applied N. Carrot petiole N ranged from 1.8 to 5.5 % and increased with rate of applied N. Bi-weekly soil N and petiole N decreased over the season, with higher rates of applied N treatments decreasing at a slower rate. Cardy petiole N followed a similar trend as LECO N but was more variable. Across sampling times, reflectance difference values (NDVI) for Greenseeker increased as petiole N decreased. In year 2 and year 3 of this study, biological carrot yield was increased as rate of applied N. Data from at least 2 crop rotation sequences will be required to validate the impact of crop rotation on N management.

Oral Presentation: Kevin Sanderson
Phone: 902-566-6881
E-mail: sandersonk@agr.gc.ca.