Physiological Mechanism and Genotypic Variation in Drought Tolerance of Processing Carrots

Abstract

Processing carrots are mainly grown under rain-fed conditions in Nova Scotia, and thus become vulnerable to frequent periods of drought. Prolonged drought results in significant reductions in the yield and quality of carrot crops. Resistance to water deficit is gene controlled and it is essential to identify the genotypes that withstand water stress. It is equally important to understand the physiological mechanism(s) that contribute to drought tolerance. Physiological measurements were made on eight carrot varieties exposed to natural drought in a controlled greenhouse. Measurements were made on net photosynthesis, soil moisture, relative water content, membrane injury index, xylem pressure potential, and stem elongation. Overall, the slicer variety Bergen sustained normal plant functions under drought stress better than any of the other varieties. Bergen maintained stem elongation, photosynthetic activity, membrane function, and relative water content under droughted conditions. Another study was conducted to identify carrot varieties that are naturally resistant to drought. A mass screening of 85 slicer, dicer, and cut and peel varieties was conducted under greenhouse conditions. Two-week-old seedlings were exposed to gradual water deficit and observed for visual symptoms of wilting each day as soil moisture declined. Each variety was assigned a wilting score based upon the number of days it withstood drought (min = 1, max = 5). The dicer variety, Prodigy, was the only variety to score a 5 indicating the most drought resistance. Other varieties that withstood drought well were `Caropak', `Interceptor', `Oranza', and `Berlanda'. Varieties such as KC713126, Cello712113, and Cello711411 were more sensitive to water deficit and began to wilt 8 days after drought was imposed.