IMPACT OF FROST ON CROP GROWTH AND DITERPENE CONTENT OF ROSEMARY (ROSMARINUS OFFICINALIS L.)

Rosemary plant extracts contain diterpenes such as carnosic acid (CA), carnosol (CAR) and 12- О-methoxy carnosic acid (MCA), which are found to have antioxidant properties. Field studies were conducted with ten rosemary cultivars in the 2004 growing season to a) examine the possibility of growing rosemary as an annual crop in southern Alberta, b) select cultivars with higher diterpene productivity, and c) evaluate the impact of frost on biomass productivity and diterpene content. Treatments were arranged in a randomized complete block design with four replicates. The crop was harvested on four separate dates (before and after first and killing frost). At each harvest date, aboveground and leaf biomass dry weights, total diterpene content (TDC), CA, CAR and MCA contents were determined. Among the cultivars tested, the cultivar Rex produced the highest aboveground and leaf biomass yields. In general, with the exception of Majorca, the first frost had no impact on biomass production of the cultivars used. TDC of Rex was slightly enhanced by first frost, and reduced by the killing frost. Killing frost significantly enhanced TDC of Majorca. In general, frost had no significant effect on CA and MCA of most of the cultivars, but increased the CAR content in several cultivars. The cultivar Barbeque and an unnamed cultivar did not contain detectable contents of MCA. Frost had minimal influence on the MCA content of all the other cultivars, except Primely Blue. These results suggest that rosemary can be successfully grown as an annual crop in southern Alberta, and the leaves can be harvested in the field, even following frost damage, without affecting the diterpene content.