Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2006
Publication Date: 4/1/2007
Citation: Gesch, R.W., Forcella, F. 2007. Differential Sensitivity to Temperature of Cuphea Vegetative and Reproductive Growth. Industrial Crops and Products. 25:305-309. Interpretive Summary: Cuphea is a new oilseed crop that recently has gone from research and development to on-farm commercial production in the northern Corn Belt. Our agronomic studies have shown that cuphea seed yields tend to be greater in Minnesota than more southerly states like Illinois and Iowa. We suspect that part of the reason for this is because these areas have higher summertime temperatures, but no one has specifically studied how temperature effects cuphea growth. Therefore, we grew cuphea in growth chambers under a range of different daily temperatures to measure its rate of photosynthesis and growth in response to temperature. We found that the growth of cuphea leaves and stems was generally good over an average daily temperature range of 60 to 88 deg F. However, the growth of cuphea’s flowers and seed were much more sensitive to temperature and grew quite poorly when daily average temperatures were above 80 deg F. The reason that leaves and stems grew so well was because leaf photosynthesis of cuphea adapts well to the different temperatures used in this study, but we are not sure exactly why flowers and seeds were so sensitive. Until a variety of cuphea is developed that is more tolerant to hot summer temperatures, farmers in the northern Corn Belt such as Minnesota, Wisconsin, and eastern North Dakota will benefit the most by growing cuphea.
Technical Abstract: Cuphea (Cuphea viscosissima Jacq. x C. lanceolata W.T. Aiton) is a new oilseed crop rich in medium-chain fatty acids similar to tropical palms. Agronomic studies suggest that temperature is a key determinant of cuphea seed yields. However, little is known about the growth and photosynthetic response of cuphea to temperature. To better understand its adaptability to different climates, cuphea was grown under four day/night temperature regimes of 18/12, 24/18, 30/24, and 35/27 deg C and optimum temperatures for photosynthesis and growth rates were determined. Vegetative growth and leaf photosynthesis adapted well over the temperature range studied. However, reproductive growth was much more sensitive showing an optimum at approximately 22 deg C. Reproductive growth rate was greatest under the 24/18 deg C treatment and declined by 50 and 85% at the lowest and highest growth temperatures. In contrast, vegetative growth declined only slightly at the lowest and highest temperatures. Photosynthesis acclimated to temperature by up-regulation of in vivo Rubisco activity with declining growth temperature. Maximum Rubisco activity (Vcmax) in leaves under the 18/12 deg C treatment was more than two-fold greater than that of leaves grown at 35/27 deg C. Photosynthetic acclimation permitted cuphea to vegetatively grow well over a wide temperature range, but does not explain the sensitivity of reproductive growth to temperature. Agronomically, cuphea will likely yield best under cool to moderate temperate climates due to reproductive sensitivity to temperature.