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Title: Guar responses to temperature: Estimation of cardinal temperatures and photosynthetic parameters

item BAATH, GURJINDER - Oklahoma State University
item KAKANI, VIJAYA - Oklahoma State University
item Gowda, Prasanna
item ROCATELI, ALEXANDRE - Oklahoma State University
item Northup, Brian
item SINGH, HARDEEP - Oklahoma State University
item KATTA, JHANSY - Oklahoma State University

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2019
Publication Date: 11/22/2019
Citation: Baath, G.S., Kakani, V.G., Gowda, P.H., Rocateli, A.C., Northup, B.K., Singh, H., Katta, J.R. 2019. Guar responses to temperature: Estimation of cardinal temperatures and photosynthetic parameters. Industrial Crops and Products.

Interpretive Summary: Guar cultivation has been expanding to non-traditional areas in many countries including the United States due to its high demand in the oil fracking industry and as forage for beef production, where the crop may encounter more extreme high or low temperatures. As information on the temperature response functions of guar is lacking in the current literature, research is needed to understand the response of growth, development, and physiology of guar to temperature. In this study, we conducted an experiment using walk-in growth chambers facility at Oklahoma State University to evaluate physiological responses of guar to different temperatures maintained in each of the six growth chambers and estimate cardinal temperatures. Results showed that guar was very sensitive to cold temperatures (<20 °C), but high temperatures favored its vegetative growth, and an optimum biomass accumulation rate was observed at 34.1 °C. However, high temperatures 36/28 and 40/32 °C also inhibited the reproductive development of guar plants, and grain yields only occurred within 19-31 °C. The estimated cardinal temperatures for growth, development, and reproduction of guar, would allow development of crop simulation models to better assess the adaptability of guar under different agrometeorological conditions and uncertainties related to its different crop management strategies. Both photosynthetic-light and A-Ci response curves indicated that the guar plant acclimatizes its photosynthetic rate to heat stress by allowing a higher rate of electron transport. There is further need for research to understand the mechanism suppressing flower initiation in guar at high temperatures to improve its temperature tolerance of reproductive growth for wider adaptability.

Technical Abstract: Temperature is the primary determinant of plant distribution and production. There has been increased interest in the cultivation of guar in many countries including the United States due to its high demand in the oil fracking industry and forage potential. However, information on its response to temperature is still lacking in the current literature. An experiment was conducted using walk-in growth chambers in the Controlled Environment Research Facility at Oklahoma State University to study the effects of six different temperature regimes (20/12, 24/16, 28/20, 32/24, 36/28 and 40/32 °C) on vegetative growth, development, and reproduction of guar to estimate the cardinal temperatures, and to evaluate its photosynthetic responses to temperature gradient. Results showed that the vegetative growth of guar was sensitive to low temperatures and has high mean cardinal temperatures (Tmin, Topt, and Tmax) of 14.2, 34.1 and 48.2 °C for biomass accumulation. High growth temperatures of 36/28 and 40/32 °C completely suppressed flower initiation and plants exhibited reproductive development within a narrow range of 19-31 °C with maximum yields observed at Topt of 25 °C. The responses of both photosynthesis to light and internal CO2 concentration (A-Ci) suggested guar photosynthetic rates acclimates to high temperatures through an increased rate of electron transport. The identified cardinal temperature limits and photosynthesis parameters can be used to develop mechanistic simulation models and evaluate adaptation strategies for guar. Further research is required to investigate the basis for the suppression of flower bud initiation and the mechanism limiting the photosynthetic rate (A) of guar leaves under heat stress.