Photosynthesis of Three Sugarcane (Saccharum officinarum) Varieties in Two Environmental Conditions.

This study evaluated the photosynthetic capacity of three sugarcane varieties in response to environmental conditions during the year (summer and winter), also yield and juice quality. Three commercial varieties of sugarcane were evaluated under rain-fed conditions during the harvest season 2013-2014 (zafra) in south of Tamaulipas (Ocampo). The study treatments were two natural seasons (summer and winter) where the air temperature is contrasting. We investigated changes in photosynthesis rate using the LI-6400 and agronomic traits as internode length, stem diameter, stem height, °Brix and millable stalks affected by air temperature. The plants for each variety were grown in four rows of 20 m length with inter and intra row spacing of 1.30 m and 0.10 m respectively. The experimental design was a randomized complete block with four replications. Analyses of variance were made using the GLM procedure for all variables. Effects associated with variety, environment, time of day and the interactions were identified. The results indicated that there were significant differences between varieties, environment, time of day and interactions. For agronomic traits: internode length, stem height and millable stalks there were significant differences. Mex 79-431 had the highest photosynthetic rate (16.9 μmolCO₂ m^-2s^-1), therefore it is assumed that was the most efficient in the use of photosynthetically active radiation (PAR) compared with CP 72-2086 range (16.3 μmolCO₂ m^-2 s^-1) and Mex 68-P-23 (13.6 μmolCO₂ m^-2 s^-1). The varieties CP 72-2086 and Mex 79-431 better adapted to the environmental conditions of the season as they were superior to Mex 68-P-23 in the photosynthetic rate in both conditions, averaging 12.2, 16.0 and 16.8 μmolCO₂ m^-2s^-1 respectively. The variety Mex 68-P-23 was higher on the variables internode length, stem height and millable stalks averaging 17.50 cm, 2.15 cm and 103 t.ha^-1 respectively. Juice quality was similar in the three varieties with 23 °Brix. In general, it concludes that the environment directly influences the photosynthetic response of plants sugarcane since winter reductions of up to 54% were recorded regarding summer.