Temperature during grain filling affects grain weight and oil concentration in sunflower hybrid both directly and through the reduction of radiation interception

ANGELONI P; ECHARTE M.M; AGUIRREZÁBAL L.A.N

Mar del Plata

Conferencia; 18 th International Sunflower Confernece; 2012

ASAGIR - ISA

ABSTRACT • Temperature and radiation during grain filling are determinant factors of crop yield. Response functions of sunflower embryo weight to temperature have been established, as well as final grain weight and oil concentration in response to intercepted solar radiation. However, the response of oil concentration to temperature and the joint effect of temperature and solar radiation on grain weight and oil concentration remains unknown. This is not an easy issue to address since temperature increase reduces grain filling duration and decreases the accumulation of intercepted radiation. The aim of this work was to characterize the sunflower grain weight and oil concentration response to temperature and determine whether such response is related to intercepted solar radiation during the grain filling period. • Two kinds of experiments were performed: 1) controlled temperature: a traditional sunflower hybrid ACA 885 was grown in growth chambers. Four daily mean temperatures (MT) during grain filling in the range of 15-25 ºC were assayed; 2) radiation x location: the same hybrid was grown in the field in different locations covering a MT range of 20.3 to 26.5 ºC during grain filling. Intercepted solar radiation was modified by thinning, 50% and 80% shading and a combination of thinning and 50% shading. Final grain weight and oil concentration were determined at physiological maturity. For both kinds of experiments intercepted solar radiation accumulated during grain filling was calculated. • In controlled temperature experiments, final grain weight and oil concentration responded to MT describing a plateau-lineal function. Above 22ºC, grain weight decreased with a slope of -8 mg/ºC and oil concentration decreased with slope of -1.7 %/ºC at MT higher than 17.2ºC. Control plants in experiments in different locations showed similar response to MT for both variables. Increasing the intercepted solar radiation in radiation x location experiments exponentially increased both variables up to a maximum. In order to elucidate whether temperature effects in chamber were due to an effect of temperature on radiation interception, radiation intercepted by plants in the chambers was calculated. Grain weight and oil concentration values were normalized with respect to the temperature plateau and superimposed on normalized (with respect to maximum value for each location) field radiation response curves. Data from chambers plotted well against field radiation response curves for grain weight and oil concentration. The shapes of the curves of grain weight vs. intercepted solar radiation were similar among locations. Correlation between radiation curve parameters values and MT was found. A mathematical relation that includes radiation and temperature response was established. This equation allowed a better data prediction than the one obtained when considering only one environmental factor. • Part of grain weight and oil concentration response to temperature can be attributed to a decrease of the amount of solar radiation accumulated as a consequence of a shorter critical period for radiation effect as well as grain filling duration. However, when taking into account a direct temperature effect in addition to radiation effects on grain weight and oil concentration, the variables prediction significantly improved. Future research will be directed towards the decorrelation of both environmental factors effects. • This work constitutes an important contribution towards understanding the effect of temperature during grain filling on sunflower yield and its relationship to radiation effects. Simple response curves to environmental factors represent ‘meta-mechanisms’ at plant or crop level. Such meta-mechanisms could be useful for different uses, especially when modeling via gene regulatory networks is not feasible because of system complexity (e.g. oil synthesis and accumulation in sunflower grain).