Maize kernel oil and episodes of shading during the grain-filling period
Previous studies documented the stability of maize (Zea mays L.) kernel oil concentration for a wide range of kernel weights promoted by contrasting post-flowering assimilate availabilities per kernel (i.e., source–sink ratios). These studies mainly modified the sink size with a low impact on the source size. In this study, we focused on kernel oil concentration response to source–sink ratio alterations promoted by different timings and intensities of shading during the effective grain-filling period. Two crosses with contrasting kernel oil concentration (‘DK752’ x DK752 and DK752 x ‘5MG’) were tested. Kernel oil concentration was positively related to the embryo–kernel ratio (r = 0.96, P < 0.001) and embryo oil concentration (r = 0.94, P < 0.001) and crosses differed in both traits. Severe shading (85% reduction of incident solar radiation) at early stages of kernel growth reduced the final embryo–kernel ratio and the embryo oil concentration of both crosses. Contrarily, moderate shading (45% reduction of incident solar radiation) did not modify the kernel oil determinants. Kernel oil concentration and kernel weight declined when severe shading shortened the kernel growth period. Our results collectively sustain the hypothesis that maize kernel oil concentration is commonly sink-limited. We established that kernel oil concentration of both crosses was reduced when post-flowering plant growth rate per kernel was less than 50% of kernel growth rate.