Understanding the sink-to-source relationship on leafy crops offers valuable insights into optimizing resource allocation for enhanced plant growth and quality. Variations in growth rates and carbon pools across individual leaves or groups of leaves at similar developmental stages allow us to understand the plant strategies of carbon allocation and partitioning. We hypothesized that products that enhance the carbon source-to-sink relationship during leaf development can lead to increased growth and dry matter accumulation. This project aimed to determine if the exogenous application of a cytokinin and B-Mo-based product during leaf development would impact carbon source-to-sink relationship and, hence, influence plant growth and quality. The experiment was a complete randomized design with two treatments consisting of a negative control and the application of the product twice during the growing cycle. The experimental unit consisted of a deep-water culture reservoir with three lettuce plants. Destructive sampling was conducted at five sampling points. At each sampling point (n=4 per experimental run), the phenological stage was determined, and root and shoot length and dry matter, leaf length, width, area, and non-structural carbon and chlorophyll contents were measured. This data was used to estimate growth rates. Results indicate that the cytokinin and B-Mo-based product increased the number of true unfolded leaves by 1 ± 0.4 and the overall size of the lettuce head by 9%. The treated lettuce reached a marketable size four days earlier than the control treatment. Statistically significant differences were observed in the shoot and root dry matter accumulation and foliar length and width at some sampling points. Some of the growth indices indicate an increase in leaf surface area investment and enhanced conversion efficiency of assimilates into biomass in plants treated with the product. Plants exhibiting these alterations had higher sucrose and total soluble sugar content. There was a noticeable pattern of higher concentrations of non-structural carbohydrates, proteins, and amino acids in the leaves compared with the roots across all plants and treatments. Overall, our study on using a cytokinin and B-Mo-based product to strengthen the source-to-sink relationship during the development of a leafy crop provides new insights into non-structural carbohydrate metabolism and the role of CKs, B, and Mo in generating a high-quality plant in a shorter timeframe.
