Improving yield of a bean ecotype using biostimulants: focus on bean amino acid profiles and plant responses

Biostimulants have emerged as having the potential to sustainably enhance crop performance as well as yield quantity and nutritional quality. Although naturally rich in lysine, beans are generally deficient in sulfur-containing amino acids like methionine and cysteine. Improving the nutritional imbalance in beans is highly desirable, especially in those with cultural and economic value, like Fagiolo di Sorana, a high-quality Protected Designation of Origin (PDO) bean variety from Pistoia, Italy. A spirulina-based (1 g/L and 3 g/L) and a commercially available (MC EXTRA; 1 g/L) biostimulant were applied as foliar sprays for two consecutive years to Fagiolo di Sorana plants grown under both open field and semi-controlled greenhouse conditions. Productivity was higher in treated plants: a 7 % increase (p-value, 0.036) was found in whole pod weight in the first year of the trial with 3 g/L and in the second year trial (p-value, 0.020) for MC EXTRA compared to the control. Improved amino acid composition of the beans were found, specifically an increase of 200 % (p-value, 0.040) and 400 % (p-value, 0.053) in methionine content with 3 g/L spirulina and MC EXTRA, respectively, compared to the control, thus addressing the bean's typical deficiency in sulfur amino acids. Bean digestibility increased 3 % (p-value, 0.013) with the higher concentration (3 g/L) of the spirulina-based biostimulant relative to the control-grown plants. Molecular barcoding identified genetic differences within a collection of ten Tuscan bean landraces, including the Fagiolo di Sorana variety, thus offering a first attempt at the genetic characterization essential for preserving landrace germplasm. These genetic data were then coupled with the assessment of protein digestibility to identify differences within the landrace collection. Thus, the use of biostimulants presents an opportunity to further enhance the yield and nutritional profile of this PDO without compromising its environmental integrity.