Silk sericin as a biostimulant for lettuce (Lactuca sativa L.): Effects of foliar spray and soil drenching under water stress

Sericin solution (SER), derived from silkworm cocoons, is a mixture with promising properties that may enhance plant growth. To evaluate the potential use of this SER preparation as a biostimulant, a study was conducted on lettuce (Lactuca sativa L.) plants, assessing both leaf spray and soil drenching methods. The experimental design included the study of plant responses to SER treatment in well-watered and water stress (WS) conditions and compared them with those of two commercially available reference biostimulants (REF1, REF2). Although some beneficial effects were observed in well-watered plants, the most significant ones occurred under WS. In this condition, the fluorescence performance index (PI) increased in plants treated with SER via leaf spray. Additionally, both SER and the commercial references reduced leaf temperature, suggesting a positive impact on leaf transpiration. Moreover, shoot head diameter remained unaffected in plants treated with REF1 and SER via leaf spray. Although SER did not fully counteract the effects caused by WS, several biochemical parameters, such as the phenolic index, and the contents of total sugars, sucrose, proline, and malondialdehyde (MDA), revealed notable differences in metabolic responses, some of which were comparable to those induced by the commercial references. Interestingly, the mode of SER application appeared to elicit distinct physiological responses. Notably, leaf application of both SER and REF1 significantly reduced leaf nitrate content under non-stress condition.This study supports the potential use of SER as a biostimulant. Being derived from textile industry waste, it aligns well with the principles of the circular economy.