Potential Use of Spent Coffee Grounds and Spent Tea Leaves Extracts in Priming Treatment to Promote In Vitro Early Growth of Salt-and Drought-Stressed Seedlings of Capsicum annuum L.

Abstract

Spent coffee grounds (SCG) and spent tea leaves (STL) are constantly rejected either on a domestic scale or more widely on an industrial level. The main objective of this work was to evaluate the potential use of their aqueous extracts as organic priming agents in pepper (Capsicum annuum L.) in vitro germination under salt (NaCl, 102.66 mM) or drought (PEG 6000, 4%) stress for 384 h. Extraction from SCG and STL were achieved by three conventional techniques (infusion, boiling and incubation at room temperature). Thereafter, different concentrations from each by-product were examined. The results showed that, under salt stress, STL extract at 1.5% dry tea leaves (DTL), obtained by infusion extraction, displayed the best response in terms of final germination percentage (FGP), time taken for cumulative germination to reach 50% of its maximum (t50) and germination uniformity (U7525), whereas, the best improve in root length was obtained with 2.25% DTL compared with unprimed culture. Against drought stress, SCG extract at 4% dry coffee ground (DCG), obtained following incubation extraction, resulted in amelioration in FGP and U7525, however, 2% DCG engendered the best stimulation of growth. Added directly to the medium culture, STL (1.5% DTL) caused a highly significant inhibition of the germination process with both types of stress. However, SCG (2% DCG) supplementation is recommended mainly in drought stress to improve seedlings growth. Organic priming and medium supplementation can be alternative pathways for SCG and STL wastes valorization. Furthermore, these techniques can be a good cropping practice to improve seed potentiality against environmental challenges in sustainable agriculture.