Amaranth cystatin inhibits the growth of broccoli (Brassica oleracea var. italica L.) pathogenic bacteria

Head soft rot is the major disease of broccoli caused by Pseudomonas fluorescens and Pectobacterium carotovorum (formerly Erwinia carotovora). However, in the present work, Pseudomonas sp. was isolated along with Pantoea agglomerans and Serratia liquefaciens, from broccoli heads with disease symptoms. Different phytopathogenic assays confirmed the ability of the isolated Serratia liquefaciens strain to produce soft rot disease in stems and florets of broccoli. This study also investigated the effect of an amaranth cystatin (AhCPI) on the growth of these three bacterial pathogens and on the development of soft rot symptoms in broccoli. AhCPI significantly reduced the severity of head soft rot symptoms caused by Pseudomonas sp., and S. liquefaciens in vitro. Bacterial growth inhibition increased with the increase in AhCPI concentration. In the same way, it was demonstrated that the application of AhCPI (10 or 20 mu M) on florets of broccoli with soft rot symptoms significantly reduced the severity of disease caused by S. liquefaciens or Pseudomonas sp. Our results suggest that S. liquefaciens can produce head soft rot in florets of broccoli and AhCPI could be a new sustainable alternative for the control of head soft rot disease in broccoli.