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 μM) 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.

The root‐knot nematode Meloidogyne incognita is one of the most damaging plant parasitic nematodes in the world. In this study, the effect of cystatin from Amaranthus hypochondriacus (AhCPI) as a potential control agent for M. incognita was explored. In vitro bioassays demonstrated that AhCPI affects the growth and development of eggs and the infectivity of juveniles (J2) of M. incognita, such as mortality and slower development, showing characteristic tissue damage. Mortality levels were quantified by Probit analysis, estimating LC50s of 1.4 mg/mL for eggs and 0.028 mg/mL for J2. In planta bioassays showed that infected tomato seedlings treated with 0.056 mg/mL of AhCPI showed a 60% reduction in the number of galls, as compared with untreated J2‐inoculated seedlings. Under greenhouse conditions, three applications of 10 mL of AhCPI (1.4 mg/mL) in the soil around the stem of M. incognita‐infected tomato plants, reduced the number of galls by 93 ± 8%, as compared to the control M. incognita‐infected plants. The application of AhCPI to the infected plants increased the yield (10.7%) of harvested tomato fruits, as compared to infected plants. These results show the potential of AhCPI for the control of M. incognita in tomato plants.