Crop rotation with broccoli suppresses Verticillium wilt of eggplant

Abstract

In this study, we assessed whether crop rotation with broccoli suppressed eggplant Verticillium wilt. In 6 trials of crop rotation in 5 fields from 2009 to 2013, broccoli rotation was coupled with postharvest residue incorporation before planting eggplant. Meta-analysis of the disease incidence data from all the trials revealed that the combined relative disease risk was 0.53 (95 % confidence interval 0.34–0.83). Thus, the disease incidence of eggplant in crop rotation with broccoli decreased to 53 % of that of eggplant without broccoli rotation. Browning of vascular tissue from Verticillium dahliae infection was observed in broccoli, but was limited to the roots and did not reach the aerial plant portion where V. dahliae forms microsclerotia. Estimation of V. dahliae population in soil using quantitative nested real-time polymerase chain reaction indicated that V. dahliae DNA copy number in soil samples tended to decrease owing to broccoli cultivation. These results suggest that broccoli root could act as a “decoy” that traps V. dahliae in soil. Further studies are necessary to elucidate the mechanisms of disease suppression; this is the first report that broccoli cultivation and subsequent incorporation of residue into the soil suppresses Verticillium wilt of eggplant.