Disease management in eggplant (Solanum melongena L.) nurseries also reduces wilt and fruit rot in subsequent plantings: A participatory testing in Bangladesh

Bacterial wilt (causal agent: Ralstonia solanacearum) and Phomopsis fruit rot (causal agent: Phomopsis vexans) are two major diseases constraining eggplant production in Bangladesh. No integrated management options to manage both diseases together are currently available; farmers spray pesticides. A 2-year participatory study was conducted to compare yield and disease severity of plants that originated from preceding nursery studies. Both soil and seed were found to be source of these pathogens. Seedlings raised according to farmers practice or in nursery soil treated with Trichoderma harzianum from seed treated either with hot water or Carbendazim were transplanted on fields either with or without soil application of T. harzianum. The seed treatments had comparable effects. Improved nursery management alone reduced wilt and fruit rot by 25-40 and 14-20 percentage points respectively, increased marketable yield by 8-19 t ha(-1) and income by (sic)1800-3700 ha(-1) compared to farmers conventional practice of spraying. In Year 1, a comparable result was obtained treating only the field but not the nursery; farmers, however, did not want to repeat this treatment in Year 2 as costs were higher. Further disease reduction (10-11 and 0.6-6 percentage points respectively for wilt and rot) occurred when improved seedlings were transplanted into T. harzianum amended fields and consequently marketable yield increased by 5-7 t ha(-1) and income by (sic)500-900 ha(-1). Both labour and material costs of the introduced technology were lower than the costs of current farmers practice. Given costs of labour and inputs and eggplant price fluctuations over years, farmers are recommended to use the improved nursery management practices. Also treating the field may depend on the capacity of farmers to invest in the additional labour and input. In fields with improved management, T. harzianum persisted at the end of the growing season and reduced populations of R. solanacearum and P. vexans. Also, seed preserved from improved management plots showed reduction of both pathogens compared to seed from farmers practice plots. The reduction of pathogens both in field soil and preserved seed for improved management plots may imply that a next crop will start with a lower level of disease pressure. Laboratory tests showed nursery raised seedlings from screenhouse experiments were always found infected with R. solanacearum, but soil application of T. harzianum alone or combined with hot water treatment of seed substantially reduced the infection. Given the positive results of our study, the technology should be made locally available to support eggplant IPM.