Biological enhancement of the cover crop Phacelia tanacetifolia (Boraginaceae) with the nematophagous fungus Pochonia chlamydosporia to control the root-knot nematode Meloidogyne hapla in a succeeding tomato plant

Root-knot nematodes cause global economic losses in a wide range of crops. We investigated the potential of seed coatings of the cover crop Phacelia tanacetifolia (Boraginaceae) when inoculated with the nematophagous fungus Pochonia chlamydosporia (Hypocreales: Clavicipitaceae) to protect subsequently grown tomato plants from root galling caused by the root-knot nematode Meloidogyne hapla (Tylenchida: Meloidogynidae). Therefore, seeds of P. tanacetifolia were coated with P. chlamydosporia blastospores and planted in M. hapla-infested pots. After 50 days of growth in infested soil, M. hapla eggs were extracted from P. tanacetifolia roots and quantified. Tomato plants grown in the remaining soil served as bioindicator of M. hapla infestation as expressed by the gall index. Results showed that seed coating of P. tanacetifolia with P. chlamydosporia (290 ± 51 CFU per seed) reduced the number of M. hapla eggs up to 95.6% in comparison to untreated controls. Pochonia chlamydosporia as blastospore suspension (5·10⁸ blastospores per 600 ml soil) reduced the number of M. hapla eggs by up to 75.5%. Additionally, tomato plants grown for 50 days in substrates previously planted with P. tanacetifolia seeds coated with P. chlamydosporia showed a significantly lower gall index than plants grown in untreated pots. In conclusion, biological enhancement of P. tanacetifolia by seed coating with P. chlamydosporia successfully reduced M. hapla and thus provides an additional tool in the management of this nematode. The method still has potential for further improvement such as increasing blastospore viability within the seed coating by optimized formulation technology.