Biological control of Meloidogyne incognita and Fusarium solani in sugar beet

Abstract

Meloidogyne incognita and Fusarium solani cause the root-knot and root-rot diseases of sugar beet (Beta vulgaris L.) in Egypt. Therefore, the effect of several commercial products containing either the fungi Paecilomyces lilacinus, P. fumosoroseus and Trichoderma album and the bacteria Bacillus subtilis and B. megaterium were tested against both pathogens on sugar beet, and compared with the nematicides fenamiphos and cadusaphos, under in vitro, greenhouse and field conditions. In vitro, the mortalities of M. incognita were within the range of 61-94% with bio-control products, compared to 96-98% with fenamiphos and cadusaphos. All treatments significantly reduced the mycelial growth of F. solani, with the greatest reduction given by T. album. In the greenhouse, B. megaterium greatly reduced the numbers of galls, females and egg-masses of the nematode in the roots of sugar beet, followed by B. subtilis, P. lilacinus, P. fumosoroseus and T. album, respectively. All treatments increased shoot length and weight, root weight and percentage of total soluble solids (TSS) in sugar beet plants. In the field, all treatments greatly reduced the population densities of second-stage juveniles in soil, and the numbers of galls, females and egg masses of M. incognita in the roots, more so at the recommended than at half the recommended dose. Aspergillus spp., A. niger, F. solani, F. oxysporum, Penicillium spp., Rhizoctonia solani, Rhizopus nigricans and Trichoderma spp. were the most common fungi found in the rhizosphere of treated and untreated sugar beet plants. All treatments affected the frequency of the isolated fungi. Soil treatments with P. lilacinus, P. fumosoroseus, fenamiphos and cadusaphos increased plant weight, foliage weight, length, diameter and weight of roots, survival of plants and tap root yield. The treatments also affected total soluble solids, sucrose content, the sucrose purity of tap roots and sugar yield.