Alternatives for control of soil-inhabiting pests are needed due to the phase-out of methyl bromide. One possible alternative is using the pesticidal properties of compounds released by macerated Brassica tissues. In this study, larvae of masked chafer beetles (Cyclocephala spp.) were placed in soil amended with Brassica juncea L. (PI 458934) tissue. Allyl isothiocyanate (AITC) levels were positively correlated to larval mortality, with the 8% B. juncea treatment resulting in 100% larval mortality with an average AITC concentration of 11.4 mg per liter of soil atmosphere. Although B. juncea produces high levels of AITC, the mass of tissue required for significant insecticidal activity against Cyclocephala spp. also is high, between 4 and 8% of soil mass for this plant accession. Accepted for publication 23 May 2002. Published 10 June 2002.
ADDITIONAL INDEX WORDS. Brassica, southern blight, soilborne pathogen, biofumigation ABSTRACT. Allyl isothiocyanate (AITC) is the predominant isothiocyanate produced by damaged tissues of Indian mustard (Brassica juncea (L) Czerniak). This study investigated Indian mustard and AITC mediated suppression of mycelial growth and sclerotial germination of Sclerotium rolfsii Saccardo, a common soilborne pathogen. Indian mustard (IM) treatments of 0, 0.1, 0.2, 0.6, 1.0, 2.0, 4.1, 5.1, 10.2, 20.4, 40.8, 81.6, and 163.3 g·L -1 (weight of reconstituted mustard per liter of air) were evaluated for suppression of mycelial growth. Treatment effect was evaluated by measuring the radial growth of mycelia. Sclerotia were placed in culture tubes containing 18 g autoclaved soil and covered with an additional 5 g soil. AITC at concentrations of 0, 4.0, 16.0, 64.0, 256.0, 1024.0, or 4096.0 µmol·L -1 was injected into the tubes. Treated sclerotia were removed from tubes and plated on potato dextrose agar to determine viability. Mycelial growth was inhibited with IM treatments (P < 0.01). Inhibiting concentrations (IC) of IM for mycelial growth inhibition of 50% and 90% were 0.7 and 1.0 g·L -1 , respectively, with death resulting with >2 g·L -1 . Inhibition attributable to AITC alone was lower than that achieved by IM producing equivalent amounts of AITC. Germination of sclerotia was negatively correlated with AITC concentration (r = 0.96; P < 0.01). The IC 50 and IC 90 of AITC were 249.0 and 528.8 µmol·L -1 , respectively, at 42 hours. The lethal concentration for sclerotia was not reached; only suppression occurred at the highest treatment concentrations. Sclerotium rolfsii mycelia were sensitive to the IM volatiles and were suppressed at low concentrations. Sclerotia were more resistant than the mycelia and required higher concentrations of AITC to suppress germination.
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