A monoclonal antibody was prepared against deoxynivalenol (DON, vomitoxin), a trichothecene mycotoxin occurring in grain contaminated with Gibberella zeae (anamorph = Fusarium graminearum), and incorporated into competitive direct and indirect enzyme-linked immunosorbent assays (ELISAs). DON antibodies were secreted by hybridomas derived from mice inoculated with DON conjugated to bovine serum albumin. Conjugation of DON to carrier proteins was facilitated by conversion of DON to 3-O-hemisuccinyl-DON after protection of two of the three available hydroxyls with a cyclic boronate ester. DON was detectable at 10-250 ng/assay (0.2-5.0 µg/mL) for direct ELISA and 10-150 ng/assay (0.2-2.0 µg/raL) for indirect ELISA. The monoclonal antibody cross-reacts with 3-acetyl-DON, 3-Ohemisuccinyl-DON, DON, 12,13-deepoxy-DON, nivalenol, and fusarenone X (in order of decreasing affinity) but has low affinity for 15-acetyl-DON and T-2 toxin. Deoxynivalenol (DON, vomitoxin) is one of the sesquiterpene mycotoxins classified as 12,13-epoxytrichothecenes (Mirocha et al, 1977). It occurs naturally in infected corn (Hart et al., 1982;Mirocha et al., 1976), small grains (Hart and Braselton, 1983; Neish and Cohen, require little sample preparation, are rapid and relatively simple to execute, yet are sensitive. In addition, enzyme immunoassays lack the health hazards associated with radioimmunoassays. Monoclonal antibodies have important advantages over polyclonal antibodies. They may be extremely specific, even if the immunizing antigen was not pure, and offer a theoretically unlimited supply of homo-

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Sporulation, spore germination, and yeast-hypha dimorphism in the ifiamentous fungus Mucor racemosus provide useful model systems to study cell development in eucaryotic cells. Three RAS genes (MRASI, MRAS2, and MRAS3) from M. racemosus have been cloned, and their nucleotide sequences have been determined. The predicted amino acid sequences and the sizes of the three MRAS proteins exhibit a high degree of similarity with other ras proteins, including that encoded by H-ras, which have been implicated in regulation of proliferation and development in eucaryotic cells by mediating signal transduction pathways. The MRAS proteins show conservation of functional domains proposed for ras proteins, including guanine nucleotide interaction domains, an effector domain, a binding epitope for neutralizing antibody Y13-259, and the COOH-terminal CAAX box, which is a site of thiocylation and membrane attachment. Amino acid sequences unique to each MRAS protein occur adjacent to the CAAX box, consistent with the location of the hypervariable region in other ras proteins. Northern (RNA) analysis was used to study expression of the three MRAS genes in relation to cell development. Gene-specific probes for two of these genes, MRAS1 and MRAS3, hybridized to different 1.3-kb mRNA transcripts. The accumulation of these transcripts depended on the developmental stage, and this pattern was different between the two MRAS genes. No transcript for MRAS2 was detected in the developmental stages examined. The unique patterns of MRAS transcript accumulation suggest that individual MRAS genes and proteins may play distinct roles in cell growth or development.The fungus Mucor racemosus is a saprophytic zygomycete that provides a useful system for studying eucaryotic cell differentiation. It is a relatively simple organism with a small genome (1.6 x 107 bp per haploid genome [34]) and an available transformation system (36) which facilitate molecular genetic investigations. M. racemosus is dimorphic: it exhibits filamentous (hyphal) growth in the presence of oxygen, but under anaerobic conditions with a fermentable hexose available, the organism grows as a single-celled, budding yeast (4). The fungus also undergoes morphogenesis during sporulation and germination of two asexual spore types, sporangiospores and arthroconidia, and a sexual spore called a zygospore.Morphogenesis in M. racemosus is correlated with changes in cyclic AMP (cAMP) and phospholipid metabolism (4,10,13,14,(21)(22)(23) large increase in phospholipid metabolism during yeast-tohypha morphogenesis, especially in the turnover of phosphatidylethanolamine and phosphatidylinositol (PI) (13). Cerulenin prevents phospholipid turnover and yeast-to-hypha morphogenesis under conditions in which cell growth continues at rates typical of yeast cells.The implication of cAMP and PI as secondary-messenger molecules in signal transduction pathways involving ras proteins, the ubiquity of ras proteins in eucaryotes, and the putative role of ras in cell differentiation and proliferation (2, 2...

Organic mulches colonized with microbial biocontrol agents, termed bioenhanced mulches, were tested for their ability to reduce Phytophthora root rot of avocado (Persea americana Mill.). Benomyl-resistant mutants of Gliocladium virens (KA 230-1) and Trichoderma harzianum (KA 159.2) isolated from suppressive soils and selected as efficient antagonists of P. cinnamomi were evaluated for their ability to colonize different mulches under controlled laboratory conditions. Sudangrass and a coarse yardwaste were found to be better substrates than a fine yardwaste, woodwaste or rice hulls for biocontrol agents propagules production. The most suitable conditions for colonization were an optimum temperature of 24°C, a moisture content of 20% for sudangrass and 30% for the coarse yardwaste, and a continuous light exposure during a 15-day incubation period. In the greenhouse, fresh sudangrass and a coarse yardwaste colonized with G. virens and used as a surface mulch proved to be the best combination for reducing the population of P. cinnamomi in 4-liter pots containing artificially-infested soil. Healthy avocado roots made up 31-37% of the roots in the G. virens-mulch combinations compared to 0% healthy in infested controls after two months.

The trichothecenes, deoxynivalenol (DON, vomitoxin) and T-2 toxin, Sensitivity to DON was not correlated with susceptibility to ear rot by a inhibited 3 H-leucine incorporation into acetone:ethanol insoluble material DON-producing strain of Gibberella zeae (anamorph = Fusarium gramiby maize and wheat tissue (leaf disks and kernel sections). These nearum) for six maize lines with a range of disease reactions from highly compounds are known to inhibit protein synthesis in animals and yeast. susceptible to highly resistant. However, the ID 50 for one moderately The toxin concentrations that gave ID 50 (50% reduction) for 3 H-leucine resistant line (A509) was 2.3 times greater than the IDs0 of the most incorporation by several maize varieties were 0.9 1-M T-2 toxin and 9-22 susceptible line (B79). 3 H-Leucine incorporation by wheat and maize was /yM DON. ID 50 values for wheat were 0.26 M M T-2 toxin and 4.5 pM DON. inhibited by DON and T-2 toxin at concentrations occurring in naturally T-2 toxin gave near-maximum inhibition in leaf tissue within 5 min after infected tissue, suggesting the need for further evaluation of these exposure to the toxin. T-2 toxin or its effects on 3 H-leucine incorporation compounds as plant disease determinants. persisted at least 120 min after removal of leaf disks from toxin solutions.