Verticillium dahliae is a soilborne fungus that causes vascular wilt diseases on numerous plant species worldwide. The production of darkly melanized microsclerotia is crucial in the disease cycle of V. dahliae, as these structures allow for long-term survival in soil. Previously, transcriptomic and genomic analysis identified a cluster of genes in V. dahliae that encodes some dihydroxynaphthalene (DHN) melanin biosynthetic pathway homologues found in related fungi. In this study, we explored the roles of cluster-specific transcription factor VdCmr1, as well as two other genes within the cluster encoding a polyketide synthase (VdPKS1) and a laccase (VdLac1), enzymes at initial and endpoint steps in DHN melanin production. The results revealed that VdCmr1 and VdPKS1 are required for melanin production, but neither is required for microsclerotia production. None of the three genes were required for pathogenesis on tobacco and lettuce. Exposure of ΔVdCmr1 and wild-type strains to UV irradiation, or to high temperature (40 °C), revealed an approx. 50 % reduction of survival in the ΔVdCmr1 strain, relative to the wild-type strain, in response to either condition. Expression profiles revealed that expression of some melanin biosynthetic genes are in part dependent on VdCmr1. Combined data indicate VdCmr1 is a key regulator of melanin biosynthesis, and that via regulation of melanogenesis, VdCmr1 affects survival of V. dahliae in response to abiotic threats. We conclude with a model showing regulation of VdCmr1 by a high osmolarity glycerol response (Hog)-type MAP kinase pathway.

Lettuce plants were artificially inoculated with three isolates of Xanthomonas campestris pv. vitians in field and greenhouse evaluations for genetic variation in resistance to bacterial leaf spot. The cultivar Little Gem had the least amount of disease, whether evaluated for disease severity or disease incidence. Disease severity levels for cultivar Batavia Reine des Glaces were not significantly different from those of Little Gem. Several cultivars including Vista Verde, Pybas 251, Pacific, Clemente, Salinas 88, and Sniper were highly susceptible. There was a strong correlation between results obtained in the greenhouse and those obtained in the field (r = 0.77, P = 0.009) indicating that greenhouse assays may be used to increase the number of cultivars evaluated and to speed breeding efforts. Accepted for publication 17 May 2007. Published 17 September 2007.

Three different cotton production strategies [certified organic, conventionally grown, and reduced insecticide input/integrated pest management (IPM)] were compared in field-sized replicates in the Northern San Joaquin Valley (NSJV), California, from 1996 to 2001. We measured arthropod abundance, plant development, plant density, pesticide use, cost of production, lint quality and yields in the three treatments. Overall pest abundance was low, and a key cotton fruit pest,Lygus hesperusKnight, known as the western tarnished plant bug (WTPB), did not exceed action thresholds in any treatment. Organic fields had significantly more generalist insect predators than conventional fields during at least one seasonal interval in all but one year. While there were no significant differences in plant development, plant densities at harvest were lower in organic than conventional and IPM fields. Some measures of lint quality (color grade and bale leaf rating) were also lower in the organic treatment than in either the IPM or the conventional treatments. Synthetic insecticides, not allowed for use in organic production, were also used in significantly lower quantities in the IPM fields than in the conventional fields. Over the 6-year period of the study, IPM fields averaged 0.63 kg of active ingredient (AI) insecticide per hectare, as opposed to 1.02 kg AI ha−1for conventional fields, a reduction of 38%. Costs of production per bale were on average 37% higher for organic than for conventional cotton. This cost differential was primarily due to greater hand-weeding costs and significantly lower yields in organic cotton, compared with either IPM or conventional cotton. Average 6-year yields were 4.4, 5.4 and 6.7 bales ha−1for organic, IPM and conventional treatments, respectively. Low world cotton prices and the lack of premium prices for organic cotton are the primary obstacles for continued production in the NSJV.

Thirteen commercial strawberry cultivars were evaluated in side‐by‐side comparisons in five experiments in organic strawberry production fields in central California. Seven cultivars were common to all five experiments; six additional cultivars were included in one to four of the experiments. Of the seven cultivars that were evaluated in all five experiments, the largest market yield was consistently obtained from Aromas, Seascape, or Pacific. Preliminary analyses detected a strong positive correlation between total fruit yield and the nitrogen status of plants, suggesting characteristics in nitrogen uptake and metabolism may be a significant factor in determining yield of commercial strawberry cultivars tested in organic fields. None of the seven commercially prepared mycorrhizal inoculants tested resulted in an increased marketable fruit yield in organic or non‐fumigated fields. However, the effects of the treatments on mycorrhizal colonization and total yield varied among experiments. For example, in one of six experiments, a commercial inoculant increased total yield over the nontreated control but did not influence marketable fruit yield.