An Outbreak of a Necrosis Disease of Tomato in California in 2008 was Caused by a New Ilarvirus Species Related to Parietaria mottle virus.

During the 2008 early-summer growing season, virus-like necrosis symptoms, most similar to those induced by Tobacco streak virus (TSV), were observed in leaves, stems, and petioles of processing tomato plants in the Central Valley of California. Symptoms were observed in numerous fields in Merced, San Joaquin, and Yolo counties, though the incidence of the disease in most fields was not high (not more than 5% but over 20% in some areas). Antibody-based tests of representative samples of the disease for infection with Tomato spotted wilt virus, TSV, and Tomato apex necrosis virus, which cause similar symptoms, were negative. A putative virus-like agent was sap- and graft-transmitted to tomato plants and induced necrotic spots in leaves and stem and petiole necrosis symptoms that were similar to those observed in the field. Eventually, these plants recovered from these symptoms. In sap-transmission experiments, the virus-like agent induced systemic symptoms in Chenopodium quinoa and C. amaranticolor (stunted growth and leaf curl and necrosis), Nicotiana benthamiana (necrotic leaf and stem lesions), N. tabacum cvs. Havana and Turkish (stunted growth and necrotic etching and ringspots followed by recovery for cv. Havana but not for cv. Turkish), and Datura stramonium (mild mottle and ringspots in newly emerged leaves followed by recovery); no symptoms were observed in inoculated common bean (cv. Topcrop), pumpkin (cv. Small Sugar), pepper, and N. glutinosa plants. Virus minipurification was performed with leaves from noninfected and infected D. stramonium plants, and polyacrylamide gel electrophoresis analyses revealed a protein band of ~29 kDa in infected but not noninfected plants. This protein was purified and subjected to liquid chromatography-mass/mass spectrometry analysis. Four peptides, obtained from the trypsin-digested protein, each had the highest match (score of 118) with the capsid protein (CP) of Parietaria mottle virus (PMoV), an ilarvirus that induces leaf and stem necrosis in tomatoes in Europe (1). Using sequences of PMoV and other ilarviruses, a single primer was designed from the 3' nontranslated region and paired with primers designed from conserved regions of ilarvirus RNAs 1, 2, and 3. In reverse transcription-PCR analyses, these primer pairs directed the amplification of the expected-sized fragments for ilarvirus RNAs 1, 2, and 3 from RNA extracts prepared from leaves with the unusual necrosis symptoms. Sequence analyses confirmed these were ilarvirus fragments. Partial RNA 1, 2, and 3 sequences were 81, 84, and 82% identical, respectively, with those of PMoV and 80, 77, and 69% identical, respectively, with those of TSV. The amino acid sequence of the CP gene (GenBank Accession No. FJ236810) was 86 and 61% identical to those of PMoV and TSV, respectively. Together, these results indicate the necrosis disease of tomato is caused by a new ilarvirus species, tentatively named Tomato necrotic spot virus, although further studies are needed to confirm this. The mode of transmission of this new ilarvirus to tomatoes in the field is unknown, but it may involve thrips feeding on infected pollen, a known method of transmission for TSV (2). References: (1) L. Galipienso et al. Plant Pathol. 54:29, 2005. (2) R. Sdoodee and D. S. Teakle. Plant Pathol. 36:377, 1987.

Outbreak of Eremothecium coryli Fruit Rot of Tomato in California.

A ripe fruit rot of tomato (Lycopersicon esculentum) associated with stink bug (Euschistus conspersus) feeding caused extensive losses in the Sacramento Valley of California in 1998. Portions of several fields were abandoned at harvest due to fruit rot levels >30%. Symptoms included a soft, water-soaked rot often surrounding a firm, dark green island. Entire fruit sometimes became watery and soft. The ascomycetous yeast, Eremothecium coryli, characterized by spindle-shaped ascospores with long, thin, whip-like terminal appendages (1), was consistently isolated from diseased tissue plated on V8 or potato dextrose agar amended with tetracycline. Ripe tomato fruit were inoculated with a 0.1-ml suspension of 1.5 × 105 ascospores per ml injected to a depth of ≈4 mm to simulate stink bug probing. Fruit were placed in plastic containers and, in initial tests, were held at room temperature. In subsequent tests, inoculated fruit were maintained at constant temperatures of 20, 25, 30, or 35°C. Controls included inoculum either placed on the fruit surface or injected with sterilized water. Each treatment consisted of one to four fruit in two to four replications. All experiments were repeated. Lesions were visible within 5 days after inoculation and were >25 mm in diameter after 7 days. Progression of rot occurred at all temperatures but was fastest at 30 and 35°C. Controls remained symptomless. E. coryli was reisolated from infected fruit. This is the first documentation of field-level losses caused by E. coryli associated with stink bug feeding. Isolates are maintained in the Herman J. Phaff Collection of Yeast and Yeast-like Microorganisms at the University of California, Davis. Reference: (1) G. S. de Hoog et al. 1998. Eremothecium Borzi emend. Kurtzman. Pages 201-208 in: The Yeasts-A Taxonomic Study. C. P. Kurtzman and J. W. Fell, eds. Elsevier Scientific Publishers, Amsterdam.

A sequential analysis of the partial reinforcement extinction effect in children*.

In a series of studies employing children between the ages of 7.6 and 10.6 years of age guessing on a modified Humphreys's board, extinction training was administered following either continuous reinforcement or various schedules of partial reinforcement training. Besides the observation of a partial reinforcement extinction effect, it was found that resistance to extinction appeared to be regulated by those sequential variables specified by extensions of Capaldi's theory of instrumental learning.