Occurrence of entomopathogenic fungi in tejocote (Crataegus mexicana) orchard soils and their pathogenicity against Rhagoletis pomonella.

AIMS: To determine the abundance and diversity of entomopathogenic fungi in tejocote orchard soils and evaluate their ability to infect Rhagoletis pomonella Walsh., the main pest of tejocote. METHODS AND RESULTS: Surveys were made in two locations in Mexico state and two in Puebla state. Soil from selected locations was baited for entomopathogenic fungi with Galleria mellonella (L.). All isolates were identified morphologically to genus level and to species level using Bloc and elongation factor 1-α gene sequence information, respectively; Beauveria bassiana ((Bals.-Criv.) Vuill.), B. pseudobassiana (S.A. Rehner & Humber) and Metarhizium robertsii (J.F. Bisch., Rehner & Humber) were found, with B. bassiana being the most abundant and widely distributed. Pathogenicity of five selected B. bassiana isolates and three M. robertsii isolates was evaluated against larvae and pupae of R. pomonella. All isolates infected larvae resulting in an average mortality of 35%. Pupae were not susceptible; however, adults emerging from inoculated pupae did die due to infection. CONCLUSIONS: At least three species of entomopathogenic fungi are present in the soil from tejocote orchards, with B. bassiana being the most abundant and widely distributed. Rhagoletis pomonella larvae were more susceptible to infection than pupae. SIGNIFICANCE AND IMPACT OF THE STUDY: Our study has produced new information about the distribution of entomopathogenic fungi in cultivated soils from this region of North America, contributing to a better understanding of their natural occurrence and underpinning the development of biological control approaches.

First Report of Lettuce big-vein associated virus (Varicosavirus) Infecting Lettuce in Mexico.

Lettuce (Lactuca sativa) is a common consumed vegetable and a major source of income and nutrition for small farmers in Mexico. This crop is infected with at least nine viruses: Mirafiori lettuce big-vein virus (MiLBVV), Lettuce big-vein associated virus (LBVaV), both transmitted by the soil-borne fungus Olpidium brassicae; Tomato spotted wilt virus (TSWV), Tomato chlorotic spot virus (TCSV), Groundnut ringspot virus (GRSV), Lettuce mottle virus (LMoV), Cucumber mosaic virus (CMV), Bidens mosaic virus (BiMV), and Lettuce mosaic virus (LMV) (1). From March to May 2012, a disease on lettuce was observed in the south region of Mexico City displaying mild to severe mosaic, leaf deformation, reduced growth, slight thickening of the main vein, and plant death. At the beginning of the epidemic there were just a few plants with visible symptoms and 7 days later the entire crop was affected, causing a loss of 93% of the plants. It was estimated by counting the number of severely affected or dead plants in three plots. No thrips, aphids, or whiteflies were observed in the crop during this time. Twenty plants with similar symptoms were collected and tested by RT-PCR using the primers LBVaVF 5'-AACACTATGGGCATCCACAT-3' and LBVaVR 5'-GCATGTCAGCAATCAGAGGA-3' specific for the coat protein gene of LBVaV, amplifying a 322-bp fragment. Primers CP829F 5'-CCWACTTCATCAGTTGAGCGCTG-3' and CP1418R 5'-TATCAGCTCCCTACACTATCCTCGC-3' were used to detect MiLBVV (2). No amplification was obtained for MiLBVaV in any plants tested. PCR products of approximately 300 bp were obtained from four out of 20 symptomatic lettuce samples tested for LBVaV, but not from healthy plant and water controls. These results suggest the presence of another virus in symptomatic lettuce plants. Amplicons were gel-purified and sequenced using LBVaVF and LBVaVR primers. A consensus sequence was generated using the Bioedit v. 5 program. Both sequences of these Mexican lettuce isolates were 100% identical (Accession Nos. KC776266.1 and KC776267.1) and had identities between 94 and 99% to all sequences of LBVaV available in GenBank. Additionally, when alignments were made using ClustalW, these sequences showed identities of 99.7% to Almeria-Spanish isolate (Accession No. AY581686.1); 99.4% to Granada-Spanish isolate (AY581689.1); 99.1% to Dutch isolate (JN710441.1), Iranian isolate (JN400921.1), Australian isolate (GU220725.1), Brazilian isolate (DQ530354.1), England isolate (AY581690.1), and American isolate (AY496053.1); 96.2% to Australian isolate (GU220722.1); 96.3% to Japanese isolate (AB190527.1); and 92.8% to Murcia-Spanish isolate (AY581691.1). Twenty lettuce plants were mechanically inoculated with leaf tissue taken from the four plants collected in the field and tested positive for LBVaV by RT-PCR; 12 days after inoculation, mosaic symptoms were observed in all inoculated plants and six of them were analyzed individually by RT-PCR obtaining a fragment of the expected size. To our knowledge, this is the first report of LBVaV infecting lettuce in Mexico. Further surveys and monitoring of LBVaV incidence and distribution in the region, vector competence of olpidium species, and impact on the crop quality are in progress. References: (1) P. M. Agenor et al. Plant Viruses 2:35, 2008. (2) R. J. Hayes et al. Plant Dis. 90:233, 2006.