No abstract

We explored the potential of biological control of alfalfa (Medicago saliva L.) seedling damping-off caused by Phytophthora megasperma f. sp. medicaginis by screening root-associated bacteria for disease suppression activity in a laboratory bioassay. A total of 700 bacterial strains were isolated from the roots of field-grown alfalfa plants by using Trypticase soy agar. A simple, rapid assay was developed to screen the bacteria for the ability to reduce the mortality of Iroquois alfalfa seedlings that were inoculated with P. megasperma f. sp. medicaginis zoospores. Two-day-old seedlings were planted in culture tubes containing moist vermiculite, and each tube was inoculated with a different bacterial culture. Sufficient P. megasperma f. sp. medicaginis zoospores were added to each tube to result in 100% mortality of control seedlings. Of the 700 bacterial isolates tested, only 1, which was identified as BaciUus cereus and designated UW85, reduced seedling mortality to 0% in the initial screen and in two secondary screens. Both fully sporulated cultures containing predominantly released spores and sterile ifitrates of these cultures of UW85 were effective in protecting seedlings from damping-off; filtrates of cultures containing predominantly vegetative cells or endospores inside the parent cell had low biocontrol activity. Cultures grown in two semidefined media had significantly greater biocontrol activities than cultures grown in the complex tryptic soy medium. In a small-scale trial in a field infested with P. megasperma f. sp. medicaginis, coating seeds with UW85 significantly increased the emergence of alfalfa. The results suggest that UW85 may have potential as a biocontrol agent for alfalfa damping-off, thus providing an alternative to current disease control strategies.

Grapevine leafroll-associated virus 3 (GLRaV-3) is the most widely prevalent and economically important of the complex of RNA viruses associated with grapevine leafroll disease (GLD). Phylogenetic studies have grouped GLRaV-3 isolates into nine different monophyletic groups and four supergroups, making GLRaV-3 a genetically highly diverse virus species. In addition, new divergent variants have been discovered recently around the world. Accurate identification of the virus is an essential component in the management and control of GLRaV-3; however, the diversity of GLRaV-3, coupled with the limited sequence information, have complicated the development of a reliable detection assay. In this study, GLRaV-3 sequence data available in GenBank and those generated at Foundation Plant Services, University of California-Davis, was used to develop a new RT-qPCR assay with the capacity to detect all known GLRaV-3 variants. The new assay, referred to as FPST, was challenged against samples that included plants infected with different GLRaV-3 variants and originating from 46 countries. The FPST assay detected all known GLRaV-3 variants, including the highly divergent variants, by amplifying a small highly conserved region in the 3’ untranslated terminal region (UTR) of the virus genome. The reliability of the new RT-qPCR assay was confirmed by an enzyme linked immunosorbent assay (ELISA) that can detect all known GLRaV-3 variants characterized to date. Additionally, three new GLRaV-3 divergent variants, represented by four isolates, were identified using a hierarchical testing process involving the FPST assay, GLRaV-3 variant-specific assays and high-throughput sequencing analysis. These variants were distantly related to groups I, II, III, V, VI, VII and IX, but much similar to GLRaV-3 variants with no assigned group; thus, they may represent new clades. Finally, based on the phylogenetic analysis, a new GLRaV-3 subclade is proposed and named as group X.

The data is being used to develop models that will better predict when the adults are active and olives are at risk.

The mealybug Ferrisia gilli Gullan is an emerging pest of wine grapes grown in California's Sierra foothills. A relatively new species, it had previously been recorded as a pest of pistachio, almond, and ornamentals. It was first reported on grape in El Dorado County in 2003 and has since established and spread. Nondestructive monitoring of grape vine sections was conducted in untreated vineyard plots and compared with destructive sampling conducted in grower-treated plots in 2008 and 2009 to determine F. gilli life stage seasonal presence, number of generations, location on the vine during the season, and damage potential to fruit clusters. Two generations were observed to be completed during the season. F. gilli overwintered under the bark at the base of the trunk, trunk, and cordon as second and third instars. Adults were found at the base of emerging shoots (spring) or on and under bark of old and new spurs. Live crawlers were born in June (first generation) and late August to September (second generation), and migrated to leaves to feed before moving to protected locations under bark or into fruit clusters. Lower mealybug densities and fruit damage were recorded on vines with than without insecticide treatment(s). Parasitized mealybugs were collected in low numbers and an Acerophagus sp. was the dominant parasitoid.