Plant-Based Culture Media for Improved Growth and Sporulation of Cercospora janseana.

Cercospora janseana is the causal agent of narrow brown leaf spot, one of the major diseases of rice in the United States. In vitro studies were conducted to evaluate various plant-based agar media in comparison with potato dextrose agar (PDA) for their effects on radial growth and sporulation of C. janseana. The agar media were evaluated individually with the following plant-extract ingredients: fresh rice leaves, dried rice leaves, dried rice stems, dried rice roots, dried rice hulls, dried rice straw, rice bran, dried sorghum leaves, and dried barnyard grass leaves. Plant-based extracts obtained from 25, 50, 100, or 200 g/liter (plant material/water) were tested either alone or in combination with 10 and 20% clarified V8 juice. PDA served as the control medium. Media with 10 and 20% V8 juice were also included for comparison. Media were inoculated with a disc of 1-week-old actively growing C. janseana at the center of Petri plates and incubated at 28°C with a 12/12-h (light/dark) cycle for 2 weeks. Radial growth was measured at 7 and 14 days after inoculation (DAI), whereas sporulation was measured at 14 DAI. Radial growth and sporulation differed among various media and their amendment concentrations. Media with extracts of fresh rice leaves, dried rice leaves, dried rice stems, dried barnyard grass leaves, and clarified V8 juice enhanced radial growth compared with the PDA control. Of all the agar media evaluated, fresh rice leaf extract amendment at 25 g/liter with no V8 supplementation consistently supported the greatest radial growth, and 10% V8-only medium resulted in greater sporulation of C. janseana than other media evaluated.

Effects of pollen dilution on infection of Nosema ceranae in honey bees.

Multiple stressors are currently threatening honey bee health, including pests and pathogens. Among honey bee pathogens, Nosema ceranae is a microsporidian found parasitizing the western honey bee (Apis mellifera) relatively recently. Honey bee colonies are fed pollen or protein substitute during pollen dearth to boost colony growth and immunity against pests and pathogens. Here we hypothesize that N. ceranae intensity and prevalence will be low in bees receiving high pollen diets, and that honey bees on high pollen diets will have higher survival and/or increased longevity. To test this hypothesis we examined the effects of different quantities of pollen on (a) the intensity and prevalence of N. ceranae and (b) longevity and nutritional physiology of bees inoculated with N. ceranae. Significantly higher spore intensities were observed in treatments that received higher pollen quantities (1:0 and 1:1 pollen:cellulose) when compared to treatments that received relatively lower pollen quantities. There were no significant differences in N. ceranae prevalence among different pollen diet treatments. Interestingly, the bees in higher pollen quantity treatments also had significantly higher survival despite higher intensities of N. ceranae. Significantly higher hypopharyngeal gland protein was observed in the control (no Nosema infection, and receiving a diet of 1:0 pollen:cellulose), followed by 1:0 pollen:cellulose treatment that was inoculated with N. ceranae. Here we demonstrate that diet with higher pollen quantity increases N. ceranae intensity, but also enhances the survival or longevity of honey bees. The information from this study could potentially help beekeepers formulate appropriate protein feeding regimens for their colonies to mitigate N. ceranae problems.

Effects of Temperature and Duration of Preconditioning Cold Treatment on Sclerotial Germination of Claviceps purpurea.

Claviceps purpurea is an important ovary-infecting pathogen that replaces seed with sclerotia in Kentucky bluegrass grown for seed. Sclerotia overwinter in the soil and germinate in the spring to produce ascospores that infect grass seed ovaries. To better understand environmental conditions affecting ascospore production, the effects of preconditioning cold treatment and subsequent incubation temperature on germination of sclerotia were determined in growth chambers under controlled conditions. Preconditioning cold treatment was essential for germination only in treatments where the incubation temperature was high (at least higher than 20°C). At lower incubation temperatures (10 to 20°C), preconditioning also played a role in improving sclerotial germination. Preconditioning at 4°C (in darkness) for 4 to 8 weeks followed by incubation at 10 and 20°C (cycle of 12 h each of darkness and light), or constant 15°C (cycle of 12 h each of darkness and light), was optimal for ergot germination. When sclerotia were preconditioned for 4 weeks or longer, number of incubation days required for initiation of germination was not affected by temperature in the range from 10 to 25°C (cycle of 12 h each of darkness and light), although the duration of germination (or the progress speed of germination) was still affected by temperature. A simple model was developed based on laboratory results and validated with historic spore trap data collected from various Kentucky bluegrass fields in Oregon (Willamette Valley, central Oregon, and Grande Ronde Valley). The prediction model could predict ascospore onset well and explained 55% of variation in the data.