Diseases and insects, particularly those that are non-native and invasive, arguably pose the most destructive threat to North American forests. Currently, both exotic and native insects and diseases are producing extensive ecological damage and economic impacts. As part of an effort to identify United States tree species and forests most vulnerable to these epidemics, we compiled a list of the most serious insect and disease threats for 419 native tree species and assigned a severity rating for each of the 1378 combinations between mature tree hosts and 339 distinct insect and disease agents. We then joined this list with data from a spatially unbiased and nationally consistent forest inventory to assess the potential ecological impacts of insect and disease infestations. Specifically, potential host species mortality for each host/agent combination was used to weight species importance values on approximately 132,000 Forest Inventory and Analysis (FIA) plots across the conterminous 48 United States. When summed on each plot, these weighted importance values represent an estimate of the proportion of the plot’s existing importance value at risk of being lost. These plot estimates were then used to identify statistically significant geographic hotspots and coldspots and of potential forest impacts associated with insects and diseases in total, and for different agent types. In general, the potential impacts of insects and diseases were greater in the West, where there are both fewer agents and less diverse forests. The impact of non-native invasive agents, however, was potentially greater in the East. Indeed, the impacts of current exotic pests could be greatly magnified across much of the Eastern United States if these agents are able to reach the entirety of their hosts’ ranges. Both the list of agent/host severities and the spatially explicit results can inform species-level vulnerability assessments and broad-scale forest sustainability reporting efforts, and should provide valuable information for decision-makers who need to determine which tree species and locations to target for monitoring efforts and pro-active management activities.

This study examined the effects of temperature and wetness duration in vitro and in vivo as well as the effects of fruit age on germination and appressoria formation by conidia of Guignardia psidii, the causal agent of black spot disease in guava fruit. The temperatures tested for in vitro and in vivo experiments were 10, 15, 20, 25, 30, 35 and 40°C. The wetness periods studied were 6, 12, 24, 36 and 48 h in vitro and 6, 12 and 24 h in vivo. Fruit 10, 35, 60, 85 and 110-days old were inoculated and maintained at 25°C, with a wetness period of 24 h. Temperature and wetness duration affected the variables evaluated in vitro and in vivo. All variables reached their maximum values at between 25 and 30°C with a wetness duration of 24 h in vivo and 48 h in vitro. These conditions resulted in 31.3% conidia germination, 33.6% appressoria formation and 32.5% appressoria melanization in vitro, and 50.4% conidia germination and 9.5% appressoria formation in vivo. Fruit age also influenced these factors. As fruit age increased, conidia germination and appressoria formation gradually increased. Conidia germination and appressoria formation were 10.8% and 2.3%, respectively, in 10-day-old fruits. In 110-day-old fruits, conidia germination and appressoria formation were 42.5% and 23.2% respectively.

In this study, we determined the influences of temperature, wetness period and guava fruit age on infection caused by Colletotrichum gloeosporioides. Optimal temperatures in vitro for germination, appressoria formation and melanization were 22.7, 20.6 and 23°C, respectively. In vivo, the optimal temperatures for germination and appressoria formation were 22.5 and 23°C, respectively. Values for germination, appressoria formation and melanization were higher as the wetness period increased. There was no difference in conidial germination and appressorial formation on fruit of different ages. On the surface of 10‐, 35‐ and 60‐day‐old fruit, despite the high percentage of appressorial formation, there was no development of the penetration peg. Penetration pegs were only observed on the 85‐ and 110‐day‐old fruit. Thickness of the cuticle, size and architecture of epidermal and parenchymal cells, as well as the content of phenolic compounds changed as the fruit ripened.

Maize white spot (MWS) is a disease widely spread in maize production regions in Brazil and causes serious economic damages to the culture. Little is known about the dissemination, growth and development conditions of the MWS causal agent, the bacterium Pantoea ananatis. The objective of this work was to determine the viability of this bacterium, as well as its distribution in the plant. P. ananatis after isolated was stored in both, Nutrient Broth (NB) medium and in mineral oil. For the viability tests, the cultures stored in NB were maintained at 12ºC and –6ºC and the cultures stored in mineral oil were maintained at room temperature. The isolate remained viable for seven months in NB medium at the two temperatures assessed, and four months when stored in mineral oil. The presence of the P. ananatis bacteria was analyzed in, 1) soil samples collected close to rhizosphere, 2) in seeds from plants severely attacked by MWS, 3) foliar segments of healthy plants and 4) the stem of healthy plants. P. ananatis was found surviving epiphytically on the leaf surface and its population increased with plant age, air relative humidity, and decreasing of temperature. This agent was not found neither rhizosphere nor in seeds, but it was isolated in low quantity in maize stem. P. ananatis resides epiphytically on leaves and, due to several factors, may trigger injuries to its host. All epiphytic isolates were characterized in regards to ice nucleation activity, a characteristic of this pathogen.

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