Determining the Timing of Spore Release by Botryosphaeriaceae Species in Oregon Vineyards.

Botryosphaeria dieback, caused by a group of pathogens in the Botryosphaeriaceae family, is one of the most common grapevine trunk disease complexes (GTDs) found in Oregon vineyards. To understand the period of spores released by Botryosphaeria spp. in Oregon vineyards, four Burkard 7-day recording volumetric spore traps were placed in vineyard blocks in northern and southern Oregon. Each trap was placed near a younger (<10 years) and older (>30 years) block in both regions. Spore traps were deployed at the beginning of December 2019 and continued until March 2021. Between these timeframes, 475 and 477 days of samples were collected from each spore trap in northern and southern Oregon, respectively. DNA extraction was performed from individual day samples and followed by qPCR analysis of Botryosphaeria spores trapped in each tape sample. Weather data such as temperature, precipitation, relative humidity (RH), and wind speed were collected from nearby weather stations. Association between these data and number of spores detected were analyzed using Pearson correlation analysis. In northern Oregon, the detection occurred between December and February, and the first spore detection occurred when cumulative growing degree day (GDD) totaled to 4,357 and 4,351 units (TBase = 0°C, biofix date = January 1) during the first and second seasons, respectively. Similarly, in southern Oregon, the detection occurred between November and January, and the first spore detection occurred when cumulative GDD was 4,405 units during the second season. Hours of continuous RH >86% was significantly associated with number of spores released (P = 0.026; r = 0.42). During the spore detected dates, the RH was >86% for at least 19 consecutive hours. These findings provide an important implication to manage Botryosphaeria dieback by protecting pruning wounds during the most-spore-released periods. Furthermore, the knowledge of weather variables and their possible association with spore detection provides important information towards developing predictive models in future studies.

Acidifying Spray Suspensions of Oxytetracycline and Kasugamycin Enhances Their Effectiveness for Fire Blight Control in Apple and Pear.

The stability of the fire blight control material, oxytetracycline, in water is strongly affected by pH, increasing with increasing acidity. From 2017 to 2021, pear and apple orchard trials were conducted to evaluate if acidic amendments to oxytetracycline sprays improve fire blight control. Compared with the water-treated control, infection suppression after two bloom applications of an acidified commercial oxytetracycline formulation averaged 85.9 ± 0.4% compared with 72.2 ± 1.7% without an acidifier, but individual trials frequently had insufficient statistical power to separate among acidified and non-acidified antibiotic treatments. Across trials, a significant linear relationship was observed for regression of relative infection suppression from oxytetracycline (hydrochloride formulation) on spray tank pH. Similar relationships were observed for oxytetracycline (calcium complex formulation) and kasugamycin (P values were 0.055 and 0.069, respectively). Also based on regression, acidified oxytetracycline and kasugamycin suppressed epiphytic populations of Erwinia amylovora on flowers to a greater degree than the antibiotic only. As spray suspensions, commercial oxytetracycline formulations at label rate and amended with citric acid (1.2 g/liter) in well water had pH values near 3.4, but after spraying, the pH of flowers washed in deionized water (1 ml/flower) measured in a range of 5.2 to 5.5 compared with a pH range of 5.8 to 6.0 after a treatment of oxytetracycline only. In pear fruit finish trials, sprays acidified with citric acid-based materials had negligible effects on fruit russeting. Based on a serological assay, the detectable residual of oxytetracycline on apple foliage was increased by co-application with citric acid compared with a non-acidified control.

A Systematic Survey on Prevalence of Grapevine Trunk Disease Pathogens in Oregon Vineyards.

Grapevine trunk diseases (GTDs) are found in vineyards worldwide and can be caused by different fungal pathogens. To characterize types of GTDs in Oregon vineyards, and how the GTD pathogens' prevalence is affected by two geographical regions, a survey was conducted in which grapevine trunk samples were collected from 15 and 14 wine grape (Vitis vinifera) vineyards in southern and northern Oregon, respectively. Fungal species were identified through culture and PCR-based methods. GTD pathogens that were identified included Botryosphaeriaceae spp. and Phaeoacremonium spp. from 72 and 21% of the surveyed vineyards, respectively; Phaeomoniella chlamydospora, Cryptovalsa ampelina, Truncatella angustata, Seimatosporium lichenicola, Hormonema viticola from 7% of the surveyed vineyards; and Dactylonectria macrodidyma, and Pestaloptiopsis sp. from 3% of the surveyed vineyards. Pathogens were identified in both regions and in young and mature vineyards. The presence of GTD from the Botryosphaeria dieback complex was significantly affected by regions (P = 0.021), with pathogens being significantly more abundant in Willamette Valley (northern region) compared with Rogue Valley (southern region) vineyards. Some differences among other tested variables such as vineyard age, cultivars, rootstocks, and pruning methods were observed for all disease complexes; however, the differences were not statistically significant. Our study summarizes that Botryosphaeria dieback and Esca disease complexes are the most prevalent diseases infecting grapevines in Oregon vineyards and management practices need to be geared toward these economically important diseases. In addition, pathogens from other disease complexes are also present, suggesting a need for regular disease monitoring and following practices to limit the spread of these pathogens.

Morphological and Molecular Characterization of Alternaria spp. Isolated from European Pears.

In a recent survey of post-harvest rot pathogens in European pear in Southern Oregon, Alternaria spp. were frequently isolated from orchard samples of pear flowers and fruits. Morphological differences were observed within the isolated cultures. A preliminary NCBI BLAST search analysis using sequences of the ATPase locus across 94 isolates of Alternaria spp. obtained from pear fruit rots revealed three major Alternaria sections: sect. Alternata, sect. Infectoriae, and sect. Ulocladioides. Thirteen isolates were selected based on their genetic and morphological diversity across three Alternaria sections and were subjected to multilocus phylogenetic analysis using sequences from plasma membrane ATPase, calmodulin, and Alt a1 loci. Within sect. Alternata, four Alternaria arborescens isolates and one A. destruens isolate were identified; within sections Infectoriae and Ulocladioides, one A. rosae isolate and two A. botrytis isolates were identified, respectively. The remaining five isolates could not be identified based on the available sequences for the three loci used in this study. In addition to the phylogenetic analysis, pathogenicity assays revealed differential responses to these isolates on four pear cultivars: Anjou, Bartlett, Comice, and Bosc. Inoculation of isolates within Alternaria sect. Alternata resulted in fruit lesions across all cultivars, with Bosc pear being significantly susceptible (P < 0.0001). Isolates within Alternaria sect. Ulocladioides caused rots on Anjou and Bosc pears, while isolates within Alternaria sect. Infectoriae developed rots on Bosc pear only. This study suggests that there is differential susceptibility of pear cultivars to Alternaria rots, and the severity of post-harvest rot depends on the type of Alternaria spp. and cultivar predominant in a region.

Water Deficits Do Not Improve Fruit Quality in Grapevine Red Blotch Virus-Infected Grapevines (Vitis vinifera L.).

Although deficit irrigation is used to improve fruit quality in healthy grapevines, it can potentially amplify negative effects of viral disease and reduce fruit quality in Grapevine Red Blotch Virus (GRBV) infected grapevines. Therefore, a 2-year field experiment was conducted to understand the interaction between GRBV infection and water deficits on disease development and vine physiology. Well-watered (WW) vines were irrigated at 100% of estimated crop evapotranspiration (ETc), while water deficit (WD) vines received water at 66 and 50% ETc in 2017 and 2018, respectively. Healthy (GRBV-) and infected (GRBV+) vines were confirmed by PCR assays. There were no significant effects of water deficits on foliar symptom onset in either year, but more severe water deficits in 2018 resulted in a more rapid symptom progression. GRBV+ vines had a higher Ψstem compared to GRBV- vines, but the effects of virus only appeared post-veraison and corresponded to decreased leaf gas exchange. In general, vine vegetative and reproductive growth were not reduced in GRBV+ vines. Yields were highest in WW/GRBV+ vines due to larger clusters containing larger berries. Consistent treatment effects on berry primary chemistry were limited to sugars, with no interactions between factors. Water deficits were able to somewhat increase berry anthocyanin concentration in GRBV+ fruit, but the effects were dependent on year. By comparison, virus status and water deficits interacted on skin tannins concentration such that they were decreased in WD/GRBV+ vines, but increased in WD/GRBV- vines. Water deficits had no effect on seed phenolics, with only virus status having a significant diminution. Although keeping GRBV+ vines well-watered may mitigate some of the negative effects of GRBD, these results suggest that water deficits will not improve overall fruit quality in GRBV+ vines. Ultimately, the control of fruit ripening imparted by GRBV infection seems to be stronger than abiotic control imparted by water deficits.

Characterization of Colletotrichum Species Causing Anthracnose of Pomegranate in the Southeastern United States.

Anthracnose fruit rot and leaf blight caused by Colletotrichum species are important diseases of pomegranate in the southeastern United States. In this study, 26 isolates from pomegranate were identified based on pathological and molecular characterization. Isolates were identified to species based on multilocus sequence analysis with the internal transcribed spacer region, glyceraldehyde-3-phosphate dehydrogenase, ß-tubulin, and chitin synthase genomic genes. Pomegranate isolates grouped within the C. acutatum and C. gloeosporioides species complexes, with more than 73% belonging to the latter group. Three species were identified within the C. acutatum species complex (C. nymphaeae [n = 5], C. fioriniae [n = 1], and C. simmondsii [n = 1]), and three other species were identified within the C. gloeosporioides species complex (C. theobromicola [n = 11], C. siamense [n = 6], and C. gloeosporioides [n = 2]). Inoculations of pomegranate fruit showed that isolates from the C. acutatum species complex were more aggressive than isolates from the C. gloeosporioides species complex. Interestingly, opposite results were observed when leaves of rooted pomegranate cuttings were inoculated. In addition, Colletotrichum isolates from pomegranate, strawberry, blueberry, mango, and citrus were cross-pathogenic when inoculated to fruit. This is the first study identifying six different species of Colletotrichum causing pomegranate leaf blight and fruit anthracnose in the southeastern United States and the potential cross-pathogenic capability of pomegranate isolates to other commercially important crops.