Use of Foliar Chemical Treatments to Induce Disease Resistance in Rhododendrons Inoculated with Phytophthora ramorum

A field study was conducted at the National Ornamental Research Site at Dominican University California (NORS-DUC). The study goal was to evaluate three chemical inducers applied as foliar treatments for controlling Phytophthora ramorum, on Rhododendron x ‘Cunningham’s White’ nursery plants. The inducers were chlorine dioxide (ElectroBiocide), hydrogen peroxide (OxiDate 2.0), and acibenzolar-s methyl (Actigard). Water samples from the electrostatic sprayer were measured for three physicochemical water properties. Visual assessment of plant foliage, based on the Horsfall- Barratt scale, was conducted at three and five months after chemical treatments. Foliar fluorescence (Fv/Fm) was measured over three dates. The success of P. ramorum inoculations were determined using qPCR methods. Visual assessment across both months showed no signs of P. ramorum infection or chemical injury symptoms. However, P. ramorum infection vis-à-vis qPCR analysis was confirmed. The September Fv/Fm results revealed that all the chemical inducer treatments were equivalent to the water treatment, except for Actigard. The qPCR results were in general agreement with the Fv/Fm results indicating that the rhododendrons were successfully inoculated with P. ramorum but were non-symptomatic. The electrostatic sprayer ionized the water droplets, resulting in increased Fv/Fm values for the water treatments 90 days after application. There was a three-month delay in fluorescence responses to the most effective chemical applications, indicating that woody plants may need to be monitored over the long term to determine accurate responses to foliar treatments

Resistance Inducers and Plant Growth Regulators Show only Limited and Transient Effects on Infection Rates, Growth Rates and Symptom Expression of Apple Trees Infected with ‘Candidatus Phytoplasma mali’

The effects of four commercially available bio-active compounds on the infection rates, symptom expression and growth rates of apple trees (Malus × domestica Borkh.) cv. Golden Delicious infected with ‘Candidatus Phytoplasma mali’ (the so-called Apple Proliferation phytoplasma or AP) were tested over a three-year period under controlled conditions. Post-infection treatments using Bion® (active ingredient: Acibenzolar-S-Methyl), Messenger® (Harpin protein), Regalis® (Prohexadione-Ca) and Dormex® (Cyanamide) had no significant effect on infection rates. Terminal growth of apple trees (grown as one-shoot pruned trees) was increased significantly by AP infection; Prohexadione-Ca was the only compound which had a significant (inhibiting) effect on the growth of both infected and non-infected apple trees. Acibenzolar-S-Methyl and Harpin had no significant effects on symptom expression. AP symptoms were masked during summer by Prohexadione-Ca, which caused severe growth abnormalities. Cyanamide changed the seasonal appearance of AP symptoms: while symptoms were delayed compared to the untreated control the first two years (2008 and 2009), symptoms appeared earlier the third year (2010). Differences in symptom expression leveled off later in the vegetative season, and no significant difference was found in October

Ascomycota: Introduction to Biodiversity, Evolutionary Genomics and Systematics

The term genome, the basic gene complement of an individual, is almost synonymous with the chromosome complement of both nucleus and organelles. Refinements in cellular, genetic and molecular methods in recent years have opened up unexplored avenues in genome research. The modern tools of gene and genome analyses, coupled with analysis of finer segments of gene sequences in chromosomes utilizing molecular hybridization, are now applied on a wider scale in different groups of plants, ranging from algae to angiosperms. The present series on Plant Genomics: Biodiversity and Evolution aims to cover, in successive volumes, comprehensive reviews, concepts and discussions on the results of genome analysis and their impact on systematics, taxonomy, phylogeny and evolution of all plant groups. This volume touches upon the Lower Groups of plants.https://scholar.dominican.edu/books/1064/thumbnail.jp

Microbial biodiversity associated with the walnut Juglans regia L. in South Tyrol (Italy)

The endophytic and epiphytic microflora from walnut trees in South Tyrol (Northern Italy) was analyzed. A total of 16 trees from 8 sites were sampled at three dates during the warm season (May, July and September) in 2005, using plant material from three different tissue types (leaves, fruit and lignified twigs). Samples were either transferred directly onto nutrient medium or surface sterilized prior to plating to distinguish between epiphytic and endophytic growth. A total of 3,880 culturable isolates were obtained, the vast majority of the isolates (3,742) belonging to fungi (96.4%); only 138 (3.6%) were bacteria. Fungal isolates were classified into 30 genera, Alternaria, Penicillium, Phoma, Botryosphaeria, Fusarium, Cladosporium, Phyllosticta and Epicoccum being the most common taxa. Although epiphytic growth predominated (73.9% of the identified isolates), a significant number of endophytes (26.1%) were isolated as well. More isolates were obtained from leaves (45.3%) than from twigs (31.8%) and fruit (23.0%). Seasonal effects were not very distinct, but a tendency towards higher isolation success in September was observed

First report of Phytophthora ramorum on Cotoneaster sp. in the USA.

Cotoneaster (Rosaceae) is a genus of woody plants native to the Palearctic region which includes popular ornamental plants; some are invasive in parts of the USA. In May 2022 symptomatic leaves were detected on Cotoneaster pannosus (Silverleaf Cotoneaster) in Marin County, California (37.89165, -122.56755 ), an area infested heavily by Phytophthora ramorum, causal agent of Sudden Oak Death. Symptoms consisted of dark brown necrotic spots mostly near the tips and sometimes on the margin of the leaves, covering less than half of the leaf surface; no die-back or symptoms on twigs were detected. Diseased leaves were surface-sterilized with 70% ethanol, washed twice with de-ionized water, and placed on PARPH(V8) media. Two Phytophthora ramorum like isolates (NORS058 and NORS059) were obtained from different leaf samples from the same tree and the internal transcribed spacer (ITS) region was sequenced. Both sequences were deposited in GenBank (OR224345 and OR224346). NORS058 and NORS059 showed 99.88% and 99.75% sequence identity to P. ramorum strain Ex-type CPHST BL 55G (MG865581.1). Detached leaves of C. pannosus and C. lacteus (Milkflower Cotoneaster) were inoculated with mycelial plugs of P. ramorum NORS058, and incubated at 20°C. Both species developed necrotic leaf spots seven days post inoculation (dpi). Sporulation of the pathogen was observed on symptomatic leaves of C. lacteus. P. ramorum was reisolated from the symptomatic leaf tissue from both Cotoneaster species. Pathogenicity tests were also performed on whole plants of C. dammeri (Bearberry Cotoneaster) using the strain NORS058. Five plants each were inoculated using three different methods: 1) a zoospore solution (concentration 2.5 x10E5 spores/mL) were sprayed on the plant surface until run off. Ten leaves per plant were wounded with a needle, the remaining leaves were not wounded; 2) 200 µL of the zoospore solution in a PCR tube were attached to 5 leaves of each plant; and 3) 10 mL of the zoospore solution was drenched into the potting mix of the five plants. Control plants were treated as above but with water instead of the zoospore solution. Leaf spots developed 7 dpi on plants sprayed with zoospores on wounded leaves; and 10 dpi on plants treated with zoospores in the tube. P. ramorum was reisolated from symptomatic leaves treated with the first two methods mentioned above. Plants treated with a soil drench did not develop symptoms on the aerial parts or on roots that were sampled 50 dpi. Tests using AGDIA- immunostrips of the roots were negative. Control plants showed no aerial or root symptoms. To our knowledge, this is the first report of P. ramorum occurring on Cotoneaster in the USA. Previously, inoculation of detached leaves of C. dammeri and C. horizontalis with P. ramorum in Serbia resulted in symptom expression (Bulajić et al. 2010). P. ramorum was reported from a Cotoneaster sp. in the UK in 2010, but no further information were presented (FERA 2015). The tree sampled in 2022 showed symptoms again in spring 2023 and official regulatory samples were taken by the CDFA (California Department of Food and Agriculture) and confirmed by the USDA. During a survey in 2023, more symptomatic Cotoneaster plants were detected in Marin County, California, indicating Cotoneaster might play a role in the epidemiology of the disease. References: FERA 2015. https://planthealthportal.defra.gov.uk/pests-and-diseases/high-profile-pests-and-diseases/phytophthora/ Bulajić et al. 2010. Plant Dis. 94(6): 703

Biodiversity of Planthoppers (Auchennorrhyncha) in Vineyards Infected With the Bois noir phytoplasma

The presence and density of plant- and leafhoppers was investigated in eleven vineyards infected with Ca. Phytoplasma solani, causal agent of Bois noir (BN), in South Tyrol (Northern Italy) using insect nets fro sampling the understory vegetation. The confirmed vector Hyalesthes obsoletus (Signoret) was sampled from early June to mid August of 2006; its abundance was positively correlated to the presence of BN symptoms on grapevines. An additional 56 Auchenorrhyncha species were sampled; the most numerous being Psammotettix confinis (Dahlbom), Laodelphax striatella (Fallen), Dicranotropis hamata (Boheman), Psammotettix alienus (Dahlbom), Falcotoya minuscula (Horvath), Macrosteles cristatus (Ribaut), Dictyophara europaea (L.), Philaenus spumarius (L.), Anaceratagallia ribauti (Ossiannilson) and Neoaliturus fenestratus (Herrich-Schaffer). Several invasive species, such as Stictocephala bisona (Koppp & Yonke) and Metcalfa pruinosa (Say) were sampled in the investigated vineyards, whereas Scaphoideus titanus (Ball), the vector of the Grapevine yellow Flavescence doree, was not found. Recilia horvathi (Then) (Cicadellidae) was found for the first time in South Tyrol

Reduced levels of calcium and other mineral elements in grapevine leaves affected by Bois noir (BN)

The concentrations of seven mineral elements (Ca, K, N, Mg, Mn, Fe and P) were analyzed in leaves of healthy gra- pevines and of grapevines infected with Bois noir (BN). The levels of calcium of all five varieties used in the study(\u27Chardonnay\u27, \u27MuÈller Thurgau\u27, \u27Pinot Noir\u27, \u27Lagrein\u27 and \u27Zweigelt\u27) were significantly lower in leaves infected with BN. The other six elements also showed a tendency towards decreased contents, but the effects were less consi-stent. A distinctive varietal influence on both visual symptoms of BN and mineral contents was observed, \u27Chardon-nay\u27 and \u27Zweigelt\u27 being the most susceptible cultivars

Integrated Pest Management Strategies for Phytoplasma Diseases of Woody Crop Plants: Possibilities and Limitations

Phytoplasmas causing diseases of woody plants in native environments and agricultural systems are responsible for considerably economic and environmental damage. In Central and Southern Europe, phytoplasma diseases of apple (Malus domestica: Apple proliferation, AP) and grapevine (Vitis vinifera: Bois noir, BN and Flavescence dorèe, FD) are widespread and impact quantity and quality of the fruits. The ecology of phytoplasma diseases is complex and involves one or more insect vectors and in some cases alternative host plants. Phytoplasma densities in infected plants and expression of symptoms can vary considerably among seasons, and remission of symptoms occurs frequently. Disease control by pesticide application generally is not very efficient, therefore a polyphasic control strategy using a mix of agronomical, chemical and biological strategies needs to be developed for each disease. In the case of Bois noir e.g., the population density of the vector Hyalesthes obsoletus is related to the presence of its main host plants Urtica dioica and Convulvulus arvensis in the understory of the vineyards, which can be managed by agronomical methods. Application of foliar fertilizer showed no significant effect on BN-infected grapevines. AP-infected apple trees were treated with four bio-active compounds (Acibenzolar-S-Methyl, Harpin protein, Prohexadione-Ca and Cyanamide) over a three-year period, but their effects on symptom expression were only limited and transient.https://scholar.dominican.edu/books/1140/thumbnail.jp

Rapid Recovery and Detection of Phytophthora ramorum Propagules in Nursery Water

Phytophthora ramorum, causal agent of sudden oak death, continues to threaten U.S. forest ecosystems and the nursery industry. Currently, USDA APHIS’s protocol (2014) utilizes the Bottle of Bait (BOB) recovery method for P. ramorum, which requires collecting water from a source, baiting with healthy rhododendron leaves for a 3-day incubation period, followed by plating on semi-selective media. Rapid methods are needed for recovery and detection of P. ramorum propagules from water sources. Working at the National Ornamentals Research Site at Dominican University of California (NORS-DUC), we are developing rapid water filtration and flocculation methods for recovery and detection of P. ramorum propagules from nursery irrigation water. A mock irrigation pond was established with flow from a P. ramorum- infested plot into an adjoining plot. Antibodies raised against P. ramorum -specific secreted proteins were applied for detection of zoospores and sporangia from 1 L samples in filter extracts or alum flocculates using standard immunoassay procedures. Results with spiked samples indicate that propagules of P. ramorum recovered by filtration or flocculation from spiked nursery water samples can be detected in 24 h or less

Field Evaluation of a Novel, Granular Soil Fumigant for Controlling Phytophthora ramorum in Field Nursery Soils

Phytophthora ramorum, the causal agent of Sudden Oak Death (SOD) and ramorum blight, infects a wide range of hardwood and nursery ornamental species. Chlamydospores of P. ramorum can survive for extended periods of time in soils. Two studies were conducted, including: 1) a laboratory study to evaluate two liquid disinfectants for controlling P. ramorum chlamydospores, and 2) a field study to evaluate a novel soil fumigation treatment as an alternative to soil steaming or methyl bromide soil fumigation. The liquid disinfectants were ElectroBiocide and Oxidate 2.0. The laboratory study resulted in complete inactivation of the P. ramorum chlamydospores after six minutes of contact time for both the liquid disinfectants The field study evaluated a chlorine dioxide granule formulation that was applied at two rates in a nursery soil. Rhododendron leaf discs were inoculated with P. ramorum, placed in permeable sachets and buried at two soil depths in a research nursery. Soil treatments also included saturated hydrogels (with and without gels) so that soil moisture effects on chlamydospore survival could be estimated. The sachets were recovered 5, 15 and 30 days after the soil treatment. Efficacy of the soil treatments was evaluated by the number of leaf discs showing P. ramorum growth recovered from the sachets. The soil fumigation treatment with highest efficacy occurred when the sachets were buried at the 5 cm soil depth, were treated with hydrogels, at the highest Z-series granule rate (800g/tube), and had a contact time of 30 days. The probability of P. ramorum growth for this soil treatment was 0.18, or 18%, i.e. the probability of that fumigation treatment inactivating the pathogen was 82%. Also, as the soil moisture increased, the efficacy of the fumigation treatments also increased