Temporal Dispersal Patterns of Phaeomoniella chlamydospora, Causal Agent of Petri Disease and Esca, in Vineyards

Although the fungus Phaeomoniella chlamydospora is the most commonly detected causal agent of Petri disease and esca, two important fungal grapevine trunk diseases, little is known about the dispersal patterns of P. chlamydospora inoculum. In this work, we studied the dispersal of P. chlamydospora airborne inoculum from 2016 to 2018 in two viticultural areas of eastern (Ontinyent) and northern (Logroño) Spain. The vineyards were monitored weekly from November to April using microscope slide traps, and P. chlamydospora was detected and quantified by a specific real-time quantitative (qPCR) method set up in this work. The method was found to be sensitive, and a good correlation was observed between numbers of P. chlamydospora conidia (counted by microscope) and DNA copy numbers (quantified by qPCR). We consistently detected DNA of P. chlamydospora at both locations and in all seasons but in different quantities. In most cases, DNA was first detected in the last half of November, and most of the DNA was detected from December to early April. When rain was used as a predictor of P. chlamydospora DNA detection in traps, false-negative detections were observed, but these involved only 4% of the total. The dispersal pattern of P. chlamydospora DNA over time was best described (R2 = 0.765 and concordance correlation coefficient = 0.870) by a Gompertz equation, with time expressed as hydrothermal time (a physiological time accounting for the effects of temperature and rain). This equation could be used to predict periods with a high risk of dispersal of P. chlamydospora.

Field evaluation of biocontrol agents against black-foot and Petri diseases of grapevine

ABSTRACTBACKGROUNDBlack-foot and Petri diseases are the main fungal diseases associated with young grapevine decline. Two field experiments were established to evaluate the preventive effect of two potential biocontrol agents (BCAs), i.e. Streptomyces sp. E1 + R4 and Pythium oligandrum Po37, and three BCA-commercial products containing Trichoderma atroviride SC1, Trichoderma koningii TK7 and Pseudomonas fluorescens+Bacillus atrophaeus on fungal infection in grafted plants and plant growth parameters.RESULTSThe effectiveness of some BCA in reducing the incidence and severity of both diseases was dependent on the plant part analyzed and the plant age. No single BCA application was able to control both diseases. Streptomyces sp. E1+R4 were able to reduce significantly black-foot disease infection while P. oligandrum Po37 and Trichoderma spp. were able to reduce significantly Petri disease infection. BCA treatments had no effect on the shoot weight, and root weight was significantly lower in all BCA treatments with respect to the control.CONCLUSIONSThe combination of the disease-suppressive activity of two or more beneficial microbes in a biocontrol preparation is required to prevent infection by black-foot and Petri disease fungi in vineyards.

Colonization of vines by Petri disease fungi, susceptibility of rootstocks to Phaeomoniella chlamydospora and their disinfection

ABSTRACT: Petri disease is complex, attacks young vine plants and it is difficult to be controlled. The fungus Phaeomoniella chlamydospora (Phc) has been identified as the main causative agent of this disease. This study aimed to evaluate the prevalent colonization of the Petri disease fungi in different portions of vine plants; to assess the susceptibility of grapevine rootstocks to the fungus P. chlamydospora; to assess the effect of solarization and biofumigation, followed by hot-water treatment (HWT), on the disinfection of cuttings of the rootstock IAC 766 infected with P. chlamydospora, and assess the effect of solarization and biofumigation, followed by HWT, on the rooting of cuttings of the rootstock IAC 766. For the prevalent colonization test, the fungus species detected and identified in ‘Niagara Rosada’ grafted on two rootstocks different were Phc and Phialemoniopsis ocularis. This is the first report of P. ocularis in a young vineyard in Brazil. Both fungi, in particular Phc, colonized only the plant’s basal part, drawing attention to the rootstock as target for control measures. Measurement of the dark streaks in the vascular system revealed that Golia was the least susceptible rootstock, and IAC 572 was the most susceptible to Phc. Moreover, biofumigation or temperature of 37°C applied for 7 and 14 days, both followed by HWT, suppressed Phc in cuttings of the rootstock IAC 766 without hampering their rooting. Meanwhile, new studies are needed to validate the efficiency of these disinfection techniques.

Survey of Phaeomoniella chlamydospora in vineyard weeds

ABSTRACT Petri disease is serious, complex and difficult to control in vines worldwide. The main causal agent of this disease is the fungus Phaeomoniella chlamydospora. This fungus also occurs in the vineyard weed Convolvulus arvensis. In Brazil, this fungus was found only in grapevines. Thus, the aim of the present study was to carry out a phytosociological survey of weeds in an area with different vine rootstocks, as well as in a field of seedlings production, in an experimental area with vines and in different areas with commercial vineyards, besides verifying which weed species could be hosting the fungus P. chlamydospora. For the phytosociological survey of weeds, a square was randomly cast ten times at the site, followed by counting, identification and sampling of all species. To verify host species of the fungus, vascular tissue of plants was isolated in culture media and DNA extraction from the same plant tissue was carried out followed by PCR with specific primers of the fungus for the elongation factor gene (Pchlamy-EF-F 5’-CTCATTATCACATTTTGCTGC-3’ and Pchlamy-EF-R 5’-GAGAACAGTCAGTGATGAGC-3’). Considering all surveyed fields, 46 weed species were detected in 17 families, especially Asteraceae and Poaceae, which had the largest number of species. Using conventional or molecular methods, the fungus P. chlamydospora was not detected infecting weeds, which highlights that Petri disease occurs only in grapevines.

Grapevine Trunk Diseases in British Columbia: Incidence and Characterization of the Fungal Pathogens Associated with Esca and Petri Diseases of Grapevine

Esca and Petri disease are two economically important grapevine diseases worldwide. This study reports for the first time the occurrence of both diseases on grapevines in British Columbia (BC) and subsequently in Canada. Visual assessment of 55,699 vines in 118 vineyards revealed a low incidence of esca with only 104 (0.2%) vines showing foliar symptoms. Young vine decline (YVD) was observed in 1,910 (7.8%) of 24,487 monitored young vines and in 52 (8%) of 654 young vines used as re-plants in mature vineyards. In 8 of 51 monitored young vineyards, YVD-affected vines ranged between 15 and 55%. Morphological studies along with DNA analyses of the ITS1-5.8S-ITS2, and part of the β-tubulin, actin, and translation elongation factor 1-α gene regions, allowed us to identify Cadophora luteoolivacea, Phaeomoniella chlamydospora, Phaeoacremonium iranianum, Togninia fraxinopennsylvanica, Togninia minima, and the novel species Phaeoacremonium canadense and Phaeoacremonium roseum from esca and Petri disease infected vines in BC. This study includes for the first time the EF1-α DNA marker in Phaeoacremonium spp. delineation. Pathogenicity studies showed all seven fungi to cause vascular symptoms similar to those observed in esca and Petri disease infected vines. Additionally, the “tiger-stripes” foliar symptom of esca was successfully reproduced when healthy potted vines were inoculated with BC isolates of Pa. chlamydospora, Pm. canadense, Pm. iranianum, T. fraxinopennsylvanica, and T. minima.

First Report of Togninia minima Perithecia on Esca- and Petri-Diseased Grapevines in South Africa

Esca and petri diseases are important grapevine trunk diseases in South Africa and most other grape-producing countries. The causal pathogens are Phaeomoniella chlamydospora and several species of Phaeoacremonium. In total, 25 species of Phaeoacremonium have been isolated from grapevines of which seven species have been linked to Togninia teleomorphs obtained through in vitro mating studies (3). Of these species, only perithecia of T. minima, T. fraxinopennsylvanica, and T. viticola have been found on grapevines in California (1,2,4). T. minima is heterothallic, and although both mating types are present in South African vineyards, perithecia have never been observed (3). In the current study, grapevine cordons and trunks were collected from vineyards and rootstock mother vines within Western Cape Province for examination in the laboratory under a dissecting microscope. The grapevines displayed general decline symptoms, including reduced vegetative growth, dead or dying shoots and cordons, as well as internal vascular streaking and/or a red/black/brown margin next to decayed wood typically associated with esca and petri disease. Rootstock mother vines were apparently healthy, although many old, cracked pruning wounds were visible. Togninia-like perithecia with distinctive long necks were found along the wood crevices, often on old pruning wounds. The perithecia were removed and placed on microscope slides with sterile water. Structures were measured and slides were washed with 500 μl of sterile water onto potato dextrose agar amended with chloramphenicol (250 mg/liter). Ascospores were allowed to germinate overnight to obtain single ascospore colonies. Perithecia were found on cultivars Muscat d' Alexandrie and Pinotage (Vitis vinifera) at Stellenbosch in May 2011 and on Ramsey (V. champinii) rootstock mother vines at Slanghoek in June 2012. Perithecia were globose to subglobose, black, and often embedded in the wood tissue but also present on the surface of the wood. The length of the necks was 250 to 300 × 47.5 to 55 μm. The asci were hyaline and ranged from 16 to 25 × 3.5 to 5 μm. Ascospores were hyaline, ellipsoid, and ranged from 5 to 6 × 1.5 to 2 μm. These measurements were similar to those reported by Mostert et al. (3) and Rooney et al. (4). Colony growth was typical of T. minima. DNA was extracted from the colonies and the partial betatubulin gene was amplified and sequenced using the primers T1 and Bt2b. Sequences were deposited into GenBank (JX962864 to 67). Based on a megablast search of the NCBI's GenBank nucleotide database, 100% similarity was found with other T. minima sequences (JQ691670.1, HQ605018.1, HQ605014.1; identities = 647/647 [100%], gaps = 0/647 [0%]). To our knowledge, this is the first report on the occurrence of T. minima perithecia on grapevines in Western Cape Province of South Africa. The removal of dead spurs and cordons will be instrumental in lowering the inoculum originating from perithecia, especially in rootstock mother blocks where no control strategies are applied for petri disease or esca. Spore trapping studies are currently in progress to study spore release patterns in order to determine whether pruning wounds are at risk during traditional pruning periods. References: (1) A. Eskalen et al. Plant Dis. 89:528, 2005. (2) A. Eskalen et al. Plant Dis. 89:686, 2005. (3) L. Mostert et al. Stud. Mycol. 54:1, 2006. (4) S. Rooney-Latham et al. Plant Dis. 89:867, 2005.