Grapevine Leaf Rust Research Articles

Mining of differentially expressed genes from Korean wild grapes responding to grapevine leaf rust pathogen (Phakopsora euvitis) infection

Mining of differentially expressed genes from Korean wild grapes responding to grapevine leaf rust pathogen (Phakopsora euvitis) infection

Variations Among Crop Seasons and Inoculum Availability Have a Higher Impact on Grapevine Rust Epidemics than Training Systems or Plastic Cover.

Canopy management practices can be effective as part of the integrated management of grapevine diseases. This study aimed to determine whether training systems and plastic covers can contribute to prevent Asian grapevine leaf rust (AGLR) development. Additionally, the influence of crop season and inoculum availability on AGLR development was investigated. Six-season experiments were carried out to characterize 16 epidemics that developed from natural inoculum (NI) or artificial inoculum (AI) sources (NI + AI), conducted in different training systems and with or without the plastic cover. The Richards model was fitted to each AGLR disease progress curve to estimate and compare the onsets and intensities of epidemics using eight curve elements. Principal components analysis (PCA) identified the incidence progress rate, the area under the severity progress curve, final disease severity, time to disease onset, and time to reach the inflection point as the main descriptors for AGLR epidemics. The results showed that AGLR epidemic development was related mainly to differences in inoculum availability and climatic conditions throughout the seasons and to a lower extent to the training system and plastic cover. The earliest disease onset was observed in epidemics when the NI was supplemented with an AI source. Differences in AGRL intensity were correlated to accumulated precipitation, being less severe in autumn-winter than in the spring-summer season. The present findings provided a better understanding of the structure and the seasonal variation of AGLR in cultivar 'Niagara Rosada'. The strategies for reducing and/or delaying inoculum buildup among seasons are discussed.

First report of Phakopsora euvitis causing leaf rust disease on grapevine (Vitis labrusca L.) in India.

Grapevine (Vitis labrusca L.), a member of the family Vitaceae and native of North America, is grown as a table grape. During the survey for the grapevine diseases in May 2022, we noticed numerous yellow pustules of rust on lower side of leaves of 'Bangalore Bule' in Nandi village (13°22'59.7"N77°42'33.4"E), Chikkaballapur district of Karnataka state of India. The crop was at maturity stage and the rust disease severity was determined using the scale given by Angelotti et al. (2008), which was up to 10%. The disease symptoms were numerous small raised yellow pustules on the abaxial surface corresponding to adaxial surface chlorotic spots. In severe conditions, spots cover the entire leaf and defoliation occurs. Similar disease symptoms were reported by Ono (2000); Weinert et al. (2003); and Primiano et al. (2017). The pathogenicity test was performed on cuttings of 'Bangalore Bule' grapevine in a glasshouse at 25±1°C. The urediniospores were collected from diseased leaves using a brush, 3×104 ml-1 suspension in distilled water was used for inoculation on the abaxial surface of leaves. Control plants were sprayed with distilled water. The leaves developed symptoms in 15-17 days after inoculation, and the pathogen was confirmed by symptomatology and microscopic observation of urediniospores. Urediniospores were short-pedicellate, sessile, obovoid to obovoid-ellipsoid, and uniformly echinulate with 42.98-32.54 x 31.37-25.15 µm in size. The aecial stage of the Phakopsora has been reported on an alternate host, Meliosma simplicifolia (Hosagoudar 1988). As the internal transcribed spacer (ITS) region offers some utility in the molecular detection of the Phakopsora genus (Rush et al. 2019), the pathogen was confirmed by studying the different regions in the ITS such as ITS1, 5.8S rRNA, and ITS2. Total DNA was extracted from urediniospore mass using the Macherey-Nagel kit (Duren, Germany) by following the manufacturer's protocol. The quantity of isolated DNA was checked using an Qubit 3.0 fluorometer (Invitrogen) before being subjected to polymerase chain reaction (PCR) amplification in a thermocycler (Eppendorf-vapo.protect) using ITS1 and ITS4 primers (IDT, Singapore) targeting ITS1, 5.8S rRNA, and ITS2 regions, and the obtained amplicon (~700 bp) was purified using Macherey- Nagel Nucleospin gel and PCR clean-up kit (Duren, Germany) as per the manufacturer's protocol and sequenced by Sanger's dideoxy chain-termination method [ABI 3730 (48 capillaries) electrophoresis]. The sequence was edited in BioEdit (https://bioedit.software.informer.com/7.2/) and aligned in MUSCLE, and the phylogenetic tree was constructed in MEGA 11 using the neighbor-joining method by following the maximum likelihood criterion (Kumar et al. 2018). The sequence data was deposited at NCBI (accession number OP221661). The basic local alignment search tool (BLAST) search sequence of the isolate Nandi-KA in GenBank revealed 97.91% homology with sequence of Phakopsora sp. (accession number KC815548.1) and 96.87% with Phakopsora euvitis (accession number AB354790.1). Based on disease symptoms, fungal morphology, the pathogenicity test, and ITS sequence, the fungus was identified as Phakopsora euvitis, the pathogen causing grapevine leaf rust disease. Though there are similar disease symptoms observed on grapevine in India (EPPO 2016); the pathogen was not confirmed. To our knowledge, this is the first report of Phakopsora euvitis causing leaf rust disease in grapevine (V. labrusca) in India.

Damage on grapevine cv. Niagara Rosada leaves caused by the combined effect of temperature and Asian grapevine leaf rust (Neophysopella tropicalis)

AbstractAsian grapevine leaf rust (AGLR), caused by Neophysopella tropicalis, is a problem for viticulture, especially in latitudes lower than 25° S, which include the most significant production regions in Brazil. Climate change has raised new concerns in agriculture as temperature can affect the resistance of plants to pathogens. With the aim of understanding how air temperature rise affects the AGLR pathosystem, measurements of leaf gas exchange and epidemiological and histopathological analyses were carried out on control and inoculated leaves of Vitis labrusca ‘Niagara Rosada’ grown at 25°C and 30°C. The lesion density and rust severity were higher at 25°C than 30°C, and the ratio between adaxial surface necrosis and the abaxial surface area occupied by pustules was >1 only at 30°C, presenting a necrosis not associated to the pathogen lesion. In fact, leaf necrosis was identified on control plants kept at 30°C and associated with gerontoplasts, representing accelerated leaf senescence. The AGLR pathogen reduced gas exchange and photosystem II activities at 25°C, with no difference between control and inoculated plants at 30°C. Our results indicate that AGLR is sensitive to increasing air temperature. However, the accelerated leaf senescence caused by the combination of N. tropicalis infection and temperature on Niagara Rosada can lead to high leaf damage.

Lack of an Intron in Cytochrome b and Overexpression of Sterol 14α-Demethylase Indicate a Potential Risk for QoI and DMI Resistance Development in Neophysopella spp. on Grapes.

Asian grapevine leaf rust, caused by Neophysopella meliosmae-myrianthae and N. tropicalis, is often controlled by quinone outside inhibitor (QoI) and demethylation inhibitor (DMI) fungicides in Brazil. Here, we evaluated the sensitivity of 55 Neophysopella spp. isolates to pyraclostrobin (QoI) and tebuconazole (DMI). To elucidate the resistance mechanisms, we analyzed the sequences of the cytochrome b (CYTB) and cytochrome P450 sterol 14α-demethylase (CYP51) target proteins of QoI and DMI fungicides, respectively. The CYP51 expression levels were also determined in a selection of isolates. In leaf disc assays, the mean 50% effective concentration (EC50) value for pyraclostrobin was about 0.040 µg/ml for both species. CYTB sequences were identical among all 55 isolates, which did not contain an intron immediately after codon 143. No amino acid substitution was identified at codons 129, 137, and 143. The mean EC50 value for tebuconazole was 0.62 µg/ml for N. tropicalis and 0.46 µg/ml for N. meliosmae-myrianthae, and no CYP51 sequence variation was identified among isolates of the same species. However, five N. meliosmae-myrianthae isolates grew on leaf discs treated at 10 µg/ml tebuconazole, and these were further exposed to tebuconazole selection pressure. Tebuconazole-adapted laboratory isolates of N. meliosmae-myrianthae showed an eight- to 25-fold increase in resistance after four rounds of selection that was not associated with CYP51 targetalterations. In comparison with sensitive isolates, CYP51 expression was induced in the presence of tebuconazole in three out of four tebuconazole-adapted isolates tested. These results suggest a potential risk for QoI and DMI resistance development in Neophysopella spp.

Early detection of Neophysopella tropicalis in grapevine leaves and on spore traps by qPCR

AbstractNeophysopella tropicalis, one of the causal agents of Asian grapevine leaf rust (AGLR), can cause severe epidemics in Brazil that lead to yield losses in commercial vineyards. An early detection of the pathogen by air sampling of urediniospores on spore traps or in symptomless leaves would be valuable to multiple studies, such as epidemics modelling, risk forecasting, monitoring of pathogen introductions in rust‐free areas, and predicting the beginning of epidemics. This study developed a quantitative PCR (qPCR) protocol to quantify N. tropicalis urediniospores attached to adhesive tapes and in grapevine leaves before symptom appearance. A specific primer pair was designed based on the internal transcribed spacer (ITS) sequence region of the AGLR pathogen. Standard amplification curves using genomic DNA from urediniospores of N. tropicalis and from urediniospores attached to adhesive tapes were established. Grapevine leaves inoculated with N. tropicalis were collected at 2, 5, and 7 days postinoculation (dpi). One primer pair (580F/720R) amplified a 140 bp product in all AGLR isolates but did not amplify products of other rust genera, such as Phakopsora, Puccinia, Hemileia, Tranzschelia, Cerotelium, and Coleosporium. As little as 0.1 pg DNA and 10 urediniospores of N. tropicalis attached to adhesive tapes could be detected. qPCR enabled the detection of the pathogen as early as 2 dpi, before symptom appearance. This method can be used to monitor N. tropicalis inoculum in grapevine‐growing areas and to quantify symptomless infections of the AGLR pathogen.

Identification and pathogenicity of Neophysopella species associated with Asian grapevine leaf rust in Brazil

AbstractAsian grapevine leaf rust (AGLR) causes severe crop losses in Brazilian viticulture, mainly in latitudes <25°S. The purpose of this study was to identify the pathogen(s) involved with AGLR in Brazil, based on phylogenetic and morphological analysis and pathogenicity tests. In total, 56 monouredinial isolates from six Brazilian states were identified using the internal transcribed spacer 2 and the large subunit rRNA gene D1/D2 regions. All 50 isolates from the south‐central region were classified as Neophysopella tropicalis, and the other six isolates from the north‐east region as Neophysopella meliosmae‐myrianthae. This result provides evidence that two pathogen introductions from different sources may have occurred in the country. For both species, paraphyses were cylindrical, incurved, aseptate, and hyaline, while urediniospores were short‐pedicellate, obovoid or obovoid‐ellipsoid, with the wall colourless or pale yellowish, evenly echinulate. Representative isolates from both species caused typical AGLR symptoms on Vitis vinifera 'Merlot' and V. labrusca 'Niagara Rosada'. Overall, regardless of the Neophysopella species, isolates caused similar leaf disease severities. Higher disease severity was observed in Niagara Rosada (average of 40.3% of diseased leaf area) compared to Merlot (20.5%). This study reports, for the first time, the characterization of Neophysopella species associated with AGLR in Brazil.

Taxonomy of Southeast Asian-Australasian grapevine leaf rust fungus and its close relatives

Rust fungi on commercial Vitis cultivars, wild Vitaceae, and Meliosma (Sabiaceae), potential alternate hosts of a grapevine leaf rust (GLR) fungus, were surveyed in Thailand and Vietnam. Molecular phylogenetic analyses using the internal transcribed spacer 2 and the large-subunit rRNA gene (D1/D2 region) and morphological examinations confirmed that the GLR fungus distributed in Southeast Asia and Australasia is distinct from Neophysopella species involved in GLRs in East Asia and the Americas. Therefore, the Southeast Asian-Australasian GLR fungus is recognized as a new Neophysopella species and named as N. tropicalis. Two fungi on Meliosma species in Thailand were aecial anamorph of Neophysopella species. One parasitic on M. simplicifolia and M. simplicifolia subsp. fordii was previously named as Aecidium wareoense, and a new name, N. wareoensis, is proposed for it. Another on M. arnottiana in Thailand was phylogenetically and morphologically distinct from all other Meliosma rust fungi, and, therefore, it is recognized as a new species, N. sriphumensis. A uredinial-telial fungus on Ampelocissus araneosa (Vitaceae) in Thailand was morphologically similar to Phakopsora cronartiiformis on Parthencissus semicordata (Vitaceae) in the Himalayas. However, the former fungus was distinct from the latter in producing characteristic urediniospores with labyrinthiform surface structure and cone-shaped projections. It is, therefore, recognized as a new species, N. doipuiensis.

Comparative study on the monocycle of Phakopsora meliosmae-myrianthae and Phakopsora pachyrhizi

Asian grapevine leaf rust, caused by Phakopsora meliosmae-myrianthae, presents symptoms similar to Asian soybean rust, caused by P. pachyrhizi, such as the presence of satellite uredinia and early leaf fall. To shed light on the epidemiological behaviour of these rusts, we compared the monocyclic components of these Phakopsora species and the effects of these pathogens on host photosynthesis over time. Both hosts were inoculated with a 104 urediniospores mL−1 suspension and incubated at 23–25 °C. Incubation and latent periods were simultaneous at 8 days in Asian grapevine leaf rust and 13 days in Asian soybean rust. The minimum infectious periods were 21 days for P. meliosmae-myrianthae and 13 days for P. pachyrhizi. The continuous production of urediniospores through a long infectious period was observed for both pathogens. Both Phakopsora rusts showed an increase in rust severity with similar progress rates to those estimated with the monomolecular model as 0.07 day−1 and 0.02 day−1 for grapevine and soybean rusts, respectively. No increase in the number of lesions was observed from the first assessment, although the number of uredinia increased over time. P. meliosmae-myrianthae and P. pachyrhizi infection reduced the net photosynthetic rates by 22% and 5%, respectively, before the onset of symptoms. Both pathogens withstand non-ideal environmental conditions for secondary infections. We concluded that, although P. meliosmae-myrianthae has a restricted host range on Vitis sp., unlike to P. pachyrhizi with a broad host range, the epidemiological behaviour of P. meliosmae-myrianthae is in some ecological aspects similar to that of P. pachyrhizi.

Assessment of grapevine germoplasm collection for resistance to grape leaf rust (Phakopsora euvitis) using a leaf disc assay

The present study aimed to assess 25 grapevine genotypes, representing different Vitis species, for resistance to grapevine leaf rust (GLR), caused by Phakopsora euvitis, using leaf disc assay. Disinfected leaf discs of 12 mm in diameter were placed in agar-water medium. On the abaxial side, a 30-µl drop at a concentration of 30,000 urediniospores/ml was deposited and incubated in a growth chamber under controlled conditions. The genotypes were assessed by the components of resistance latent period, number of pustule per cm2, diameter of pustules (DP; mm), number of urediniospores per disc, severity (%), and area under the disease severity progress curve. The ANOVA revealed a significant difference (p < 0.05) among genotypes for all components of resistance tested. Significant correlation was observed for all components of resistance evaluated. Based on disease severity, the genotypes were classified into four resistance categories: (1) resistant, (2) partially resistant, (3) susceptible, and (4) highly susceptible. None of the genotypes were asymptomatic and 32% were considered resistant or partially resistant. ‘IAC766’ and ‘Seibel 405’ were the most resistant, showing the lowest severity of 0.03 and 1.48%, respectively. ‘Seibel 128’, V. del rioi Sd1, V. slavinii and V. candicans were partially resistant. From the resistant and partially resistant genotypes, only V. candicans has trichomes on the abaxial leaf surface. Particularly, the resistant genotypes are resistance sources to GLR to be explored in future breeding programs and for genetic analysis to localize resistant genes to P. euvitis.

Formation of satellite uredinia as an important trait related to grapevine colonization by Phakopsora meliosmae‐myrianthae

Phakopsora meliosmae‐myrianthae, the causal agent of Asian grapevine leaf rust, significantly reduces the photosynthetic efficiency of grapevine leaves in green symptomless tissues surrounding lesions. This study took a close look at grapevine leaf colonization kinetics by P. meliosmae‐myrianthae and compared it to P. pachyrhizi–soybean and Uromyces appendiculatus–bean colonization. It is already known from the literature that soybean rust, similar to grapevine rust, has a negative effect on leaf photosynthesis greater than would be expected based on visual lesions. However, in contrast to soybean and grapevine rusts, the effect of bean rust on leaf photosynthesis is proportional to the diseased leaf area. Colonization progress was monitored by fungal biomass assessed via histological staining and quantitative polymerase chain reaction (qPCR). Individual lesions of P. meliosmae‐myrianthae on grapevine, P. pachyrhizi on soybean and U. appendiculatus on common bean leaves were evaluated every 3–4 days, and the number of uredinia was counted. Staining showed that mycelial colonization did not extend beyond the lesion border. The number of P. pachyrhizi and P. meliosmae‐myrianthae uredinia within the lesions increased over time (on average 14‐fold), whereas the number of U. appendiculatus uredinia remained the same. These findings were corroborated by qPCR, which revealed a greater increase in fungal biomass for Phakopsora spp. than for U. appendiculatus until 12 days post‐inoculation. The high number of satellite uredinia within lesions might be directly related to the impact of this pathogen in photosynthetic efficiency on symptomless areas of diseased grapevine leaves. This study identified accelerated formation of satellite uredinia as an important feature of grapevine colonization by P. meliosmae‐myrianthae.

Seasonal progression of leaf rust in ‘Niagara Rosada’ grapevine in a biannual crop system in Brazil

Grapevine leaf rust, which is caused by the fungus Phakopsora euvitis, is an important late-season disease of ‘Niagara Rosada’ (Vitis labrusca) grapevine in Brazil. The early defoliation of plants caused by the disease impairs fruit ripening and reduces marketable yield. In a study carried out in northern Parana State, the temporal progression of grapevine leaf rust was quantified in a production system of ‘Niagara Rosada’ grapevine with two growing seasons per year: mid-summer-autumn and late winter-spring. The influence of weather-related variables on rust progression was examined through correlation analyses. It was observed that the rust was more severe in summer-autumn than in winter-spring. Significant positive linear correlations (P ≤ 0.05) were found between rust severity and rainfall (r ≥ 0.90) and average daily hours of leaf wetness (r ≥ 0.82). In addition, negative correlation was found between rust severity and temperature (r ≥ −0.84) in the mid-summer/autumn season. Mild temperatures in autumn were considered decisive for rust progression. In Brazilian tropical viticulture, management strategies for grapevine leaf rust must consider the risk of rust damage in autumn caused by temperature.

Biosecurity tool-set: optimising quarantine zones for eradication through consideration of Australia’s success with plant pathogen eradications in horticulture

Plant pathogen eradication programs can be both expensive and cause social conflicts due to restrictions imposed within quarantine zones (QZs) and significant potential damage to host populations in agricultural, residential, urban and semi-natural environments. The optimisation of QZs, particularly destruction zones, is therefore highly desirable to improve the efficiency of containment and minimise negative impacts of eradication programs. Knowledge gained from previous eradication programs in Australia can be useful for identifying the factors and issues that influence pathogen containment, particularly the effectiveness of QZs. This study therefore examined the influence of features of disease outbreaks on pathogen containment using several past programs launched to eradicate exotic plant pathogens in horticulture as case studies. Australia has had considerable success in eradicating serious horticultural pathogens over the past 100 years. Eradication programs of ten horticultural plant pathogens were reviewed, most of which were successfully eradicated. The most important factor for success was that the QZ be as large as practicable while delimitation activities are taking place. Once the size of the incursion is known and eradication is considered feasible, the size of the pest quarantine areas and destruction zones should be informed foremost by the pathogen biology and behaviour, plus consideration of location, topography and host prevalence. Some diseases such as citrus canker, grapevine leaf rust and black Sigatoka required large destruction zones, tens of km in radius, while others such as angular leaf spot and potato spindle tuber viroid required very small destruction zones of several m in radius. This review also demonstrated the value of flexibility to revise the QZs accordingly as eradication progresses and the importance of commitment to eradicate by all parties. The information identified will be useful to further strengthen the containment of plant pathogens in different incursion settings in Australia.

Phylogenetic study of indigenous grapevine leaf rust fungi in North America and biological identity of an invasive grapevine leaf rust fungus in Brazil

Two American grapevine leaf rust (GLR) fungi, Phakopsora muscadiniae and P. uva, were found to be phylogenetically different from Asian-Australasian GLR fungi. In the phylogram based on rDNA region sequences, a clade of the American fungi was sister to an inclusive clade of three autoecious species on Meliosma and a heteroecious species host-alternating between Meliosma and Parthenocissus. An invasive Brazilian GLR fungus (as P. meliosmae-myrianthae) was included in the Asian-Australasian GLR fungi clade, or the clade of the Thai population of Phakopsora sp. It could be assumed that the Brazilian GLR fungus originated from an inadvertently introduced Thai population.

Occurrence of Asian grapevine leaf rust disease caused by Phakopsora meliosmae-myrianthae in Mexico

During the falls of 2015 and 2016, rust symptoms were observed on grapevine leaves in a backyard garden located in Tlaxiaco, Oaxaca, Mexico. Based on morphology, analysis of the variable D1/D2 region of the large subunit rDNA, and the fulfilment of Koch’s postulates on grapevine leaves, the causal agent was identified as Phakopsora meliosmae-myrianthae. This is the first report of Asian grapevine leaf rust disease caused by Phakopsora meliosmae-myrianthae in Mexico.

Asian grapevine leaf rust caused by Phakopsora euvitis: an important disease in Brazil

Anthropogenic influences such as tourism and climate change affect ecosystems. One consequence is that invasive species can spread to and colonize novel areas. A recent example of this scenario is the appearance, in the early 2000s in Brazil and Australia, of the plant pathogenic fungus Phakopsora euvitis, which causes Asian grapevine leaf rust. It is speculated that the disease was introduced either by long distance transport of spores in the atmosphere or the import of contaminated plant material. While the disease could be eradicated from the Australian continent it is still present in Brazil. The pathogen has spread successfully throughout most Brazilian grapevine‐growing regions, most probably because of the lack of resistant plant cultivars. Today, the disease is endemic in Brazil. This review was written to highlight the increasing impact of the disease in Brazil and summarizes the current knowledge on the disease monocycle under different environmental conditions and the consequences for grapevine management. Gaps in the present state of knowledge are highlighted with the purpose of stimulating further research aimed at identifying efficient strategies to combat the disease.

Mixed infections of grapevine leaf rusts Phakopsora meliosmae-myrianthae and P. montana in Japan

Mixed infections of grapevine leaves by the grapevine leaf rust fungi Phakopsora meliosmae-myrianthae and P. montana were assumed because of the frequent sympatric occurrences of the two species in Honshu, Japan. This assumption was proven by experimental basidiospore inoculations of Meliosma myriantha and M. tenuis. Basidiospores formed on telial clusters from one rusted grapevine leaf infected both M. myriantha and M. tenuis, resulting in spermogonium and aecium production on the inoculated leaves. However, the aeciospores formed on the two Meliosma species differed; those on M. myriantha were apically thick-walled, characteristic of P. meliosmae-myrianthae, and those on M. tenuis were evenly thin-walled, characteristic of P. montana.

Taxonomic identity of a Phakopsora fungus causing the grapevine leaf rust disease in Southeast Asia and Australasia

Three distinct groups were revealed among the grapevine leaf rust fungi from Japan, Taiwan, Thailand, Malaysia, Indonesia, East Timor and Australia in phylograms generated from sequence analyses of the internal transcribed spacer 2 and the large-subunit rRNA gene (D1/D2 region). A group of Thai, Malaysian-Indonesian and East Timorese-Australian fungi was distinct from two other groups of grapevine leaf rust fungi, Phakopsora meliosmae-myrianthae and P. montana, distributed in temperate East Asia. Although complete life cycle and native host plants are unknown for the Southeast Asian and Australasian fungus, it is likely to be a biologically distinct species.

Phakopsora montana, another grapevine leaf rust pathogen in Japan

A new grapevine leaf rust (GLR) was found to be caused by Phakopsora montana. This new fungus naturally infects Crimson Glory vine (Vitis coignetiae), forming uredinia and telia on the leaves. Under experimental conditions, the fungus was pathogenic to table grape cultivars Delaware and Kyoho (V. × labruscana), Amur River grape (V. amurensis), and V. ficifolia, on which it produced urediniospores. Inoculation experiments proved that the pathogen alternates hosts, forming spermogonia and aecia on Meliosma tenuis. The new pathogen resembles P. meliosmae-myrianthae (=P. euvitis), a common GLR fungus; however, its spermogonial/aecial stage is restricted to M. tenuis, contrary to P. meliosmae-myrianthae with its spermogonial/aecial stage restricted to M. myriantha. Aeciospores of the new pathogen are evenly thin-walled, whereas the aeciospore wall is conspicuously thickened apically in P. meliosmae-myrianthae. Phakopsora montana is known to occur only on V. coignetiae in nature; however, table grape cultivars Delaware and Kyoho were not resistant to P. montana under experimental conditions. These results indicate that P. montana has caused a certain proportion of the GLR disease recorded in Japan with a possible mixed infection with P. meliosmae-myrianthae.

Phylogeny and taxonomy of the Asian grapevine leaf rust fungus, Phakopsora euvitis, and its allies (Uredinales)

Heteroecious Phakopsora euvitis, P. vitis, and P. ampelopsidis, autoecious P. meliosmae, and an unconnected Aecidium on Meliosma are closely allied. A total of 45 collections representing the five rust fungi from Japan, Australia, and East Timor were subjected to molecular phylogenetic analyses: the D1/D2 region of nuclear large subunit rDNA and nuclear small subunit internal transcribed spacer 2 (ITS2) region including 5.8S rDNA were analyzed. Tree topologies generated from parsimony and distance methods of the D1/D2 and ITS2 sequences were similar. The 45 collections (44 for ITS2 and 33 for D1/D2, with 32 common for both analyses) are grouped into seven clades: P. ampelopsidis, P. vitis, unconnected Aecidium, P. euvitis from Japan, P. euvitis from Australia and East Timor, P. meliosmae on M. myriantha, and P. meliosmae on M. tenuis. The results confirm the phylogenetic distinctness of P. euvitis, P. ampelopsidis, and P. vitis distributed in Japan. A grapevine leaf rust fungus in Australia and East Timor has genetically diverged from P. euvitis in Japan. The unconnected Aecidium is highly likely to be an aecial anamorph of a Phakopsora fungus. Autoecious Phakopsora fungi on M. meliosmae and M. tenuis need further host-specificity and morphological studies to confirm their taxonomic status.