Gnomonia Comari Research Articles

PLANT PROTECTION CHALLENGES IN STRAWBERRY PRODUCTION IN NORTHERN EUROPE

Strawberry is cultivated in north Europe, also in the higher latitudes and it is the most important soft fruit crop in Finland. The cool climate has limited the spread of many strawberry pests to Finland, but this is now changing. Benefiting from the warming climate, strawberry tarsonemid mite (Tarsonemus pallidus) continues to be the most important pest. Biological control by use of predatory mites is widely adopted by growers. Two-spotted spider mite (Tetranychus urticae) is favoured by use of fibre cloth used to protect plants during winter and spring. Strawberry blossom weevil (Anthonomus rubi) and European tarnished plant bug (Lygus rugulipennis) are among the key pests, and in northern Finland strawberry leaf beetles (Galerucella spp.) can cause severe damage. Monitoring methods have been developed for these pests. Warming climate has increased thrips damage on fruits, and favours also the black vine weevil (Otiorhynchus sulcatus). Grey mould (Botrytis cinerea) is the main disease, and controlled with fungicides. Recently, also biological control has become more popular. Crown rot (Phytophthora cactorum) has spread to production fields. However, anthracnose (Colletotrichum acutatum) has not established itself in production fields. Leaf diseases (Mycosphaerella fragariae, Diplocarpon earlianum and Gnomonia comari) are quite common and powdery mildew (Podosphaera aphanis) has not been an important disease in open field. The main vector of strawberry viruses, strawberry aphid (Chaetosiphon fragaefolii), occurs not yet in Finland. In the future, mites are expected to be more harmful and also thrips and black vine weevil are favoured by warmer conditions. Considering diseases, Phytophthora species can be expected to increase in Finnish strawberry fields.

Methyl Anthranilate and γ-Decalactone Inhibit Strawberry Pathogen Growth and Achene Germination

Plant volatile compounds have been shown to affect microbial growth and seed germination. Here two fruity volatiles found in strawberry ( Fragaria × ananassa ), γ-decalactone ("peachlike" aroma) and methyl anthranilate ("grapelike" aroma), were tested for effects on relevant pathogens and seedling emergence. Significant growth reduction was observed for Botrytis cinerea , Colletotrichum gloeosporioides , Colletotrichum acutatum , Phomopsis obscurans , and Gnomonia fragariae at 1 mM γ-decalactone or methyl anthranilate, and 5 mM γ-decalactone or methyl anthranilate supplemented medium resulted in complete cessation of fungal growth. Phytophthora cactorum was especially sensitive to 1 mM γ-decalactone, showing complete growth inhibition. Bacteriostatic effects were observed in Xanthamonas cultures. Postharvest infestations on store-bought strawberries were inhibited with volatile treatment. The γ-decalactone volatile inhibited strawberry and Arabidopsis thaliana germination. These findings show that two compounds contributing to strawberry flavor may also contribute to shelf life and suggest that γ-decalactone may play an ecological role by preventing premature germination.

Infection and colonization of strawberry by Gnomonia fragariae strain expressing green fluorescent protein

Gnomonia fragariae is a poorly studied ascomycete, which was recently demonstrated to be a cause of severe root rot and petiole blight of strawberry. The pathogen was genetically transformed with the GFP as a vital marker and hygromycin resistance gene. Several stable transformants were obtained, which did not differ in their phenotype from the wild type isolate. Using one of the GFP-tagged isolates the infection process and colonization of roots and petioles of host plant by the pathogen were studied. Fluorescence microscopy examinations of the inoculated plants at different time points showed that plant infection occurs 24 h after inoculation and intensively continues during first 3 days. The specific penetration sites on epidermal cells and preferences in colonization for certain root and petiole tissues were observed. The pathogen intensively colonized and destroyed cortex of roots and petioles and spread rapidly longitudinally within intercellular spaces. The petioles were colonized by the hyphae, which grew mostly in the intracellular spaces of the cortical cells while in the roots the intracellular growth of hyphae occurred only in the later stages of infection. The fungus was also capable to infect the vascular tissues of petioles although these were not the primary tissues colonized by the pathogen. The mature ascomata were formed on the infected petiole bases several weeks after the inoculation. This study presents a genetic transformation method for Gnomonia fragariae and it demonstrates details on infection process and colonization of root, crown and petiole tissues of strawberry by the pathogen.

MICROBIOLOGICAL QUALITY OF ORGANIC STRAWBERRY FRUIT

The effect of different irrigation methods, mulches and alternative preparations for grey mould control in organic strawberry production was investigated in Jokioinen, Mikkeli and Ruukki, Finland. In the irrigation trial, grey mould infection of fruit was studied from petals and receptacles from early to late flowering. Rainy periods during the flowering season could be seen in the Botrytis cinerea infection of flowers, but on fruit, dry harvest periods kept visible infection low. As a whole, microbial contamination of fruit was more affected by weather conditions than irrigation practice. Organic mulches of green mass, buckwheat husks, straw, birch woodchips, pine woodchips and flax fibre mat were compared with black plastic. Only green mass increased fungal infections on fruit and shortened shelf-life. Biological sprays Trichoderma (Binab ® TF-WP) and Gliocladium (Prestop), compost and garlic extracts as well as seaweed and silicon solution used for grey mould control did not affect fruit quality. In marketable fruit, fungi such as Cladosporium, Acremonium, Penicillium, Trichoderma, Fusarium, Mucor and Alternaria species were abundant while Hainesia lythri and Zythia fragariae (Gnomonia comari ) were uncommon. Infection of Escherichia coli in fruit was investigated on VRB plates, but E. coli was not detected in the fruit.

EFFECT OF CHAMOMILE ESSENTIAL OIL ON GNOMONIA COMARI CONTROL AND STRAWBERRY FRUIT PRODUCTION UNDER ORGANIC SYSTEM

The strawberry crop is host of several pathogens and pests. The Gnomonia leaf spot (Gnomonia comari) is an emergent disease that has been occurring and limiting the production of this small fruit in the Rio Grande do Sul state, Brazil. However, there is no information about any efficient control method of this disease and also, no resistant strawberry cultivar available to organic production systems. Therefore, an experiment was carried out in order to evaluate the effect of the chamomile oil (Matricaria chamomiilla) on the control of G. comari and on yield of six strawberry cultivars ('Camarosa', 'Galexia', 'Earlibrite', 'Festival', 'Plarionfre' and 'Sabrosa'). The work was conducted at the Embrapa Temperate Climate Research Center, in Pelotas-RS, Brazil. Sixty days after the planting, the strawberries were sprayed weekly with chamomile oil at 500 ppm during 40 days. After appearing the first symptoms, the disease severity (%) of Gnomonia and some parameters which one related to fruit production were evaluated. After appearance of the first symptoms, the disease severity (%) of Gnomonia and some parameters related to fruit production were evaluated. Based on the severity values, the area under disease progress curve (Audpc) was calculated for each material tested. Thereafter, the Audpc and fruit yield data were submitted to Anova and Duncan test at 5%. It was verified that the disease severity was reduced in the 'Festival', 'Galexia' and 'Sabrosa' cultivars when plants were sprayed with chamomile oil. Although the use of chamomile oil has not affected fruit yield, 'Camarosa' and 'Galexia' showed the highest yield and 'Plarionfre' was the lowest yielder and the most susceptible to leaf spot of Gnomonia, independently of the application of chamomile essential oil.

GNOMONIA COMARI ON STRAWBERRY: PRELIMINARY STUDY ON CONTROL STRATEGY IN THE NORTH OF ITALY

In the autumn 2005, in the province of Forli-Cesena (Emilia-Romagna), several strawberry plots were affected by the fungus Gnomonia comari. During the growing season, more than 50% of the foliage was blighted by the epidemic causing severe yield losses. Disease severity is mainly due to the use of susceptible cultivars (Alba) and wet climate in autumn. In the following spring two trials were set up with the aim to: 1) evaluate the efficacy of six fungicides on foliage, applied from beginning of the vegetative growth until bloom; 2) evaluate the efficacy of four fungicides applied from bloom to harvest to control both foliage and fruits. In trial 1, two surveys were carried out on foliage. The results showed that pyraclostrobin+boscalid , azoxystrobin and miclobutanil were the most effective in controlling the foliage blight. Slightly less effective were cyprodinil+fludioxonil, penconazole and tolylfluanide. In trial 2, one survey on foliage and three on fruits were carried out. On leaves, in spite of the fact that chemicals were applied after the occurrence of the symptoms in the field, pyraclostrobin+boscalid and azoxystrobin allowed to better reduce the epidemic compared with the check. Cyprodinil+fludioxonil was less effective, while tolylfluanide was not statistically different from the check. On fruits, pyraclostrobin+boscalid, cyprodinil+fludioxonil and azoxystrobin proved to be the most effective, while tolylfluanide failed to give satisfactory results.

Molecular characterization of strawberry pathogen Gnomonia fragariae and its genetic relatedness to other Gnomonia species and members of Diaporthales

Gnomonia fragariae is a poorly studied ascomycete belonging to Diaporthales. Originally G. fragariae was considered a saprophyte occurring on dead tissues of strawberry plants. Recently this fungus was found in Latvia and Sweden, and it was proven to be the cause of severe root rot and petiole blight of strawberry. Thirteen isolates of this pathogen and several other Gnomonia species occurring on rosaceous hosts were characterized by molecular analysis using nucleotide sequences of partial LSU rRNA gene and the total ITS region. The homologous regions from relevant diaporthalean taxa available in the GenBank were also included and compared with the taxa sequenced in this study. Phylogenetic analyses revealed that G. fragariae, G. rubi, and Gnomonia sp. (CBS 850.79) were genetically different from G. gnomon, the type species of the genus, and other members of Gnomoniaceae. The analyses showed that G. fragariae and Hapalocystis were genetically very closely related, forming a phylogenetic clade, which is possibly presenting a new family in the Diaporthales. Morphological comparisons of the Gnomonia species on the basis of commonly used criteria for the taxonomy of Diaporthales, so far did not reveal any evident features for the polyphyletic status of Gnomonia.

THE SENSITIVITY OF STRAWBERRY CULTIVARS TO MAJOR FUNGAL FOLIAR DISEASES IN CROATIA, AND THE POSSIBILITIES FOR THEIR CONTROL

In Croatia, the production of strawberries has been increasing steadily in recent years. The assortment has been changing from year to year, owing to the introduction of new cultivars.The most important common cultivars in production are: Elsanta, Marmolada, Miranda, Maya, Madeleine, Miss and Raurica. The aim of our research was to determine the sensitivity of these cultivars to major fungal diseases of leaves in Croatia, namely leaf spot (Mycospahaerella fragariae), leaf scorch (Diplocarpon earliana), leaf blotch (Gnomonia comari), and leaf blight (Phomopsis obscurans). In order to determine the possibilities for controlling these diseases, we conducted tests foof fungicide efficacy on the most sensitive cultivars. The infection intesity of each disease was assessed according to the Townsend-Heuberg formula based on an analysis of 200 leaves and our own scale of 0-5, while fungicide efficacy was determined by Abbotts formula. Among the cultivars tested for leaf spot, the most sensitive cultivars were Madeleine and Marmolada, while the other cultivars were relatively resistant to this disease. The cultivar most sensitive to leaf scorch was Raurica and somewhat less, Marmolada. All cultivars proved to have a low sensitivity to leaf blotches and leaf blight. Among the fungicides, Folicur M and Euparen M had the best eficacy for all tested diseases. Kidan had a good efficacy on leaf scorch, as did Quadris on leaf spot. Based on the results obtained, we created a leaf protection plan, dependant on the cultivars grown.

Gnomonia fragariae, a Cause of Strawberry Root Rot and Petiole Blight

Gnomonia fragariae has been occasionally listed among the fungi associated with diseased strawberry plants. However its pathogenicity has not been established. During the investigation on strawberry decline in Latvia and Sweden, a fungus was repeatedly recovered from discoloured root and crown tissues of severely stunted plants. Attempts to induce sporulation of the isolates grown on several agar media resulted in the formation of mature ascomata only on potato carrot agar and oatmeal agar. On morphological grounds and comparisons with reference herbarium specimens these isolates were identified as Gnomonia fragariae. The pathogenicity of the fungus was evaluated initially in the detached leaf assay and subsequently in three bioassays on strawberry plants. All the bioassays showed that G. fragariae was pathogenic on strawberry and capable of causing severe root rot and petiole blight. The symptoms that developed in the greenhouse experiments closely resembled those observed in the fields. The fungus did not cause rapid plant death but growth and development of inoculated strawberry plants was severely affected. To our knowledge this is the first time when pathogenicity of G. fragariae as a root rot pathogen has been clearly established. Our study shows that G. fragariae is one of the serious pathogens involved in the root rot complex of strawberry in Latvia and Sweden.

THIS ARTICLE HAS BEEN WITHDRAWN: Glomerella acutata

THIS ARTICLE HAS BEEN WITHDRAWN: <i>Glomerella acutata</i>

Dynamics of most important fungal diseases of strawberries in Croatia and suggestions for integrated control

During trials (1998–2001) in the strawberry’s plantation of the cv. Marmolade we monitored the appearance of the most important fungal diseases, their biology and possibilities of integrated control. Monitoring the biology of the determined fungi we established the way of overwintering, appearance of fruiting bodies and discharging of spores as well as beginning of primary infection and first symptoms of the following fungi: Mycosphaerella fragariae, Diplocarpon earliana, Gnomonia comari, Phomopsis obscurans on leaves and Botrytis cinerea on fruits. While checking the efficacy of fungicides, those most effecting to leaf diseases were Folicur Multi and Quadris, and on B. cinerea Switch and Teldor. Testing the resistance on botryticides the fungus B. cinerea showed low level of resistance to anilinopyrimidines and phenilsulfamides and high level to dicarboximides.

Effect of fungicides, seaweed extracts, tea tree oil, and fungal agents on fruit rot and yield in strawberry

Seven fungicides, 2 seaweed extracts (Maxicrop and Seasol), tea tree oil (Multicrop), and fungal agents including yeasts and an isolate of a Trichoderma sp., were compared for the control of fruit rots in strawberries in 5 field trials in Victoria, Australia. The fungicides tested were thiram, iprodione, dichlofluanid, chlorothalonil, fluazinam, phosphorous acid and fosetyl-aluminium. All treatments were applied as foliar sprays (at recommended rates) at weekly intervals, except for one of the Trichoderma treatments in which Trichoderma was cultured on rice and applied around plants at 1 and 5 weeks after the start of the trial. Rots were assessed after harvest by incubating fruit for 3 days at room temperature (15–25˚C). Between 55 and 71% of fruit developed rot in the unsprayed plots and consisted mainly of grey mould (Botrytis cinerea), leak (Rhizopus and Mucor spp.), anthracnose (Colletotrichum acutatum), leather rot (Phytophthora cactorum), and stem end rot (Gnomonia comari). All fungicides except fosetyl-aluminium and phosphorous acid significantly (P&lt;0.05) reduced the total incidence of fruit rots by 27–72%. Thiram, dichlofluanid and chlorothalonil reduced grey mould by 61–94%, anthracnose by 63–100% and leather rot by 65–100%; iprodione reduced grey mould by 60–94% and leak by 74–96%. In one experiment each, fluazinam reduced grey mould by 85% and leather rot by 100%, and phosphorous acid reduced leather rot by 100%. Thiram, iprodione and phosphorous acid also reduced stem end rot by 55–100%. Of the biocontrols, seaweed extracts and oil, only tea tree oil in 1 trial of 3 reduced the total incidence of fruit rots significantly (by 31%), and in 2 trials significantly reduced anthracnose, and leather rot by 60–88% and 71–72% respectively. In 2 out of 3 trials, Trichoderma sp. reduced (P&lt;0.05) grey mould by 29–63%. In one trial each, seaweed extract 1, and a yeast treatment amended with malt extract, both reduced grey mould by 40 or 54% respectively. The addition of sucrose to the yeast treatments significantly increased the incidence of anthracnose infection. Chlorothalonil, dichlofluanid, thiram and iprodione sprays increased the yield (weight) of healthy fruit significantly (P&lt;0.05) compared with that from untreated plants by 43–114%. By contrast, none of the biocontrol treatments, the seaweed extracts or tea tree oil increased fruit yields.

Mycoflora of strawberry in Ontario

Mycelial fungi associated with leaves, flowers, and fruits of strawberry (Fragaria × ananassa Duchesne) were monitored in a field plot from August 1986 to July 1987. The principal fungi found on leaves of various developmental stages were Alternaria alternata, Botrytis cinerea, Cladosporium spp., Colletotrichum dematium, Coniella fragariae, Epicoccum purpurascens, Gliocladium roseum, Gloeosporium sp., Gnomonia comari, Penicillium spp., Trichothecium roseum, and Verticillium spp. A majority of the fungi were observed more frequently on leaves that were washed and then plated on agar media than on leaves that were plated without washing. Trichothecium roseum, however, was found mainly on the unwashed leaves. Principal fungi on calyces, petals, and fruits were A. alternata, B. cinerea, Gloeosporium sp., Pencillium spp., T. roseum, and Verticillium spp. Other fungi variously found on the flowers and fruits included Rhizopus stolonifer, Paecilomyces spp., C. dematium, and Fusarium spp. Many of the fungi found frequently on the strawberry plants were present at most or all stages of development and decline of the various plant organs. The mycofloral observations are discussed in relation to the biocontrol of strawberry diseases. Key words: strawberry, mycoflora, Botrytis cinerea, population dynamics.

STUDIES ON FUNGUS PARASITES OF STRAWBERRY LEAVES IN ONTARIO

Four fungi were isolated from lesions on strawberry foliage in Ontario during the growing seasons of 1948 and 1949. They are Mycosphaerella fragariae (Tul.) Lindau. Diplocarpon carliana (Ell. &amp; Ev.) Wolf, Dendrophoma obscurans (Ell. &amp; Ev.) H. W. And., and Gnomonia fructicola (Arnaud) n. comb. (Zythia fragariae Laibach), and they cause the diseases known as leaf spot, leaf scorch, leaf blight and leaf blotch respectively. Apparently this is the first report of Zythiae fragariae in North America and of Dentrophoma obscurans in Canada. From field surveys, strawberry varieties were found to vary in resistance, especially to spot and scorch, and market differences in seasonal distribution of the diseases were also evident. Spot was most prevalent in the spring and fall; scorch increased in severity during the warmer months; and blight became prominent after the cropping period. As a result of inoculation with M. fragariae only the middle-aged leaves of vigorously growing strawberry plants developed lesions. Premier plants, although resistant to spot in the field, proved susceptible when artificially inoculated. Penetration by M. fragariae may occur without lesion formation if the temperature is below 15 °C. Symptom expression was best within the 20°–25 °C range. Adding strips of strawberry leaves to a suspension of conidia of Diplocarpon earliana greatly enhanced spore germination. Only leaves which are old or middle-aged develop scorch lesions, and these may be blotchy or diffuse depending on the variety. Dendrophoma obscurans appears to attack mainly the older leaves near the margins. The conidiophores are long and branched, the conidia slightly pointed, and the pyenidia are dark, leathery, and clumped in culture. Zythia fragariae has simple conidiophores, biguttulate conidia with rounded ends, and soft light brown pyenidia. The name Gnomonia fructicola is proposed for the fungus Gnomonia fragariae Klebahn form fructicola Arnaud because it is considered to be a different species from Gnomonia fragariae Klebahn.