Polygalacturonase S31PG1 from <Emphasis Type="Italic">Geotrichum candidum</Emphasis> citrus race S31 expressed in <Emphasis Type="Italic">Schizosaccharomyces pombe</Emphasis> versus S31PG2 regarding soft rot on lemon fruit

Gene S31pg1, which encodes a polygalacturonase (PG), was previously isolated from citrus race S31 of Geotrichum candidum, the causal agent of citrus sour rot. We have now isolated and sequenced an additional PG gene, S31pg2, with 95% identity to S31pg1 in the mature proteins. To evaluate the contribution of the two PG genes in the development of citrus sour rot, each gene was expressed in the fission yeast Schizosaccharomyces pombe. Both genes conferred PG activity to the yeast. Crude enzyme solutions containing S31PG1 severely degraded the albedo tissue of lemon peel, but those containing S31PG2 did not. Concentrated crude S31PG1 solutions also caused soft rot on lemon fruit, indicating that not S31PG2 but S31PG1 is an important pathogenicity factor in citrus sour rot. Next, the protopectinase (PP) activity of each PG was measured. Although S31PG1 and S31PG2 are highly homologous, S31PG1 had high PP activity, whereas S31PG2 had much lower activity. PG from G. candidum noncitrus race S63 (nonpathogenic to citrus fruits) was also assayed but did not have any PP activity at all. These results suggest that the different PP activities of the PGs are a key to the pathogenicity of G. candidum to lemon fruit.     

Fruit spot of sweet lime (<Emphasis Type="Italic">Citrus limetta</Emphasis>) caused by <Emphasis Type="Italic">Septoria</Emphasis> sp. in Peru

In 2002, a severe fruit spot of sweet lime (Citrus limetta) was observed in Piura and Lambayeque provinces in northern Peru. Affected fruits showed large oval and sunken lesions, often surrounded by chlorotic haloes. Septoria sp. was isolated from affected fruits. Sweet lime isolates showed larger pycnidia and pycnidiospores than those of Septoria spp. previously described on citrus. In addition, phylogenetic analysis of the ITS sequences clearly separated the sweet lime isolates from S. citri and S. citricola. Isolates were pathogenic to detached sweet lime fruits and the fungus was isolated from lesions on inoculated fruits.     

Phenotypic,molecular and pathogenic characterization of Phlyctema vagabunda,causal agent of olive leprosy

Olive leprosy, caused by the fungus Phlyctema vagabunda, is a classic fruit rot disease widespread in the Mediterranean basin. From 2009 to 2013, new disease symptoms consisting of small circular necrotic leaf lesions, coin branch canker and shoot dieback were observed in Spanish and Portuguese olive orchards showing intense defoliation. Phlyctema‐like anamorphs were consistently isolated from leaves and shoots with symptoms. Representative isolates from affected leaves, shoots and fruits were characterized based on morphology of colonies and conidia, optimum growth temperature and comparison of DNA sequence data from four regions: ITS, tub2, MIT and rpb2. In addition, pathogenicity tests were performed on apple and olive fruits, and on branches and leaves of olive trees. Maximum mycelial growth rate ranged between 0.54 and 0.73 mm per day. Conidia produced on inoculated apple fruits showed slight differences in morphology among the representative fungal isolates evaluated. Phylogenetic analysis clustered all of the Phlyctema‐like isolates in the same clade, identifying them as Phlyctema vagabunda. On fruits, influence of wounding, ripening and cultivar resistance was studied, with cv. Blanqueta being the most susceptible cultivar. On branches, a mycelial‐plug inoculation method reproduced olive leprosy symptoms and caused shoot dieback. On leaves, Koch's postulates were fulfilled and the pathogen caused characteristic necrotic spots and plant defoliation. This is the first time that the pathogenicity of P. vagabunda in olive leaves has been demonstrated.     

Multiple Alternaria species groups are associated with leaf blotch and fruit spot diseases of apple in Australia

Leaf blotch and fruit spot of apple caused by Alternaria species occur in apple orchards in Australia. However, there is no information on the identity of the pathogens and whether one or more Alternaria species cause both diseases in Australia. Using DNA sequencing and morphological and cultural characteristics of 51 isolates obtained from apple leaves and fruit with symptoms in Australia, Alternaria species groups associated with leaf blotch and fruit spot of apples were identified. Sequences of Alternaria allergen a1 and endopolygalacturonase gene regions revealed that multiple Alternaria species groups are associated with both diseases. Phylogenetic analysis of concatenated sequences of the two genes resulted in four clades representing A. arborescens and A. arborescens‐like isolates in clade 1, A. tenuissima/A. mali isolates in clade 2, A. alternata/A. tenuissima intermediate isolates in clade 3 and A. longipes and A. longipes‐like isolates in clade 4. The clades formed using sequence information were supported by colony characteristics and sporulation patterns. The source of the isolates in each clade included both the leaf blotch variant and the fruit spot variant of the disease. Alternaria arborescens‐like isolates were the most prevalent (47%) and occurred in all six states of Australia, while A. alternata/A. tenuissima intermediate isolates (14%) and A. tenuissima/A. mali isolates (6%) occurred mostly in Queensland and New South Wales, respectively. Implications of multiple Alternaria species groups on apples in Australia are discussed.     

Effect of apple cultivars and storage periods on the virulence of Neofabraea spp.

Bull’s eye rot is a typical quiescent postharvest apple disease in major fruit-growing areas. The susceptibility of different apple cultivars to Neofabraea spp. (N. vagabunda and N. malicorticis) was assessed, with Granny Smith showing the most resistance and Cripps Pink the most susceptibility. To assess the factors involved in conidial germination, Neofabraea spp. were grown on crude protein extracts (CPEs) collected from apple fruits at different storage periods. Fungal germ tube growth rate and pathogenic enzyme (cellulase and xylanase) activity were assessed. Results showed that CPEs collected after 2 and 4 months of storage progressively stimulated conidial germination and germ tube elongation, while a lesser effect was observed from CPEs after 1 month of storage. Xylanase proved to be the main degrading enzyme secreted by all the isolates, while cellulase was produced only by N. vagabunda isolates. Overall, the isolate ID02 was the most virulent, based on more rapid germ tube elongation and greater activity of the lytic enzymes.     

A during-infection spray strategy using sulphur compounds,copper, silicon and a new formulation of potassium bicarbonate for primary scab control in organic apple production

In a field experiment conducted over two growing seasons, the effectiveness and phytotoxicity of inorganic fungicides such as sulphur, lime sulphur, copper, silicon and Armicarb (a new formulation of potassium bicarbonate) was compared with water for the control of primary apple scab infections in Belgium on high, medium and low scab-susceptible cultivars (cvs ‘Pinova’, ‘Pirouette’ and ‘Reinette des Capucins’, respectively). In order to drastically reduce the amount of fungicide applied in the orchard, two approaches were used: (1) a strategy involving spraying during the infection process, before fungal penetration and (2) a tunnel sprayer machine for treatment applications. Under field conditions highly favourable for disease, low rates of elemental sulphur (31.8 and 38.6 kg ha⁻¹ year⁻¹ in 2005 and 2006, respectively) combined with low rates of copper (2.1 kg ha⁻¹ year⁻¹ in both years) provided the best scab control and reduced scab severity on the fruits of cv. ‘Pinova’ by 97 and 98% compared with water control in 2005 and 2006, respectively. Lime sulphur was much more effective than wettable sulphur and appeared to be efficient at temperatures below 10°C, but its effectiveness against apple scab decreased if the treatments were applied 12–24 h later than in the ‘during-infection’ spray strategy. Armicarb used alone significantly reduced apple scab severity on the leaves and fruits of the three cultivars compared with the water control. Its effectiveness was as good as wettable sulphur applied using the same timing and dosage. Silicon reduced apple scab on fruits very slightly, but not on leaves. The amounts of wettable sulphur, lime sulphur, copper, silicon and potassium bicarbonate used in this experiment to control apple scab were not phytotoxic, did not increase fruit russet, did increase the yield of each cultivar and did not affect summer density of the beneficial Typhlodromus pyri. The potential and limitations of ‘during-infection’ spraying as a protection strategy against apple scab in organic farming are discussed.     

First report of whisker mold,a postharvest disease on citrus caused by <Emphasis Type="Italic">Penicillium ulaiense</Emphasis> (in Japan)

In March 2006, stored fruits of the medium-to-late-ripening citrus variety Shiranuhi ([Citrus unshiu × C. sinensis] × C. reticulata) were found to have a disease similar to blue mold. The fungus causing this disease differed distinctly from the well-known, blue mold agent, Penicillium italicum, because it formed whisker-like coremia measuring 1–8 mm. On the basis of the morphological characteristics and the phylogenetic analysis based on the nucleotide sequence of the β-tubulin gene, the fungus was identified as P. ulaiense. This is the first report of citrus whisker mold caused by P. ulaiense in Japan.     

Viability and release of Neonectria ditissima ascospores on apple fruit in Brazil

During European canker monitoring in an apple experimental orchard, 14 mummified fruit (two and three trees with 10 and four positive records in 2018 and 2019, respectively) showed perithecia. Perithecium production on apple fruit, confirmation of pathogenicity of Neonectria ditissima isolated from mummified fruit, and ascospore release from fruit tissues has rarely been reported, and their role in the epidemiology of European canker has been largely overlooked. Thus, the objectives of our study were to (a) prove the presence of both conidia and ascospores of N. ditissima in mummified fruit in an experimental field, confirming pathogenesis in different apple cultivars, and (b) monitor production of the two types of inoculum in infected apple fruit over time. Canker incidence in this orchard was 47% of trees with symptoms in 2018 and 48% in 2019. Molecular and morphological tests confirmed that the fungus detected in the mummified apple fruit was N. ditissima. Apple fruit with sporodochia and perithecia washed immediately after collection from the orchard showed conidia but no ascospores of N. ditissima. However, after 4 days’ incubation, perithecia on mummified fruit showed many ascospore cirri. Koch's postulates were fulfilled on apple plants and mature fruit. Fruit inoculated with N. ditissima released spores for over a year under Brazilian field conditions. The release of both spore types peaked in May (Brazilian leaf fall) and October (spring); release of conidia also peaked in February (early harvest). These results support our hypothesis that fruit can serve as primary inoculum for European canker in Brazilian apple orchards.     

Correlation of ethylene synthesis in Citrus fruits and their susceptibility to Alternaria alternata pv. citri

The susceptibility of Fortune (Citrus clementina × Citrus reticulata), Citrus paradisi and Citrus limon fruits to Alternaria alternata pv. citri was investigated using different artificial inoculation methods. The results obtained reveal that the C. paradisi and C. limon fruits are less susceptible to A. alternata pv. citri than Fortune fruits, although all showed symptoms of Alternaria brown spot when the cuticle was broken and the flavedo or flavedo + albedo was removed. Furthermore, it was seen that susceptibility to the fungus decreased as the age of the fruit increased. There was a positive correlation between the susceptibility of the different Citrus fruits to A. alternata pv. citri and their “in vivo” ethylene levels, the most susceptible fruit (Fortune) producing more ethylene during growth than the less susceptible C. limon and C. paradisi. This suggests that ethylene may well be considered as a possible marker of Citrus fruit susceptibility to A. alternata pv. citri. Disease development increased when the Fortune fruits were treated with 1 mM ACC (a precursor of ethylene biosynthesis) or 1 mM Ethephon (an ethylene-releasing compound) prior to inoculation with A. alternata pv. citri. The role of ethylene as a factor involved in disease development is discussed.     

Development of a molecular marker for specific detection of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">cubense</Emphasis> race 4

Fusarium oxysporum f. sp. cubense is the causal agent of Panama disease of banana. A rapid and reliable diagnosis is the foundation of integrated disease management practices in commodity crops. For this diagnostic purpose, we have developed a reliable molecular method to detect Foc race 4 isolates in Taiwan. By PCR amplification, the primer set Foc-1/Foc-2 derived from the sequence of a random primer OP-A02 amplified fragment produced a 242 bp size DNA fragment which was specific to Foc race 4. With the optimized PCR parameters, the molecular method was sensitive and could detect small quantities of Foc DNA as low as 10 pg in 50 to 2,000 ng host genomic DNA with high efficiency. We also demonstrated that by using our PCR assay with Foc-1/Foc-2 primer set, Foc race 4 could be easily distinguished from other Foc races 1 and 2, and separated other formae speciales of F. oxysporum. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The effect of environmental factors on infection of blueberry fruit by Colletotrichum acutatum

Anthracnose fruit rot of blueberries caused by Colletotrichum acutatum is a serious problem in humid blueberry‐growing regions of North America. In order to develop a disease prediction model, environmental factors that affect mycelial growth, conidial germination, appressorium formation and fruit infection by C. acutatum were investigated. Variables included temperature, wetness duration, wetness interruption and relative humidity. The optimal temperature for mycelial growth was 26°C, and little or no growth was observed at 5 and 35°C. The development of melanized appressoria was studied on Parafilm‐covered glass slides and infection was evaluated in immature and mature blueberry fruits. In all three assays, the optimal temperature for infection was identified as 25°C, and infections increased up to a wetness duration of 48 h. Three‐dimensional Gaussian equations were used to assess the effect of temperature and wetness duration on the development of melanized appressoria (R² = 0·89) on Parafilm‐covered glass slides and on infection incidence in immature (R² = 0·86) and mature (R² = 0·90) blueberry fruits. Interrupted wetness periods of different durations were investigated and models were fitted to the response of melanized appressoria (R² = 0·95) and infection incidence in immature (R² = 0·90) and mature (R² = 0·78) blueberry fruits. Additionally, the development of melanized appressoria and fruit infection incidence were modelled in relation to relative humidity (R² = 0·99 and 0·97, respectively). Three comprehensive equations were then developed that incorporate the aforementioned variables. The results lay the groundwork for a disease prediction model for anthracnose fruit rot in blueberries.     

桃小食心虫成虫种群动态监测与防治指标

为明确桃小食心虫Carposina sasakii Matsumura成虫的种群动态变化,2002—2014年在陕西省礼泉县当地具有代表性的苹果园中,采用性诱剂诱捕器对桃小食心虫成虫的种群动态进行系统监测,并于2010年和2011年的7—8月桃小食心虫成虫盛发期,系统调查了成虫发生量与苹果着卵量的关系,建立基于性诱剂监测的桃小食心虫成虫防治指标。结果显示,苹果园桃小食心虫成虫的种群动态、始见期和终见期在年度之间差异很大,每年主要集中在6—8月发生;桃小食心虫成虫每年出现多次无规律的高峰,但第1代成虫高峰期发生的早晚与越冬代成虫高峰期出现的早晚有密切联系,即越冬代成虫高峰期出现早,则第1代成虫高峰期出现也就相对较早,且越冬代成虫发生量明显多于第1代成虫。性诱剂诱捕的成虫与卵果率之间呈极显著的对数关系,当以卵果率1%或2%为防治指标时,性诱剂诱捕器诱蛾量为8.3头/诱捕器·日或30.0头/诱捕器·日。     

Involvement of carbon catabolite repression on regulation of endopolygalacturonase gene expression in citrus fruit

 The Acpg1 gene of Alternaria citri encodes an extracellular endopolygalacturonase that is important for virulence in citrus fruits. Expression of Acpg1 is regulated by substrate induction and carbon catabolite repression. A green fluorescent protein (GFP) gene was employed as a reporter gene to define 813 bases upstream of the translation start site comprising the Acpg1 promoter. This upstream sequence contains five putative binding sequences of catabolite repressive element A (CreA), a cis-acting zinc finger repressor involved in carbon catabolite repression. We constructed each CreA-binding site-deleted Acpg1 promoters with GFP reporter gene and transformed them to A. citri. The construct PGPDL4 deleted from −401 to −813 showed both substrate induction and catabolite repression, whereas PGPDL5 additionally deleted from −1 to −84, including one putative CreA-binding site, resulted in a loss of catabolite repression function. Green fluorescence of PGPDL4 was induced by pectin in the peel but was repressed completely in the juice sac area of citrus fruit. However, green fluorescence of PGPDL5 was induced in both the peel and juice sac area, indicating that repression of Acpg1 in the juice sac area is likely accomplished by carbon catabolite repression. Received: October 4, 2002 / Accepted: October 31, 2002 Acknowledgments The authors thank Drs. D. Cullen, A. Van den Wymelenberg, and J. Andrews, University of Wisconsin, for providing pTEFEGFP containing GFP and Dr. T. Tsuge, Nagoya University, for providing transformation vector pSH75. The nucleotide sequence data of Acpg1 promoter region in the DDBJ, EMBL, and GenBank sequence databases is under accession number AB047543. This research was supported in part by grants to K.A. from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.     

Temporal development and relationship amongst brown rot blossom blight,fruit blight and fruit rot in integrated and organic sour cherry orchards

The aim of this 4‐year study was to characterize temporal development of brown rot blossom blight and fruit blight (caused by Monilinia spp.) and their sporulating areas in sour cherry orchards; and to determine the relationships amongst incidence and sporulating area of blossom blight, fruit blight and fruit rot. The study was performed in integrated and organic orchard blocks on two cultivars (Újfehértói fürtös and Érdi b?term?). On both cultivars, disease progress on flowers and fruits was 2–10 times slower in the integrated than in the organic management system. The peak incidence values were 9 and 31 days after petal fall for blossom blight and fruit blight, respectively. After these dates, no new blight symptoms on flowers and/or fruits appeared and the disease was levelling off. Final blossom blight incidence ranged from 1 to 5% and from 12 to 34%, and fruit rot incidence from 2 to 6% and from 11 to 26% in the integrated and the organic orchards, respectively. The sum of fruit blight incidence ranged from 9 to 22% for the organic system, but was below 5% for the integrated system, while the final sporulating area was 5–16 mm² and <3 mm², respectively. Among the five highest Pearson's correlation coefficients, relationships between blossom blight and early fruit blight stage (r = 0·845, P = 0·0087 integrated; r = 0·901, P = 0·0015 organic), and between sporulating area and fruit rot (r = 0791, P = 0·0199 integrated; r = 0·874, P = 0·0039 organic) were the most significant relationships from an epidemic standpoint as they indicated a connection between different brown rot symptom types.     

Establishment of heterologous expression of polygalacturonase S63PG1 from nonpathogenic isolate S63 of <Emphasis Type="Italic">Geotrichum candidum</Emphasis>

Previously, we established an expression system of polygalacturonase (PG) S31PG1 and S31PG2 from Geotrichum candidum pathogenic isolate S31 using the fission yeast Shizosaccharomyces pombe and clarified the importance of S31PG1 in the pathogenicity of G. candidum S31 on lemon fruit. In the present study, we established an expression system for S63PG1 from the nonpathogenic isolate S63. When S63PG1 was expressed, only PG activity was detected, whereas both PG and protopectinase (PP) were active when S31PG1 was expressed. Furthermore, S63PG1 had no ability to cause soft rot, while S31PG1 did. These results indicate that the PP activity of PG is a key to the pathogenicity of the fungus.     

Pathogenicity,colony morphology and diversity of isolates of <Emphasis Type="Italic">Guignardia citricarpa</Emphasis> and <Emphasis Type="Italic">G. mangiferae</Emphasis> isolated from <Emphasis Type="Italic">Citrus</Emphasis> spp.

In the present study, the pathogenicity of 36 isolates of Guignardia species isolated from asymptomatic ‘Tahiti’ acid lime fruit peels and leaves, ‘Pêra-Rio’ sweet orange leaves and fruit peel lesions, and a banana leaf were characterized. For pathogenicity testing, discs of citrus leaves colonized by Phyllosticta citricarpa under controlled laboratory conditions were kept in contact with the peels of fruit that were in susceptible states. In addition, pathogenicity was related to morphological characteristics of colonies on oatmeal (OA) and potato dextrose agar (PDA). This allowed the morphological differentiation between G. citricarpa and G. mangiferae. Polymerase chain reactions (PCRs) were also used to identify non-pathogenic isolates based on primers specific to G. citricarpa. A total of 14 pathogenic isolates were detected during pathogenicity tests. Five of these were obtained from leaf and fruit tissues of the ‘Tahiti’, which until this time had been considered resistant to the pathogen. Given that the G. citricarpa obtained from this host was pathogenic, it would be more appropriate to use the term insensitive rather than resistant to categorize G. citricarpa. A non-pathogenic isolate was obtained from lesions characteristic of citrus black spot (CBS), indicating that isolation of Guignardia spp. under these conditions does not necessarily imply isolation of pathogenic strains. This also applied to Guignardia spp. isolates from asymptomatic citrus tissues. Using fluorescent amplified fragment length polymorphism (fAFLP) markers, typically pathogenic isolates were shown to be more closely related to one another than to the non-pathogenic forms, indicating that the non-pathogenic isolates display higher levels of genetic diversity.     

Species‐specific real‐time PCR for diagnosis of Phyllosticta citricarpa on Citrus species

Phyllosticta citricarpa (teleomorph Guignardia citricarpa) is the causal agent of citrus black spot, a disease causing lesions on fruits and leaves of different Citrus species in Asia, Australia, South Africa and South America. It is a quarantine organism in the European Union and the USA and hence a reliable differentiation between this species and other Phyllosticta species found on Citrus is essential. A differentiation based on morphology is often problematic, hence a range of molecular tests have been developed to distinguish P. citricarpa from other species present on citrus fruits, especially the endophyte Phyllosticta capitalensis (teleomorph Guignardia mangiferae). However, these tests cannot distinguish P. citricarpa from the closely related Phyllosticta citriasiana, the causal agent of tan spot disease. In this study, a real‐time PCR was designed which is specific for P. citricarpa and does not amplify P. citriasiana or P. capitalensis DNA.     

Lack of host specificity of Colletotrichum spp. isolates associated with anthracnose symptoms on mango in Brazil

The aim of the present study was to analyse the genetic and pathogenic variability of Colletotrichum spp. isolates from various organs and cultivars of mango with anthracnose symptoms, collected from different municipalities of São Paulo State, Brazil. Colletotrichum gloeosporioides isolates from symptomless citrus leaves and C. acutatum isolates from citrus flowers with post‐bloom fruit drop symptoms were included as controls. Sequencing of the ITS region allowed the identification of 183 C. gloeosporioides isolates from mango; only one isolate was identified as C. acutatum. amova analysis of ITS sequences showed larger genetic variability among isolates from the same municipality than among those from different populations. fAFLP markers indicated high levels of genetic variability among the C. gloeosporioides isolates from mango and no correlation between genetic variability and isolate source. Only one C. gloeosporioides mango isolate had the same genotype as the C. gloeosporioides isolates from citrus leaves, as determined by ITS sequencing and fAFLP analysis. Pathogenicity tests revealed that C. gloeosporioides and C. acutatum isolates from either mango or citrus can cause anthracnose symptoms on leaves of mango cvs Palmer and Tommy Atkins and blossom blight symptoms in citrus flowers. These outcomes indicate a lack of host specificity of the Colletotrichum species and suggest the possibility of host migration.     

Decay control and fungicide residues in citrus fruits seal-packed in a high-density polyethylene film

The effects of a new packaging method of sealing individual fruits in film of highdensity polyethylene (HDPE), on decay control and the residue levels of various fungicides applied to the fruit, were investigated with four different citrus cultivars. HDPE seal-packaging by itself reduced the decay of Marsh grapefruit but slightly enhanced the decay of Valencia orange fruit in comparison with conventionally handled fruit. Seal-packaging of individual fruit resulted in much less decay than sealing a whole carton of fruit together. The fungicides imazalil, sec-butylamine, 2-phenylphenol, benomyl and thiabendazole markedly reduced the decay of sealed fruit in all cultivars of citrus fruits tested. Residue levels in treated fruit were below the tolerances permitted. The new method of packaging had no effect on the residue levels of benomyl, 2-phenyl-phenol and thiabendazole in the fruit; neither did it affect the extent of absorption of these fungicides into the fruit. Only the volatile fungicide sec-butylamine was found at a higher level (73% higher in the packaged fruit compared with conventionally treated fruit).     

Frequency of brown rot fungi on blossoms and fruit in stone fruit orchards in Greece

Brown rot is a devastating disease of stone fruits caused by Monilinia spp. This study was conducted to investigate the disease aetiology on blossoms and fruit in peach, apricot, sweet cherry and plum orchards, in Greece. In total, 1433 isolates obtained from orchards located in the main stone fruit production regions of Greece were identified to species based on the presence/size of a cyt b intron. Monilinia laxa and M. fructicola were detected at frequencies of 59 and 41%, respectively, while M. fructigena was absent. Monilinia fructicola was more common on fruit whereas M. laxa occurred in similar frequency on blossoms and fruit. Monilinia laxa was replaced by M. fructicola in fruit infections of peach in both regions investigated and in fruit infections of plum in the Imathia region. Assessments of aggressiveness of 30 isolates of both species on the petals and fruits of the hosts showed that M. fructicola isolates were more aggressive. This suggests that the predominance of M. laxa on the blossoms cannot be explained by higher aggressiveness. Measurements of the effect of temperature on mycelial growth showed that M. laxa isolates had a higher growth rate than M. fructicola at the lowest temperature tested of 5°C, whereas M. fructicola isolates showed higher growth rates at higher temperatures. The observed high frequency of M. fructicola in Greece represents a major threat for stone fruit production. Furthermore, the information obtained about delineation of species and plant organ preference could be useful for the implementation of disease management strategies.