Bitter Rot Research Articles

Quantification of Colletotrichum fioriniae in Orchards and Deciduous Forests Indicates It Is Primarily a Leaf Endophyte.

Colletotrichum fioriniae of the C. acutatum species complex is an important hemibiotrophic pathogen of vegetables and fruits in temperate regions worldwide. In apple, it is one of the primary species responsible for bitter rot disease. Understanding the disease cycle is complicated because many broadleaf plants can be hosts of C. fioriniae. By detecting and quantifying rain-splashed C. acutatum species complex conidia in more than 500 samples from heavily bitter-rot-infected apple orchards and nearby forested woodlots over two summers, we show that conidial quantities were higher in the woodlots than in the orchards. Testing of more than 1,000 surface-disinfected leaves of apple and 24 different forest plant species showed that overall C. fioriniae was an abundant leaf endophyte, with high variation in leaf colonization area. Endophytic isolates from leaves were pathogenic on apples, and multilocus sequence analysis showed 100% identity between most isolates from leaves and diseased fruits. Apple leaves endophytically infected with C. fioriniae were present in a conventionally managed orchard and abundant in an untreated orchard. These lines of evidence, in the context of previously published research, lead us to hypothesize that the main ecological role of C. fioriniae is that of a leaf endophyte, which we present as a generalized C. fioriniae infection cycle that provides an updated framework for its integrated management in agricultural systems.

Characterization of Bacillus velezensis AK-0 as a biocontrol agent against apple bitter rot caused by Colletotrichum gloeosporioides

Bacillus genus produces several secondary metabolites with biocontrol ability against various phytopathogens. Bacillus velezensis AK-0 (AK-0), an antagonistic strain isolated from Korean ginseng rhizospheric soil, was found to exhibit antagonistic activity against several phytopathogens. To further display the genetic mechanism of the biocontrol traits of AK-0, we report the complete genome sequence of AK-0 and compared it with complete genome sequences of closely related strains. We report the biocontrol activity of AK-0 against apple bitter rot caused by Colletotrichum gloeosporioides, which could lead to commercialization of this strain as a microbial biopesticide in Korea. To retain its biocontrol efficacy for a longer period, AK-0 has been formulated with ingredients for commercialization, named AK-0 product formulation (AK-0PF). AK-0PF played a role in the suppression of the mycelial growth of the fungicide-resistant pathogen C. gloeosporioides YCHH4 at a greater level than the non-treated control. Moreover, AK-0PF exhibited greater disease suppression of bitter rot in matured under field conditions. Here, we report the complete genome sequence of the AK-0 strain, which has a 3,969,429 bp circular chromosome with 3808 genes and a G+C content of 46.5%. The genome sequence of AK-0 provides a greater understanding of the Bacillus species, which displays biocontrol activity via secondary metabolites. The genome has eight potential secondary metabolite biosynthetic clusters, among which, ituD and bacD genes were expressed at a greater level than other genes. This work provides a better understanding of the strain AK-0, as an effective biocontrol agent (BCA) against phytopathogens, including bitter rot in apple.

First report of preharvest fruit rot of 'Pink Lady' apples caused by Colletotrichum fructicola in Italy.

In late summer 2019, a severe outbreak of fruit rot was observed in commercial 'Pink Lady' apple orchards (>20 ha in total) in the region Emilia-Romagna (Northern Italy). The symptoms on the fruit appeared as small circular red to brown lesions. Disease incidences of over 50% of the fruits were observed. To isolate the causal agent, 15 affected apples were collected and small portions of fruit flesh were excised from the lesion margin and placed on potato dextrose agar (PDA). The plates were incubated at 20°C in the dark, and pure cultures were obtained by transferring hyphal tips on PDA. The cultures showed light to dark gray, cottony mycelium, with the underside of the culture being brownish and becoming black with age. Conidia (n=20) were cylindrical, aseptate, hyaline, rounded at both ends, and 12.5 to 20.0 × 5.0 to 7.5 μm. The morphological characteristics were consistent with descriptions of Colletotrichum species of the C. gloeosporioides species complex, including C. fructicola (Weir et al. 2012). The identity of two representative isolates (PinkL2 & PinkL3) from different apples was confirmed by means of multi-locus gene sequencing. Genomic DNA was extracted using the LGC Mag Plant Kit (Berlin, Germany) in combination with the Kingfisher method (Waltham, USA). Molecular identification was conducted by sequencing the ITS1/ITS4 region and partial sequences of four other gene regions: chitin synthase (CHS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), and beta-tubulin (TUB). The sequences have been deposited in GenBank under accession numbers MT421924 & MT424894 (ITS), MT424612 & MT424613 (CHS), MT424616 & MT424617 (GAPDH), MT424614 & MT424615 (ACT), and MT424620 & MT424621 (TUB). MegaBLAST analysis revealed that our ITS sequences matched with 100% identity to Colletotrichum fructicola (Genbank JX010177). The CHS, GAPDH, ACT and TUB sequences of both isolates were 100% identical with C. fructicola culture collection sequences in Genbank (JX009807, JX009923, JX009436 and JX010400, respectively), confirming the identity of these isolates as C. fructicola. Koch's postulates were performed with 10 mature 'Pink Lady' apples. Surface sterilized fruit were inoculated with 20 μl of a suspension of 105 conidia ml-1 after wounding with a needle. The fruits were incubated at 20˚C at high relative humidity. Typical symptoms appeared within 4 days on all fruit. Mock-inoculated controls with sterile water remained symptomless. The fungus was reisolated and confirmed as C. fructicola by morphology and sequencing of all previously used genes. Until recently the reported causal agents of bitter rot of apple in Europe belong to the Colletotrichum acutatum species complex (Grammen et al. 2019). C. fructicola, belonging to C. gloeosporioides species complex, is known to cause bitter rot of apple in the USA, Korea, Brazil, and Uruguay (Kim et al. 2018; Velho et al. 2015). There is only one report of bitter rot associated with C. fructicola on apple in Europe (France) (Nodet et al. 2019). However, C. fructicola is also the potential agent of Glomerella leaf spot (GLS) of apple (Velho et al. 2015; 2019). To the best of our knowledge this is the first report of C. fructicola on apples in Italy. It is important to stress that the C. gloeosporioides species complex is still being resolved and new species on apple continue to be identified, e.g. C. chrysophilum that is very closely related to C. fructicola (Khodadadi et al. 2020). Given the risks of this pathogen the presence of C. fructicola in European apple orchards should be assessed and management strategies developed.

Study of infection process of five species of Colletotrichum comparing symptoms of glomerella leaf spot and bitter rot in two apple cultivars

Bitter rot (BR) and glomerella leaf spot (GLS) occur in all the Brazilian South orchards with different species frequency per region. The main species found in Brazil belong to the Colletotrichum acutatum complex (Cac) and to the C. gloeosporioides complex (Cgc). The objectives of this study were to evaluate the favorable conditions for the germination and growth of five Colletotrichum species and, to compare pathogenicity and aggressiveness among species and between two apple cultivars in fruit, causing BR, and in leaves, causing GLS. The highest germination of conidia (above 90%) was achieved between 15 and 30 °C for Cgc species while for Cac species the highest germination (mean of 71%) was at 25 °C. The optimal temperature for mycelial growth did not differ between complexes and ranged from 23 to 27 °C. Althought, Cgc had a higher estimated maximum temperature then Cac. C. siamense cause BR symptoms regardless of cultivar or type of inoculation. C. nymphaeae and C. melonis caused symptoms in wounded and unwounded fruit but for C. paranaense and C. fructicola the symptoms were observed only in wounded fruit. Leaf symptoms of GLS was more severe in stressed leaves inoculated on the abaxial side compared to non-stressed leaves inoculated on the adaxial side. C. fructicola and C. nymphaeae were able to cause GLS symptoms in leaves with severity varying from 17.5 to 25% (cv. Gala). C. fructicola was the most severe causing GLS symptoms in cv. Gala (severity around 20.5%) and, in cv. Eva (severity around 11%). We discuss the roles that each species plays as a pathogen to better understand BR and GLS in different orchards conditions.

Genome Sequences of Two Pathogens of Cruciferous Crops, Xanthomonas campestris pv. raphani MAFF 106181 and X. campestris pv. campestris MAFF 301176.

Xanthomonas campestris pv. raphani and X. campestris pv. campestris are the causal agents of bacterial spot and black rot of crucifers (Brassicaceae), respectively. Both pathogens are threats in the cultivation of cruciferous crops such as cabbage. Here, we sequenced a strain of each of these pathogens.

Addition of preservatives to minimally processed ‘BRS Kampai’ peaches (Prunus persica L.)

Fruits that go through processes of sanitation, peeling, cutting and packaging, to be consumed soon afterwards, are called minimally processed fruits. Since fruit consumption is important in the human diet, consumers have looked for practicality in both preparation and consumption, a situation that includes minimally processed food. However, minimal processing can damage plant tissues, mainly by pulp browning and by accelerating changes in natural characteristics of the product. This study aimed at minimizing changes in minimally processed sliced peaches by immersing them in solutions which contained preservatives. The experiment was a completely randomized design in a 5x3 factorial scheme (5 anti-browning agents x 3 storage periods), with 4 trays per replicate and six slices of peaches in every replicate. Sliced fruits were treated with T1 = control (distilled water); T2 = ascorbic acid at 1% (m/v); T3 = sodium isoascorbate at 1% (m/v); T4 = ascorbic acid at 0.5% (m/v) + sodium isoascorbate at 0.5% (m/v); and T5 = citric acid at 0.5% (m/v) + sodium isoascorbate at 0.5% (m/v). Afterwards, they were placed on trays, covered with 9µ PVC film and stored at 4±1ºC for 0 (S1), 6 (S2) and 12 (S3) days. The following variables were evaluated: mass loss, pulp color, pulp firmness, soluble solids, titratable acidity, pH, rot spots, total phenols and antioxidant activity. The treatment that consisted of citric acid at 0.5% (m/v) + sodium isoascorbate at 0.5% (m/v) was the most efficient one to control oxidation; its values of browning indexes were the lowest ones, i. e., 15.62 (S1), 17.74 (S2) and 17.58 (S3). Besides, it kept the creamy-white color of the pulp throughout storage time.

Exploiting Potential of Trichoderma harzianum and Glomus versiforme in Mitigating Cercospora Leaf Spot Disease and Improving Cowpea Growth.

Trichoderma species are of utmost importance in agro-biotechnological applications because, in their interactions with plant hosts, they out-compete most pathogenic microorganisms. This study aimed at exploiting the potential of Trichoderma harzianum together with Glomus versiforme and its mutants, in inhibiting cowpea leaf spot rot induced due to Cercospora canescens infestation and improving agronomic growth parameter in a screen house experiment. The experiment was designed using single and co-inoculation of the bioagents: in all, eleven treatments were applied, consisting of Glom_verwild, Glom_ver30, Glom_ver60, Glom_ver90, Trich_h, Glom_verwild+Trich_h, Glom_ver30+Trich_h, Glom_ver60+Trich_h, Glom_ver90+Trich_h, Pathogen alone and control. Cowpea growth yield parameters and disease severity were assessed after 7 weeks. The deployed treatments improved agronomic growth parameters substantially (p<0.05) relative to control. Glom_ver 60+Trich_h treatment exerted the highest agronomic growth improvement yield. In addition, the best reduction in the incidence and severity of cowpea leaf spot disease was obtained using Glom_ver 60+Trich_h. A significantly higher germination rate in seeding, confirms both inhibitory and growth improvement potency of the bio inoculants treatment. This study's findings confirmed the beneficial impacts of the treatment of seed and soil with dual T. harzianum and G. versiforme, in improving the immunity of cowpea to Cercospora canescens leaf spot infection and improve cowpea growth.

Colletotrichum acutatum complex isolated from apple flowers can cause bitter rot and Glomerella leaf spot

The Glomerella leaf spot (GLS) and bitter rot (BR) are important apple diseases in Brazil, caused by species of Colletotrichum, which are usually related with quiescent infection. This study aimed to detect quiescent infections of Colletotrichum spp. in flowers and in unripe fruits from apple commercial orchard cultivars Eva and Gala. The pathogen was observed in various structures of the flower in both cultivars. In unripe fruits, the pathogen was recovered only from ‘Eva’. Five isolates were obtained and were inoculated by mycelial (with and without wound) on ripe apple fruits and by conidia suspension (without wound) on ripe apple fruits and leaves of ‘Gala’. On inoculated fruits by mycelial, the isolates induced symptoms of BR, and on inoculated fruits by conidia without wound the isolates induced symptoms of GLS. On inoculated leaves, isolates induced symptoms of GLS. The isolates were characterized by cultural, morphological and pathogenic aspects. Detection of Colletotrichum spp. in asymptomatic apple flowers is epidemiologically important, since the flowers can be a route for infection in unripe fruits. This is the first investigation of quiescent infection of this pathogen on apple flowers.

Present Status of Shrimp Farming in Satkhira, a Southwestern District of Bangladesh

Shrimp has become one of the most important export products in recent decades due toincreasing international demand. Shrimp farming is performing significant role in thelivelihoods of rural people of southwestern part of Bangladesh which is considered thecore areas for shrimp farming. To continue the trend of exporting shrimp worldwide it isvery much needed to be familiar with the current culture practices with the precautionstaken by the shrimp farmers. A total of 30 shrimp farmers in Shyamnagarupazilla ofSatkhira district were interviewed to understand the present status of shrimp farming alongwith to identify the problems faced by the farmers, and to formulate somerecommendations for better shrimp production development. Study showed thatpolyculture was the only culture technique followed by the shrimp farmers using naturalwater sources like rain and tide. Bagda (Penaeusmondon) was the dominant culturedspecies followed by Harina (Metapenaeusmonoceros) because of their economicsignificance. Although wild post-larvae (PL) are better in quality than hatchery producedPL, farmers collected PL from both sources. Farmers usually used inorganic fertilizers likeUrea and TSP instead of organic one, but they preferred natural feeds for cost efficiencyand management purposes. The study also identified that shrimp diseases (white spot, gillrot and fin rot), lower market price, flood, high mortality and lack of scientific knowledgewere the major constraints in shrimp farming. Government, donor agencies, planners,researchers and NGOs, therefore, should come forward to assist farmers for mitigatingproblems and achieve sustainable shrimp export earnings of Bangladesh.&#x0D; Res. Agric., Livest. Fish.7(2): 311-320, August 2020

Control of postharvest grey spot rot of loquat fruit with Metschnikowia pulcherrima E1 and potential mechanisms of action

In the present study, the biocontrol efficacy of Metschnikowia pulcherrima E1 against grey spot rot (Pestalotiopsis vismiae) on loquat fruits was assessed and along with potential mechanisms of action. Results indicated that decay incidence and lesion diameter were both significantly reduced by treatment of fruits with the yeast, M. pulcherrima E1. M. pulcherrima E1 quickly colonized wounds in loquat fruit stored at either 20 °C or 4 °C. Scanning electron microscopy revealed that the yeast formed a biofilm on the wound surface in loquat fruit which inhibited the invasion of pathogenic fungi. M. pulcherrima E1 also competed with the pathogen for nutrients (iron) and space. Results of dual-culture petri dish assay indicated that M. pulcherrima E1 produces volatile antifungal compounds that inhibit the growth of P. vismiae. SPME-GC–MS analysis revealed that 3-methyl-1-butanol, phenylethyl alcohol and 1-Hexanol are the main volatile organic compounds produced by M. pulcherrima E1 and that had a significant inhibitory effect on the growth of fungal mycelia. M. pulcherrima E1 induced a higher level of defense-related enzyme activity in loquat fruit, including polyphenol oxidase, peroxidase, catalase, ascorbate peroxidase, and phenylalanine ammonia-lyase. Collectively, the results of the present study indicate that M. pulcherrima E1 has good potential to be used as a biocontrol agent against postharvest grey spot rot on loquats. The different mechanisms of action exhibited by M. pulcherrima E1 enhances its ability to control P. vismiae.

First Report of Colletotrichum salicis Causing Bitter Rot of Apple in Italy.

Apple (Malus domestica Borkh.) is the most important fruit crop in South Tyrol (northern Italy), with a total production of 905.089 tons in 2019 (Chamber of Commerce, Industry, Crafts and Agriculture of Bozen-Bolzano 2020). Symptoms of bitter rot were observed on organic apples of the cultivar 'Roho 3615'/Evelina® collected in a packinghouse in South Tyrol at the end of March 2018 after approximately six months of storage in controlled atmosphere. Lesions were circular and light brown with orange conidial masses. Tissue samples were removed under aseptic conditions from surface-cleaned fruit at the margin between healthy and diseased pulp tissue, transferred to Petri dishes with potato dextrose agar (PDA), and incubated in the dark at room temperature for two weeks. Single spore cultures were obtained by adapting the procedure of Choi et al. (1999). Pure cultures were grown in quadruplicate on PDA at 20°C in the dark for two weeks. The colony appearance on the upper side was mostly flat with a distinct margin, the surface was covered with short, floccose aerial mycelium, and the color ranged from light gray to dark gray, while the reverse side appeared yellow. From each replicate culture, conidia were harvested, and the length and width of 50 randomly selected conidia were measured using a compound light microscope coupled to a digital camera (Leica DMLS, Leica Microsystems, Wetzlar, Germany). Conidia were cylindrical to fusiform, pointed at one end, and measured 10.0 to 19.5 × 2.5 to 5.0 μm (14.5 ± 1.9 × 3.9 ± 0.7 μm [mean ± SD]) in consistency with Damm et al. (2012). In order to determine the species of isolate 18-DSS-BS-EL-1-012, a multi-locus DNA sequence analysis was performed. Genomic DNA was extracted by following the protocol described by Cassago et al. (2002). Four loci, actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), histone H3 (HIS3) and the internal transcribed spacer (ITS) region of the rRNA operon were amplified by PCR and Sanger sequenced (Damm et al. 2012; Lévesque and de Cock 2004). The obtained DNA sequences of ACT, GAPDH, HIS3 and ITS were 186, 150, 317 and 505 bp long and were submitted to GenBank under the accession numbers MT347599, MT347600, MT347598 and MT337388, respectively. A MegaBLAST analysis resulted in 100% sequence identity at all four loci with a type culture of Colletotrichum salicis (CBS 607.94; GenBank accession numbers: JQ949781, JQ948791, JQ949451 and JQ948460), which belongs to the C. acutatum species complex (Damm et al. 2012). A pathogenicity test was performed with twelve 'Golden Delicious' apples by wounding the fruit with a sterile piercing tool and inoculating 20 μl of spore suspension (104 conidia per ml) from a 21-day-old PDA culture. Inoculated fruits were incubated for 21 days in a moist chamber at 20°C in the dark. The symptoms were recorded at 3, 5, 7, 10, 14 and 21 days post-inoculation (dpi). Symptoms appeared after 7 days on all inoculated fruits and resembled those observed on the original fruit, while mock-inoculated controls with sterile water remained symptomless. Fungal colonies resembling the original culture were re-isolated from lesions on the apple and plated on PDA. Their identity was confirmed by DNA sequence analysis of the ITS region, thereby proving Koch's postulates. Bitter rot occurs globally and is considered one of the most important diseases of apple that has the potential to cause significant crop losses (Sutton et al. 2014). Other Colletotrichum species have been commonly reported from apple in Europe, such as C. godetiae and C. fioriniae, whereas C. salicis has been reported solely in New Zealand and Belgium (Damm et al. 2012; Grammen et al. 2019). To the best of our knowledge, this is the first report of C. salicis causing bitter rot of apple in Italy.

Identification and characterization of Colletotrichum species causing apple bitter rot in New York and description of C. noveboracense sp. nov.

Apple bitter rot caused by Colletotrichum species is a growing problem worldwide. Colletotrichum spp. are economically important but taxonomically un-resolved. Identification of Colletotrichum spp. is critical due to potential species-level differences in pathogenicity-related characteristics. A 400-isolate collection from New York apple orchards were morphologically assorted to two groups, C. acutatum species complex (CASC) and C. gloeosporioides species complex (CGSC). A sub-sample of 44 representative isolates, spanning the geographical distribution and apple varieties, were assigned to species based on multi-locus phylogenetic analyses of nrITS, GAPDH and TUB2 for CASC, and ITS, GAPDH, CAL, ACT, TUB2, APN2, ApMat and GS genes for CGSC. The dominant species was C. fioriniae, followed by C. chrysophilum and a novel species, C. noveboracense, described in this study. This study represents the first report of C. chrysophilum and C. noveboracense as pathogens of apple. We assessed the enzyme activity and fungicide sensitivity for isolates identified in New York. All isolates showed amylolytic, cellulolytic and lipolytic, but not proteolytic activity. C. chrysophilum showed the highest cellulase and the lowest lipase activity, while C. noveboracense had the highest amylase activity. Fungicide assays showed that C. fioriniae was sensitive to benzovindiflupyr and thiabendazole, while C. chrysophilum and C. noveboracense were sensitive to fludioxonil, pyraclostrobin and difenoconazole. All species were pathogenic on apple fruit with varying lesion sizes. Our findings of differing pathogenicity-related characteristics among the three species demonstrate the importance of accurate species identification for any downstream investigations of Colletotrichum spp. in major apple growing regions.

Review of the Impact of Apple Fruit Ripening, Texture and Chemical Contents on Genetically Determined Susceptibility to Storage Rots.

Fungal storage rots like blue mould, grey mould, bull’s eye rot, bitter rot and brown rot destroy large amounts of the harvested apple crop around the world. Application of fungicides is nowadays severely restricted in many countries and production systems, and these problems are therefore likely to increase. Considerable variation among apple cultivars in resistance/susceptibility has been reported, suggesting that efficient defence mechanisms can be selected for and used in plant breeding. These are, however, likely to vary between pathogens, since some fungi are mainly wound-mediated while others attack through lenticels or by infecting blossoms. Since mature fruits are considerably more susceptible than immature fruits, mechanisms involving fruit-ripening processes are likely to play an important role. Significant associations have been detected between the susceptibility to rots in harvested fruit and various fruit maturation-related traits like ripening time, fruit firmness at harvest and rate of fruit softening during storage, as well as fruit biochemical contents like acidity, sugars and polyphenols. Some sources of resistance to blue mould have been described, but more research is needed on the development of spore inoculation methods that produce reproducible data and can be used for large screenings, especially for lenticel-infecting fungi.

Pestalotiopsis spp. causing grapevine leaf spot and postharvest berry rot in southern Brazil

<i>Pestalotiopsis</i> spp. causing grapevine leaf spot and postharvest berry rot in southern Brazil

Poly(lactic acid) nanocapsules containing lemongrass essential oil for postharvest decay control: In vitro and in vivo evaluation against phytopathogenic fungi

The increased demand for pesticide-free foods has also increased the search for healthier and environmentally friendly alternatives in agriculture. Essential oils are known to possess natural antifungal properties, becoming a reliable alternative for commercial fungicides, especially for postharvest decay control. However, essential oils are volatile and photodegradable, which reduces their long-term activities. This work presents the development of a lemongrass essential oil-containing poly(lactic acid) nanocapsules. They have shown in vitro antifungal activity against Colletotrichum acutatum and Colletotrichum gloeosporioides with a MIC dosage of 0.1% (v/v) for both phytopathogens. In the in vivo assay with postharvest apples, the ones treated with encapsulated essential oil showed bitter rot lesions three times smaller than the ones treated with non-encapsulated essential oil, or in comparison to the apples in positive control. The methodology led to stable nanocapsules with spherical morphology, a mean diameter of 96.4 nm, and with an encapsulation efficiency of 99%.

2-Phenylethyl Isothiocyanate Exerts Antifungal Activity against Alternaria alternata by Affecting Membrane Integrity and Mycotoxin Production.

Black spot caused by Alternaria alternata is one of the important diseases of pear fruit during storage. Isothiocyanates are known as being strong antifungal compounds in vitro against different fungi. The aim of this study was to assess the antifungal effects of the volatile compound 2-phenylethyl isothiocyanate (2-PEITC) against A. alternata in vitro and in pear fruit, and to explore the underlying inhibitory mechanisms. The in vitro results showed that 2-PEITC significantly inhibited spore germination and mycelial growth of A. alternata—the inhibitory effects showed a dose-dependent pattern and the minimum inhibitory concentration (MIC) was 1.22 mM. The development of black spot rot on the pear fruit inoculated with A. alternata was also significantly decreased by 2-PEITC fumigation. At 1.22 mM concentration, the lesion diameter was only 39% of that in the control fruit at 7 days after inoculation. Further results of the leakage of electrolyte, increase of intracellular OD260, and propidium iodide (PI) staining proved that 2-PEITC broke cell membrane permeability of A. alternata. Moreover, 2-PEITC treatment significantly decreased alternariol (AOH), alternariolmonomethyl ether (AME), altenuene (ALT), and tentoxin (TEN) contents of A. alternata. Taken together, these data suggest that the mechanisms underlying the antifungal effect of 2-PEITC against A. alternata might be via reduction in toxin content and breakdown of cell membrane integrity.

Carrot biotic stresses: challenges and research priorities

Among the main biotic stresses of carrot crops, the pests such as nematodes and carrot fly and diseases including cavity spot, crown or cottony rot, black rot or leaf blight are targets for scientific researches over the world. Components of integrated control programs for all these organisms are under development. Success of such programs requires systemic approaches including knowledge about genetic diversity of the targets, their epidemiology, host physiology and host resistance mechanisms and compatibility among the different control tools or between programs targeting different goals.

The growth rate of apple bitter rot lesion, caused by Colletotrichum spp., is affected by temperature, fungal species, and cultivar.

The growth and symptom development of two fungal species, Colletotrichum siamense, and C. fioriniae were examined using in vitro and in planta assays. In a plate assay, C. siamense grew fastest at 30 °C and at 25 °C, but C. fioriniae grew slower at 30 °C than at 25 °C. With apple inoculation assay, the mean lesion diameters at 30 °C were significantly larger (P ≤ 0.05) than that at 20 °C on a cultivar Ida Red for both fungal species. On the other hand, the mean lesion diameter on a cultivar Golden Delicious was significantly larger at 20 °C than at 30 °C for both fungal species. Therefore, the rate of lesion development was influenced not only by fungal species and incubation temperature but also by apple cultivar. In this study, cultivar ‘Ida red’ was found to be more susceptible to C. siamense under warm environmental condition. Although both species were able to grow at 10 °C in the plate assay, no disease symptoms were developed at 10 °C with the inoculation assay. Although the numbers of cultivar and fungal species are small, to our knowledge, this is the first report to describe potential interactive effect among Colletotrichum species, temperature, and apple cultivar on the rate of bitter rot symptom development.

First Report of Bitter Rot of Apple Caused by a Colletotrichum sp. in the C. kahawae Clade in Kentucky

First Report of Bitter Rot of Apple Caused by a <i>Colletotrichum</i> sp. in the <i>C. kahawae</i> Clade in Kentucky

Sensitivity of the Colletotrichum acutatum Species Complex From Apple Trees in Brazil to Dithiocarbamates, Methyl Benzimidazole Carbamates, and Quinone Outside Inhibitor Fungicides

Glomerella leaf spot (GLS) and bitter rot (BR) on apples are often caused by Colletotrichum acutatum in Paraná State, Brazil. GLS control is difficult because of its rapid development, with an incubation period of only 2 days under favorable conditions. Therefore, producers use successive fungicide applications every season; however, failure to control GLS has been commonly reported. The objectives of this study were to determine the sensitivity of isolates of the C. acutatum species complex obtained from apple orchards in Brazil to mancozeb, thiophanate-methyl, and azoxystrobin fungicides. Isolates from the different parts of the plant (leaves, flowers, buds, and twigs) and cultivars (Gala and Eva) showed different levels of sensitivity to mancozeb, thiophanate-methyl, and azoxystrobin. For mancozeb, the frequencies of isolates were 25% highly resistant, 50% low-resistance, and 25% sensitive. For thiophanate-methyl, the frequencies of isolates were 72.2% highly resistant, 11.1% resistant, and 16.7% moderately resistant. For azoxystrobin, the frequencies of isolates were 11.1% highly resistant, 5.6% resistant, and 83.3% sensitive. Interestingly, no mutations in the β-tubulin and cytochrome b genes were observed in any of the isolates resistant to thiophanate-methyl and azoxystrobin fungicides.