Dieback caused by Colletotrichum spp. is an emerging disease in California citrus groves. A large-scale survey with emphasis on seasonal variations of latent infections was conducted throughout citrus orchards in Fresno, Kern, and Tulare counties in 2019 and 2020. Latent infections on citrus leaves and twigs varied markedly between years. Isolates of Colletotrichum spp. were obtained from asymptomatic tissue and two groups were formed based on colony and spore morphology. The morphological groups were further identified based on multigene sequence analysis using the DNA regions ITS1-5.8S-ITS2, TUB2, and GAPDH. Results revealed that isolates belong to two phylogenetic species, C. gloeosporioides and C. karstii, being C. karstii more frequently isolated. Representative isolates of each species were further selected and characterized based on the response of physiological variables to temperature. Both species had similar optimum growth temperatures but differed in maximum growth rates, with C. gloeosporioides exhibiting a greater growth rate than that of C. karstii on media. Pathogenicity tests on citrus trees demonstrated the ability of C. gloeosporioides and C. karstii to cause lesions on twigs and no differences in aggressiveness. A fungicide screening performed in this study determined that the DMI fungicides were the most effective in reducing the mycelial growth of C. gloeosporioides and C. karstii. The QoI fungicides showed a remarkably inhibitory impact on spore germination of both species. On average, C. karstii was more sensitive to the DMI fungicides than C. gloeosporioides. The findings of this study provide new information to understand the Colletotrichum dieback of citrus.
Colletotrichum species infect temperate fruit trees and symptoms can occurin various parts of the plant such as twigs, leaves, fl owers, and fruits. The damage caused by these diseases is severe in Brazilian subtropical conditi ons, where a high primary inoculum potential is present. This review addresses e ological and epidemiological studies of Colletotrichum spp. in persimmon, apple, peach, and grapevine crops. General aspects of the management of the diseases under subtropical conditi ons are also discussed. Regarding etiology, new taxonomic classifications of species, brief history of nomenclature, phylogenetic studies for species identification and survey of species reported as causal agents of diseases were reviewed. Regarding epidemiology, favorable conditions for the pathogen and the stages of the disease cycles were addressed. For persimmon and apple crops, a more in-depth discussion about the diseases was held. Two disease cycles, in the form of illustrative fi gures were proposed: Colletotrichum spp. x persimmon and Colletotrichum spp. x apple tree. The cycles were based on literature and on epidemiological studies developed by our research group. The etiological and epidemiological studies reported here provide support for integrated management strategies for the diseases that are causing damage to these fruit trees in Brazil and worldwide
Maize (Zea mays L.) is one of the most important commodities, and Brazil is the second-largest maize exporter country in the world. In April 2019, the period of the second crop maize (safrinha), it was observed black decayed lesions on roots and wilting of some maize plants, causing a "sudden death" in a commercial area in the west of Paraná state, Brazil (Figure 1A-C). Symptomatic root and stalk were collected, and tissues surface disinfected with 70% ethanol for 30 s, 1.5% NaOCl for 1 min and rinsed three times in sterile distilled water, slices of necrotic tissues were transferred to potato dextrose agar (PDA) medium and grown for 7 days at 27 ± 1ºC with a photoperiod of 12 h. Pure cultures were obtained through monosporic isolation. The fungal morphology is alike Gaeumannomyces radicicola, which is a synonym of Phialophora radicicola var. radicicola, Harpophora radicicola, P. zeicola, H. zeicola and G. graminis var. maydis (Hernández-Restrepo et al. 2016). Colonies on PDA showed flat, white to light gray at first (Fig. 1D), turning gray to black with age (Fig. 1E). Colony diameter approximately 5.2 cm on PDA in the dark after 7 days at 27ºC. Conidiophores with slightly thickened wall, mostly branched, varying in dimensions, with a range of 57.5-166.5 (avg. 128.7 μm) × 2.9-5.9 (avg. 4.2 μm) n = 25 (Fig. 1H-J). The conidia showed lunate-shaped with rounded ends, produced successively at the apex of phialide, 3.3–9.7 (avg. 6.6 μm) × 1.5–3.6 μm (avg. 2.5 μm), n = 100 (Fig. 1G-J). Morphological characteristics were comparable to the description of this specie (Cain 1952; Gams 2000; McKeen 1952). The total genomic DNA of a representative isolate, LEMIDPRZm 19-01 was extracted and the partial large subunit (28S nrDNA; LSU), internal transcribed spacer nrDNA including the intervening 5.8S nrDNA (ITS), and part of the largest subunit of the RNA polymerase II gene (RPB1) were amplified and sequenced, as following by Hernández-Restrepo et al. (2016) and Klaubauf et al. (2014). The primers to LSU – NL1 (O’Donnel, 1993) and LR5 (Vilgalys; Hester, 1990); ITS – ITS5 and ITS4 (White et al., 1990); and RPB1 – RPB1F and RPB1R (Klaubauf et al., 2014) were used in this study. The gene sequences of LSU (MT123866), ITS (MT114427), and RPB1 (MT123867) were deposited in GenBank and showed 99.67%, 99.75%, and 100% identity with type material G. radicicola CBS 296.53 (KM484962, KM484845, and KM485061). A multi-locus phylogenetic analysis based on Bayesian Inference showed the isolate LEMIDPRZm 19-01 in the G. radicicola clade (Fig. 2). To confirm pathogenicity, ex vivo assays were performed with mycelial PDA discs of 5 mm from a 7-day-old culture using detached roots (adapted method by Degani et al., 2019), on wounded and unwounded stalk and leaves, each treatment consisted of five replications. PDA discs without fungal were used in negative tissue controls. Pathogenicity tests were also conducted in vivo, two experiments performed: i) the stalk tissue was inoculated by sterilized toothpick grown on PDA with fungal mycelium and the leaves inoculated as ex vivo assay, and toothpick without fungal mycelium was used to stalk negative control, whereas PDA discs without fungal were used in the tested leaves; ii) 6 mycelial PDA discs/500 mL were placed on potato dextrose broth (PDB) media and it remained in agitation for 10 days to obtain a mycelial suspension. Subsequently, the mycelial was crushed to soil infestation, and 50 mL from this suspension were dropped in each 2 L maize pot with soil sterilization 10 days after emergence. Maize pots with soil sterilization without mycelium fungal were used as negative controls. Four replications (maize pots), for each treatment, were used in both tests. Experiments were repeated twice. In the ex vivo assay, all inoculated tissues with and without wounds showed necrotic lesions (Fig. 1K-N). In the first in vivo assay, stalk rot symptoms, including wilting of the inoculated plants causing premature plant death, were observed within 6 days (Fig. 1O-Q). In the second in vivo assay, inoculated plants had inferior growth than compared with plant control. Sixty days after inoculation, the plants were removed from the pots and it was observed a roots degeneration with symptoms of necrosis (Fig. 1R-U). No symptoms were detected in the control treatments and the pathogen was re-isolated from symptomatic tissues confirming Koch’s postulate for all assays. So far, to our knowledge, the pathogen distribution was reported solely in the west area of Paraná state, but it may become a potential threat to Brazilian maize production. Further monitoring is necessary to better understand the epidemiology of this pathogen to address a strategy for disease control. The pathogen has already been detected in Canada, South Africa, and China. To our knowledge, this is the first report of G. radicicola in Brazil, as well as in South America.
The persimmon tree is known for its rusticity and productivity and was first introduced to Brazil in the late 19th century. However, anthracnose disease is causing immature fruit drop and severe disease symptoms in persimmon fruit, shoots, flowers, and twigs. The causal agent was first described as the fungal species, Colletotrichum horii, which was first confirmed using only the ITS region. In this study, we compared the aggressiveness of 13 isolates of Colletotrichum spp. obtained from fruit and shoots of persimmon grown in the Metropolitan Region of Curitiba, Paraná State, Brazil. A multilocus molecular analysis was carried out based on ITS, GPDH, and EF genes, and we confirmed that the isolates were confirmed as C. horii. All isolates were pathogenic for unwounded and wounded persimmon fruit but differed in aggressiveness. Only one isolate was non-pathogenic when inoculated into unwounded persimmon shoots. Most isolates caused cankers and shoot death whether shoots were wounded or unwounded. In this study, we emphasized the importance of shoots as a source of primary inoculum. In future studies, it will be critical to further elucidate the epidemiological basis of anthracnose disease by conducting field studies to establish a more effective strategy for disease control.
Brazil is currently the world's sixth largest producer of persimmon (Diospyros kaki), with a total yield of 156,935 tonnes in 2018, cultivated in an area of 8148 ha and an average of 22.4 t/ha (Food & Agriculture Organization, 2020). The Brazilian persimmon production is concentrated in the southern and south-eastern regions, with approximately 80% of the cultivated area concentrated in the states of São Paulo (SP), Rio Grande do Sul (RS) and Paraná (PR) (Instituto Brasileiro de Geografia e Estatística, 2020).The cultivars grown in these regions vary depending on the weather and market; for example, in the south-east, cultivars Rama Forte, Fuyu, Guiombo and Taubaté are the most planted, whereas Fuyu and Kyoto are more frequently grown in the south (Aguiar et al., 2014).Persimmons were grown as low-maintenance plants in the south of Brazil, with high productivity and demanding few cultural practices and phytosanitary treatments (Danielli et al., 2002). However, since 2006, mainly in the state of Paraná, growers and extension personnel began to report an increase in the incidence of anthracnose in
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