First Report of Twig Canker on Peach Caused by Phomopsis amygdali in China

Rapid Detection of Peach Shoot Blight Caused by Phomopsis amygdali Utilizing a New Target Gene Identified from Genome Sequences Within Loop-Mediated Isothermal Amplification

Peach shoot blight (PSB), caused by Phomopsis amygdali, is a serious threat to the healthy development of the peach industry and leads to 30 to 50% damage to peach production in southern China. In this study, loop-mediated isothermal amplification (LAMP) technology was used to detect the P. amygdali target of a gene of GME6801 that was unique in the whole genome of the pathogen compared with that of Diaporthe (Phomopsis) longicolla TWH P74, Fusarium graminearum PH-1, Colletotrichum gloeosporioides SMCG1 and Magnaporthe oryzae 70-15. Blast comparison of this gene sequence in NCBI database showed that no homologous sequences were found. Therefore, the gene sequence of GME6801 was used to design two pairs of LAMP primers and one pair of PCR primers. The results showed that both primer sets were specific to the 15 strains of P. amygdali, and the other 15 fungal strains presented negative reactions, similar to the control. In addition, 50 pg of genomic DNA of P. amygdali in a 25-μl reaction system could be detected by LAMP assay, which was 100 times more sensitive than PCR. Furthermore, the GME6801 LAMP assay was used to detect artificially inoculated twigs of the pathogen, disease twigs within significantly symptomatic PSB in the fields, and healthy twigs in the same orchard, with detection rates of 100, 75, and 20.8%, respectively. However, detection rates of conventional PCR were separately 100, 62.5, and 16.7%. The results indicated that GME6801-based LAMP could be used for P. amygdali detection as its specificity, sensitivity, and simplicity. This study provides a rapid experimental basis for the identification and prediction of P. amygdali that causes PSB and is beneficial for precise prevention and control of the disease.

Molecular and Biological Characterization of Two New Species Causing Peach Shoot Blight in China

Peach shoot blight (PSB), which kills shoots, newly sprouted leaf buds, and peach fruits, has gradually increased over the last 10 years and resulted in 30 to 50% of total production loss of the peach industry in China. Phomopsis amygdali has been identified as the common causal agent of this disease. In this study, two new species, Phomopsis liquidambaris (strain JW18-2) and Diaporthe eres (strain JH18-2), were also pathogens causing PSB, as determined through molecular phylogenetic analysis based on the sequences of the internal transcribed spacer (ITS) region, translation elongation factor 1-α (EF1-α) and beta-tubulin (TUB), and colony and conidial morphological characteristics. Biological phenotypic analysis showed that the colony growth rate of strain JW18-2 was faster than that of strains JH18-2 and ZN32 (one of the P. amygdali strains that we previously found and identified). All three strains produced α-conidia; however, JW18-2 could not produce β-conidia on alfalfa decoction and Czapek media, and the β-conidia produced by strain JH18-2 were shorter in length and thicker in width than those produced by strain ZN32. Pathogenicity tests showed that JW18-2 presented the strongest pathogenicity for peach fruits and twigs and was followed by strains JH18-2 and ZN32. The results shed light on the etiology of PSB and provide a warning that P. liquidambaris or D. eres might develop into dominant species after a few years while also potentially benefitting the development of effective disease control management strategies.

Characterization of Diaporthe species associated with peach constriction canker, with two novel species from China

Species of Diaporthe infect a wide range of plants and live in vivo as endophytes, saprobes or pathogens. However, those in peach plants are poorly characterized. In this study, 52 Diaporthe strains were isolated from peach branches with buds, showing constriction canker symptoms. Phylogenetic analyses were conducted using five gene regions: internal transcribed spacer of the ribosomal DNA (ITS), translation elongation factor 1-α (TEF), ß-tubulin (TUB), histone (HIS), and calmodulin (CAL). These results coupled with morphology revealed seven species of Diaporthe, including five known species (D. caryae, D. cercidis, D. eres, D. hongkongensis, and D. unshiuensis). In addition, two novel species D. jinxiu and D. zaofenghuang are introduced. Except for the previously reported D. eres, this study represents the first characterization of Diaporthe species associated with peach constriction canker in China, and contributes useful data for practicable disease management.

Identification and Characterization of Diaporthe spp. Associated with Twig Cankers and Shoot Blight of Almonds in Spain

Two hundred and twenty-five Diaporthe isolates were collected from 2005 to 2019 in almond orchards showing twig cankers and shoot blight symptoms in five different regions across Spain. Multilocus DNA sequence analysis with five loci (ITS, tub, tef-1α, cal and his), allowed the identification of four known Diaporthe species, namely: D. amygdali, D. eres, D. foeniculina and D. phaseolorum. Moreover, a novel phylogenetic species, D. mediterranea, was described. Diaporthe amygdali was the most prevalent species, due to the largest number of isolates (85.3%) obtained from all sampled regions. The second most frequent species was D. foeniculina (10.2%), followed by D. mediterranea (3.6%), D. eres and D. phaseolorum, each with only one isolate. Pathogenicity tests were performed using one-year-old almond twigs cv. Vayro and representative isolates of the different species. Except for D. foeniculina and D. phaseolorum, all Diaporthe species were able to cause lesions significantly different from those developed on the uninoculated controls. Diaporthe mediterranea caused the most severe symptoms. These results confirm D. amygdali as a key pathogen of almonds in Spain. Moreover, the new species, D. mediterranea, should also be considered as a potential important causal agent of twig cankers and shoot blight on this crop.

Endophytic fungi from the branches of Camellia taliensis (W. W. Smith) Melchior, a widely distributed wild tea plant

Camellia taliensis (W. W. Smith) Melchior is a wild tea plant endemic from the west and southwest of Yunnan province of China to the north of Myanmar and is used commonly to produce tea by the local people of its growing areas. Its chemical constituents are closely related to those of C. sinensis var. assamica, a widely cultivated tea plant. In this study, the α diversity and phylogeny of endophytic fungi in the branches of C. taliensis were explored for the first time. A total of 160 fungal strains were obtained and grouped into 42 species from 29 genera, which were identified based on rDNA internal transcribed spacer sequence analysis. Diversity analysis showed that the endophytic fungal community of the branches of C. taliensis had high species richness S (42), Margalef index D' (8.0785), Shannon-Wiener index H' (2.8494), Simpson diversity index D_S (0.8891), PIE index (0.8947) and evenness Pielou index J (0.7623) but a low dominant index λ (0.1109). By contrast, that in the branches of C. taliensis had abundant species and high species evenness. Diaporthe tectonigena, Acrocalymma sp. and Colletotrichum magnisporum were the dominant endophytic fungi. The phylogenetic tree was established by maximum parsimony analysis, and the 11 orders observed for endophytic fungi belonging to Ascomycota and Basidiomycota were grouped into 4 classes.

Identification and Characterization of Phomopsis amygdali and Botryosphaeria dothidea Associated with Peach Shoot Blight in Yangshan, China

Peach (Prunus persica (L.) Batsch) is produced locally in Yangshan, Wuxi City, China. In recent years, a widespread shoot blight has been observed in many peach orchards of Yangshan that kills the twigs and results in high losses in fruit production. Disease incidences ranged from 10 to 20% in the affected orchards and, in extreme cases, 40% of the trees were affected. Shoot blight of peach is caused by a fungus, previously identified as Phomopsis amygdali. Between 2014 and 2015, samples were collected four times from three peach orchards located in Yangshan to understand the etiology of shoot blight. Interestingly, two types of shoot blight symptoms were observed: one characterized by necrotic lesions with rings and one without rings. Based on conidial morphology, cultural characteristics, and analysis of nucleotide sequences of three genomic regions (the internal transcribed spacer region, a partial sequence of the β-tubulin gene, and the translation elongation factor 1-α), isolates were identified as P. amygdali and Botryosphaeria dothidea. Remarkably, most of the P. amygdali isolates were recovered from twigs showing necrotic lesions without rings. In contrast, most of the B. dothidea isolates were recovered from twigs with rings in the necrotic lesions. Correlations among pathogens, sampling regions, and disease symptoms were noted, and growth rates of these pathogens were characterized. Pathogenicity tests showed that B. dothidea isolates could induce necrotic lesions with rings but P. amygdali isolates could only induce necrotic lesions. Moreover, the B. dothidea isolates exhibited higher levels of virulence than P. amygdali isolates on the peach twig. Additionally, high frequencies of detection of both P. amygdali and B. dothidea from buds indicated that buds may be the primary site of fungal invasion. Cankers and necrotic twigs may also serve as infection courts. Our results suggest that B. dothidea and P. amygdali are the common causal agents of peach shoot blight in Yangshan, China. This finding provides a basis for the development of effective management strategies.

Phomopsis Blight: A New Disease of Pieris japonica Caused by Phomopsis amygdali in the United States

Pieris japonica, also known as Japanese andromeda, is an economically valuable broadleaf evergreen used in landscapes across the United States. From spring 2010 to 2012, P. japonica 'Mountain Fire' plants growing in Maryland nurseries were observed with a high incidence of stem canker, shoot dieback, and blight symptoms. Necrosis was evident on shoot tips and often advanced into lateral shoots, as well as to the crowns, leading to plant death. Phomopsis amygdali, known as a destructive pathogen of peach and almond, was consistently isolated from symptomatic plants. P. amygdali also caused similar symptoms on Mountain Fire test plants following inoculations. P. amygdali was consistently recovered and its identity was confirmed with both morphological and molecular tools, thus fulfilling Koch's postulates. In addition, nursery sampling in 2012 revealed that P. amygdali could also be isolated from asymptomatic plants. In all instances, infected plants were shipped from a West Coast nursery, indicating that this pathogen was inadvertently introduced to new locations. P. amygdali may be emerging as an important pathogen in nurseries because this is the first known association of this pathogen with an ornamental plant species.