Black Leaf Spot Research Articles

First report of Pseudocercospora platanigena in Australia

A distinct black leafspot with fungal growth was found on Platanus orientalis ‘Digitata’ (cut-leaf oriental plane tree) in northern Sydney, New South Wales, Australia, in February 2019. Morphological characteristics, internal transcribed spacer sequencing and phylogenetic analysis of the associated fungus identified it as Pseudocercospora platanigena (= Stigmina platani). This pathogen has previously been reported from Pl. orientalis (oriental plane tree) in Europe and Asia and more recently from Pl. orientalis ‘Digitata’ in New Zealand. This is the first report of Ps. platanigena in Australia. Pseudocercospora platanigena is now common on Pl. orientalis ‘Digitata’ throughout Sydney and has been found as far north as Dorrigo in northern New South Wales and west to the Blue Mountains. Pseudocercospora platanigena has not been observed on Pl. orientalis other than the cultivar ‘Digitata’, nor on the more commonly planted London plane tree (Pl. x acerifolia) in Australia. It has not been found in other states in Australia.

Klasifikasi penyakit citra daun anggur menggunakan model CNN-VGG16

This study aims to classify the disease image on grape leaves using image processing. The segmentation uses the k-means clustering algorithm, the feature extraction process uses the VGG16 transfer learning technique, and the classification uses CNN. The dataset is from Kaggle of 4000 grape leaf images for four classes: leaves with black measles, leaf spot, healthy leaf, and blight. Google images of 100 pieces were also used as test data outside the dataset. The accuracy of the CNN model training is 99.50 %. The classification yields an accuracy of 97.25 % using the test data, while using test image data outside the dataset obtains an accuracy of 95 %. The designed image processing method can be applied to identify and classify disease images on grape leaves.

Phoma medicaginis Isolate Differences Determine Disease Severity and Phytoestrogen Production in Annual Medicago spp.

Phoma black stem and leaf spot disease of annual Medicago spp., caused by Phoma medicaginis, not only can devastate forage and seed yield but can reduce herbage quality by inducing production of phytoestrogens (particularly coumestrol and 4'-O-methylcoumestrol), which can also reduce the ovulation rates of animals grazing infected forage. We determined the consequent phytoestrogen levels on three different annual Medicago species/cultivars (Medicago truncatula cultivar Cyprus, Medicago polymorpha var. brevispina cultivar Serena, and Medicago murex cultivar Zodiac) after inoculation with 35 isolates of P. medicaginis. Across the isolate × cultivar combinations, leaf disease incidence, petiole/stem disease incidence, leaf disease severity, petiole disease severity, and leaf yellowing severity ranged up to 100, 89.4, 100, 58.1, and 61.2%, respectively. Cultivars Cyprus and Serena were the most susceptible and cultivar Zodiac was the most resistant to P. medicaginis. Isolates WAC3653, WAC3658, and WAC4252 produced the most severe disease. Levels of phytoestrogens in stems ranged from 25 to 1,995 mg/kg for coumestrol and from 0 to 418 mg/kg for 4'-O-methylcoumestrol. There was a significant positive relationship of disease incidence and severity parameters with both coumestrol and 4'-O-methylcoumestrol contents, as noted across individual cultivars and across the three cultivars overall, where r = 0.39 and 0.37 for coumestrol and 4'-O-methylcoumestrol, respectively (P < 0.05). Although cultivar Serena was most susceptible to P. medicaginis and produced the highest levels of phytoestrogens in the presence of P. medicaginis, cultivar Zodiac contained the highest levels of phytoestrogens in comparison with other cultivars in the absence of P. medicaginis. There was a 15-fold increase in coumestrol in cultivar Serena but only a 7-fold increase in cultivar Zodiac from infection of P. medicaginis. The study highlights that the intrinsic ability of a particular cultivar to produce phytoestrogens in the absence of the pathogen, and its comparative ability to produce phytoestrogens in the presence of the P. medicaginis, are both important and highly relevant to developing new annual Medicago spp. cultivars that offer improved disease resistance and better animal reproductive outcomes.

Mangrove Dieback and Leaf Disease in Sonneratia apetala and Sonneratia caseolaris in Vietnam

Even though survival rates for mangrove restoration in Vietnam have often been low, there is no information on fungal pathogens associated with mangrove decline in Vietnam. Therefore, this research was undertaken to assess the overall health of mangrove afforestation in Thanh Hoa Province and fungal pathogens associated with tree decline. From a survey of 4800 Sonneratia trees, the incidence of disorders was in the order of pink leaf spot &gt; shoot dieback &gt; black leaf spot for S. caseolaris and black leaf spot &gt; shoot dieback &gt; pink leaf spot for S. apetala. Approximately 12% of S. caseolaris trees had both pink leaf spot and shoot dieback, while only 2% of S. apetala trees had black leaf spot and shoot dieback. Stem and leaf samples were taken from symptomatic trees and fungi were cultured in vitro. From ITS4 and ITS5 analysis, four main fungal genera causing leaf spots and shoot dieback on the two Sonneratia species were identified. The most frequently isolated fungal taxa were Curvularia aff. tsudae (from black leaf spot),Neopestalotiopsis sp.1 (from stem dieback), Pestalotiopsis sp.1 (from pink leaf spot), and Pestalotiopsis sp.4a (from black leaf spot). The pathogenicity of the four isolates was assessed by under-bark inoculation of S. apetala and S. caseolaris seedlings in a nursery in Thai Binh Province. All isolates caused stem lesions, and Neopestalotiopsis sp.1 was the most pathogenic. Thus, investigation of fungal pathogens and their impact on mangrove health should be extended to other afforestation projects in the region, and options for disease management need to be developed for mangrove nurseries.

Nigrospora oryzae Causing Black Leaf Spot Disease of Hibiscus mutabilis in China.

Cotton rose (Hibiscus mutabilis Linn.) is a deciduous shrub native to China. It has been widely cultivated in many provinces in China for its ornamental and ecological value (Shang et al., 2020). In May 2017, an unknown leaf spot symptom was first observed on H. mutabilis at the Chengdu Campus of Sichuan Agricultural University (30°42'31″ N, 103°51'28″ E). The disease occurred from May to September with approximately 81% incidence by field sample survey of 300 plants in Chengdu Greenway. The symptoms at first appeared as irregular black spots on the leaves. Then the lesions grew and coalesced into large, black necrotic areas, which later produced leaf chlorosis and abscission (Fig. 1-A). This disease seriously reduced the ornamental value of H. mutabilis. Forty diseased lesions (4 × 5 mm) were surface sterilized with 75% alcohol for 60 s and 3% NaClO for 45 s, rinsed three times in sterile water, placed onto potato dextrose agar (PDA), and then incubated in a dark at 25°C. From the 7 obtained isolates, 4 isolates exhibited the morphology described as Nigrospora oryzae (Hao et al., 2020). The fungus produced initially circular white colonies, and then the centers turned dark gray or black with age on the PDA. Hyphae were smooth, branched, septate, hyaline, or pale brown. Conidia (N = 100 spores) were abundant, and were solitary, dark-brown to black, smooth, aseptate, and measured 11 to 15 μm in diameter (Fig. 1). DNA was extracted from the fungal colonies using a DNeasyTM Plant Mini Kit (Qiagen). The internally transcribed spacer (ITS), β-tubulin gene (TUB), and translation elongation factor 1-alpha (TEF1) were amplified with primers ITS1/ITS4 (White et al., 1990), BT2A/BT2B (Glass and Donaldson 1995), and EF1-728F/EF1-986R (O'Donnell et al., 1998; Carbone and Kohn 1999), respectively. BLAST results indicated that the ITS, TUB, and TEF1 sequences (GenBank accession Nos. MN515070, MN733956, and MN635723, respectively) had 99% identity with N. oryzae sequences (GenBank accession Nos. KX986031, KY019553, and KY019358). The result was confirmed by multilocus phylogenetic analysis (Fig. 2). The morphological characteristics and molecular analyses of the isolate matched the description of N. oryzae. To confirm pathogenicity, Koch's postulates were fulfilled under controlle conditions. The seedlings of 20 two-year-old potted H. mutabilis plants were inoculated by spraying conidial suspension at the concentration of 1 × 106 conidia/ml on both sides of leaves. Sterilized distilled water (20 seedlings) were used as negative controls. The experiment was performed three times. All plants were incubated at 25°C ± 2°C under a 16 h/8 h photoperiod and 70%-75% relative humidity (RH) after inoculation, and observed daily for disease development. Two weeks later, the inoculated plants showed the same symptoms as the original diseased plants and the controls remained asymptomatic. The pathogen N. oryzae was re-isolated from all ioculated plants, and the culture and fungus characteristics were the same as those of the original isolate. But N. oryzae was not isolated from the control plants. The results indicated that N. oryzae is a causal agent of the disease. N. oryzae was reported as a leaf pathogen on cotton (Zhang et al., 2012), but this is the first report of N. oryzae causing leaf black spot on H. mutabilis in the world. The identification could provide relevant information for adopting appropriate management strategies to control the disease.

The response of alfalfa genotypes to different concentrations of mobile aluminium

AbstractThe morphological traits of alfalfa under acid soil conditions with different mobile aluminium (Al) concentrations were investigated. The study site was Vėžaičiai Branch of the Lithuanian Research Centre for Agriculture and Forestry, 55°70 N, 21°49 E. The experiment featuring the 30 most Al-tolerant alfalfa accessions (populations and cultivars), determined from laboratory trials was established on a Bathygleyic Dystric Retisol in 2018. In 2019 and 2020, the biological and morphological traits were evaluated: plant regrowth, plant height before flowering, wintering, leafiness, stem thickness, plant vigour, stem density, seed yield and resistance to spring black stem leaf spot. The resistance of alfalfa to mobile Al toxicity was determined using a filter-based screening method of selection cycles C1 and C2. The accessions grown in the soil with mobile Al (20.6–23.4 mg/kg) showed better tolerance to Al toxicity in the cycle C2. The hypocotyl tolerance index of these accessions was better at 8, 16, 32 and 64 mm AlCl3 concentrations in the cycle C2. The correlation analysis showed strong significant positive and negative relationships between the morphological traits. A cluster analysis showed that the accessions, grown in the soil with mobile Al (20.6–23.4 mg/kg) were the most resistant to Al toxicity in the cycle C2. These accessions produced a better seed yield and demonstrated lower values of morphological traits compared to cluster 2. Also, these accessions are considered as tolerant to mobile Al toxicity and might be used as donors in breeding for Al toxicity tolerance.

Genome-Wide Analysis of Coding and Non-coding RNA Reveals a Conserved miR164-NAC-mRNA Regulatory Pathway for Disease Defense in Populus.

MicroRNAs (miRNAs) contribute to plant defense responses by increasing the overall genetic diversity; however, their origins and functional importance in plant defense remain unclear. Here, we employed Illumina sequencing technology to assess how miRNA and messenger RNA (mRNA) populations vary in the Chinese white poplar (Populus tomentosa) during a leaf black spot fungus (Marssonina brunnea) infection. We sampled RNAs from infective leaves at conidia germinated stage [12 h post-inoculation (hpi)], infective vesicles stage (24 hpi), and intercellular infective hyphae stage (48 hpi), three essential stages associated with plant colonization and biotrophic growth in M. brunnea fungi. In total, 8,938 conserved miRNA-target gene pairs and 3,901 Populus-specific miRNA-target gene pairs were detected. The result showed that Populus-specific miRNAs (66%) were more involved in the regulation of the disease resistance genes. By contrast, conserved miRNAs (>80%) target more whole-genome duplication (WGD)-derived transcription factors (TFs). Among the 1,023 WGD-derived TF pairs, 44.9% TF pairs had only one paralog being targeted by a miRNA that could be due to either gain or loss of a miRNA binding site after the WGD. A conserved hierarchical regulatory network combining promoter analyses and hierarchical clustering approach uncovered a miR164–NAM, ATAF, and CUC (NAC) transcription factor–mRNA regulatory module that has potential in Marssonina defense responses. Furthermore, analyses of the locations of miRNA precursor sequences reveal that pseudogenes and transposon contributed a certain proportion (∼30%) of the miRNA origin. Together, these observations provide evolutionary insights into the origin and potential roles of miRNAs in plant defense and functional innovation.

First Report on Neopestalotiopsis aotearoa of Rubber Tree in China.

Natural rubber is an important industrial raw material and an economically important perennial in China. In recent years, A new leaf fall disease, caused by Neopestalotiopsis aotearoa Maharachch., K.D. Hyde & Crous, has occurred in Indonesia, Malaysia, Thailand, Sri Lanka, and other major rubber planting countries. In May and July of 2020, this disease was first found on 2-year-old rubber seedlings in two plantations located in Ledong and Baisha counties in Hainan Province, China. In the two plantations of approximately 32 ha, 15% of the rubber seedlings had the disease and the defoliation was more than 20%. The infected leaves turned yellow and watery, and dark brown and nearly round lesions of 1-2 mm in diameter were formed on the leaves. When the humidity was high, the center of the lesion was grey-white, and the lesions had many small black dots, black margins and surrounded by yellow halos. When the disease was severe, leaves fell off. To identify the pathogen, leaf tissues were collected from lesion margins after leaf samples were surface-sterilized in 75% ethanol, rinsed with sterile water for three times, and air dried. The leaf tissues were plated on potato dextrose agar (PDA) and incubated at 28°C for seven days. Fungal cultures with similar morphology were isolated from 90% of tested samples and two isolates (HNPeHNLD2001 and HNPeHNLD2002) were used in pathogenicity and molecular tests. Rubber leaves (clone PR107) were inoculated with conidial suspension (106 conidia/ml), and inoculated with PDA were used as the control, Each treatment had 3 leaves, and each leaf was inoculated with 3 spots and incubated at 28oC under high moisture conditions. Five days later, leaves inoculated with conidial suspension showed black leaf spots resembling the disease in the field, whereas the control leaves remained symptomless. The fungal cultures isolated from the inoculated tissues, had identical morphology compared with the initial isolates. Colonies on PDA were 55-60 mm in diameter after seven days at 28°C, with undulate edges, pale brown, thick mycelia on the surface with black, gregarious conidiomata; and the reverse side was similar in color. Black conidia were produced after eight days of culture on PDA. Conidia were fusoid, ellipsoid, straight to slightly curved, 4-septate, ranged from 18.35 to 27.12 μm (mean 22.34 μm) × 4.11 to 7.03 μm (mean 5.41 μm). The basal cells were conic with a truncate base, hyaline, rugose and thin-walled, 4.35 to 6.33 μm long (mean 4.72 μm). Three median cells were doliform, 12.53 to 18.97 μm long (mean 15.26 μm), hyaline, cylindrical to subcylindrical, thin- and smooth-walled, with 2-3 tubular apical appendages, arising from the apical crest, unbranched, filiform, 14.7 to 25.3 μm long (mean 19.94 μm). The basal appendages were singlar, tubular, unbranched, centric, 3.13 to 7.13 μm long (mean 5.48 μm). Morphological characteristics of the isolates were similar to the descriptions of N. aotearoa (Maharachchikumbura et al. 2014). The rDNA internal transcribed spacer (ITS) region, translation elongation factor 1-αgenes (TEF), and beta-tubulin (TUB2) gene were amplified using the primer pairs ITS1/ITS4, EF1-728F/EF1-986R and T1/Bt-2b (Pornsuriya et al. 2020), respectively. The sequences of these genes were deposited in GenBank (ITS Accession Nos.: MT764947 and MT764948; TUB2: MT796262 and MT796263; TEF: MT800516 and MT800517). According to the latest classification of Neoprostalotiopsis spp. (Maharachchikumbura et al. 2014) and multilocus phylogeny, isolates HNPeHNLD2001 and HNPeHNLD2002 were clustered in the same branch with N. aotearoa. Thus, the pathogen was identified as N. aotearoa, which is different from N. cubana and N. formicarum reported in Thailand (Pornsuriya et al. 2020; Thaochan et al. 2020). The Neopestalotiopsis leaf spotdisease of rubber tree (H. brasiliensis) was one of the most serious and destructive leaf diseases in major rubber planting countries in Asia. ( Tajuddin et al. 2020) The present study of leaf fall disease on rubber tree caused byN. aotearoa is the first report in China. The finding provides the basic pathogen information for further monitoring the disease and its control.

Analysis on Digital Image Processing for Plant Health Monitoring

The country's ability to become self-sufficient in food production is becoming increasingly important. Agriculture is the primary occupation of a large portion of the population in equatorial countries like India, where the climate is ideal for the spread of plants. Pests and diseases are in control of about 25% of crop loss, according to a recent study released by the Food and Agriculture Organization. Black spot, leaf spot, rust, mildew, and botrytis blight are the most common plant diseases. Deep learning is a relatively new research technique for image processing and pattern recognition that has been proven to be highly productive in detection of plant leaf diseases.

PRESENCE OF FOLIAR DISEASES CAUSED BY FUNGI IN MANGROVES ON THE EAST COAST OF PENINSULAR MALAYSIA

Mangrove health is very important for the ecosystem to survive the challenges and threats due to climate change and anthropogenic pressures. However, unhealthy mangroves due to pathogenic fungi causing diseases may demote the survival rate of younger plants to grow and information on the status of foliar disease incidence is limited. This study aimed 1) to observe the foliar disease symptoms that occurred on Rhizophora apiculata and Avicennia marina and 2) to identify the fungi isolated from the symptomatic leaves. Samples were collected from the mangrove area located in Universiti Malaysia Terengganu (UMT) campus, along the South China Sea. All isolates were identified based on their morphological characteristics. A total of five foliar disease symptoms were observed namely black leaf spot, grey leaf spot, leaf rot, sunken leaf blight, and anthracnose. Rhizophora apiculata has a greater number of leaf spots than A. marina. Four genera of fungi; Pestalotiopsis sp., Curvularia sp., Colletotrichum sp. and Rhizopus sp. were successfully isolated from symptomatic leaves where the most dominant was Pestalotiopsis sp. to both mangrove species. This finding highlights the need to obtain the status of foliar diseases and their impact on the resilience of mangroves in Malaysia.

First Report of Neofusicoccum parvum Causing Leaf Spot on Geodorum eulophioides in China.

Geodorum eulophioides Schltr. is a critically endangered orchid listed in the International Union for Conservation of Nature (IUCN) Red List of threatened species. At present, only two natural populations were found in China. It has important scientific and ornamental values because of its uniqueness. During the summer of 2019, a black leaf spot disease occurred on G. eulophioides, in Yachang Orchid National Nature Reserve (E106°13'32″，N24°44'19″) in Guangxi province, China. More than 60% of leaves of these plants were infected. The disease symptoms initially appeared as small yellow circular spots, which enlarged into irregular brown spots (6 to 9 cm length and 3 to 5 cm width). In later stages of the disease development, the center of the spots became dark brown with a clear edge and surrounded by a yellow halo. In severe infections, the spots coalesced covering the entire leaf. Six symptomatic leaves were collected from three infected plants, surface sterilized in 75% ethanol for 15 s and 0.1% HgCl2 for 4 min, and subsequently washed three times with sterile water, then plated onto potato dextrose agar (PDA), and incubated at 28℃ for three days. Eighteen fungal cultures with similar morphological characteristics were obtained from the infected tissues. Colonies were initially white, then turned dark grey after nine days. To induce sporulation, isolates were grown on 2% water agar and incubated under UVA light at 28℃ for nine days. Three isolates were selected for morphological characterization. Conidia were hyaline, unicellular, nonseptate, ellipsoidal to fusiform, externally smooth, thin-walled, and ranged from 10.7 to 16.6 μm (avg. 13.8 μm) × 4.1 to 6.7 μm (avg. 5.1 μm) (n=50). The isolate DBL-1 was selected as a representative for molecular identification. Genomic DNA was extracted and used for PCR to amplify the rDNA internal transcribed spacer region (ITS), translation elongation factor 1-alpha gene (EF1-α), and beta-tubulin gene (TUB2), using the primer pairs ITS1/ITS4 (White et al., 1990), EF1-728F/EF1-986R（Alves et al. 2008；Carbone & Kohn, 1999）, and T1/T2 (O'Donnell et al., 1997), respectively. The obtained ITS sequence (GenBank Accession No. MN918440), EF1-α sequence (MN963815), and TUB2 sequence (MN963816) showed >99% homology with several GenBank sequences of Neofusicoccum parvum (JX513636, KU997497 for ITS, KU997261, MH252401 for EF1-α, and KJ841779, MK412882 for TUB2, respectively). Based on morphological characteristics of the asexual morph and maximum likelihood analyses of a combined rDNA-ITS, EF1-α and TUB2 gene sequences, was identified as N. parvum. Pathogenicity test was performed using isolate DBL-1 by inoculating 3 leaves of G. eulophioides plants. The test was repeated three times. Each leaf was wounded using a sterile needle, and a mycelial plug (6 mm diameter) harvested from the periphery of a 3-day-old colony grown on PDA was placed on each wound. Plants were then covered with plastic bags to maintain high relative humidity of 90% and kept at 28℃ in a greenhouse under natural daylight conditions. An equal number of leaves on the same plant were inoculated using sterile PDA plugs and served as mock inoculated controls. After three days, all the inoculated leaves showed black spot symptoms resembling those observed in the field, whereas controls remained symptomless. The fungus was re-isolated from the symptomatic leaves, thus completing Koch's postulates. N. parvum has been reported to cause leaf spot disease on Myristica fragrans (Jayakumar, et al., 2011), Ginkgo biloba (Mirhosseini, et al., 2014), Vitis heyneana (Wu, et al., 2015), and Hevea brasiliensis (Liu et al., 2017), respectively. To the best of our knowledge, this is the first report of N. parvum causing leaf spot disease on G. eulophioides in China. The disease control measures and in-situ conservation method need to be strengthened to protect this rare species.

First record of Septoria rudbeckiae on Rudbeckia in the United Kingdom

Species of Rudbeckia, often known as black-eyed Susan or coneflower, are used as bedding plants in UK gardens. The large, daisy-like flowerheads typically have bright yellow petals and a conspicuous black centre which may be raised into a cone shape. During the summer of 2016, Rudbeckia fulgida var. sullivantii cv. Goldsturm plants, purchased in the preceding May from a nursery in south-east England, were observed with black leaf spots in outdoor beds at the Royal Horticultural Society (RHS) Garden Wisley. Lower leaves exhibited small black lesions in July, which coalesced as the season progressed leading to complete necrosis of the bottom leaves and spotting on higher leaves. Spots showed no halos and became necrotic only later in the season. Flowering did not appear to be reduced. Pycnidia within the leaf spots were epiphyllous, 50-75 μm diameter, with a neck protruding slightly above the leaf surface. Conidia were filiform, 30-60 times 1.5-2 μm, with three septa. A single-spore isolate was obtained on water agar and cultured on potato dextrose agar. Living cultures were deposited in the RHS culture collection held at RHS Garden Wisley (Accession No. RHS454672) and at Westerdijk Fungal Biodiversity Institute, Netherlands (Accession No. CBS145765). The internal transcribed spacer (ITS) region of rDNA, the β-tubulin (Btub) gene and the translation elongation factor 1-alpha (EF1) gene were amplified using the primers ITS4:ITS5, T1:B-Sandy-R, and EF1-728F:EF2, respectively, according to the method by Verkley et al. (5). The DNA amplicons were sequenced (GenBank Accession Nos. MN093336 (ITS), MN105980 (Btub) and MN166626 (EF1)). The ITS sequence differed by one base pair from the only ITS sequence available for Septoria rudbeckiae (JQ677043). No previous sequences were available for comparison for Btub and EF1 and none of the available sequences had more than 90% identity. Pathogenicity was confirmed by spraying Rudbeckia fulgida sullivantii ‘Goldsturm’ plants with a conidial suspension (1 × 106 conidia/ml) prepared from spores from 21-day-old cultures on potato dextrose agar, incubated at 20°C with a 12 hr light/ 12 hr dark cycle. Plants were kept in high humidity for 72 hr after inoculation. After four weeks, black lesions were observed on leaves. Pycnidia and conidia consistent with S. rudbeckiae were found within each lesion. Control plants sprayed with sterilised water showed no symptoms. Septoria rudbeckiae was described from the USA (Ellis & Halsted, 1) where it is now widespread causing disfigurement of Rudbeckia in gardens. Although the fungus has been recorded from a number of different Rudbeckia species, Rudbeckia fulgida var. sullivanti cv. Goldstrum has been recognised in the USA as one of the most susceptible cultivars. Septoria rudbeckiae has also been reported from Canada, Bulgaria and Romania (Farr & Rossman, 2), Turkey (as Septoria sp.; Gumrukcu, 3) and Korea (Park, 4). To our knowledge, this is the first report of S. rudbeckiae in the United Kingdom. The authors would like to thank Jane Renshaw for aid in preparation of fungal cultures.

Morphological and SSR marker-based genetic diversity analysis of Indian mustard (Brassica juncea L.) differing in Alternaria brassicicola tolerance

Alternaria black leaf spot disease of oilseed mustard is a primary cause of yield penalty not only in India but also throughout the world. To assess the degree of tolerance, 47 Indian mustard (Brassica juncea) genotypes were evaluated based on the performance against the causal pathogen Alternaria brassicicola. Genotypes were divided into six tolerance groups including resistant, highly tolerant, moderately tolerant, moderately susceptible, susceptible, and highly susceptible, keeping the nonhost resistant Sinapis alba as resistant control. Genotypes EC399312 and PAB-9511 were found to be the most tolerant. Fourteen morphological traits were evaluated which revealed considerable morphological variability among the genotypes. A number of seeds/siliqua and 1000 seed weight were positively correlated with yield per plant. Insignificant negative correlations had been found among plant height, days to maturity, and disease resistance with yield per plant. Correlation data indicate that seeds/siliqua and siliqua on the main shoot can be highly effective for higher grain yield. Genetic diversity of all genotypes was evaluated using simple sequence repeats (SSR) markers. The genotypes were evaluated for polymorphisms after amplification with 41 SSR primer pairs. Nineteen SSR markers in total were found to be highly informative with a polymorphic information content value > 0.50. The evaluation of genetic similarity and cluster analysis together with disease resistance provides some useful guides for assisting plant breeders in selecting suitable genetically diverse parents for the crossing program as well as for the development of mapping population.

Occurrence of black leaf spot caused by Alternaria alternata on Korla fragrant pear in Xinjiang of China

Occurrence of black leaf spot caused by Alternaria alternata on Korla fragrant pear in Xinjiang of China

First Report of Leaf Black Spot on White Chrysanthemum (Chrysanthemum morifolium) Caused by Phoma bellidis in China

First Report of Leaf Black Spot on White Chrysanthemum (<i>Chrysanthemum morifolium</i>) Caused by <i>Phoma bellidis</i> in China

Characterization of Alternaria brassicae causing black leaf spot disease of cabbage (Brassica oleracea var. capitata) in the southern part of Kazakhstan

Cabbage plants showing symptoms of leaf spot were detected from various fields in the Almaty region of Kazakhstan in the winter seasons of 2015 and 2016. The disease incidences of approximately 50% were recorded in various fields visited in the Almaty region. The pathogen was aseptically isolated from the symptomatic leaves and maintained in an in vitro culture media. Morphological characteristics and sporulation of the fungus was determined under both light and electron microscopy. The extracted genomic DNA of the fungi was subjected to Polymerase Chain Reaction (PCR) using ABCsens/ABCrev and ITS1/ITS4 primers amplifying ABC transporter (Atr1) gene and the internal transcribed spacer regions, respectively. The amplified products of PCR were sequenced, aligned, blasted and compared for similarity with other species in the NCBI GenBank. The cluster analysis result showed 99% homology with related fungi retrieved from the NCBI GenBank for the ITS region. The fungal isolate was pathogenic towards twenty-two-day-old plants, namely, Brassica oleracea, Lycopersicon esculentum, Solanum melongena, and was established as the causal agent of leaf spot on these plants. This is the first record implicating A. brassicae for black leaf spot disease of cabbage in Kazakhstan.

Unique gene Pmhyp controlling melanization of pycnidia in Phoma medicaginis

Phoma medicaginis (syn. Ascochyta medicaginicola Qchen & L. Cai) causes spring black stem and leaf spot of alfalfa and the model legume Medicago truncatula. Phoma medicaginis produces uninucleate conidia in melanized pycnidia and is genetically tractable through Agrobacterium tumefaciens-mediated transformation (ATMT), which can result in insertional mutants. One T-DNA-tagged mutant, P1A17 produced conidia in non-melanized (hyaline) pycnidia. Pycnidial melanization recovered if the mutant was supplemented with melanin precursors or allowed to age. DNA sequences flanking the insertion did not predict any disrupted open reading frames (ORF) unless a Coccidioides prediction algorithm was used. Pmhyp gene was expressed in the wild type, but not the mutant, and has not been annotated in any genomes, to date. Expression of two conserved genes flanking the T-DNA disrupted Pmhyp was unchanged from the wild type. Knockout of Pmhyp strain displayed same cultural phenotype (non-melanized pycnidia). Complementation of Pmhyp strains with wild type PmHYP partially recovered pycnidial melanization. Both knockout and complementation transformants were confirmed using RT-PCR and southern blot analysis. Taken together, PmHYP appears to be a novel regulator of pycnidium specific melanization.

Evaluation of virulence and pathogenicity of Alternaria patula on French marigold (Tagetes patula)

Alternaria patula, the cause of French marigold leaf black spot and flower blight, was first isolated from seeds of French marigold cv. Queen Sophia. It is described as a new species of Alternaria and has a considerable morphological variation with a preferential pathogenicity to Asteraceae, Solanaceae and Cucurbitaceae plants. Alternaria patula produces an array of pectin depolymerases that can break 1,4‐α‐glycosidic bonds either by hydrolysis of polygalacturonases (PG, E.C. 3.2.1.15) or via trans‐elimination of pectate lyases (PL, E.C. 4.2.2.2) and pectin lyases (PNL, E.C. 4.2.2.10). This study is the first to emphasize the variability and significance to pathogenesis of the pectinolytic enzymes of A. patula that target various pectic polymers structures during host tissue invasion. Alternaria patula also produced zinniol derivatives as non‐host‐specific toxins (nHSTs), albeit without phytotoxic symptoms in French marigold. The management of Alternaria blight caused by A. patula via the application of pyrifenox and antagonistic Bacillus amyloliquefaciens effectively reduced disease severity, without adverse effects on French marigold in both in vitro and in vivo bioassays.

First Report of Alternaria steviae Causing Black Leaf Spot of Stevia in China

First Report of <i>Alternaria steviae</i> Causing Black Leaf Spot of Stevia in China

Time-course metabolic profiling in alfalfa leaves under Phoma medicaginis infection.

Information on disease process and pathogenicity mechanisms is important for understanding plant disease. Spring black stem and leaf spot caused by the necrotrophic pathogen Phoma medicaginis var. medicaginis Malbr. & Roum causes large losses to alfalfa. However, till now, little is known about alfalfa-P. medicagnis interactions and the pathogenicity mechanisms of the pathogen. Here, alfalfa inoculated with P. medicaginis was subjected to GC-MS based metabolic profiling. The metabolic response in P. medicaginis-inoculated and mock-inoculated alfalfa leaves was assessed at 2, 4, 6, 8, 12, 16, 20, 24, 26 and 28 days post inoculation. In total, 101 peaks were detected in the control and inoculated groups, from which 70 metabolites were tentatively identified. Using multivariate analysis, 16 significantly regulated compounds, including amino acids, nitrogen-containing compounds and organic acids, polyols, fatty acids, and sugars were tentatively identified (Variable importance values, VIP>1.0 and p <0.05). Among these metabolites, the levels of malate, 5-oxoproline, palmitic acid and stearic acid were increased significantly in P. medicaginis-infected alfalfa leaves compared to the controls. In contrast, the levels ofγ-aminobutyric acid and 2-pyrrolidinone were significantly decreased in infected leaves compared to the controls. Further metabolic pathway analysis of the 16 significantly regulated compounds demonstrated that glycolysis, the tricarboxylic acid cycle, and β-oxidation of fatty acids were significantly induced in the alfalfa leaves at later stages of P. medicaginis infection. The strong induction of tricarboxylic acid cycle pathways at later infection stages caused by the pathogen may induce senescence in the alfalfa leaves, leading to plant death. However, intermediate metabolites of these metabolic pathways, and inositol phosphate, glutathione, the metabolic pathways of some amino acids accumulated rapidly and strongly at early stages of infection, which may enhance the ability of alfalfa to resist necrotrophic P. medicaginis disease. Understanding metabolic pathways is essential for understanding pathogenesis.