Alternaria Leaf Spot Research Articles

Biological Control of Alternaria Leaf Spot Caused by Alternaria spp. in Jerusalem Artichoke (Helianthus tuberosus L.) under Two Fertilization Regimes.

The objectives of this study were to evaluate the efficacy of integrating resistant genotypes of Jerusalem artichoke with Trichoderma harzianum isolate T9 to control Alternaria leaf spot caused by Alternaria spp. under two fertilization regimes and to determine whether T9 application induced chitinase and β-1,3-glucanase activity in Jerusalem artichoke leaves. Six Jerusalem artichoke varieties (resistant varieties JA15, JA86, and JA116 and susceptible varieties HEL246, HEL293, and JA109) and three disease control methods (a non-inoculated control, application of T. harzianum T9, and fungicide sprays (propiconazole at a rate of 30 mL/20 L of water, 375 ppm)) was conducted in two separate trials (different fertilization regimes) at the experimental farm of the Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand. Resistant genotypes controlled Alternaria leaf spot effectively. Application of Trichoderma showed low efficacy to control Alternaria leaf spot, but in specific susceptible genotypes—HEL246 and HEL293—the application of Trichoderma could reduce disease severity up to 10%. The application of Trichoderma was associated with a rise in production of chitinase and β-1,3-glucanase in HEL246 seedlings. The number of Trichoderma propagules in soil, as well as the extent of colonization of roots and leaves, were monitored. The results indicated that application of Trichoderma had higher propagules than non-inoculated control. Neither varietal resistance nor the disease control methods used in this study impacted the yield or yield components of Jerusalem artichoke.

First Report of Leaf Spot Caused by Alternaria alternata on Ginseng (Panax ginseng) in China

Ginseng (Panax ginseng) is a perennial herbaceous plant and a precious traditional Chinese medicine. P. ginseng is widely cultivated in Asia, particularly the Changbai Mountain area in China (Wang et al. 2019). Alternaria species can grow under a wide range of temperatures that occur worldwide (Konstantinova et al. 2002). Alternaria panax was reported as the main cause of Alternaria leaf spot of ginseng (Deng et al. 2013); however, a small-spored Alternaria species was isolated from leaf spot symptoms during recent surveys. In our study, leaf spot disease of P. ginseng was observed during 2017 in the Fusong district, Jilin, China. The disease was widespread, with 20 to 30% of the fields affected. Leaves of the affected plants showed brown to black necrotic spots. The fungus was isolated from symptomatic leaves on potato dextrose agar and characterized morphologically under the microscope. Colonies of pure cultures were initially dark brown and then turned black after 7 days. Strains (TCS 15013001 and TCS 15013002) were grown on water agar embedded with surface-sterilized ginseng spot tissues under a 12/12-h light/dark cycle at room temperature. Conidia observed on the lesions were dark brown or olive-brown, ovoid or ellipsoid, short beaked, with three to seven transverse and zero to five longitudinal septa, and 14.9 to 36.5 μm (average 25.8 μm) × 5.8 to 17.9 μm (average 12.5 μm). Based on its morphological characteristics, the pathogen was identified as Alternaria sp. (Simmons 2007). Single-spore cultures were obtained, and their genomic DNA was extracted. The rDNA internal transcribed spacer (ITS, GenBank accession nos. MN394879 and MN394880), endopolygalacturonase (endoPG, MN410909 and MN410910), Alternaria major allergen (Alta1, MN410911 and MN410912), and the portion of the histone 3 (H3, MN410913 and MN410914), elongation factor 1-alpha (EF1-α, MN410915 and MN410916), the RNA polymerase II 2nd largest subunit (RPB2, MN410917 and MN410918), and glyceraldehyde 3-phosphate dehydrogenase (gpd, MN410919 and MN410920) gene were amplified from the two isolates, respectively (Woudenberg et al. 2015). Sequence analysis of the two isolates showed 99 to 100% identity to that of A. alternata (MG182428 for ITS, MG598798 for endoPG, MG598796 for Alt a1, MG182429 for H3, KU738723 for EF1-α, KU738707 for RPB2, and KP851761 for gpd). Pathogenicity tests were conducted in a greenhouse. Sixty healthy 2-year-old P. ginseng seedlings grown in potting medium were tested in a greenhouse at 20/26°C and about 90% relative humidity with natural light. Of the plants, 30 were sprayed with spore suspension (1 × 10⁵ spores/ml) until most of the leaves were wet. Control treatments (30 plants) were treated with distilled water. The two isolates were tested, and all test plants were covered with clear plastic bags for 3 days to increase humidity. Each treatment had three replicate plants. Six days after inoculation, leaf spots similar to the original ones developed at inoculation sites for all isolates, and A. alternata was consistently reisolated from the induced symptoms. The pathogenicity test was performed three times. A. alternata causing leaf spot of American ginseng was reported in China (Hill and Hausbeck 2008). Also, leaf spot of Panax notoginseng caused by A. alternata was reported in China (Yang et al. 2018). To our knowledge, this is the first report of A. alternata on P. ginseng in China.

Diversity and occurrence of major diseases of vegetables and fruit crops during spring season at Aanbukhaireni rural municipality of Tanahun district, Nepal

A survey has been conducted to assess the diversity and occurrence of major vegetables and fruits cultivated in Aanbukhaireni rural municipality of Tanahun district, Nepal during spring season of 2019.The surveyed areas were Satrasayaphant, Baradiphant and Dumridanda villages of ward no 1, Yeklephant, Markichowk and Pateni villages of ward no2 , Gaadapani village of ward no 3, Saakhar village of ward no 4 and Ghummaune village of ward no. 5. The surveyed area consists of upper tropical and sub tropical climate. The total no of farmers field selected for the survey was 34, 32, 24, 17 and 21 from ward no 1,2,3,4 and 5 respectively.The major vegetables cultivated during survey period in the surveyed area were bean, bitter-gourd, brinjal, chilli, cowpea, cucumber, okra, pumpkin, sponge-gourd, tomato, snake-gourd and bottle-gourd. Similarly, the fruits found in the region were banana, papaya, grapes, mango, litchi, peach, guava, lemon, mandarin orange etc. The major diseases of vegetables noticed were early blight, late blight, cercospora leaf spot, powdery mildew, downey mildew, fruit rot, bacterial wilt, bacterial spot, leaf curl and mosaic. In case of fruits, sigatoka leaf spot, panama wilt, black rot, algal leaf spot, canker, root rot, foot rot, sooty mold, red rust, anthracnose, rust, mosaic, alternaria leaf spot, downey mildew and leaf curl were the major diseases. The higher disease incidence (70%) and severity (48%) in vegetables were recorded in ward no 2 where as the lower incidence (45.2%) and severity (37.71%) were found in ward no 4. Similarly, the higher fruit disease incidence (70.24%) and severity (51.27%) in ward no 1 followed by ward no 2 with disease incidence and severity of 66.79% and 45.14% respectively. The reasons for those results are low educational level, lack of best bet technology, no proper irrigation and fertilizer, unavailability of pesticides for controlling the diseases. This study will be useful to identify the major diseases of vegetables and fruits of terai and inner terai region of Nepal and applying control measure, looking for the best possible solutions.

First Report of Alternaria Leaf Spot Caused by Alternaria tenuissima on Sugar Beet (Beta vulgaris) in Minnesota, U.S.A.

Minnesota is the top sugar beet (Beta vulgaris L.) producing state in the United States. In September 2018, foliar symptoms were first observed on older sugar beet leaves in about 3% of the cultivars in a coded variety trial in Renville (N 44.78, W –95.15), Minnesota. Symptoms were dark brown circular or irregular spots on healthy plants. Initially, the lesions were confined within distinct parallel veins of the leaves but eventually expanded and coalesced across veins. In severely affected plants, the entire symptomatic leaves died. Small square pieces (5 mm²) from the margin of lesions were excised with a sterile scalpel, surface sterilized with 70% ethanol for 1 min, rinsed thrice with sterile distilled water, air dried, transferred to potato dextrose agar, and incubated at 25°C with a 12-h photoperiod for 7 days. A colony that had white-brown velvety mycelia grew on the medium. Suspect isolates were further purified using a single-spore isolation method (Choi et al. 1999). Isolates were the same morphologically. Conidia were club-shaped, four to seven transverse septa, one to three longitudinal septa, and pale brown, with a beak-like apical cell, often in long chains or solitary. Conidia dimensions were 28 to 54 × 4.5 to 6 µm, and beaks when present were 2 to 4 µm (Kou et al. 2014). Based on the morphological characters, the fungus was tentatively identified as Alternaria species (Simmons 2007; Woudenberg et al. 2015). Fungal genomic DNA was extracted from two representative isolates using a Qiagen kit followed by PCR amplification with internal transcribed spacer (ITS) ITS 1/ITS 4 primers. The amplified PCR products were cleaned and sent for Sanger sequencing by GenScript (Piscataway, NJ). Isolates 1422F (GenBank accession MK611645) and 1424F (MK611649) had 98 and 100% sequence identity with Alternaria tenuissima (GenBank accessions MF373440 and MH374277), respectively (Ziedan et al. 2018). Pathogenicity testing was conducted by spraying a conidial suspension (5 × 10⁵ conidia/ml) onto 14-leaf growth stage sugar beet plants (Crystal Beet Seed proprietary material). Mock-inoculated plants were sprayed with autoclaved water as a control. Plants were kept at 25°C and 75 to 85% relative humidity in a humidity chamber for 7 days and then transferred to a greenhouse kept at 23 ± 2°C and a 12-h photoperiod. Plants were watered daily. The experiment was done twice with four replicates and 10 plants per replicate. Two weeks postinoculation, about 30% of the inoculated leaves were infected and started to display irregular to circular lesions as observed in the field. No symptoms were observed on the control plants. The fungus was reisolated from diseased leaf tissues as described above, and macroscopic and microscopic analysis indicated the similar white-brown colony morphology and conidial structure, respectively. Genomic DNA was extracted from a single isolate as described above. Molecular detection performed using the same primers further confirmed that the isolate (MN384262) was 100% similar to A. tenuissima (GenBank accession MK611651). A. tenuissima has the potential to become a problem if susceptible varieties are grown over large production areas. Alternaria leaf spot on sugar beet has been reported in California (French 1989) and Michigan (Rosenzweig et al. 2019), where the disease has been associated with economic loss since 2015. To our knowledge, this is the first report of A. tenuissima causing leaf spot disease on sugar beet in Minnesota, U.S.A.

Nested PCR assay for specific and sensitive detection of Alternaria carthami.

Alternaria leaf spot (ALS) caused by Alternaria carthami Chowdhary is one of the major threats to the cultivation of safflower in the world. The pathogen is seed borne and requires early detection for restricting its transmission and proliferation. A PCR-based diagnostic assay was developed for easy, quick and reliable detection of A. carthami in infected seeds and leaf samples of safflower. A primer set, AcSPF and AcSPR was designed using ribosomal internal transcribed spacer regions of A. carthami that consistently produced a distinct amplicon of 340bp with DNA extracted from thirty A. carthami isolates. The specificity of the primer was confirmed using strains of 26 other strains of Alternaria and four other fungal pathogens of safflower. The sensitivity of detection was further enhanced from concentration of 100pg by simple PCR to as low as 10pg fungal DNA by a nested PCR assay using ITS and AcSPF and AcSPR primers. The primer pair also facilitated detection of A. carthami in infected seeds and leaf samples. The study provides an accurate and sensitive diagnostic tool for detection of A. carthami.

Fungal Disease in Cotton Leaf Detection and Classification using Neural Networks and Support Vector Machine

Agriculture productivity is the main factor for improving economic status of India. Reduction in production rate is mainly due to various diseases in plants. Identification of plant disease in early stage is the main challenge for improving the production rate as well as economic status. This paper presents automatic disease detection in cotton crop for three types of diseases Alternaria Leaf Spot Fungal Disease (ALSFD), Grey Mildew Cotton Disease (GMCD), and Rust Foliar Fungal Disease (RFFD). The K-means clustering algorithm is used for disease segmentation for cotton leaf. The diseased cluster is segmented into three clusters. From cluster 2 the features Mean , Contrast, Energy, Correlation, Standard Deviation, Variance , Entropy, and Kurtosis are extracted. The extracted features for 30 samples are given to Artificial Neural Network (ANN) and Support Vector Machine (SVM) classifiers for disease classification. The performance of these classifiers are compared. The ALSF disease is classified 77.4% for ANN and 84.3% for SVM, GMC disease is 87.8% for ANN and 98.7% in SVM, RFF disease is 90.1%for ANN and 93.2% for SVM. The overall average accuracy of ANN classifier is 85.1% for three diseases and overall average accuracy for SVM is 92.06% for three diseases. It is clearly observed from the analysis SVM classifier gives accurate disease detection compared to ANN.

First Report of Alternaria alternata Causing Leaf Spot on Spinach (Spinacia oleracea) in Italy

Spinach (Spinacia oleracea L.) is widely cultivated in many countries and is affected by a complex of foliar diseases (Correll et al. 1994). During March 2018, disease symptoms were observed on 15 to 30% of leaves of 90-day-old spinach cultivar Matador plants grown for the fresh market, at a density of 80 to 90 plants/m², in an open field of approximately 0.5 ha in Cuneo province in Piedmont, northern Italy. Symptoms first appeared on the basal and middle leaves as small circular spots (1 to 3 mm), developing as concentric rings, which were dark brown in color, and each spot was surrounded by a chlorotic halo. As the disease progressed, lesions expanded, sometimes covering the entire leaf surface. Small pieces (1 to 2 mm) of affected leaf tissues were surface sterilized in 1% sodium hypochlorite for 1 min, rinsed in sterile water, and plated on potato dextrose agar amended with 25 mg of streptomycin sulfate per liter. Alternaria sp. was consistently isolated from lesions on 15 plants after 4 days of incubation of the leaf sections at 22°C (Simmons 2007). Ten-day-old monoconidial cultures of AltSpin2-18, selected as representative of 10 morphologically similar isolates grown on potato carrot agar, produced chains of 10 to 13, multicellular, obclavate to obpyriform conidia measuring 14.7 to 41.0 µm (average 27.1 µm) in length and 7.2 to 12.1 µm (average 9.6 µm, n = 40) in width, with zero to three longitudinal and two to five transverse septa. When present, the beak measured 1.3 to 8.3 µm in length. Genomic DNA was extracted from the isolate AltSpin2-18, and the following genes were amplified: internal transcribed spacer (ITS) region of rDNA, endopolygalacturonase (endoPG) gene, β-tubulin (tub2) gene, and histone 3 (H3) (Woudenberg et al. 2015). Polymerase chain reaction products were sequenced at the BMR Genomics Centre (Padova, Italy). A BLASTn search of the sequences showed 100% identity to the ITS rDNA region of Alternaria alternata KX343153 and several other Alternaria spp. Moreover, the AltSpin2-18 isolate showed 100% sequence identity to A. alternata AB047682 (endoPG), MH521955 (tub2), and MF070866 (H3). The sequences of the AltSpin2-18 isolate were deposited to GenBank with accession numbers MK078634 (ITS rDNA), MK085978 (endoPG), MK085977 (tub2), and MK085979 (H3). The overall sequence analysis of these four loci assigned the species to A. alternata. Pathogenicity tests were performed by spraying leaves of 30-day-old healthy cultivar Matador plants grown in six pots (10 plants/pot) with a suspension (10⁶ conidia/ml) of AltSpin2-18. Plants sprayed with sterile water served as a control. Plants were covered with plastic bags for 5 days after inoculation at 19 to 22°C and maintained in a greenhouse. Lesions similar to those observed in the field first developed on leaves 6 days after inoculation, resulting in 50 to 60% disease severity 20 days after inoculation, whereas control plants remained healthy. Alternaria sp. morphologically identical to the original isolate was reisolated consistently (100% frequency) from the inoculated plants. Two independent replication runs of the pathogenicity tests provided the same results. Alternaria leaf spot caused by A. alternata on S. oleracea has been reported in the Kingdom of Saudi Arabia (Marraiki et al. 2012), Poland, India, and China (Farr and Rossman 2019). To our knowledge, this is the first report of A. alternata causing leaf spot on S. oleracea in Italy. The disease could become a significant problem owing to the importance of the crop in Italy, covering approximately 5,540 ha in open field production and 43,141 ha under protection.

Incidence and severity of fungal diseases of safflower in India

Field surveys were conducted in two major safflower growing states of India for two consecutive cropping seasons (2015-16 and 2016–17). A total of 872 fields spanning 22 districts of Karnataka and Maharashtra were examined to determine the occurrence and distribution of various fungal diseases on safflower. Safflower fields were found to be infested by four fungal diseases, namely Alternaria leaf spot, Fusarium wilt, Cercospora and Ramularia leaf spot. Among these, Alternaria leaf spot and Fusarium wilt were most widespread and found in all the districts investigated, while Ramularia leaf spot was confined to the districts of Karnataka. The disease prevalence, incidence and severity varied among districts, cropping seasons, with sowing periods and cropping patterns. The first survey recorded higher disease in both states. In both cropping seasons, Karnataka showed higher disease parameters compared to Maharashtra. District Dharwad (Karnataka) exhibited the maximum mean disease incidence for both Alternaria leaf spot and Fusarium wilt (55.41% and 41.42%) among all the districts. The disease prevalence was less in fields with late as compared to early sown crops. Intercropping with chickpea, cotton, sorghum alone and chickpea and sorghum together decreased disease prevalence in comparison to monocrop fields of safflower. This is the first comprehensive survey reporting the distribution of fungal diseases on safflower in India. The study encourages agriculturalists to adopt cultural practices such as late sowing and intercropping with chickpea and sorghum as an effective management strategy for reducing disease in safflower.

Fungicide Sensitivity Monitoring of Alternaria spp. Causing Leaf Spot of Sugarbeet (Beta vulgaris) in the Upper Great Lakes.

Alternaria leaf spot (ALS), caused by Alternaria spp., can occur wherever sugarbeet is grown. Infection by Alternaria spp. and disease management has historically been considered a minor issue in sugarbeet production in the United States. An increase of both incidence and severity in 2016 of ALS high enough to cause yield loss has been observed in Michigan. With a renewed need to consider potential management of this disease, the sensitivity was determined for populations of Alternaria spp. to three classes of fungicides currently labeled for management of leaf spot on sugarbeet, including demethylase inhibitor (DMI), quinone outside inhibitor (QoI), and organo-tin fungicides. Leaves with symptoms of ALS were sampled from sugarbeet fields in east-central Michigan and southwestern Ontario, Canada. Monoconidial isolates were obtained to determine sensitivity to each fungicide class above. A spiral gradient dilution method was used to estimate the fungicide effective concentration (in milligrams per liter) that caused a 50% inhibition of fungal growth in vitro for all isolates. Significant temporal shifts were detected in the frequencies of sensitivity phenotypes to DMI and QoI but not organo-tin fungicides from 2016 through 2017. Individual isolates of Alternaria spp. were recovered with cross-resistance to DMI and multiple resistance to DMI, QoI, and triphenyltin hydroxide fungicides. To our knowledge, this is the first report of a fungus other than Cercospora beticola with resistance to organo-tin fungicides. Fungicide sensitivity monitoring indicates that an effective integrated disease management approach combining fungicide efficacy trials and monitoring pathogen biology is essential for developing effective resistance management recommendations.

QoI Fungicide Resistance Mutations in Alternaria solani and Alternaria alternata are Fully Established in Potato Growing Areas in Bavaria and Dual Resistance against SDHI Fungicides is Upcoming

Alternaria leaf spots caused by Alternaria solani and Alternaria alternata are a major foliar disease of potatoes. Reduced sensitivity of A. solani and A. alternata towards Quinone outside inhibitors (QoI) fungicides has been observed in Europe. QoI-insensitive A. alternata isolates carry a G143A amino acid exchange caused by a single nucleotide polymorphism (SNP) in the cytochrome b gene. A. solani evolved a similar F129L mutation. A shift from the predominant A. solani genotype I to genotype II, which was exclusively associated with the F129L mutation, was observed in Germany after QoI approval for Alternaria control. Here, we found QoI mutations to be highly abundant in A. solani and A. alternata field isolates, collected in 2016 in Bavaria, located in southeastern Germany. The frequency of the F129L mutation, but not of A. solani genotype II, was higher than in the last available study. This might be due to that we also found the F129L mutation in genotype I, indicating QoI resistance progression through the previously unaffected genotype. In contrast to previous data, QoI mutations were present in all examined areas. An analysis of SNP diversity pointed to the region of Lower Bavaria as a hotspot for F129L mutation evolution. Reduced sensitivity of Alternaria spp. towards succinate dehydrogenase inhibitors (SDHI) fungicides is an emerging issue in Europe. We observed the presence of SDHI mutations, but only in combination with QoI mutations, indicating a further adaption to applied fungicides and a selection for dual fungicide resistance.

OCCURRENCE OF ALTERNARIA LEAF SPOT DISEASE ON ALOE VERA AND ITS MANAGEMENT

Aloe vera is a valuable medicinal crop of the world. It suffers from several diseases but among them alternaria leaf spot and dry rot is most serious fungal disease which effects the commercial production and quality losses to Aloe vera. A survey was conducted to estimate the prevalence of dry rot disease in different nurseries located in urban areas of Faisalabad. During this survey maximum disease incidence was recorded in Horti club nursery (100%) and minimum disease incidence recorded at Faiz baho nursery and Qadir baksh form (13.8%). Among in-vitro tested fungicides Score gives maximum mycelial growth inhibition (89.5%) and maximum disease control (17.7%) as compared to control and other tested chemicals. Among in-vitro tested plant extracts Neem gives maximum mycelial growth inhabitation (41.2%) and in green house gives 14.2% disease control. Out of four tested fungicides and plant extracts Score and Neem gives best results against A. alternata mycelial growth and disease control.

Variability of Alternaria Leaf Spot Resistance in Jerusalem Artichoke (Helianthus tuberosus L.) Accessions Grown in a Humid Tropical Region

Alternaria leaf spot is an emerging disease of Jerusalem artichoke (Helianthus tuberosus L.) in tropical regions. The lack of known resistant germplasm sources is an important constraint to development of Jerusalem artichoke varieties with resistance to Alternaria leaf spot. The objectives of this study were to identify variability of Jerusalem artichoke genotypes for resistance to Alternaria leaf spot under field conditions and to investigate the relationships among resistance characters, yield, and yield components for selection of resistant varieties. Ninety six accessions of Jerusalem artichoke were evaluated in replicated trials under field conditions in early rainy and late rainy seasons in Khon Kaen, Thailand during 2014. Parameters evaluated included disease incidence, disease score, disease severity index, area under disease progress curve of disease incidence, area under disease progress curve of disease severity index, number of tubers/plants, tuber size, and fresh tuber yield. The genotypes HEL 335, HEL 256, HEL 317, HEL 308, and JA 86 were identified as sources of leaf spot resistance in both seasons. These genotypes can be used as sources of leaf spot resistance for Jerusalem artichoke breeding programs. HEL 293 and HEL 246 showed susceptibility to leaf spot disease in both seasons and should be used as standard susceptible checks.

Fungicidal protection of sunflower against the main leaf diseases

Goal. To determine the technical efficiency of the novel fungicides against the diseases of leaves sunflower and to establish the optimal terms of fungicidal treatments for the zone of the Right Bank Forest-steppe of Ukraine.
 Research methods. Field and laboratory. The research was conducted during 2014—2017 in the Right-bank Forest-steppe of Ukraine (Khmelnytsky region) on the Canyon hybrid investigated the effect of fungicides Pictor, SC (0.5 l / ha), Retengo, EC (0.75 l / ha), Amistar Extra 280 SC, SC (0.75 l / ha) was investigated. The treatments were carried out in two terms: once — on 32 and 53 stages on the BBCH scale and twice — at the same terms. The records were performed before application and on the 15th and 30th day after it. The observations were conducted according to generally accepted methods; the incidence and severity of diseases, technical efficiency were determined.
 Results. It was determined that crops annually struck affected leaf disease Alternaria and Septoria. The highest development was recorded for alternaria leaf spot — 22.5%. For both single and double spraying, the highest level of protection against septoria leaf blotch was observed for the application of Amistar Extra 280 SC, SC (0.75 l / ha), while Pictor, SC (0.5 l / ha) was more efficient against alternaria leaf spot.
 Conclusions. Te two-fold application of fungicides is more effective, it reduces the development of leaf diseases by 78—96% and preserves the crop within 0,41—0,53 t / ha. Among the studied fungicides, Pictor, EC and Amistar Extra 280 SC, SC showed superior efficacy for all investigated terms.

An Improved Crop Scouting Technique Incorporating Unmanned Aerial Vehicle-Assisted Multispectral Crop Imaging into Conventional Scouting Practice for Gummy Stem Blight in Watermelon.

Multispectral imaging is increasingly used in specialty crops, but its benefits in assessment of disease severity and improvements in conventional scouting practice are unknown. Multispectral imaging was conducted using an unmanned aerial vehicle (UAV), and data were analyzed for five flights from Florida and Georgia commercial watermelon fields in 2017. The fields were rated for disease incidence and severity by extension agents and plant pathologists at randomized locations (i.e., conventional scouting) followed by ratings at locations that were identified by differences in normalized difference vegetation index (NDVI) and stress index (i.e., UAV-assisted scouting). Diseases identified by the scouts included gummy stem blight, anthracnose, Fusarium wilt, Phytophthora fruit rot, Alternaria leaf spot, and cucurbit leaf crumple disease. Disease incidence and severity ratings were significantly different between conventional and UAV-assisted scouting (P < 0.01, Bhapkar/exact test). Higher severity ratings of 4 and 5 on a scale of 1 to 5 from no disease to complete loss of the canopy were more consistent after the scouts used the multispectral images in determining sampling locations. The UAV-assisted scouting locations had significantly lower green, red, and red edge NDVI values and higher stress index values than the conventional scouting areas (P < 0.05, ANOVA/Tukey), and this corresponded to areas with higher disease severity. Conventional scouting involving human evaluation remains necessary for disease validation. Multispectral imagery improved watermelon field scouting owing to increased ability to identify disease foci and areas of concern more rapidly than conventional scouting practices with early detection of diseases 20% more often using UAV-assisted scouting.

Etiology of Alternaria Leaf Spot of Cotton in Southern New Mexico.

Alternaria leaf spot (caused by Alternaria spp.) is one of the most common foliar diseases of cotton (Gossypium spp.) and occurs in most cotton-growing regions of the world. In surveys of commercial cotton fields, Alternaria leaf spot has increased in prevalence and incidence in southern New Mexico due to favorable environmental conditions in recent years. Incidence, severity, and etiology of leaf spot of cotton in southern New Mexico were determined. Fourteen cotton fields with plants exhibiting leaf spot symptoms were evaluated in October and November 2016, when plants were at late growth stage. Disease incidence was 100% in 13 of the fields, and averaged 70% in the 14th field. Average disease severity index for all fields ranged from 21.5 to 87.0. For identification of the causal agent, 14 isolates (one from each field) were characterized based on morphological features and PCR using universal primers ITS4/ITS5 and primers targeting the plasma membrane ATPase gene. Colonies of all 14 isolates were olive green with distinct white margins and relatively small spores when compared with reference isolates of large-spored species. All 14 isolates were identified as A. alternata. The fungus grew on potato dextrose agar from 5 to 35°C, and optimum growth occurred at temperatures between 20 and 30°C. Cotton plants inoculated with selected isolates of A. alternata displayed symptoms similar to those observed under field conditions. This is the first report of A. alternata as a causal agent of Alternaria leaf spot on cotton in southern New Mexico.

Alternaria leaf spot of cotton seedlings grown in New South Wales, Australia is predominantly associated with Alternaria alternata

Alternaria leaf spot (ALS) of cotton, especially on cotyledons is generally considered a minor disease in Australia. However, severe disease outbreaks were recorded in multiple cotton crops in southern New South Wales (NSW) in the 2017/18 season. Due to ALS being considered a minor disease, causal species have not been formally characterised in Australia. In this study, putative small-spored Alternaria alternata was predominantly recovered from diseased cotyledons sampled from ALS hot spot fields in southern NSW as well as other locations across NSW. Species status of recovered isolates as A. alternata was confirmed through morphology and sequence analyses of the internal transcribed spacer (ITS) and translation elongation factor 1-alpha (TEF1) regions. Phylogenetic analyses of the two regions both individually or in combination resulted in a well-supported group of 69 isolates (83%) clustering with the ex-type specimen of A. alternata CBS 916.96, thus confirming the preliminary morphological identifications. In artificially inoculated assays on 15-day-old cotton seedlings, a subset of selected A. alternata isolates produced similar ALS symptoms at 7 days after inoculation (DAI) as seen in the field. Koch’s postulate was fulfilled by re-isolating A. alternata from infected ALS cotyledons at 21 DAI. This is the first main stream published report of A. alternata causing ALS on cotton cotyledons in NSW, Australia.

Control of Alternaria leaf spot of coriander in organic farming

The European Union’s Seventh Framework Programme (KBBE.2012.1.2–05: 311875) TESTA (Seed health: Development of seed treatment methods, evidence for seed transmission and assessment of seed health).

Design, synthesis and antifungal activities of novel pyrrole- and pyrazole-substituted coumarin derivatives.

We synthesized a series of novel pyrrole- and pyrazole-substituted coumarin derivatives and evaluated their antifungal activity against six phytopathogenic fungi invitro. The primary assay results demonstrated that some designed compounds displayed potent activities. Among them, compounds 5g, 6a, 6b, 6c, 6d and 6h exhibited more effective control than Osthole against Cucumber anthrax and Alternaria leaf spot. Furthermore, compound 5g displayed stronger antifungal activity against Rhizoctorzia solani (EC50 = 15.4µg/mL) than positive control Osthole (EC50 = 67.2µg/mL).

Effect of seed bio-/chemo-priming and triazole fungicide on important foliar diseases of sunflower (Helianthus annuus L.)

Sunflower (Helianthus annuus L.), an important edible oil seed crop, is prone to severe attack by necrosis, Alternaria leaf spot and powdery mildew diseases which lead to poor seed germination and loss of seedling vigour and yield. The present study was conducted for 3 consecutive years with the aim to manage these foliar diseases under field conditions through seed priming (bio or chemo) followed by fungicide/insecticide spray. The result revealed that among the treatments tested, seed priming with carbendazim @ 2 g + thiamethoxam @ 4 g kg−1 seeds followed by foliar spray of propiconazole @ 0.1% + thiamethoxam @ 0.04% twice (30 and 45 days after sowing) gave effective control of necrosis (2.27%), leaf spot (19.6 PDI) and powdery mildew (17.94 PDI) diseases with seed yield increase (1443 kg ha−1) over control. This was followed by Trichoderma viride priming which recorded 7.1% necrosis, 38 PDI of leaf spot and 36.31 PDI of powdery mildew. Seed bio-or chemo-priming promoted higher and uniform seed germination under field conditions. Seed priming with carbendazim @ 2 g kg−1 + thiamethoxam @ 4 g kg−1 along with two foliar sprays of propiconazole @ 0.1% + thiamethoxam @ 0.04% (30 and 45 DAS) were effective.

Real-Time Detection of Apple Leaf Diseases Using Deep Learning Approach Based on Improved Convolutional Neural Networks

Alternaria leaf spot, Brown spot, Mosaic, Grey spot, and Rust are five common types of apple leaf diseases that severely affect apple yield. However, the existing research lacks an accurate and fast detector of apple diseases for ensuring the healthy development of the apple industry. This paper proposes a deep learning approach that is based on improved convolutional neural networks (CNNs) for the real-time detection of apple leaf diseases. In this paper, the apple leaf disease dataset (ALDD), which is composed of laboratory images and complex images under real field conditions, is first constructed via data augmentation and image annotation technologies. Based on this, a new apple leaf disease detection model that uses deep-CNNs is proposed by introducing the GoogLeNet Inception structure and Rainbow concatenation. Finally, under the hold-out testing dataset, using a dataset of 26,377 images of diseased apple leaves, the proposed INAR-SSD (SSD with Inception module and Rainbow concatenation) model is trained to detect these five common apple leaf diseases. The experimental results show that the INAR-SSD model realizes a detection performance of 78.80% mAP on ALDD, with a high-detection speed of 23.13 FPS. The results demonstrate that the novel INAR-SSD model provides a high-performance solution for the early diagnosis of apple leaf diseases that can perform real-time detection of these diseases with higher accuracy and faster detection speed than previous methods.