Circular Leaf Spot Research Articles

Dense Convolutional Neural Network-Based Deep Learning Pipeline for Pre-Identification of Circular Leaf Spot Disease of Diospyros kaki Leaves Using Optical Coherence Tomography.

Circular leaf spot (CLS) disease poses a significant threat to persimmon cultivation, leading to substantial harvest reductions. Existing visual and destructive inspection methods suffer from subjectivity, limited accuracy, and considerable time consumption. This study presents an automated pre-identification method of the disease through a deep learning (DL) based pipeline integrated with optical coherence tomography (OCT), thereby addressing the highlighted issues with the existing methods. The investigation yielded promising outcomes by employing transfer learning with pre-trained DL models, specifically DenseNet-121 and VGG-16. The DenseNet-121 model excels in differentiating among three stages of CLS disease (healthy (H), apparently healthy (or healthy-infected (HI)), and infected (I)). The model achieved precision values of 0.7823 for class-H, 0.9005 for class-HI, and 0.7027 for class-I, supported by recall values of 0.8953 for class-HI and 0.8387 for class-I. Moreover, the performance of CLS detection was enhanced by a supplemental quality inspection model utilizing VGG-16, which attained an accuracy of 98.99% in discriminating between low-detail and high-detail images. Moreover, this study employed a combination of LAMP and A-scan for the dataset labeling process, significantly enhancing the accuracy of the models. Overall, this study underscores the potential of DL techniques integrated with OCT to enhance disease identification processes in agricultural settings, particularly in persimmon cultivation, by offering efficient and objective pre-identification of CLS and enabling early intervention and management strategies.

Exhaustive identification and characterization of Colletotrichum siamense and Colletotrichum fructicola as causative agents of circular leaf spot disease of rubber tree (Hevea brasiliensis) in India

The rubber tree (Hevea brasiliensis) is one of the major domesticated crops planted commercially for the production of natural rubber (NR) worldwide. In recent years, rubber trees in the Southern states of India and other rubber-producing countries have experienced a severe leaf spot disease, characterized by the appearance of several brown circular spots in the initial stage, which later spread all over the lamina of fully matured leaves, leading to yellowing and defoliation. The causal organism of this Circular Leaf Spot (CLS) disease has not been conclusively identified in any previous studies. In this study, we collected infected leaf samples from various locations in the South Indian states. We aimed to identify the actual fungal pathogen that causes the CLS disease on rubber trees. Based on the morphological and molecular analysis of the most frequently isolated fungi from infected leaf samples were identified as Colletotrichum siamense and Colletotrichum fructicola. Pathogenicity tests also confirmed the involvement of isolated Colletotrichum spp. in the development of CLS disease. These findings provide valuable insights into understanding the CLS disease and its impact on rubber cultivation. To our knowledge, it is the first report of C. siamense and C. fructicola associated with CLS disease of rubber trees in India.

Comprehensive whole-genome sequencing reveals genetic characteristics of Colletotrichum fructicola (Nara gc5) the causative organism of circular leaf spot disease of rubber (Hevea brasiliensis)

Comprehensive whole-genome sequencing reveals genetic characteristics of Colletotrichum fructicola (Nara gc5) the causative organism of circular leaf spot disease of rubber (Hevea brasiliensis)

Modeling Inoculum Availability of Plurivorosphaerella nawae in Persimmon Leaf Litter with Bayesian Beta Regression.

Circular leaf spot (CLS), caused by Plurivorosphaerella nawae, is a serious disease affecting persimmon (Diospyros kaki) that is characterized by necrotic lesions on leaves, defoliation, and fruit drop. Under Mediterranean conditions, P. nawae forms pseudothecia in the leaf litter in winter, and ascospores are released in spring, infecting susceptible leaves. Persimmon growers are advised to apply fungicides for CLS control during the period of inoculum availability, which was previously defined based on ascospore counts under the microscope. A model of inoculum availability of P. nawae was developed and evaluated as an alternative to ascospore counts. Leaf litter samples were collected weekly in L'Alcúdia (Spain) from 2010 to 2015. Leaves were soaked and placed in a wind tunnel, and the released ascospores of P. nawae were counted. Hierarchical Bayesian beta regression methods were used to model the dynamics of ascospore production in the leaf litter. The selected model included accumulated degree-days (ADDs) and ADDs taking into account the vapor pressure deficit (ADDvpd) as fixed effects and year as random effect. This model had a mean absolute error of 0.042 and a root mean square error of 0.062. The beta regression model was evaluated in four orchards from 2010 to 2015. Higher accuracy was obtained at the beginning and the end of the ascospore production period, which are the events of interest to schedule fungicide sprays for CLS control in Spain. This same modeling framework can be extended to other fungal plant pathogens whose inoculum dynamics are expressed as proportion data.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Changes in the secondary compounds of persimmon leaves as a defense against circular leaf spot caused by Plurivorosphaerella nawae.

Circular leaf spot, caused by the ascomycetous fungus Plurivorosphaerella nawae (= Mycosphaerella nawae), is the most problematic fungal disease of persimmon worldwide. In Korea, persimmon exposed to P. nawae inoculum (ascospores) from May to August shows visible circular leaf spot disease symptoms from the end of August to early September. It is important to identify factors affecting this long latent period. The objective of this study was to elucidate the relation between the development of symptom of circular leaf spot and the content of phenolics compounds and vitamin C as well as the antioxidant activities in leaves. Healthy leaves (both young and old) and infected leaves of circular leaf spot-susceptible persimmon cultivar were harvested in 2016. The content of phenolics (total phenols, flavonoids, and tannins) and vitamin C, and their antioxidant activities were analyzed in all types of leaves. Compared with the asymptomatic leaves (old) and the asymptomatic parts of the infected leaves, the symptomatic parts of the infected leaves, symptomatic leaves, and asymptomatic young leaves showed significantly higher content of phenolics and vitamin C, and higher antioxidant activities. Disease incidence and severity were estimated for older leaves (emerged in early May) and younger leaves (emerged at the end of June) in 2017 and 2018. The AUDPC was higher in old leaves than younger leaves. The disease progression was much faster and severe in the older than in the younger leaves. Similar results were found in field experiments. Higher content of phenolics and antioxidant activities in the younger leaves may contribute to circular leaf spot resistance in persimmon. Furthermore, accumulation of phenolics and antioxidant activity in the infected leaves is a post-infection response and the first stage of the defense mechanism.

Effect of spray volume, application timing and droplet size on spray distribution and control efficacy of different fungicides against circular leaf spot of persimmon caused by Plurivorosphaerella nawae

In recent years, Spain has been the scenario of the largest production growth of persimmon worldwide. However, circular leaf spot of persimmon, caused by Plurivorosphaerella nawae, was responsible for causing severe yield and economic losses. This work studied the effect of spray volume rate, droplet size, and application timing on spray distribution and disease control efficacy for mancozeb, pyraclostrobin and difenoconazole applications. Also fungicide degradation dynamics on persimmon leaves were studied. A method to inoculate persimmon plants using natural inoculum of P. nawae was developed. Results showed that spray volume influenced canopy spray coverage regardless of the fungicide used, but it did not influence disease control efficacy, except when pyraclostrobin was applied as pre-inoculation spray. Pyraclostrobin also showed a good post-inoculation activity. Influence of droplet size on spray coverage depended on the leaf side considered but it did not affect disease control efficacy except for pyraclostrobin applied 14 days after inoculation, when coarse droplets had lower control than fine ones. In general, slight degradation dynamics of fungicide residues on leaves were observed at 14 days.

Phylogenetic and Morphological Reassessment of Mycosphaerella nawae, the Causal Agent of Circular Leaf Spot in Persimmon.

Persimmon (Diospyros kaki) fruit production is severely affected by circular leaf spot worldwide. Mycosphaerella nawae causes circular leaf spot of persimmon (CLSP) and can result in leaf spot, defoliation, early fruit maturation, and subsequent softening and abscission. The morphology and phylogenetic position of M. nawae within the family Mycosphaerellaceae is, therefore, of utmost importance given its impact on persimmon production. Based on previous morphological and molecular studies, the phylogenetic position of the anamorphic genera associated with M. nawae remain in confusion. In the present study, 15 isolates of M. nawae were collected from the tissue of living leaves exhibiting leaf spot symptoms. A subsample of three isolates was characterized phylogenetically and morphologically. Isolates were compared based on DNA sequence data for the internal transcribed spacer region (ITS1-5.8S ITS2), part of the 28S nrDNA including domains D1-D3 (LSU), actin (Act), translation elongation factor 1-alpha (EF-1α), and RNA polymerase II second largest subunit (rpb2). The anamorph and teleomorph structures, ascospore germination patterns, as well as host specificity were used to describe the isolates. The phylogenetic and morphological analyses revealed that M. nawae requires a new holomorphic genus within Mycosphaerellaceae, described herein as Plurivorosphaerella gen. nov. A host specificity test revealed that Plurivorosphaerella nawae comb. nov. (M. nawae) can superficially colonize, but not infect, apple, peach, cherry, and plum.

Inoculum dynamics and disease progress of circular leaf spot of persimmon caused by Mycosphaerella nawae in inland Korea

Circular leaf spot is one of the most serious diseases of persimmons in many areas where the crop is grown. This disease is caused by the fungal species Mycosphaerella nawae Hiura & Ikata. Disease cycle of circular leaf spot of persimmon in terms of seasonal pattern of ascospore dispersal and the disease development based on field survey and ascospore potential was studied in the cold inland areas of central Korea (Sangju) for two consecutive years. Based on the number of rain-released and airborne ascospores collected, seasonal release of M. nawae ascospores from pseudothecia occurred from May to September but most ascospores were detected between mid-June and mid-July in both years. There was a strong correlation between the number of water-dispersed ascospores and cumulative rainfall. The first disease symptoms were observed at late August. Disease incidence became maximum at the end of September. Experiments under controlled conditions, including the effects of misting duration, soaking time, and temperature on ascospore release were performed. Over 90% of the total ascospores were released within 2 h of misting. M. nawae ascospores began to be released just after leaf soaking, and the release rate increased exponentially over 8 h. Temperature significantly (P = 0.008) affected the release of M. nawae ascospores from soaked leaf litter during 8 h at controlled condition. The outcome of our experiments suggested that the quantity and temporal distribution of airborne and waterborne M. nawae inoculum is closely related to seasonal rainfall patterns, duration of rainfall, irrigation system, soaking period and temperature.

Evaluation of Ascospore Prediction Model for Circular Leaf Spot caused by <i>Mycosphaerella nawae</i> of Persimmon

Circular leaf spot(CLS) disease causes considerable economic damage to persimmon(Diospyros kaki) in South Korea. Mycosphaerella nawae ascospores are the primary inoculum for CLS epidemics. In this study, we investigated the seasonal fluctuation of spore release and its relationship to environmental factors, based on spore trapping. We evaluated the seasonal pattern of released M. nawae ascospores in South Korea. During three persimmon growing seasons(2010 to 2012), we recorded the release of ascospores in two regions, Jinju and Gimhae, which are major producing regions of sweet persimmon in South Korea. The release of CLS ascospores was from the first week of May to the end of July. The maximum release of spores was observed in late June. A computer model used accumulated degree days to simulate ascospore release. The overall mean accumulated degree days, from 01 May to 50% ascospore release for the observed data(1174℃ days), was not significantly different from the predicted value of 1144℃ days. The mean differences between predicted and observed release percentages for the sampling periods were not significantly different from zero.

Nested PCR–based Assay for Diagnosis of Circular Leaf Spot Disease–causing Mycosphaerella nawae and its Application

Nested PCR–based Assay for Diagnosis of Circular Leaf Spot Disease–causing Mycosphaerella nawae and its Application

Control and yield loss modelling of circular leaf spot of persimmon caused by Mycosphaerella nawae

ABSTRACTSymptoms of circular leaf spot of persimmon (CLSP), caused by Mycosphaerella nawae, consisted of necrotic spots on leaves, chlorosis and premature defoliation. Although CLSP is a foliar disease, early fruit maturation and abscission are frequently associated with the presence of lesions on leaves and defoliation, resulting in severe economic losses. Despite their importance for the design of efficient disease management programmes, quantitative relationships between CLSP incidence and yield loss are unknown. Therefore, fungicide efficacy trials were conducted during two consecutive years in Spain to induce different levels of disease severity, defoliation and yield loss. The effects of fungicide treatments on CLSP severity were analysed by ordinal logistic regression models. Relative yield loss values were regressed against the percentage of affected leaves or defoliated obtained at different evaluation dates. The disease had high negative impact and complete yield loss was observed in the absence of effective fungicide treatments. Preventive applications of pyraclostrobin, trifloxy‐strobin and mancozeb provided the best disease control and highest yields, up to 95.77 kg tree−1. An exponential relationship of CLSP incidence and defoliation with yield loss was found. In general, model fit and predictive ability was superior when defoliation, rather than incidence, was used as explanatory variable. The impact of defoliation on yield loss was higher in earliest evaluation dates, suggesting that early leaf abscission may be the main factor contributing to premature fruit drop and subsequent yield loss. Substantial yield losses were observed even with relatively low levels of CLSP incidence and defoliation. Therefore, it was not possible to define a critical action threshold for CLSP management based on foliar symptoms.

Optical Inspection and Morphological Analysis of Diospyros kaki Plant Leaves for the Detection of Circular Leaf Spot Disease.

The feasibility of using the bio-photonic imaging technique to assess symptoms of circular leaf spot (CLS) disease in Diospyros kaki (persimmon) leaf samples was investigated. Leaf samples were selected from persimmon plantations and were categorized into three groups: healthy leaf samples, infected leaf samples, and healthy-looking leaf samples from infected trees. Visually non-identifiable reduction of the palisade parenchyma cell layer thickness is the main initial symptom, which occurs at the initial stage of the disease. Therefore, we established a non-destructive bio-photonic inspection method using a 1310 nm swept source optical coherence tomography (SS-OCT) system. These results confirm that this method is able to identify morphological differences between healthy leaves from infected trees and leaves from healthy and infected trees. In addition, this method has the potential to generate significant cost savings and good control of CLS disease in persimmon fields.

단감수출단지 과원과 수출단감 병해충 조사

Between 2010 and 2012, diseases and insect pests of sweet persimmon were surveyed at sweet persimmon export complexes and non-export orchards in Suncheon, Jeonnam Province; Jinju, Changwon (Dongeup and Bukmyeon), and Gimhae, Gyeongnam Province; and Ulzu, Ulsan. The following diseases were found in the sweet persimmon orchards: angular leaf spot (Cercospora kaki), anthracnose (Colletotrichum gloeosporioides and Colletotrichum acutatum), circular leaf spot (Mycosphaerella nawae), powdery mildew (Phyllactinia kakicola), and gray mold (Botrytis cinerea). Circular leaf spot was the most frequent and serious disease, and C. gloeosporioides and C. acutatum were found on fruits. Thirty-three insect pest species that belonged to 32 genera of 20 families in 5 orders were found in the sweet persimmon orchards; the two-spotted spider mite, Tetranychus urticae, was also found in the surveyed orchards. Apolygus spinolae, Pseudaulacaspis cockerelli, and Adoxophyes orana were widely found in the surveyed orchards; Spodoptera litura and Homona magnanima were also recorded. Damage by insect pests was low, and the quarantine insect pests peach pyralid moth (Dichocrocis punctiferalis) and persimmon fruit moth (Stathmopoda masinissa) were rarely or not found in the sweet persimmon export complexes. In addition, other quarantine insect pests, such as persimmon false spider mite (Tenuipalpus zhizhilashviliae) and Japanese mealybug (Planococcus kraunhiae), were not detected. These quarantine insect pests were also not found in the sorting places, storage houses, and fruits for export; however, scale insects and two-spotted spider mites were found at a low rate. Although anthracnose (C. acutatum) infested fruit was found in the storage houses, only one in Jinju and Gimhae.

A nested-polymerase chain reaction protocol for the detection of Mycosphaerella nawae in persimmon

Mycosphaerella nawae is the causal agent of circular leaf spot of persimmon. A polymerase chain reaction (PCR) based protocol was developed for M. nawae-specific identification from pure culture, or infected symptomatic and asymptomatic persimmon tissues. Variation among the internal transcribed spacer regions (ITS) of the ribosomal DNA (rDNA) sequences of potentially related fungal species in persimmon orchards was analyzed for a primer pair design. Specificity was confirmed using multiple isolates of these species, other fungal pathogens that cause foliar diseases in persimmon and contaminants commonly obtained in the isolation process. The detection threshold for M. nawae DNA was lowered from 50 pg to 500 fg when nested-PCR was evaluated instead of single PCR. The nested-PCR protocol developed in this study showed its suitability to be applied for the specific detection of M. nawae from three types of naturally infected persimmon tissues: from lesions in fresh leaves, from pseudothecia present in lesions in leaf litter, and from infected asymptomatic leaves. The protocol can be useful for routine diagnosis, disease monitoring programs and for epidemiological research.

THE MAIN DISEASES ON CHINESE PERSIMMON TREE

The persimmon (Diospyros kaki L.) is native to China, with a long cultivation history and rich resource types. Persimmon trees in China grow from the north to the south because of their strong adaptability. The Chinese persimmon trees live in complex habitat, and the cultivation and management are relatively extensive, so diseases are quite common. The main diseases on Chinese persimmon trees include persimmon anthracnose, persimmon cercospora leaf spot, persimmon circular leaf spot, persimmon powdery mildew, persimmon madness and so on. This paper introduces the main diseases above mentioned, including pathogenic characteristics and symptoms, pathogen, epidemicity, and finally some integrated control strategy is discussed.

Inoculum and disease dynamics of circular leaf spot of persimmon caused by Mycosphaerella nawae under semi-arid conditions

The epidemiology of circular leaf spot of persimmon, caused by Mycosphaerella nawae, was studied in a semi-arid area in Spain for two consecutive years. No conidia were observed on diseased leaves and all infections were thought to be caused by ascospores formed in the leaf litter. Ascospores were released mainly in April and May, but relatively low numbers in June were able to induce severe symptoms on trap plants. Temperature was not significantly correlated with ascospore catches or disease incidence on trap plants, indicating that it was not a limiting factor for disease development during the period of study. Rainfall was above normal, but still considerably lower than in endemic areas of Korea. Most infections coincided with rains, but the disease was observed also on trap plants exposed to less than 1 mm of precipitation and even in the absence of rain. Orchards were flood irrigated once inoculum deposits in the leaf litter had already been depleted, so it was not possible to determine its effects on ascospore release and disease development. The use of a wind tunnel to determine inoculum production allowed detection of physiologically mature ascospores of M. nawae in the leaf litter 1–2 weeks before they were released to air in the orchard. Disease progress was fitted to the monomolecular growth curve, associated with monocyclic pathogens and diseases with a variable incubation period as a function of the host phenology.

Control of circular leaf spot of persimmon by pyraclostrobin-boscalid water powder

Control of circular leaf spot of persimmon by pyraclostrobin-boscalid water powder

Estimation of Leaf Wetness Duration Requirements of Foliar Fungal Pathogens with Uncertain Data—An Application to Mycosphaerella nawae

Wetness of the host surface is a critical environmental factor for the development of foliar fungal diseases, but it is difficult to estimate the wetness durations required by pathogens for infection when only few experimental data are available. In this paper, we propose a method to estimate wetness duration requirements of foliar fungal pathogens when precise experimental data are not available. The proposed method is based on approximate Bayesian computation. It only requires lower and upper bounds of wetness duration requirements for one or fewer temperatures. We describe the method, show how to apply it to an infection model, and then present a case study on Mycosphaerella nawae, the causal agent of circular leaf spot of persimmon. In this example, the parameters of a simple infection model were estimated using experimental data found in the literature for the pathogen, and the model was applied to assess the risk in a Spanish area recently affected by the disease. The results showed that the probability of successful infection was higher than 0.5 for 32% of the on-site wetness durations recorded in the affected area. Results obtained with simulated data showed that our method was able to improve the estimation of wetness duration requirement. Given the flexibility of the proposed method, we expect it to become adopted for assessing the risk of introduction of exotic fungal plant pathogens.

Evaluation of fungicides to control circular leaf spot of persimmon caused by Mycosphaerella nawae

The efficacy of ten fungicides against Mycosphaerella nawae, the causal agent of circular leaf spot (CLS) of persimmon, was evaluated in vitro and in field experiments. Field trials were conducted in 2009 and 2010 to investigate the comparative efficacy of the fungicides alone or combined using alternating sequences in spray programmes based on two, three or four applications. Disease incidence was assessed by estimating the percentage of affected leaves, which included leaves showing at least one necrotic spot and defoliation. Fenpropimorph, pyraclostrobin, tebuconazole and thiophanate-methyl were the most effective fungicides in inhibiting mycelial growth of M. nawae isolates (EC 50 < 2 ppm). In field experiments, the most effective fungicides using two spray applications were captan, chlorothalonil, mancozeb and pyraclostrobin which significantly reduced disease incidence compared with untreated plots. Regarding the number of spray applications, two applications of captan and mancozeb were less efficient than three to control the disease. However, the percentage of affected leaves provided by three applications of captan and mancozeb alone or combined with pyraclostrobin using alternating sequences in spray programmes, was not significantly different from that provided by four applications. Experimental results demonstrated that spray programmes based on three applications of these fungicides could effectively control CLS of persimmon. The advantages of spray programmes based on alternated use of strobilurins and protective fungicides are discussed.

Effects of temperature, water regime and irrigation system on the release of ascospores of Mycosphaerella nawae, causal agent of circular leaf spot of persimmon

Experiments were conducted under controlled conditions to quantify the effects of temperature, water regime and irrigation system on the release of Mycosphaerella nawae ascospores from leaf litter in Spanish persimmon orchards. The effect of temperature on ascospore release was best described by a Gompertz model. The end of the lag phase of ascospore release occurred at 9·75°C, and the end of the exponential phase at 15·75°C. Few ascospores were discharged from dry leaves wetted with 0·1 or 0·5 mm water, but significant amounts were recovered with 1–50 mm water. About half of the total ascospores were released after three wetting and drying cycles, but 32 cycles were necessary for a complete discharge. No significant difference in ascospore release was detected when the leaf litter was wetted by flood and drip irrigation. However, considering the proportion of soil area wetted in both systems, inoculum release was significantly reduced by drip irrigation. The potential of drip irrigation as a cultural control measure should be investigated.