Circular Leaf Spot Of Persimmon Research Articles

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.

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.

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.

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.

First Report of Circular Leaf Spot of Persimmon Caused by Mycosphaerella nawae in Spain.

Production of persimmon (Diospyros kaki L. f.) has increased significantly during the last decade in Spain as a profitable alternative for fruit growers. In August 2008, after a mild and rainy spring, symptoms of a new disease were observed in commercial persimmon fields located in Valencia Province (eastern-central Spain). Symptoms included circular necrotic spots on the leaves and defoliation. Early fruit maturation and premature abscission were associated with early symptom development in the trees. A fungus was consistently isolated from the margins of leaf lesions. All isolates obtained were hyphal-tipped twice and transferred to potato dextrose agar (PDA). The cultures grew slowly and reached a diameter of 21 to 29 (mean 26) mm within 4 weeks on PDA at 25°C in the dark. Mycelium was initially dark green and ultimately became dark gray to black. Several media and incubation conditions were tested to induce sporulation, but conidia formation was not observed. In April 2009, mature spherical pseudothecia were observed in lesions on fallen leaves that had remained in affected fields during the winter. Ascospores were uniseptate and mostly spindle shaped, 10 to 11.5 (mean 10.3) μm long, and 3 to 3.9 (mean 3.4) μm wide. Fungal colonies obtained from the ascospores were identical to those isolated from the leaf lesions. Morphological characters observed matched those described for the pathogen Mycosphaerella nawae Hiura & Ikata (1). In Korea, the circular leaf spot of persimmon caused by M. nawae was considered an economically important disease in the 1990s, especially in the southern regions (2). Sequences of the internal transcribed spacer (ITS) region of the rDNA were obtained for isolates MY2 and MY3 and deposited in GenBank (Accession Nos. GQ465767 and GQ465768). These sequences were identical to each other and to the sequence obtained from a Korean isolate of M. nawae. Symptoms of the disease were reproduced after inoculation of 2-year-old persimmon trees growing in individual pots. A ground mycelial suspension (5 × 105 CFU ml-1) of strain MY2 was sprayed onto 20 potted trees (200 ml per individual tree) in late May of 2009. Ten trees were sprayed with sterile distilled water as a control. Trees were incubated at 20°C in a growth chamber with a 12-h photoperiod and covered with a semitransparent plastic hood for the first 10 days after inoculation, after which the plastic was punctured for ventilation and trees were incubated at 22°C. The first symptoms (small circular spots on the leaves) appeared on inoculated trees 15 days after inoculation. One month after inoculation, all inoculated trees showed circular leaf spots and severe defoliation, whereas noninoculated trees remained healthy. M. nawae was successfully reisolated from the lesions. To our knowledge, this is the first report of M. nawae causing circular leaf spot of persimmon in Spain.

감나무 둥근무늬낙엽병의 발생과 병원균(Mycosphaerella nawae)의 전염원 동태

The circular leaf spot of persimmon is occurred almost every place where persimmon is cultivated, especially the disease outbreak severely in southern part of Korea. The disease reveals unusually long incubation period after pathogen invade into leaf tissue and no practical control measure is available once the symptom has appeared. Most of the farmers just follow the suggested spray schedules calculated on the basis of weather condition of ordinary years. Therefore the damages due to circular leaf spot greatly differ year after year. In this article, we tried to describe and summarized the investigation on the circular leaf spot pathogen, Mycosphaerella nawae, related to disease outbreak such as overwintering of pathogen, inoculum formation and spread, incubation period after infection, and secondary inoculum. With the summary of these results, we suggest the disease cycle of circular leaf spot of persimmon. The pathogen overwinters in diseased leaves as mycelial form or pseudoperithecial premodium. The pseudoperitheria become matured in spring as the temperature raise and forms asci and ascospores. The maturation of pseudoperithecia are closely related to the temperatures during March and early April. The ascospores completely mature in early May and the ascospores released when the pseudoperithecia absorbed enough moisture after rainfall. The release of ascospores are diverse greatly with the variation of maturity of pseudoperithecia. Generally the spore start to release from middle of May to early of July. Duration of ascospore release is depend on the weather condition of particular year, especially amount and number of precipitation. The ascospores produced from pseudoperithecia is known to the only inoculum for circular leaf spot disease. But according to the results obtained from our investigations, the conidia formed on the lesions which incited by natural infection. This conidia are infectious to persimmon leaves and formed identical symptom as natural infection. The time of producing secondary inoculum of circular leaf spot of persimmon is considered too late to develop new disease. Generally the importance of secondary inoculum is low but the conidia produced in early September are competent to develop new disease and new infection also significantly affect to harvest of persimmon. The importance of circular leaf spot disease is recognized well to farmers. The approaches to control of the disease should be initiated on the basis of the knowledges of inoculum dynamics and ecology of disease development. The forecasting system for circular leaf spot is need to be developed.