Brown Leaf Spot Disease Research Articles

Pathogenic variability among Curvularia species causing brown leaf spot disease of rice

Pathogenic variability among Curvularia species causing brown leaf spot disease of rice

Screening of rice genotypes against brown leaf spot (Bipolaris oryzae) (Breda de Haan) shoemaker, under field and laboratory conditions at Banke, Nepal

A field experiment was carried out to screen 60 rice genotypes against brown leaf spot disease caused by Bipolaris oryzae with Sabitri as a resistant check and Mansuli as a susceptible check at Banke, Nepal. The field experiment was laid out in a randomized completed block design, and the seed infection screening was done in a laboratory with a completely randomized design. The disease assessment was done by calculating disease severity, the area under the disease progress curve (AUDPC), and the seed infection rate. The disease severity and AUDPC significantly varied for the tested genotypes. Based on the AUDPC and disease severity values, this study observed that one genotype was moderately resistant, 11 were susceptible, and 48 were highly susceptible. From our experiment, rice genotypes were primarily susceptible rather than resistant; thus, for the next-generation breeding program for brown leaf spot-resistant genotypes, more landraces should be screened from diverse environments of Nepal.

Evaluation of the control efficacy of antagonistic bacteria from V-Ti magnetite mine tailings on kiwifruit brown spots in pot and field experiments.

Seemingly barren heavy-metal-polluted vanadium (V) and titanium (Ti) magnetite mine tailings contain various functional microbes, yet it is unclear whether this includes microbial resources relevant to the biological control of plant diseases. Kiwifruit brown leaf spot disease, caused by Corynespora cassiicola, can seriously reduce kiwifruit yield. To discover effective control measures for kiwifruit leaf spot, 18 bacteria strains among 136 tailing-isolated bacteria from V-Ti magnetite mine tailings were identified as inhibiting C. cassiicola by the confrontation plate method, indicating that antagonistic bacteria surviving in the V-Ti magnetite mine tailings were present at a low level. The 18 antagonistic strains could be divided into two BOX-A1R clusters. The 13 representative strains that were selected for phylogenetic tree construction based on their 16S rRNA sequences belonged to the Bacillus genus. Five predominant strains exhibited different toxin-production times and intensities, with four of them initiating toxin production at 32 h. Among them, Bacillus sp. KT-10 displayed the highest bacteriostatic rate (100%), with a 37.5% growth inhibition rate and an antagonistic band of 3.2 cm against C. cassiicola. Bacillus sp. KT10 also showed a significant inhibitory effect against the expansion speed of kiwifruit brown spots in the pot. The relative control effect was 78.48 and 83.89% at 7 days after the first and last spraying of KT-10 dilution, respectively, confirming a good effect of KT-10 on kiwifruit brown leaf spots in the field. This study demonstrated for the first time that there are some antagonistic bacteria to pathogenic C. cassiicola in V-Ti magnetite mine tailings, and Bacillus sp. KT10 was found to have a good control effect on kiwifruit brown leaf spots in pots and fields, which provided an effective biological control measurement for kiwifruit brown leaf spots.

Isolation and Identification of Alternaria alternata from Potato Plants Affected by Leaf Spot Disease in Korea: Selection of Effective Fungicides.

Brown leaf spot disease caused by Alternaria spp. is among the most common diseases of potato crops. Typical brown spot symptoms were observed in commercial potato-cultivation areas of northern Korea from June to August 2020-2021. In total, 68 isolates were collected, and based on sequence analysis of the internal transcribed spacer (ITS) region, the collected isolates were identified as Alternaria spp. (80.9%). Phylogenetic analysis revealed that a majority of these isolates clustered within a clade that included A. alternata. Additionally, the ITS region and rpb2 yielded the most informative sequences for the identification of A. alternata. Pathogenicity tests confirmed that the collected pathogens elicited symptoms identical to those observed in the field. In pathogenicity tests performed on seven commercial cultivars, the pathogens exhibited strong virulence in both wound and non-wound inoculations. Among the cultivars tested, Arirang-1ho, Arirang-2ho, and Golden Ball were resistant to the pathogens. Furthermore, among the fungicides tested in vitro, mancozeb and difenoconazole were found to be effective for inhibiting mycelial growth. In summary, our findings suggest that A. alternata plays a critical role in leaf disease in potato-growing regions and emphasise the necessity of continuous monitoring and management to protect against this disease in Korea.

Coniolariella gamsii Causes Poplar Leaf Spot Disease in Xinjiang, China

Populus laurifolia is one of the most valuable tree species in the world and an important silvicultural tree species in the Xinjiang Uygur Autonomous Region, China. In July 2017, an unreported brown leaf spot disease was observed on P. laurifolia in Altay City, Xinjiang. The causal agent of this leaf spot disease was isolated, and Koch’s postulates were performed to confirm its pathogenicity. Based on a morphological characterization and phylogenetic analyses, the causal organism was identified to be a fungal species, Coniolariella gamsii. The optimum mycelial growth conditions for C. gamsii are on PLPDA (Populus leaves potato dextrose agar) medium, at 28 °C, in the dark. The sporulation time when using PLPDA medium (12 days) is much less than that for PDA medium (25 days). Pathogenicity tests revealed that C. gamsii can also infect two other Populus species (P. bolleana and P. tomentosa). This is the first report of C. gamsii causing brown leaf spot disease on P. laurifolia, and the optimum culture and sporulation conditions have also been optimized for the first time. This study provides a theoretical basis for the diagnosis of this disease and the monitoring of the disease’s occurrence and epidemic status.

English

Narrow brown leaf spot disease of rice caused by fungus Cercospora oryzae Miyake emerged as potential threat to rice crop in previous few years worldwide and can cause more than 40% yield loss. The disease symptoms were noted on various commercially important rice varieties in the rice growing districts of Punjab province of Pakistan. Hence, the studies were planned to assess the effects of Propiconazole fungicide application timings and different rice varieties on the severity of narrow brown leaf spot (NBLS) disease of rice to develop an accurate management strategy for the disease. The Propiconazole fungicide was tested at three various growth phases (early booting, late booting, and soft dough) of four rice varieties against the percent severity of the NBLS disease The experiments were designed under strip-plot (crisscross) design with four replications at research area of Plant Pathology Department, University of Agriculture Faisalabad. Analysis of variance has demonstrated that the main and interactive effects of fungicide applications and rice varieties were found significant. The main effects of years were found non-significant but their interactions with fungicide application timings and rice varieties were significant. Fungicide applications at soft dough and late booting phases of rice variety B-515 were found least effective to reduce the disease severity, respectively. Fungicide application at early booting of rice variety PK-1121 was found most effective by reducing the maximum percent diseases severity (47.25%) compared to control. It is concluded that, to minimize hazardous effects of chemicals on the environment by practicing multiple sprays at inappropriate growth phases of rice crop, fungicides must be applied during the early and late booting phases of rice varieties on mildly resistance, susceptible and highly susceptible rice varieties to reduce NBLS disease severity and to enhance the rice production and quality

First Report of Leaf Blotch Caused by Phyllosticta capitalensis on Daphne odora in China.

Daphne odora Thunb. an evergreen shrub with scented flowers, is used for ornamental purposes but it also has medicinal benefits (Otsuki, et al. 2020). In August 2021, leaf blotch symptoms were observed on roughly 20% of leaves of D. odora var. marginata plants in Fenghuangzhou Citizen Park, Nanchang city (28°41'48.12″ N, 115°52'40.47″ E), Jiangxi Province, China. Brown lesions first appeared on the edges of leaves, which eventually dried and died (Fig. 1A). For fungal isolation, 12 symptomatic leaves were randomly collected, the edges between diseased area and healthy area were cut into small pieces (4×4 mm), surface-sterilized by dipping in 70% ethanol for 10 s and 1% sodium hypochlorite for 30 s, and then rinsed three times with sterile distilled water. Leaf pieces were then plated on potato dextrose agar (PDA) and incubated at 28 ℃ for 3-4 days. A total of 10 isolates were recovered from the diseased leaves. The pure colonies of all fungal isolates had similar characteristics, and three isolates were randomly selected (JFRL 03-249, JFRL 03-250 and JFRL 03-251) for further study. Colonies of this fungus were gray and uneven, with a granular surface, and irregular white edges, finally turning black on PDA (Fig. 1B, C). Pycnidia were black, globose and 54-222 μm in diameter (Fig. 1D). Conidia were hyaline, single-celled, and nearly elliptical, which ranged from 7 to 13 × 5 to 7 μm (n=40) (Fig. 1E). These morphological characteristics were consistent with those described for the fungus Phyllosticta spp. (Wikee et al. 2013a). To confirm the fungal identity, the internal transcribed spacer (ITS) region, actin (ACT), translation elongation factor 1-alpha (TEF1-a), glyceradehyde-3-phosphate dehydrogenase (GPD) and RNA polymerase II second largest subunit (RPB2) genes were amplified using primers ITS5/ITS4, ACT-512F/ACT-783R, EF-728F/EF2, Gpd1-LM/Gpd2-LM and RPB2-5F2 /fRPB2-7cR, respectively (Wikee et al. 2013b). The sequences of the selected isolates were 100% identical. Hence, sequences of one representative isolate JFRL 03-250 were deposited in GenBank (OP854673, ITS; OP867004, ACT; OP867007, TEF1-a; OP867010, GPD; and OQ559562, RPB2). BLAST search analysis in GenBank showed 100% similarity with those of P. capitalensis (GenBank accession nos. ITS, MH183391; ACT, KY855662; TEF1-a, KM816635; GPD, OM640050 and RPB2, KY855820). From a phylogenetic perspective, a maximum likelihood phylogenetic tree was constructed by using IQtree V1.5.6 based on multiple sequences (ITS, ACT, TEF1-a, GPD and RPB2) (Nguyen et al. 2015), and the cluster analysis resulted the representative isolate JFRL 03-250 within a clade comprising Phyllosticta capitalensis (Fig. 2). Based on morphological and molecular characters, the isolate was identified as P. capitalensis. To confirm pathogenicity and fulfill Koch's postulates, 6 healthy potted plants were inoculated with 1× 106 conidia/ml suspension of isolate JFRL 03-250 by spraying on the leaves, whereas 6 plants were sprayed with sterile distilled water to serve as control. All potted plants were incubated at 28°C, 80% relative humidity and 12-h light/12-h dark alternating conditions in a climate cabinet. After 15 days, similar symptoms were observed in the inoculated leaves as in the field (Fig. 1F), whereas control leaves remained asymptomatic (Fig. 1G) and P. capitalensis was successfully re-isolated from the symptomatic leaves. Previously, P. capitalensis has been reported to cause brown leaf spot disease of various host plants around the world (Wikee et al. 2013b). However, to our knowledge, this is the first report of brown leaf spot caused by P. capitalensis on D. odora in China.

First Report of Brown Leaf Spot Caused by Epicoccum tobaicum on Oat (Avena sativa) in Korea.

Oat (Avena sativa) is one of the Korean winter crops, and oat consumption has been increasing because it is widely perceived as a superfood. Recently, various fungal diseases have been reported likely due to climate changes during the winter season in Korea (Choi et al., 2018; Kim, 2020). During the 2020-2021 winter to spring, we surveyed new fungal diseases among cereals, including oats, in the southern region of Korea. In April 2021, brown leaf spots on oat leaves were observed in Gangjin, Jeollanam-do, Korea. These brown spots were irregular circles, ranging from 2-7 mm in diameter. Samples from three infected leaves were surface sterilized by treating them with 70% ethanol for 1 min and 1% NaOCl for 1 min. The samples were subsequently rinsed at least twice with distilled water and dried with a sterile paper towel before being placed on 1.5% water agar supplemented with 100 ppm streptomycin. Hyphal tips derived from infected tissues after incubation at 25C for 7 days were transferred to a fresh potato dextrose agar (PDA). Three isolates, labeled as KJO-AN2-S1, KJO-AN2-S2 and KJO-AN2-S3, were obtained via single hyphal tip purification. Colonies on PDA were pigmented vermilion and subsequently turned to saffron color with irregular margins after 7 days. Conidia produced on PDA were golden to dark brown, globose to subglobose, solitary, and measured 15.5-21.5 μm in diameter (n=50). Cultural and morphological characteristics suggested that these isolates belong to Epicoccum species (Chen et al. 2017). For identification by sequencing, the ITS (MW691866-68), tub2 (MW691872-74), and rpb2 (MW691869-71) regions of three isolates were amplified using the primer pairs ITS5/ITS4 (White et al., 1990), Btub2Fd/ Btub4Rd (Woudengerg et al., 2009), and RPB2-5F2 (Sung et al., 2007)/fRPB2-7cR (Liu et al., 1999), respectively. A maximum likelihood phylogenetic analysis based on the concatenated ITS, tub2, and rpb2 sequences placed the three isolates within a clade comprising E. tobaicum CBS 384.36. A mycelial plug (5 mm diameter) was inoculated onto wounded and unwounded leaves of healthy 12-day-old oat (cv. Choyang) seedlings. The control leaves were inoculated with a sterile PDA plug. All inoculated and control plants were placed in a plastic box and incubated at 20℃ in darkness with 100% humidity. After 1 day, the inoculated mycelial plug or sterile PDA plug from plants was removed; the plants in plastic boxes were then transferred to a growth chamber set at 20℃ with 12 h light and 60-70% humidity. While brown spot lesions were observed in both unwounded and wounded leaves 7 days post-inoculation, both wounded and unwounded control leaves remained asymptomatic. The pathogen was recovered from all symptomatic leaf tissues but could not be isolated from control leaves. The re-isolated pathogen was identified as E. tobaicum through morphological characterization and sequence-based identification, fulfilling Koch's postulates. This study is the first to report a causal relationship between E. tobaicum and brown leaf spot disease of oat in Korea. Identification of this newly emerging fungal disease on oats will help prepare for effectively managing this disease.

Effect of Nutrient Management and Weeds on Incidence of Fungal Diseases in Rice

High-input, modern agriculture uses large amounts of energy, water, fertilizers, and pesticides to produce high crop yields. One of the major bottlenecks of the modern agriculture in the tropics is substantial yield losses due to fungal diseases including rice blast, leaf spots and leaf scald. The aim of this study was to compare the incidence of fungal diseases in judicious nutrient management systems, including organic, integrated, and conventional, under different weed categories during dry season (May to September 2020) and wet season (November 2020 to March 2021). Rice disease incidence were collected for both seasons from 48-84 days after sowing. Additionally, disease incidences on grasses and sedges weeds were also calculated. Brown spot, narrow brown leaf spot, leaf scald, and rice blast incidences were substantial in wet season, while the disease incidences during dry season in 2020 were negligible. The disease incidences were significantly higher (P<0.05) in organic and conventional input systems compared to the integrated input system. Disease incidences of brown spot and leaf scald were found in the dry season. Higher disease incidences were recorded in the wet season than in the dry season. The incidences of the brown spot were higher on sedges than in grasses and vice versa were observed for narrow brown leaf spot disease. Leaf scald incidences were positively correlated with the significant nitrogen status of the rice crop. Disease incidence was low in integrated input system compared to conventional and organic input systems, while weeds were reported as alternative hosts. It can be concluded that the integrated nutrient management with recommended dosage of nitrogen application with proper weed management can lead to low disease incidents, hence is ecologically more sustainable.

Transcriptome profiling uncovers the involvement of CmXyn1, a glycosyl hydrolase 11, in Cochliobolus miyabeanus pathogenicity

Necrotrophic pathogen Cochliobolus miyabeanus (C. miyabeanus) causes rice brown leaf spot disease and drastically affects the yield and quality of rice grains. However, the molecular mechanism of rice-C. miyabeanus remains poorly understood due to the limited research conducted on this pathosystem. To elucidate the molecular mechanism of rice-C. miyabeanus, a transcriptome analysis was conducted from in vitro and in planta grown C. miyabeanus. This analysis led to the identification of a total of 24,060 genes of which 426 in vitro and 57 in planta expressed genes were predicted to encode for secretory proteins. As these 57 genes were specifically expressed in planta and were predicted to be secretory in nature, these were consider as putative effectors, highlighting their possible roles in the fungal pathogenicity. Notably, among these putative effectors, CmXyn1 which encodes a glycosyl hydrolase 11 displayed the highest expression level under in planta conditions and was thus selected for further functional characterization. Interestingly, the extracellular expression of CmXyn1 transiently induced cell death in Nicotiana benthamiana leaves, while intracellular expression was comparatively lesser effective. In addition, transcriptome analysis on rice leaves during C. miyabeanus infection and comparing it to the rice leaf transcriptome data obtained during hemibiotrophic pathogen Magnaporthe oryzae infection led to the discovery of 18 receptors/receptor-like kinases that were commonly expressed in response to both pathogens, indicating their key roles in rice defense response. Taken together, our findings provide new insights into rice-C. miyabeanus interaction as well as the unique and common defense responses of rice against hemibiotroph and necrotroph model systems.

Characterisation and in-vitro Control of Curvularia lunata , the Causal Agent of Brown Leaf Spot Disease of Rice in Ghana

Irrigated rice production is common in the coastal savannah zone of Ghana. Recent observations have shown the incidence of a new leaf spot disease in some rice basins in the area. Research was carried out to determine the incidence and severity of the disease in the area, identify the causal agent using its cultural and morphological features, complemented with phylogenetic studies of the internal transcribed spacer region. Also, the effect of some selected fungicides and an antagonistic Trichoderma harzianum on the mycelial growth of the fungus was determined in vitro. The disease was found in all the major rice growing districts in the coastal savannah zone with severities ranging from 22.6 to 50.9%. Curvularia lunata was identified as the causal agent of the disease. Carbendazim, Nordox and Mancozeb, totally depressed the mycelial growth of the fungus whiles T. harzianum inhibited the growth of the fungus. These fungicides and antagonistic organism have the potential for the control of the disease in the field.

First report of Neofusicoccum parvum causing leaf spot disease on Macadamia integrifolia in China.

The macadamia industry is developing rapidly in China. A brown leaf spot disease was noted in six Macadamia integrifolia plantations in Lincang, Yunnan, in October 2021. Over 60% of trees sampled had brown leaf spot symptoms, among approx.15,000 trees planted in these areas. Lesions (3 to 5 mm dia.) were small round brown spots with yellow edges. Lesions on severely infected leaves were darker and larger, with irregular shape (8 to 10 mm long, 3 to 6 mm wide). About 10% of diseased leaves had lesions characterized by a shot hole surrounded by a yellow halo. Potential pathogens were isolated from four randomly-selected symptomatic leaves from each of the six plantations by cutting lesion edges into small pieces. The pieces were surface sterilized, placed onto water agar containing 100 ppm aureomycin and incubated for 5 days at 24°C in the dark. Subculturing microbial growth on potato dextrose agar produced single-hyphal isolates with white fluffy aerial mycelia that turned pale olivaceous gray after 4 to 5 days. In four randomly-selected cultures, conidia were single celled, hyaline, spindle shaped to oval, and measured 10.9 to 16.3 µm long and 4.0 to 6.2 µm wide (n = 50). These characteristics matched those of Neofusicoccum parvum (Pavlic et al. 2009). Isolate LC013 was randomly selected as a representative individual for molecular identification. Internal transcribed spacer (ITS; ITS1/ITS4 primers; White et al. 1990), beta-tubulin gene (tub2; BT2A/BT2B primers; Glass and Donaldson 1995) and translation elongation factor 1-alpha gene (tef1-α; EF1-728F/EF2 primers; Carbone and Kohn 1999; O'Donnell et al. 1998) regions were PCR amplified from genomic DNA. Sequences of the products were used to BLAST probe the type specimen nucleotide sequences in GenBank. The LC013 sequences (GenBank accessions OM392021 (ITS); OM453641 (tub2); OM567656 (tef1-α)) had >99% sequence identity with analogous sequences from the type specimen of N. parvum CBS 138823 (accessions AY236943 (ITS); AY236917 (tub2); AY236888 (tef1-α)). Isolate LC013 was sister to N. parvum type strain in a maximum-likelihood (ML) tree constructed from analogous concatenated ITS, tef1-α, and tub2 sequences of 27 species that are phylogenetically closely-related to LC013 based on the ITS single locus ML tree. Koch's postulates were tested twice with two isolates by wounding leaves of four 14-month-old M. integrifolia seedlings with a sterile needle and placing a 5-mm-diameter agar plug containing N. parvum on the wound site. PDA plugs alone were used as uninoculated controls. Leaves were covered with sealed bags to maintain >90% humidity for 24 hours. All plants were kept in the same glasshouse under natural conditions. Leaves of inoculated plants began to discolor at 5 days post-inoculation (dpi). Brown spot symptoms were observed at 9 dpi. Control plants were symptomless. N. parvum was re-isolated from leaf lesions of the infected plants, but not from control plants, thus fulfilling Koch's postulates. N. parvum is an aggressive pathogen that causes severe disease on important tree and woody species, including M. integrifolia (Liddle et al. 2019). In China, it has been reported to cause leaf spot disease on 26 plant species (Farr and Rossman 2022), but this is the first report of N. parvum causing leaf spot disease on M. integrifolia. Further investigation is required to estimate the importance of this pathogen to the macadamia industry in China.

Effect of Sowing Times and Rice Varietal Resistance on the Severity of Narrow Brown Leaf Spot Disease in Relation to Environmental Conditions

The objective of this study was to investigate the effects of sowing times and genetic resistance of 10 commercially important rice varieties on the percent disease severity (PDS) of narrow brown leaf spot (NBLS) caused by Cercospora oryzae. Two sowing time treatments (mid-May and mid-June) each year were evaluated for this 2-year study. Rice varieties were drill seeded and arranged in randomized complete block designed plots with four replications for each variety. The effects of environmental factors (high and low temperature, relative humidity and precipitation) on the NBLS severity of the rice varieties at both sowing times were also evaluated. Disease data was analyzed using computer software GenStat 10th edition. Results: By changing cultivation timing of rice varieties, B-Chenab, KSK-434, PK-386, B-Kissan, and KSK-133 from mid-May to mid-June, their resistance levels were also changed from a higher to a lower. Weather conditions during the mid-June cultivation of 2019 induced a higher level of disease severity than did the mid-May weather conditions of 2018. The variation in temperatures affected the percent disease severity more as compared to relative humidity and precipitation. High temperature of 31-33˚C and low temperature of 18-21˚C were found to be most effective in enhancing the NBLS development. Minimum NBLS severity 4.75% and 8.25% was noted on variety B-515 in mid-May and mid-June sowings respectively. Thus, its rating changed from resistant to mildly susceptible by changing sowing timing. Rice variety PK-1121 depicted maximum NBLS severity 60.25 % in mid-May sowings, rated as very highly susceptible, while severity increased to 79.25% in mid-June sowings, and rated as completely susceptible. It is concluded that the severity of NBLS was affected by genetic resistance level of rice varieties, sowing times and weather conditions thus consideration of these factors is the key to the integrated management of the NBLS in rice.

Morpho-Cultural Variability Characterization of Bipolaris oryzae Causing Brown Leaf Spot of Rice in Jammu Sub-Tropics

Extensive fortnightly surveys were undertaken in major rice growing districts of Jammu division to study cultural and morphological variability amongst the isolates of brown leaf spot disease causing fungus (Bipolaris oryzae). Based on disease severity 24 isolates (BO1 to BO24) were divided into three groups (I, II and III). Group ‘I’ comprised 11 isolates with disease severity values between 51.22-67.44% and categorized under highly virulent and group ‘II’ comprised disease severity values between 43.17-48.17% and were categorized under moderately virulent isolates. Group ‘III’ included eight isolates with disease severity value between 26.11-38.17% and categorized under less virulent isolates. On the basis of colony growth pattern, margin and colour, the isolates were categorized into 4 groups (A, B, C and D). Group A comprised of six isolates had entire margin, circular form, umbonate elevation with smooth surface and black to fluffy growth. Eleven isolates were categorised under group B developed colonies with undulated margin, irregular form, umbonate elevation with grey fluffy growth and greyish colour. Group C comprised three isolates had undulated margin, irregular form, umbonate elevation with smooth surface. Group D contained four isolates developed entire margin, circular form; raised elevation with wrinkled surface, mycelium was grey which turned to black and showed grey to black pigmentation. The largest conidial size was recorded in isolate BO1 (98.43-101×24.54-25.54 µm). The conidia developed mean septa of 4.5-7.4 with straight to curve shaped. The sporulation of different isolates of B. oryzae ranged between 6.1-7.6×106 spores/ml.

Effect of Rates and Sources of N Fertilizer Application on Dynamics of Rice Brown Leaf Spot Disease (Bipolaris oryzae) Incidences in the Dry Zone of Sri Lanka

Nitrogen inputs; sources or application amounts are key determinants of yield determination and determination of resistance or sensitivity to pathogen activities. This study aimed at assessing the impact of source and rate of application of N fertilizers on Rice Brown Leaf Spot (RBLS) disease incidences and dynamics in lowland irrigated rice crops. Leaf N using relative leaf chlorophyll content, leaf N concentration and crop yield were assessed during the wet 2018/19, 2019/20 and 2020/21 seasons and dry 2019 and 2020 seasons in the field research facility of Rajarata University of Sri Lanka. The conventional systems (The Department of Agriculture recommended inorganic fertilizer application at 100% N), integrated system (50% N with conventional through inorganic fertilizer and 25% N with organic manure mixture), and organic system (50% of N conventional through organic manure) were tested using a new improved rice variety Bg300, using a randomized complete block design with six replicates. Wet and dry seasons were contrastingly different in disease prevalence, where critical levels of incidences were visible earlier in the wet season compared to the dry season. Initial stages of the study, organic systems resulted in higher disease incidences, thus reaching infections of the full crop before conventional and integrated. Several seasons of continuous organic manure incorporation enhanced the resistance of organic systems to RBLS disease compared to the rest. The leaf N concentrations were higher in conventional, thus the RBLS incidences were relatively low, due to negative correlations between disease incidences. Rice yields also resulted in a significant negative correlation with disease incidences and were diminished in integrated and organic systems later. The yield suppression due to diseases such as RBLS in organic transition can be overcome by using an integrated approach and building a balanced substitutable nutrient management strategy.

Brown leaf spot of Jacaranda mimosifolia Caused by Colletotrichum karstii in Sichuan, China.

Jacaranda mimosifolia D. Don is widely cultivated in southwest China (Yunnan, Sichuan, and other regions). It is widely applied in papermaking, medicine, environmental monitoring, timber, urban and rural afforestation, and soil and water conservation. In October 2020, a new brown leaf spot disease of J. mimosifolia was discovered in Xichang City (27°49' to 27°56'N, 102°16' to 102°11'E), with approximately 66.23% disease incidence. Firstly, the typical symptoms showed deep yellow necrotic lesions in the center or on the margin of the leaves. Gradually, the necrotic lesions expanded and developed into brown spots. Under humid conditions, the edges of necrotic lesions turned dark brown progressively. Finally, the leaves withered, died, and fell off. Infected tissues from ten samples were cut into small pieces of 2.5 × 2.5 mm. The surfaces of infected tissues were sterilized for 30 s in 3% sodium hypochlorite, 60 s in 75% ethanol, and rinsed three times in sterile water. They were then blot-dried with autoclaved paper towels and cultured on potato dextrose agar (PDA) at 25℃ for 3 to 8 days. After culturing for 8 days at 25℃ and 12 h/12 h light/dark on PDA, the colony diameter reached 78.2 to 82.7 mm. The colonies were light orange, turned pale pink with light orange beneath. The conidia were single-celled, aseptate, cylindrical, smooth-walled, straight, hyaline with both ends bluntly rounded, measuring 12.3 to 16.8 × 4.3 to 5.6 μm (n = 100; average=14.5 × 5.1μm). These morphological characteristics were consistent with the description of C. karstii (Zhao et al. 2021). For molecular identification, the genomic DNA of the representative isolate JM202010 was extracted using a fungal genomic DNA extraction kit (Solarbio, Beijing). The internal transcribed spacer (ITS) [ITS1/ITS4 (White et al., 1990)], calmodulin (CAL) [CL1C/CL2C (Weir et al., 2012)], actin (ACT) [ACT512F/ACT-783R (Carbone & Kohn, 1999)], chitin synthase (CHS-1) [CHS-79F/CHS-345R (Carbone & Kohn, 1999)], β-tubulin (TUB2) [BT2A/BT2B (O'Donnell et al., 1997)], and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) [GDF/GDR (Templeton et al. 1992)] were amplified. Sequences were deposited in GenBank (ITS: OL454787, CAL: OL518966, ACT: OL518967, CHS-1: OL518968, TUB2: OL518969, and GAPDH: OL518970). BLAST results indicated that the ITS, CAL, ACT, CHS-1, TUB2 and GAPDH sequences showed >99% identity with Colletotrichum karstii sequences at NCBI (GenBank MW494453.1, MW495036.1, MG387951.1, MW495038.1, MW495042.1, and MG602034.1). The conidial suspension (1 × 106 conidia/ml) was sprayed on the leaves of 4-year-old J. mimosifolia plants (10 plants) and inoculated for pathogenicity test. Fifteen leaves of each plant (10 pots in total) were inoculated with spore suspensions on both sides of the leaves. An equal number of control leaves was sprayed with sterilized distilled water as a control. Finally, all pots were kept in a greenhouse at 26°C under a 16 h/8 h photoperiod and 60 to 68% relative humidity. The inoculated plants showed symptoms similar to those of the original diseased plants, but the controls remained asymptomatic. Colletotrichum karstii was re-isolated from the infected leaves and identified by both morphological characteristics and DNA sequence analysis. The pathogenicity test was repeated thrice, which showed similar results, confirming Koch's postulates. To our knowledge, this is the first report of brown leaf spot on J. mimosifolia caused by C. karstii in China. C. karstii was previously reported as the causal agent of anthracnose on Fatsia japonica (Xu et al. 2020) and Nandina domestica (Li et al. 2017) in China. This finding provides an important basis for further research on the control of this disease.

EFFECT OF AGRO-MET CONDITIONS ON THE PROGRESSION OF BROWN LEAF SPOT DISEASE IN BASMATI-370 RICE

Basmati-370 rice variety was used for the present investigation that has a distinct flavor and aroma, along with fine quality and moderately resistant to brown leaf spots. The primary emphasis of the research had been on the impact of climatic variables on brown leaf spot disease progression. The infection was initially identified in the late vegetative stage of each cropping season, viz., 2019 and 2020, and reached its peak during the maturity phase. In Kharif, 2018 the maximum infection rate (r) was observed during43rdMSW, whereas, in 2019 maximum infection rate (r) was observed during 39th MSW. The relation betweenweather factors and disease severity during 2018 designated a significantly negative correlation of -0.928and -0.903 with maximum and minimum temperature, respectively. Relative humidity (morning) had asignificant positive correlation (0.640), but relative humidity (evening), rainfall, and sunlight hours exhibitednon-significant negative correlations of -0.505, -0.418, and -0.362, respectively. In 2019, a substantial negativeassociation was found between illness severity and meteorological conditions. A significantly negativecorrelation of -0.917 and -0.937 with maximum and minimum temperature respectively, was observed.During the kharif, 2019 until the end of agricultural seasons, correlation study of disease progression withrelative humidity (morning), relative humidity (evening), sunlight (hr), and rainfall revealed non-significantand negative correlations.

Identification of the Causal Agent of Brown Leaf Spot on Kiwifruit and Its Sensitivity to Different Active Ingredients of Biological Fungicides.

Kiwifruit (Actinidia chinensis) is an important commercial crop in China, and the occurrence of diseases may cause significant economic loss in its production. In the present study, a new pathogen that causes brown leaf spot disease on kiwifruit was reported. The fungus was isolated from an infected sample and identified as Fusarium graminearum based on morphological and molecular evaluation. Koch’s postulates were confirmed when the pathogen was re-isolated from plants with artificially induced symptoms and identified as F. graminearum. Based on the biological characteristics of the pathogen, it was determined that: its optimal growth temperature was 25 °C; optimal pH was 7; most suitable carbon source was soluble starch; most suitable nitrogen source was yeast powder; and best photoperiod was 12 h light/12 h dark. Further investigations were conducted by determining 50% effective concentrations (EC50) of several active ingredients of biological fungicides against F. graminearum. The results showed that among the studied fungicides, tetramycin and honokiol had the highest antifungal activity against this pathogen. Our findings provide a scientific basis for the prevention and treatment of brown leaf spot disease on kiwifruit.

ECOFRIENDLY APPLICATIONS OF PLANT HORMONES TO ENHANCE RICE RESISTANCE AGAINST BROWN SPOT OF RICE DISEASE

The plant hormones application increased the resistance in rice plants against brown leaf spot disease. That’s, why, the effect of five plant hormones (salicylic acid, citric Acid, K2HPO4, KH2PO4, benzoic acid) on the resistance of rice plants (Oryzae sativa L.) to brown leaf spot disease cause by Bipolaris oryzae were evaluated in field. The results showed that all of the plant hormones evaluated distinctly increased resistance of rice to BLS disease. All plant hormones employed at three concentrations (0.5, 0.75 and 1%), significantly decreased the incidence of brown leaf spot. Salicylic Acid exhibited minimum disease incidence (%) as compared to benzoic acid, K2HPO4, KH2PO4, and citric acid under greenhouse and field condition as compared to control. Interaction between treatments and concentration (T×C) expressed that salicylic acid expressed minimum disease incidence at 0.05% (22.52), 0.75% (19.92) and 1.0% (17.32) %, followed by benzoic acid (27.26,25.23,22.92), K2HPO4 (28.78,25.72,22.83), KH2PO4 (32.61,29.94,27.62) and citric acid (36.96,34.27,31.55) % respectively in field condition. These results recommended that plant hormones have key role in controlling the brown leaf spot disease through inducing resistance in rice plants.

Evaluation of Fungicides for Management of Brown Leaf Spot Disease of Rice

Evaluation of Fungicides for Management of Brown Leaf Spot Disease of Rice