Severe Stem Rot Research Articles

Effect of integration of eco-friendly components for the management of stem rot of berseem caused by Sclerotinia spp under in vivo conditions

Stem rot of berseem caused by Sclerotinia spp. is the most devastating and cosmopolitan plant disease, infecting more than 400 species of plants worldwide. The disease is reported to cause by a soil-borne plant pathogen and is responsible for significant amount of green fodder and seed yield losses in the forage crop. Integrated disease management is the practice of using a range of measures to prevent and manage diseases in crops. Total seven different combinations of eco-friendly components were integrated for their effect on the management of stem rot of berseem caused by Sclerotinia spp. under in vivo conditions. The experiment was conducted in a polyhouse using sick soil pots. Out of them, treatment T7 (TRN-10 + Eupatorium adenophorum + panchgavya + ghanjeevamrit) was found the most promising integration for the management of the stem rot disease, with terminal disease severity (13.17%) & AUDPC value (177.33) and maximum disease control (75.00%) after 35 days of inoculation. Thus it was inferred that the integration of various eco-friendly management components proved to be most effective in reducing the disease severity of stem rot of berseem.. KEYWORDS :Berseem, fodder, stem rot, Sclerotinia spp. , yield loss

Identification and Characterization of Colletotrichum truncatum and C. destructivum Causing Stem Rot of White Clover in China.

White clover (Trifolium repens L.) is an excellent quality forage legume species with superior planting efficiency, which reduces the cost of artificial weeding and nitrogen fertilizer inputs, and has feeding and economic value. However, from June to September 2022, severe stem rot affected the yield and quality of white clover crops in Harbin, Heilongjiang Province, China. The aim of this study was to identify the causative agents of the disease. Overall, Colletotrichum truncatum (6 isolates) and C. destructivum (10 isolates) were obtained from rotten white clover stems and identified based on morpho-molecular characteristics and phylogenetic analyses. Pathogenicity tests of the isolates revealed that C. destructivum had a higher pathogenicity to white clover than C. truncatum. In addition, all isolates were highly pathogenic to broad bean, fodder soybean, soybean, pak choi, and chickpea, were pathogenic to mint, and did not infect corn, wheat, or cilantro. C. destructivum and C. truncatum isolates were very sensitive to tebuconazole and pyraclostrobin, with EC50 values of 0.54 to 0.70 μg/ml and 0.42 to 0.62 μg/ml, respectively, efficacies ranging between 93.2 to 94.9% and 90.2 to 95.2% at 600 μg/ml and 450 μg/ml, respectively, and EC90 values of 1.88 to 13.36 μg/ml and 1.32 to 23.39 μg/ml, respectively. Therefore, intercropping of host and nonhost plants and chemicals can be considered to control stem rot in white clover. These results provide a basis for controlling C. destructivum and C. truncatum in white clover in China.

Significance of Direct and Indirect Impacts of Temperature Increase Driven by Climate Change on Threat to Oilseed Rape Posed by Sclerotinia sclerotiorum.

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, threatens oilseed rape (Brassica napus) crops internationally. The development of this disease is strongly controlled by the weather, which is why global climate change is likely to influence its spread and impact. Climate change may affect the pathogen directly or indirectly via the host plant. This study investigates the potential impact of climate warming on Sclerotinia stem rot severity in oilseed rape in Poland. The aim of this investigation was to assess the relationship between the direct impact (DI) and indirect impact (II) of climate change on disease severity using the 4.5 and 8.5 representative concentration pathways (RCPs). Under the RCP4.5 scenario, nearly 60% of the simulations performed for 16 regions in four periods (2020-2039, 2040-2059, 2060-2079, 2080-2099) showed reductions in disease severity in comparison to those conducted for 1986-2005, while under RCP 8.5, this reduction was generated for nearly 90% of the cases. The effect of the RCP scenario on clustering the regions according to the value of Sclerotinia stem rot severity was also investigated. The simulations revealed that, for all periods, the lowest disease severities are expected for Zachodniopomorskie and Pomorskie. The results obtained also show the superior effects of the II over the DI on Sclerotinia stem rot severity in the future. Under the RCP4.5 scenario, the rate of IIs was greater than that of DIs for 10 regions, while under RCP8.5, this relationship was registered for 16 regions. These outcomes result from the acceleration of the oilseed rape flowering period triggered by expected temperature increases. The novelty of this study lies in a detailed analysis of the relationships between the DI and II of climate change, expressed numerically, for 16 regions in Poland. The obtained results highlight the role of the indirect impact in shaping disease severity and indicate that it should be incorporated into assessment methods of climate change effects alongside the direct impact.

First Report of Botrytis cinerea Causing Stem Rot on Pea (Pisum sativum L.) in China.

Pea (Pisum sativum L.) is one of the most important cool season legumes consumed as vegetable in the world. In March 2022, a severe stem rot was observed on pea cultivars in vegetative stage in Wuhan, Hubei Province, China (30°39' N, 114°66' E). The infection started on the lower stems, and the lesions were water soaked, then girdled the stem, resulting in wilting of the leaves. Eventually, the entire plant died, and some necrotic stems were covered with gray conidia. To investigate the causal agent, small pieces cut from diseased stems were surface sterilized with 2% NaOCl for 1 min, then incubated on potato dextrose agar (PDA) at 25°C for 3 days. Pure cultures were obtained by hyphal tip transfer and five isolates were studied further. Colonies initially appeared white, turned gray from the center, then became taupe with cottony aerial mycelia, and finally black hard, round or irregular sclerotia (0.92 to 5.34 × 0.86 to 4.42 mm, n = 20) developed. The sealing film of several plates were removed after 5 days, and abundant conidia were produced 3 days later. The conidia are terminally arranged at the end of long, grayish branched conidiophores, conidia are unicellular, hyaline and round or elliptical, (9.2 to 11.4 × 6.7 to 9.2 μm, n = 50), and the conidiophores are (10.7 to 13.0 μm × 760 to 1080 μm, n=20) in size. The morphological characteristics were consistent with descriptions of Botrytis cinerea (Li et al., 2016). Genomic DNA of the five isolates was extracted, and the internal transcribed spacer region (ITS), glyceraldehyde-3-phosphate dehydrogenase (G3PDH) gene, heat-shock protein 60 (HSP60) gene, and DNA-dependent RNA polymerase subunit II (RPB2) gene were amplified using the primers described by Aktaruzzaman et al. (2018). The sequences were deposited in GenBank (accession nos. ON533694 and ON566787-ON566790 for ITS; ON600613 to ON600617 for HSP60; ON600608 to ON600612 for G3PDH; ON600603 to ON600607 for RPB2). The BLASTn analysis of these sequences showed that the isolates had high similarity (99 to 100%) with other B. cinerea isolates. A phylogenetic tree was constructed by MEGA11, and our isolates clustered in the B. cinerea clade. In pathogenicity test, 2-week-old seedlings of pea cultivar 'Zhongqin1' were inoculated. Mycelial plugs (5 mm diameter) taken from a 3-day-old colony of each isolate were placed on the axil of a stipule at the 4th node of potted pea plants (n=5 per isolate), and PDA plugs were placed on the same location of control (n=3). Inoculated and control plants were kept in a humid plastic box at 23°C for 2 days, and then placed in a glasshouse. Symptoms with water-soaked lesions were observed on the inoculated plants after 2 days, stems showed soft rot and broke off after 3 to 5 days, disease symptoms similar to those in the field, while the controls remained healthy. The pathogen was re-isolated from the affected stems, fulfilling Koch's postulates. B. cinerea had been reported to cause foliar, pod, seed and stem rot of pea after flowering in many pea production regions in the world (Kraft and Pfleger, 2001). Pea was recorded as a host of B. cinerea in Zhejiang, Sichuan and Yunnan Provinces (Tai, F. L. 1979; Zhuang, W.-Y. 2005; Zhang, Z. 2006.), but there has been no detailed disease description and identification of pathogen. To our knowledge, this is the first report of B. cinerea causing stem rot on pea in vegetative stage in China. Since B. cinerea can infect pea at any developmental stage, it could have a high economic impact as green pea production increases in China.

First Report of Sclerotium rolfsii Causing Southern Blight on Stephania tetrandra in China.

Stephania tetrandra S. Moore is a perennial liana and is widely cultivated in southern China for traditional Chinese medicine as a diuretic, anti-inflammatory, and antirheumatic treatment (Jiang et al. 2020). In August 2021, it was observed that a severe stem rot disease affected St. tetrandra cultivated in Anfu, Jiangxi province, China (114°27'26" E, 27°22'46" N). The disease symptoms included constriction and rot at the base of the stem, and covered with a layer of white mycelia. The plants above-ground finally wilted and dried with a disease incidence ranging from 8% to 16%. Lots of dried plants formed withered patches of field. Sections (1.0~2.0 cm) from browning stem tissues were surface-disinfected with 75% ethanol for 15 s, followed by 60 s in 4% NaClO, rinsed twice in sterile water, dried on sterilized filter paper, placed on potato dextrose agar (PDA), and incubated at 26°C in the dark for 3 days. A white rhizomorphic fungal mycelium, that is similar to the mycelium of strain FJSR0 on the surface of an infected plant in the field, was isolated from the cultured tissues with 67% frequency. When incubated on PDA, white and fluffy mycelia with even margins and a slight halo formed. Mycelia-produced clamp connections were observed. Colonies grew quickly and covered the dish (diameter: 9 cm) in 5 or 6 days. After that, sclerotia were initially white, then turned yellow, and chestnut brown at maturity. Spherical and subspherical sclerotia were observed after 8 days, with each plate containing 448 to 634 sclerotia (0.8 to 1.4 mm diameter; mean = 0.94 mm; n = 50). On the basis of morphology, the pathogen was similar to Sclerotium rolfsii Sacc. [teleomorph: Athelia rolfsii (Curzi) Tu & Kimbrough] (Sun et al. 2020; Ling et al. 2021). For molecular confirmation, the internal transcribed spacer (ITS) region with approximately 680 bp was amplified from strains FJRS0 and FJRS1 using primers ITS1/ITS4 (White et al. 1990). Two distinct types (different in one SNP and one 1-bp InDel) of ITS sequences were obtained from each isolate, and all isolates contain the two types (FJSR0: ON972516, ON972517; FJSR1: ON972520, ON972518). BLAST analysis of each type found that the hits, with identities >99%, are A. rolfsii except for two Sc. delphinii sequences (GU567775.1 and MK073010.1). Phylogenetic analysis placed strains FJSR0 and FJSR1 in the same clade as Sc. rolfsii but away from Sc. delphinii based on the previous method (Sun et al. 2021). Both morphological and molecular characteristics confirmed that the strains were Sc. rolfsii. For pathogenicity tests, PDA plugs (8 mm in diameter) covered with 5-day-old fungal mycelium were inoculated at the stem bases of three healthy St. tetrandra seedings and incubated at 26℃ and relative humidity of 80%. On the fifth day, inoculated plants were wilting. The infected stem bases turned brown to black and constricted as previously observed in the field. Some leaves, infected by the mycelium expanded from the PDA plugs, developed an orange and irregular spot. Sclerotia were observed 20 days post inoculation. In contrast, the leaves and stems of non-inoculated control plants remained symptomless. Pathogenicity tests were repeated three times. The fungus was reisolated consistently from each symptomatic tissue, thus completing Koch's postulates. Although Sc. rolfsii has been previously reported to cause a southern blight symptoms on vegetables, ornamentals, grass, and medicinal and leguminous crops (Sun et al. 2020; Ling et al. 2021), this is the first report of Sc. rolfsii causing similar symptoms of southern blight on St. tetrandra in China.

Single and combined effects of Pythium oligandrum Po37 and a consortium of three rhizobacterial strains on Sclerotinia stem rot severity and tomato growth promotion

Individual plant growth-promoting rhizobacterial (PGPR) strains (Bacillus thuringiensis B2, Bacillus subtilis B10 and Enterobacter cloacae B16) and their combination were used, with or without Pythium oligandrum, against Sclerotinia sclerotiorum. In vitro, all biological control agents (BCAs) reduced successfully hyphal growth of the targeted pathogenic fungus. They displayed antifungal activity by more than 50% compared to controls. In planta trials were conducted two years in the row and led to a significant decrease in stem rot severity two months after the antagonist’s application onto infected tomato plants. The reduction reached 75% using rhizobacterial mixtures and 72% using P. oligandrum alone, compared to controls. The plant growth-promoting potential of the three-strain consortium and P. oligandrum was also assessed. Increased height in disease-free plants was obtained with rhizobacterial mixtures (60%) compared to P. oligandrum (47%). The BCA’s mixture increased the height of treated plants inoculated with S. sclerotiorum (up to 80%) compared to inoculated and untreated plants. The fresh weight of the aerial parts and roots of disease-free plants was increased by 42 and 30% over control following their treatment with mixtures of rhizobacteria and P. oligandrum alone, respectively. On plants inoculated with S. sclerotiorum in both trials, the highest growth-enhancing effect was achieved using the combined treatment based on P. oligandrum and the three-strain rhizobacterial consortium (Po37 + B2 + B10 + B16). The rhizospheric microbial communities were assessed using Single Strand Conformational Polymorphism (SSCP). Differences in the genetic structure of the fungal and bacterial communities were observed following treatments applied in both trials.

Harvesting and phytosanitary parameters with particular regard to mycotoxin content of maize as a function of different seasonal, fertilisation and hybrid effect

The aim of our three consecutive years (2017–2019) field trial was to obtain information as to the effect of weather conditions of the actual year as well as to assess the impact of some technological parameters such as fertilisation, the choice on the hybrid type on the yield parameters, phytosanitary conditions and mycotoxin contamination of maize. According to our results, the climatic characteristics of the years, the examined hybrid characters (FAO 310 and 490) and the fact of N-fertilisation had significant effects on yield parameters and grain moisture content. The additional N-supply did not affect the development or severity of stem rot in any of the hybrid effects. In this respect, the year effect appeared to be the decisive factor since much higher stem rot values were recorded in the plots of the longer growing season hybrids. Among the mycotoxins examined, only zearalenone and fumonisin found in the harvest were significantly influenced by the effect of the year, the length of the growing season as well as nutrient replenishment. It can be stated that the applied technological parameters have a major effect on the expression of this toxin load in maize. Dry maize stocks that have lost their water in the vegetation are predisposing factors for toxin accumulation. N-content of soil and that of plants can play a different role in mycotoxin accumulation in maize plants.

Survey for the Incidence of Stem Rot (Sclerotium rolfsii sacc) of Groundnut in Andhra Pradesh

Background: Groundnut is an important edible leguminous oilseed crop and stem rot caused by Sclerotium rolfsii is one of the major soil borne disease affecting groundnut severely in India. The current study aimed to get an understanding regarding the incidence level and pattern of prevalence of the disease in the agro-ecological condition of Andhra Pradesh. Methods: Roving survey was taken up from major groundnut growing areas in Andhra Pradesh during kharif, 2019 and kharif, 2020 in five districts. From each district predominant groundnut growing areas were chosen for assessment of the disease. Five spots of one square meter area in each field were selected randomly and Per cent disease incidence was recorded. Result: From the data it is observed that the stem and pod rot incidence was higher during kharif, 2020 when compared with kharif, 2019. The pooled data indicated that the mean stem rot incidence for the two years ranges from 5.39% to 23.56% with highest mean stem rot incidence in Krishnapuram (v), Kothapatnam (m) of Prakasam dist (23.56%) and lowest in Bandarupalli (v), Yerpedu (m) of Chittoor dist (5.39%). Among different districts highest mean stem rot incidence was recorded in Prakasam dist (18.71%) and lowest was recorded in Chittoor dist (7.11%). The stem rot severity was high in sandy soils with TAG24 variety where groundnut is being grown followed by red sandy loams and least in clay loam soils. The groundnut sole crop recorded high disease incidence when compared with intercrop of red gram. Siginificant positive correlation was recorded between stem rot, pod rot and leaf spot incidence.

Histopathological and biochemical aspects of grafted and non-grafted cucumber infected with stem rot caused by Fusarium spp.

Cucumber grafting has been used in Egypt recently to induce soil diseases tolerance. The impact of various grafting techniques on the vulnerability of grafted cucumber seedlings to Fusarium which stimulates the stem rot was investigated. Consequently, the anatomical and physiological studies were carried out on the diseased and healthy grafted cucumber seedlings, comparing with the non-grafted ones. Fusarium equiseti (MW216971.1) caused a severe stem rot of the grafted seedling through affecting the connection area of the different grafting methods, leading to complete seedling death. The hole insertion grafting method significantly exhibited the highest diseases incidence (100%), and mean disease severity index (5) when inoculated with F. equiseti. The pathogen remarkably affected the graft union area causing tissue discoloration and decay. The levels of antioxidant enzymes and total phenols were significantly enhanced in the diseased grafted and self-rooted cucumber. However, the diseased grafted cucumber recorded significantly the highest values of the antioxidant enzymes activities and total phenolic content when compared with the self-rooted ones. The results of SDS-PAGE profile revealed variations in the leaves protein profile of the grafted and self- rooted seedlings in response to Fusarium infection. Taken together, grafting cucumber onto a resistant rootstock using the splice technique can alleviate the stem rot severity caused by Fusarium spp. by enhancing the histological, physiological and molecular defense response of the grafted seedling.

Stem rot management by nitrogen and potassium fertilization and effect on grain yield and quality of rice in Uruguay

Stem rot (Nakataea oryzae) limits rice (Oryza sativa) production in Uruguay when there are high inoculum levels in the soil. This disease is particularly damaging in potassium (K)-deficient soils that receive excessive nitrogen (N) fertilization. Nevertheless, no data exist for the response to stem rot in modern rice cultivars with respect to the interaction between balanced N and K fertilization. The aim of this work was to evaluate the combined effect of K and N fertilization and a foliar phosphite (Phi) in reducing stem rot severity in rice to prevent significant yield losses. A 3-year field study was conducted in a rice-producing region of Uruguay to investigate the effects of: (1) K fertilization rate, 0 or based on the Mg:K ratio; (2) N fertilization rate, 0 or 140 kg ha–1 N; and (3) Phi treatment, with or without foliar Phi (1.775 kg ha–1 of K Phi, 71%), at growth stage R2-R3. While the experiment was conducted in a soil with sufficient potassium, K fertilization reduced the severity and percentage of rice tillers that were severely affected by stem rot, resulting in a mean yield increment of 2% to 18% depending on the year (mean 7.5%). Nitrogen fertilization increased stem rot severity in only 1 year, but resulted in a mean yield increment of 10% over the 3 years of the experiment. Foliar Phi applied at the late boot to panicle exertion stage did not reduce disease incidence or severity and failed to increase the total rice grain and milling yield.

Seed-borne endophytic Bacillus velezensis LHSB1 mediate the biocontrol of peanut stem rot caused by Sclerotium rolfsii.

This study aimed to obtain an antagonistic endophyte against Sclerotium rolfsii from peanut seeds, evaluate the biocontrol efficacy towards peanut stem rot and explore its antifungal mechanism against S. rolfsii. Thirty-seven endophytic bacteria were isolated from peanut seeds, six of which exhibited stronger antagonistic activities against S. rolfsii (inhibition rate, IR of hyphae growth ≥70%). Strain LHSB1, the strongest antagonistic strain, was identified as Bacillus velezensis. LHSB1 showed 93·8% of radial growth inhibition of S. rolfsii hyphae and exhibited obvious antagonistic activity against another six pathogenic fungi of peanut. Pot experiments showed two different LHSB1 treatments both significantly reduced the disease incidence and severity of stem rot (P<0·05) compared to the controls, and the biocontrol efficacy reached 62·6-70·8%, significantly higher than that of Carbendazim control (P<0·05). Further analyses revealed LHSB1 culture filtrate significantly inhibited sclerotia formation and germination, caused the abnormalities and membrane integrity damage of S. rolfsii hyphae, which might be the possible mode of action of LHSB1 against S. rolfsii. Three antifungal lipopeptides bacillomycin A, surfactin A and fengycin A, were detected in LHSB1 culture extracts by UPLC-ESI-MS, which could be responsible for the biocontrol activity of LHSB1 against S. rolfsii. Our results suggested that the seed-borne endophytic B. velezensis LHSB1 would be a tremendous potential agent for the biocontrol of peanut stem rot caused by S. rolfsii. This comprehensive study provides a candidate endophytic biocontrol strain and reveals its antifungal mechanism against S. rolfsi. To the best of our knowledge, this is the first time that seed-borne endophytic B. velezensis was used as the biocontrol agent to control peanut stem rot.

First Report of Fusarium avenaceum Causing Stem Rot on Polygonatum cyrtonema in Sichuan, China

Polygonatum cyrtonema Hua, which is an important perennial medicinal herb used for the treatment of diabetes and asthma, is planted extensively in China. In May 2018, the plants showed leaf wilt and severe stem rot symptoms. A survey showed 5% of the collected plants were diseased, with pink mold on the stem in the greenhouse and the wild in Sichuan Province. Over time, the necrosis extended around the stem so that the plants collapsed. Morphological and molecular analyses were carried out to confirm the causal agent. Six diseased plant tissues were surface disinfested with 75% ethanol for 30 s, 0.1% HgCl₂ for 1 min, rinsed in sterile water, dried, transferred onto potato dextrose agar (PDA), and incubated at 25°C for 7 days. Morphological characteristics were observed on PDA and synthetic low nutrient agar (SNA) (Garcia-Nunez et al. 2016). The genomic DNA of the isolates was extracted and sequenced to confirm the identity by rDNA internal transcribed spacer (ITS) region, the translation elongation factor 1-alpha (TEF-1α) gene, β-tubulin (TUB2), RNA polymerase II largest-subunit gene (RPB2), and large subunit (LSU) rDNA with primer pairs ITS4/ITS5, EF1/EF2 (O’Donnell et al. 1998), T1/T22 (Wang et al. 2014), fRPB2-5F/fRPB2-7CR (Liu et al. 1999), and LROR/LR5 (Rehner and Samuels 1994; Vilgalys and Hester 1990), respectively. Three isolates from diseased stems with similar morphology were isolated from single spores. Colonies on PDA grew rapidly and generated aerial mycelia with white to orange floccose and carmine to rose pigmentation on the reverse. On SNA medium, macroconidia were falcate, slender, curved with an elongated apical cell, usually three to five septa, measured 22.93 to 57.88 × 2.82 to 5.43 μm (n = 50), and occasionally one to two septa, 18.71 to 26.79 × 2.21 to 4.90 μm (n = 50). Microconidia were usually one-septate, hyaline, ovoid, smooth, and measured 10.09 to 19.39 × 2.22 to 4.28 μm (n = 50). Chlamydospores were not observed. The newly generated sequences (ITS, 561 bp, MK204577; TEF-1α, 673 bp, MK226333; TUB2, 1,261 bp, MK253102; RPB2, 1,125 bp, MK396098; and LSU, 885 bp, MK392034) of the isolate SICAUCC18-0001 indicated that those molecular data had high identity with those of Fusarium avenaceum (Fr.) Sacc. (ITS, KP265354 [100%], KP265365 [100%]; TEF-1α, MG670378 [100%]; TUB2, KY055838 [99%], KP170733 [99%]; RPB2, GQ915486 [99%]; and LSU, MH866319 [100%], MG274300 [100%], MG274299 [100%]) obtained from Solanum tuberosum L., wheat, Beta vulgaris L., and Vitis amurensis Rupr., respectively. The identification was confirmed by multilocus phylogenetic analysis. Based on morphological features and phylogenetic analysis, this fungus was identified as F. avenaceum (Garcia-Nunez et al. 2016). To complete Koch’s postulates, a pathogenicity test of the F. avenaceum was performed on sterile stems of P. cyrtonema. Ten stems wounded with a sterile toothpick were smeared with 20 μl of conidial suspension (1 × 10⁶ conidia/ml). Control plants were treated with sterile distilled water. Plants were placed in an aseptic incubator at 25°C and 95% relative humidity with 12-h light/dark. Seven days later, the inoculated plants developed symptoms similar to those observed in the field, and the controls were asymptomatic. The pathogens were successfully isolated from symptomatic stems. To our knowledge, this is the first report of F. avenaceum causing stem rot on P. cyrtonema.

SOIL SOLARIZATION IN THE CONTROL OF BEAN DISEASES CAUSED BY Sclerotium rolfsii

This study aimed at assessing the effects of soil solarization on diseases caused by Sclerotium rolfsii in bean plants. Treatments consisted of solarization of a soil previously infested with S. rolfsii and a standard treatment (no solarization). A randomized block experimental design was adopted, with four replications. We assessed disease severity by measuring emergence, final stand, incidence, and severity of the disease. Soil microbial activity and number of viable sclerotia were evaluated after the second crop was grown in the first year of the experiment. Soil solarization reduced the incidence and severity of stem rot caused by the fungus S. rolfsii in beans, as well as sclerotia viability. However, solarization was not effective for total control of the pathogen.

Streptomyces sp. RP1A-12 mediated control of peanut stem rot caused by Sclerotium rolfsii

Sclerotium rolfsii Sacc. is a destructive soilborne fungal pathogen with a wide host range that includes peanuts. Biological control offers an interesting alternative to fungicides for sustainable management of soilborne diseases. The current investigation is aimed at evaluating one potential biocontrol agent Streptomyces sp. RP1A-12 for growth promotion and the management of peanut stem rot disease caused by S. rolfsii under field conditions. Preliminary studies conducted under in vitro and the greenhouse conditions showed promising results against the stem rot pathogen. Further in vitro and pot experiments conducted to assess Streptomyces sp. RP1A-12 for its growth promoting abilities using whole organisms have shown an increase in seed germination, root and shoot length. Other parameters like nodule number and plant biomass were also significantly increased over control treatments indicating that the test bioagent possesses growth promoting abilities along with disease suppression capabilities. Subsequently field studies were carried out for two consecutive rainy seasons. The bioagent was applied as whole organism and partially purified crude metabolites. Results indicate the bioagent reduced stem rot disease incidence by 64–67% and 22–49% respectively in two field trials conducted with notable increase in yield. Partially purified Streptomyces sp. RP1A-12 metabolites exhibited an even greater effect in reducing the incidence and severity of stem rot compared to the pathogen inoculated control.

Stem rot on Cymbidium ensifolium (Orchidaceae) caused by Fusarium oxysporum in China

Cymbidium ensifolium is an important cultivated herb in southern China. A severe stem rot disease was observed on C. ensifolium in Fujian Province, China, in April 2016. Initially, the junction of the stem and root turned dark black, and the bottom leaves turned yellow. Subsequently, the leaf base began to rot and the stem turned brown and the entire stem became necrotic. A fungus was isolated from diseased stems with typical symptoms of stem rot. The pathogenicity of the isolated fungus was tested with successful infection of inoculated C. ensifolium plants. Koch’s postulates were confirmed by reisolation of the fungus from the infected tissue on artificially inoculated stems. Based on morphological characteristics and sequence analysis of the internal transcribed spacer and actin genes, the pathogen was identified as Fusarium oxysporum. This is the first report of F. oxysporum causing stem rot in C. ensifolium.

Identification of Neocosmospora ipomoeae causing tomato stem rot in Korea

Severe stem rot in hydroponically grown tomatoes was observed in Jinju, South Korea in early spring, 2016. Initial symptoms were water-soaked lesions on the lower stems, near the collar. Infected tomato plants gradually wilted leading to death of the plants. Advanced lesions were brown in color. Fungal isolates were identified by morphology and sequences of the gene encoding translation elongation factor 1-alpha (TEF1-α). To fulfill Koch’s criteria, pathogenicity tests were completed on potted 2-month-old tomato plants. The causal fungus was identified as Neocosmospora ipomoeae. This is the first report of tomato stem rot caused by Neo. ipomoeae in Korea.

STUDIES ON FIELD EVALUATION OF BRASSICA GERMPLASM/VARIETIES AGAINST SCLEROTINIA SCLEROTIORUM UNDER INOCULATED CONDITION

Indian mustard, Brassica juncea belong to Brassicaceae and Centre of origin Mideterian. Sclerotinia stem rot/ blight caused by Sclerotinia sclerotiorum is one of the most important fungal diseases in rapeseed and other crops in the world. The present study was undertaken to access the forty seven germplasm/varieties to find out the resistance against S. sclerotiorum under inoculated condition. The reaction of forty-seven germplasm was evaluated in randomized complete block design with thrice replications at the experimental field, Department of Plant Pathology, College of Agriculture, Gwalior during Rabi season 2014-15 and laboratory work was done in the Department of Plant Pathology, College of Agriculture, Gwalior (M.P.). Observations for severity of stem rot on main stem were recorded after 120 days of sowing using 0 - 4 scale. (Assessment scale 0-4 where 0 = no disease (resistance), 1 = less than half stem girdled (moderate resistance), 2 = more than half stem girdled (susceptible), 3 = whole stem girdled (moderate susceptible), 4 = plant dead (highly suscepitble). Forty-seven germplasm/varieties were evaluated for their reaction against Sclerotinia blight (Sclerotinia sclerotiorum). Out of forty seven germplasm / varieties, tested two Cultivar SBG-14-5 and SBG-14- 6 gave highly resistance reactions, while twenty six varieties are found resistant SBG-14-2, SBG-14-3, SBG-14-4, SBG-14-7, SBG-14-8, SBG-14-9, SBG-14-10, SBG-14-11, SBG-14-13, SBG14-15, SBG-14-17, SBG-14-18, SBG-14-23, SBG-14-27, SBG-14-28, SBG-14-30, SBG-14-31, SBG-14-32, SBG-14-33, SBG-14-34, SBG-14-35, SBG-14-36, SBG- 14-41, SBG-14-42, NDNSR-14-76, NDNSR-14-77, twelve varieties are found susceptible SBG-14-1, SBG-14-12, SBG- 14-14, SBG-14-16, SBG-14-21, SBG-14-22, SBG-14-24, SBG-14-26, SBG-14-29, SBG-14-37, SBG-14-39, SBG-14-40 and seven varieties SBG-14-19, SBG-14-20, SBG-14-25, SBG-14-38, Varuna, Rohini and BIOYSR were found highly susceptible against Sclerotinia blight (Sclerotinia sclerotiorum).

Effects of combined application of potassium phosphite and fungicide on stem and sheath disease control, yield, and quality of rice

Phosphite has been shown to suppress some diseases in different plant species but disease control in rice has not been investigated. In 2012/13 and 2013/14 potassium phosphite was sprayed at 1775 g ha−1 and 3550 g ha−1 in field plots of rice in Uruguay to determine if phosphite alone or in combination with label rates of a mixed strobilurin and triazole fungicide could be used to effectively control stem rot and aggregate sheath spot in irrigated rice. Six treatments consisting of different combinations of potassium phosphite alone or with a fungicide and an unsprayed control were assayed in one application at late-boot to early-heading. Phosphite alone in single and double rate slightly reduced severity and incidence of stem rot and produced a small yield increase over the unsprayed control. Fungicide at a 50% label rate with phosphite reduced stem rot severity and incidence to a similar level as the fungicide alone applied at the label rate. Disease severity was reduced by approximately 25% and incidence by 17–20% when compared with untreated control. Yield increase was 5% for both treatments over the unsprayed control. Fungicide combined with phosphite at single and double rates reduced stem rot severity by 40–45% and incidence by 34–38% when compared with untreated control, with yield increased by 10% over the unsprayed control and 5% over plots treated with a fungicide. These results indicate that a single application of potassium phosphite combined with fungicide can be used efficiently to manage of rice stem diseases.

Effect of β-aminobutyric acid on resistance of tomato against Pectobacterium carotovorum subsp. carotovorum

Stem rot of tomato caused by Pectobacterium carotovorum subsp. carotovorum (Pcc) results in economic yield loss worldwide. Previous studies have demonstrated the role of β-aminobutyric acid (BABA) in control of numerous plant diseases. To extend our understanding for the efficacy of BABA as an inducer agent against plant diseases, we evaluated the effect of BABA on disease severity of stem rot during infection of tomato by Pcc. BABA at concentration of 200 µM reduced the disease severity and offered protection against Pcc. On the other hand, BABA did not have direct antibacterial effect in vitro. Furthermore, we examined the effects of BABA on expression of pathogenesis-related gene 1 (PR-1), pathogenesis-related gene 2 (PR-2), phenylalanine ammonia-lyase (PAL) and catalase (CAT). Pretreatment with BABA led to more expression of PR-1 and PR-2 after Pcc infection when compared with their counterparts pretreated with water (control). PR-1 expression in BABA/Pcc treatment increased 2.83-, 4.31-, 2.46- and 1.88-fold at 24, 48, 72 and 96 h postpathogen inoculation (hpi), respectively, compared to water/Pcc treatment. Moreover, PR-2 expression in BABA/Pcc treatment increased 2.66-, 3.43-, 2.19- and 1.91-fold at 24, 48, 72 and 96 hpi, respectively, compared to water/Pcc treatment. On the other hand, PAL expression was transient during enhanced resistance by BABA. In comparison with water/Pcc treatment, PAL expression enhanced 2.42-fold at 24 hpi in BABA/Pcc treatment, whereas PAL expression was remained unchanged at 48, 72 and 96 hpi. CAT expression increased in early stages of the resistance induced by BABA. In BABA/Pcc treatment, CAT expression enhanced 4.6- and 3.1-fold at 24 and 48 hpi, respectively, compared to water/Pcc treatment. Our data confirmed the role of BABA as an effective resistance inducer against Pcc that might be considered in integrated diseases management programs.

Assessing the prospects of Streptomyces sp. RP1A-12 in managing groundnut stem rot disease caused by Sclerotium rolfsii Sacc

Stem rot of groundnut caused by the soilborne pathogen Sclerotium rolfsii can cause significant yield losses. Biological control of stem rot using actinomycetes is a viable alternative to existing fungicidal management. Though actinomycetes are prolific antibiotic producers, reports pertaining to their use in groundnut disease management are limited. Here, actinomycetes were isolated from groundnut rhizospheric soils and screened for antagonism against S. rolfsii through a dual culture assay. Culture filtrates and crude extracts of the potential candidates were screened further for extracellular antifungal activity and characterized for biocontrol and plant-growth-promoting traits. A promising candidate was tested under greenhouse conditions as whole organism as well as crude extracts. Isolate RP1A-12 exhibited high antagonism against S. rolfsii in dual culture assay (69 % inhibition), culture filtrate assay (78–100 % inhibition at various concentrations) and crude extract assay (100 % inhibition with 1 % crude extracts). Moreover, germination of sclerotia of the test pathogen was inhibited with 1 % crude extracts. Strain RP1A-12 produced hydrogen cyanide, lipase, siderophores and indole acetic acid. Oxalic acid production by S. rolfsii was also inhibited by crude extracts of RP1A-12. In greenhouse studies, RP1A-12 reduced stem rot severity. Overall, our results suggest that isolate RP1A-12 has potential biocontrol capabilities against stem rot pathogen. Molecular characterization based on 16S rRNA gene sequencing of RP1A-12 identified it as a species of Streptomyces, closely related to S. flocculus.