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International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 9 Number 11 (2020) Journal homepage: http://www.ijcmas.com
Review Article https://doi.org/10.20546/ijcmas.2020.911.147
A Review on Symptomatology, Epidemiology and Integrated Management Strategies of Some Economically Important Fungal Diseases of Soybean (Glycine max)
Munmi Borah* and Bishakha Deb
ICAR-All India Coordinated Research Project on Soybean, Jorhat center; Department of Plant Pathology, Assam Agricultural University, Jorhat-785013, Assam, India
*Corresponding author
ABSTRACT
K e yw or ds
Soybean diseases, Among different production constraints in soybean, the most serious being seed and seedling diseases. These diseases are caused principally by fungi or bacteria diseases of soybean, however fungal diseases causing greater threat to the crop production. The Rhizoctonia root damage caused by foliar diseases is mostly of minor importance except rot, Pod blight, Rhizoctonia aerial diseases like soybean rust, Pod blight, Rhizoctonia aerial blight or web blight/ web blight, blight etc. which can reduce yields when weather conditions favor disease Charocal rot, Rust disease and collar development. Correct identification and early detection are critical in the rot proper management of soybean diseases. In this review we are discussing
about economic importance, symptomatology, causal organism, disease Article Info cycle, epidemiology and integrated management of some economically
important fungal diseases of soybean viz. Seed and seedling diseases of Accepted: 10 October 2020 soybean, Rhizoctonia root rot, Pod blight, Rhizoctonia aerial blight or web Available Online: blight, Charocal rot, Rust disease and collar rot. 10 November 2020
Introduction soluble sugars (Hou et al., 2009). Among the grain legumes, it has the greatest potential of Soybean is valued globally for its relatively producing the cheapest source of food protein high-quality oil and protein, which comprise (Rao and Reddy, 2010). A frequent soybean approximately 20 and 40% of the soybean, protein consumption lowers the cholesterol respectively (Clemente and Cahoon 2009). levels and also reduces the risk of coronary Due to high protein content, soybean is heart disease (FDA, 1999; Henkel, 2000). known as ―poor man‘s meat‖. Seeds of Moreover, it improves the glucose tolerance soybean also contain about 33% in some diabetic patients (Messina, 1999). carbohydrates, up to 16.6% of which are 1247
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Currently, India ranks fourth in respect to management. The economic impact of these production of soybean in the world. The crop diseases has spurred research on their biology, helps earn valuable foreign exchange (Rs. epidemiology, and management. Some of the 62000 millions in 2012-13) by way of soya important soybean diseases along with their meal exports. Soybean has largely been epidemiology and management aspects are responsible in uplifting farmer‘s economic described in this review. status in many pockets of the country. It usually fetches higher income to the farmers Seed and seedling diseases of soybean owing to the huge export market for soybean de-oiled cake (FICCI). Seedlings diseases have been a major constraint to Soybean (Glycine max (L.) Unfortunately, soybean is susceptible to many Merr.) production in North America. From diseases and pests that can cause significant 2006 to 2009, seedling diseases ranked third yield losses. Although potential threats to among diseases and pests that reduced soybean production vary by growing regions soybean yield in United States and Canada some pathogens are consistent causes for (Olutoyosi and Carl, 2017). concern. Anthracnose, bacterial diseases, brown spot, charcoal rot, frog eye leaf spot, Seedling diseases of soybean (Glycine max) Fusarium root rot, pod and stem blight, Purple can be common under cool and moist soil seed stain & Cercospora leaf blight, conditions and may be caused by a complex Rhizoctonia aerial blight, Sclerotium blight, of pathogens in North Dakota (Bradley, Seedling diseases, Soybean rust, Virus 2008). diseases and a few other diseases have been reported in India (Wrather et al., 2006). Symptoms Another report states major biotic stresses of soybean crop in India are diseases like yellow Seed and seedling disease is caused by a mosaic virus, rust, rhizoctonia, anthracnose, complex of organisms, which mainly etc., and insect pests like stem fly, gridle includes: beetle, and various defoliators (Agarwal et al., 2013). In India, the Asian soybean rust Phytophthora-infected seedling stems are soft disease was first reported on soybean in 1951 and water-soaked. Overall, infected seedlings (Sharma and Mehta, 1996). Frog eye leaf spot will be wilted and stunted (Crop Protection (Cercospora sojina), rust (Phakospora Network, 2015). At the primary leaf stage pachyrhizi), powdery mildew (Microsphaera (V1), infected stems appear bruised and soft, difJusa) and purple seed stain (Cercospora secondary roots are rotted, the leaves turn kikuchii) were recorded in moderate to severe yellow, and plants frequently wilt and die form is prevalent in North Eastern Hill region (Malvick, 2018). (Prasad et al., 2003). Pythium- The characteristic symptom of most Identification followed by prevention of the Pythium infections is soft, brownish-colored, diseases is the first step towards management rotting tissue (Malvick, 2018). Emerged of diseases. Increased knowledge about the plants may be killed before the first true leaf location and quantity of the pathogen in stage. These plants have a rotted appearance. relation to weather conditions provides Diseased plants may easily be pulled from the numerous benefits to growers and researchers soil because of rotted roots (Crop Focus, by providing more accurate timing of disease 2013).
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Rhizoctonia- Infection is characterized by a Rhizoctonia solani is a common pathogen shrunken, reddish-brown lesion on the with a wide host range. The most common hypocotyl at or near the soil line. Infection strains of this pathogen (anastamosis groups, may be superficial, causing no noticeable AG) that infect soybean are AG-2-2 and AG- damage, or may girdle the stem and kill or 4. AG groups can have different optimal stunt plants. Causes loss of seedlings conditions for infection. (damping-off) in small patches or within rows; is usually restricted to the seedling Hyphal branch originates from distal dolipore stage (Crop Focus, 2013). septum with a characteristic constriction at the branching point. Conidia, clamp Fusarium - Causes light- to dark-brown connections, rhizomorphs, and cultural lesions on soybean roots that may spread over pigmentations other than brown are never much of the root system. May attack the tap observed. Basidiomal structure of sexual state root and promote adventitious root growth is characterized by a vertically branching near the soil surface, and may also degrade hymenium succeeded by layers of elongated lateral roots, but usually does not cause seed basidia slightly wider than basal hyphae. rot (Crop Focus, 2013). Domain: Eukarya Causal organism Kingdom: Fungi Subkingdom: Dikarya Phytophthora sojae is a fungal-like pathogen Phylum: Basidiomycota that survives in soil for up to five to 10 years Subphylum: Agaricomycotina C in association with decomposed soybean Class: Agaricomycetes tissues. Soybean is the only known crop host Order: Ceratobasidiaceae for this pathogen. It is favored by saturated, Family: Cantharellales warm soil. Phytophthora sojae is an oomycete Genus: Rhizoctonia (Ajayi-Oyetunde and pathogen of soybean, classified in the Bradley, 2018) kingdom Stramenopiles. It causes ‗damping off‘ of seedlings and root rot of older plant Fusarium seed and seedling blight of soybean is caused by a complex of different species Super kingdom: Eukaryota that may prefer different conditions. For Kingdom: Stramenopila example, some species may prefer warm and Phylum: Oomycota dry soils and others may prefer cool and wet Class: Peronosporomycetidae soils. Some Fusarium species may also have a Order: Pythiales broad host range that includes corn and wheat Family: Pythiaceae (Malvick, 2018). Genus: Phytophthora (Tyler, 2007). Disease cycle Pythium is a soilborne, fungal-like pathogen. Several different species damage soybeans. The major stages in life cycles of most root- The various species of Pythium that infect infecting oomycete species of Pythium and soybean have a wide host range that can Phytophthora are similar. The asexual cycle is include corn and many other crops. Pythium characterised by the production of sporangia. tend to be favored by cool and soil, but some Sporangia may germinate either directly in species may do more damage in warm soils liquid or on a surface to produce a germ tube (Malvick, 2018) (direct germination) or may differentiate by a
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process of cytoplasmic cleavage to form enhanced by slow germination and growth of uninucleate, biflagellate zoospores (indirect soybeans, poor quality seed, and plant stress germination). The released zoospores swim in (Malvick, 2018). water in search of host tissues (seeds, roots, stems or leaves) where they settle and encyst. Phytophthora root rot occurs across many The cyst germinates by developing a germ environments, but is most common in warm tube that may penetrate the host either (>60°F/15°C) and wet conditions, while directly, or via an appressorium or Pythium Prefers cold soil temperatures appressorium-like structure. The sexual cycle (<60°F). High-residue fields, and heavy or generates thick walled oospores that are compacted soils are at higher risk because of adapted for over-wintering and survival under cooler, wetter conditions (Crop Focus, 2013). harsh environmental conditions. Oosporogenesis involves the production of a Fusarium root rot is often associated with female oogonium and a male antheridium that stressed plant (Crop Protection Network, grows towards and fuses with the oogonium. 2015). Fertilisation occurs through the emptying of some of the contents of the antheridium into Integrated management the oogonium, leading to the development of an oospore, which has a thick inner wall. This Bacillus subtilis (6 g/kg), Pseudomonas resting spore can exhibit extended dormancy fluorescens (6 g/kg), B. subtilis+P. and can over-winter in the soil and then fluorescens (6 g/kg), Trichoderma viride (6 germinate under suitable conditions to g/kg), T. harzianum (6 g/kg), thiram+ produce single or multiple germ tubes. These carbendazim (2 g/kg). Seed treatments with germ tubes can then form sporangia thereby bioagents and fungicides while significantly recapitulating the asexual cycle of the bringing down seed borne fungi and seedling pathogen (Van et al., 2003). mortality both under laboratory and field conditions, enhanced seed quality, Rhizoctonia solani isolates generally do not germination, vigour and yield (Rajeswari and produce vegetative or asexual spores, and the Kumari, 2009). role of basidiospores as an inoculum source for the seedling diseases they incite on Fungicide seed treatments vary in efficacy, soybean is unknown. Its survival in the soil is and products that control Pythium and aided by the formation of long-lived ‗nutrient- Phytophthora diseases (such as ethaboxam, independent propagules‘ called sclerotia. For metalaxyl (-M), and mefenoxam) do not most Rhizoctonia infections to occur, affect Rhizoctonia and Fusarium species. sclerotia must first germinate to form mycelia Similarly, fungicides that are effective against that grow towards the host plant (Ajayi- Rhizoctonia and Fusarium have little effect Oyetunde and Bradley, 2018). on oomycetes (Crop Protection Network, 2015). Epidemiology Pioneer Premium Seed Treatment helps General conditions that promote seed and protect against all of these stand-reducing seedling disease diseases include wet, poorly- pathogenic fungi. Pioneer offers several drained, and compacted soils. However, the fungicide, insecticide and biological seed different pathogens have different optimal treatment choices to help meet specific local conditions. Seed and seedling diseases may be needs for stand protection. Allegiance® for
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Pythium and Phytophthora control, and 2) Andrus & W.D. Moore reported as a disease EverGol™ Energy (new for 2013), a next- of above ground parts. generation technology with multiple modes of action for enhanced protection against a broad Conidia were falcate, tapered towards the spectrum of early-season disease pathogens, apex, hyaline, unicellular and aseptate, with including Rhizoctonia, Fusarium and Pythium variable dimensions, formed in the acervuli, (Crop Focus, 2013). usually produced on the top of dark brown to black stromata (Rogerio et al., 2017). Pod blight disease of soybean Domain: Eukaryota Estimates of max. reductions in seed yield Kingdom: Fungi were 16-26% (av. 19.7%). Yields were Phylum: Ascomycota typically reduced as the pods became infected Subphylum: Pezizomycotina in USA (Backman et al., 1982). Class: Sordariomycetes Subclass: Sordariomycetidae Estimated yield reduction of soybean Family: Glomerellaceae (thousand metric tonnes) due to Anthracnose Genus: Colletotrichum /Pod Blight disease in 2006 was 45.3 Species: Colletotrichum truncatum (Argentina), 220 (Brazil), 1663.5 (China), 117.6 (India), 0.3 (Paraguay), 492.9 (USA). Disease cycle
Anthracnose occurs regularly in Delhi, The life styles of Colletotrichum species can Uttarakhand, Himachal Pradesh, Madhya be broadly categorised as necrotrophic, Pradesh, and Rajasthan. This pathogen can hemibiotrophic, latent or quiescent and attack soybean from early seedling stage to endophytic; of which hemibiotrophic is the maturity. It reduces yield by causing pod most common (De Silva et al., 2017). blight in various parts of India (Wrather et al., 2010). Epidemiology
Symptoms Do and Paik, 1987 reported in their findings
Infected seeds become shriveled, mouldy and that appressoria formation of C. truncatum brown. Laterally the infected tissues are was promoted in light treatment than in dark covered with black fruiting bodies of the treatment, reasonable pH of pH6-pH8. fungus. Under high humidity symptoms on leaves are veinal necrosis and premature Integrated management defoliation occurs (Borah, 2019). Benomyl followed by carbendazim, thiram The fungus cause anthracnose on leaves and and captan were highly effective in vitro. In blight on pods. Infected pods were shriveled vivo, benomyl followed by zineb, captan and and contain no seed (pod blanking) or more thiram gave good control. Among 7 varieties two seeded pods, with shriveled moldy seeds screened under artificial epiphytotic (Koelkar, 2017). conditions, varieties JS-22 and PKV-1 were highly resistant; variety MACS-13 was also Causal organism resistant (Ghawde et al., 1996). The most economical treatment found with highest C: B Anthracnose/Pod Blight of soybeans caused ratio (1:14.45) was the fungicide by Colletotrichum truncatum (Schwein.) Carbendazim followed by the fungicides 1251
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Carbendazium + Mancozeb (C:B ratio, brown at maturity. The pathogen may infect 1:8.92) (Jagtap et al., 2012). leaves, pods, and stems in the lower canopy. Reddish-brown lesions can form on infected Future approaches in disease management petioles, stems, pods and petiole scars. Long strands of web-like hyphae can spread along Jagtap et al., 2012 reported use of aqueous affected tissue and small (1/16 to 3/16 in. in leaf extracts of garlic, tulsi and onion which diameter), dark brown sclerotia form on inhibited 81.82%, 65.17% and 60.31% growth diseased tissue (Faske and Kirkpatrick, n.d.). of C. truncatum. Causal organism Rhizoctonia aerial blight /web blight of soybean The anamorph or imperfect stage of pathogen causing aerial blight in soybean is Estimated reduction in soybean yield Rhizoctonia solani Kühn. (thousand metric tonnes) in 2006 due to Rhizoctonia aerial blight were 300 (Brazil), Domain Eukarya 1188.2 (China), 39.2 (India), 12.5 (USA) Kingdom Fungi (Wrather et al., 2010). Subkingdom Dikarya Phylum Basidiomycota Aerial Blight/ web Blight of soybean caused Subphylum Agaricomycotina C by a fungus i.e. Rhizoctonia solani Kuhn Class Agaricomycetes (Teleomorph: Thanatephorus cucumeris Order Ceratobasidiaceae (Frank) (donk) is a serious problem in Family Cantharellales soybean and considered to be menacing and Genus Rhizoctonia causes heavy losses in yield particularly in Species: R. solani warm and humid part of the country. R. solani include septate hyphae, Aerial blight is an important disease of multinucleate cells in young hyphae, brown soybean, in USA and other soybean growing colouration of mature hyphae, right-angled countries including India and causes hyphal branching, constriction at the point of substantial losses in yield. Several estimates branching, dolipore septa that permits of yield losses due to disease have been unrestricted cell-to-cell movement of estimated. Aerial blight caused by cytoplasm, mitochondria and nuclei, Rhizoctonia solani is one of the most soil production of monilioid cells, and sclerotia of borne diseases of soybean particularly in the uniform texture (Ajayi‐Oyetunde and northern zone comprising the states of Bradley, 2018). Haryana, Punjab, Uttar Pradesh and Uttarkhand (Kumar et al., 2016). Disease cycle
Symptoms Rhizoctonia solani isolates generally do not produce vegetative or asexual spores, and the Foliar symptoms often occur during late role of basidiospores as an inoculum source vegetative growth stages on the lower portion for the seedling diseases they incite on of the plant following canopy closure. soybean is unknown. Its survival in the soil is Initially leaf symptoms appear as water- aided by the formation of long-lived ‗nutrient- soaked, grayish green lesions that turn tan to independent propagules‘ called sclerotia. For
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most Rhizoctonia infections to occur, Simulations from a soyabean growth model sclerotia must first germinate to form mycelia (SOYGRO) indicated that higher yields could that grow towards the host plant (Ajayi- be expected with wider row spacings during Oyetunde and Bradley, 2018). drought years (Joye et al., 1990).
Epidemiology Charcoal rot of soybean
The epidemiology of aerial blight may be Charcoal rot was most severe in the dry areas divided into two phases, one before and one of Argentina, Bolivia, Brazil, India, Paraguay, after canopy closure. The first phase is soil and the United States. Estimated reduction of borne and determines the number of potential soybean yields (thousand metric tonnes) due disease foci in the crop canopy. The second to Charcoal rot in 2006 were 905 (Argentina), phase is leaf borne and is important to the 500 (Bolivia), 360 (Brazil), 1.6 (Canada), expansion of disease foci. During the growing 39.2 (India), 1.6 (Paraguay), 697.6 (USA) season, patterns of rainfall between the two (Wrather et al., 2010). phases are an important determinant of the development of aerial blight (Yang et al., In India Charcoal rot was one of the diseases 1990). of Soybean causing most yield losses in 2006. Charcoal rot has accounted for more yield High soil moisture (80%) and 25 0C loss in India since 2004 due to erratic rainfall temperature were the most favourable for root and greater periods of drought. It has caused rot development while web blight was best the most damage to soybean in the major favoured at >85% relative humidity coupled soybean states of Madhya Pradesh, with 25 0C temperature. Continuous leaf Maharashtra, Rajasthan, and Karnataka. Yield wetness for at least 6 hrs was essential for losses have been as high as 77% in some disease initiation, while increase in leaf fields (Wrather et al., 2010). The charcoal rot, wetness duration for 6-12 hrs showed which is used to be a minor disease of corresponding disease incubation period soybean until 2004 in India, became a serious observed with further increase in leaf wetness pest due to altered weather conditions (Kumar et al., 2016). particularly on the account of longer drought spells during crop growth period (Gupta et al., Integrated management 2012).
The use of resistant varieties is the cheapest, Symptoms easiest, safest and most effective method to manage the aerial blight disease. The efforts On seedlings, after emergence, symptoms can through conventional breeding so far made in be visible on cotyledons as brown to dark developing commercial cultivars resistant to spots. Sometimes, the margins of the aerial blight (Kumar et al., 2016). cotyledons become brown to black and shed at an early stage. From the unifoliate leaf Rotate with poor or non-host crops such as stage onwards, the symptoms appear on corn or grain sorghum for two-years and emerging hypocotyls of infected seedlings as avoid narrow row widths and high plant circular to oblong, reddish-brown, lesions that populations are good management practices may turn dark brown to black after several (Faske and Kirkpatrick). days. These lesions may extend up the stem. Infected seedlings may die if hot and dry
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conditions persist. The pathogen causes Disease cycle lesions on the roots, stems, pods and seeds. Foliar symptoms progress from top of the The pathogen mainly produces either plant downwards. Leaves of infected plants microsclerotia (primary source of inoculum) remain smaller than normal and subsequently or pycnidia. The pathogen life cycle begins turn yellow prior to wilting. with microsclerotia germination into the soil. Under favorable environmental conditions A reddish-brown discolouration of the (low water potential and high soil vascular elements of roots and lower stem temperature) and in the presence of the host precedes the premature yellowing as the plants, microsclerotia germinate and produce fungus spreads up the stem during the season. a mass of hyphal threads. The hyphae grow The infected mature and dry pods are covered towards the host's roots and colonize the with locally or widely distributed black seedlings roots during the first weeks of seed bodies (microsclerotia). germination. When plants approach the end of the growing season and pathogen enters into After the death of the plant, numerous, its necrotrophic phase, plants show symptoms minute, pinhead-sized microsclerotia appear, like wilting and necrosis due to blockage of which can be seen readily when the epidermal vascular bundles with microsclerotia, tissue of the lower stems and roots is peeled enzymes activity and secretion of pathogenic from the affected parts. The infected crop in toxins. The most diagnostic symptom of the field exhibits premature yellowing in charcoal rot in invaded soybean plants is the scattered patches (Gupta et al., 2012). black and dusty speckled appearance of microsclerotia on stems, pods and seeds as Causal organism well as interior tissues like vascular, cortical, and pith tissues (Hemmati et al., 2018). Macrophomina phaseolina is a soil inhabiting organism capable of infecting soybean at any Epidemiology crop growth stage, but usually, it infects at post flowering stage. The fungus is also seed- Meyer et al., 1974 in his findings found that borne in many crops including soybean. It disease was greatest at 30-35˚C, although produces microsclerotia in root and stem some infections occurred on soybean tissues of host plants, which enable it to seedlings at 20-25˚C. Infected seedlings may survive in soil for 2–15 years and act as serve as a latent source of inoculum of the primary source of inoculum. The mature plant phase over a wide temperature pycnidiospores in Macrophomina are range. With increase in number of viable M. ellipsoid to obovoid and measure 20–24 · 7–9 phaseolina propagules, the disease seedlings µm (Gupta et al., 2012). also increased.
Domain: Eukaryota Seedlings can be infected in years when soils Kingdom: Fungi are exceptionally dry and soil temperatures PhySubphylum: Pezizomycotina are continuously above 35C for 2–3 weeks. Class: Dothideomycetes The germination of microsclerotia in soybean Order: Botryosphaeriales fields is favoured by dry soils, high soil C: N Family: Botryosphaeriaceae ratios of amendments, low bulk density Genus: Macrophomina (Gupta et al., 2012). Species: Macrophominaphaseolina
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Fig.1 (A)-(B) Soybean seeds infected by Pythium sp. Image: Borah, 2019; (C) cotyledons affected by Phytophthora root Rot Image: Borah, 2019; (D)-(E) Seedlings affected by Rhizoctonia root Rot Image: Borah, 2019; (F) Seedlings affected by by Fusariumsp Image: Borah, 2019.; (G) Disease cycle of Phytophthora sp. and Pythium sp.Van et al., 2003; (H) Disease cycle of Rhizoctonia solani’ Image: Ajayi-Oyetunde and Bradley 2018; (I) Disease cycle of Fusarium Image: Dweba et al., 2017
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Fig.2 (A)Symptoms on Cotyledons; Image; Kolekar, 2017; (B) Symptoms on leaf, Image ; Kolekar, 2017; (C) Symptoms on pods; Image; Kolekar, 2017.; (D) Disease cycle of Colletotrichum
Fig.3 (A) Web-like hyphae of Rhizoctonia solani spreading along the stem of soybean Image: Faske and Kirkpatrick, n.d.; (B) Water soaked, greenish lesions Image: Faske and Kirkpatrick, n.d.; (C) Mature sclerotia of Rhizoctonia solani on soybean petiole Image: Faske and Kirkpatrick, n.d.; (D) Disease cycle of Rhizoctonia solani Image: Ajayi-Oyetunde and Bradley, 2018
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Fig.4 (A) Stunted / wilted plants Image : Crop Protection Network; (B) A reddish-brown discolouration of the vascular elements of roots and lower stem ;(C) Disease cycle of Macrophomina phaseolina Image Hemmati et al., 2018
Fig.5 (A)-(B) Symptom of rust on Soybean leaf Image: Rupe and Sconyers, 2008; (C) Disease cycle of Phakopsora pachyrhiz; Image: Goellner et al., 2010)
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Fig.6 Collar rot of soybean showing sclerotia at the collar region of the plant Image: Borah, 2019
Fig.7 (A) Young plants killed by R. solani Image: Malvick, 2018‘; (B) Rhizoctonia root and stem rot Image: Malvick, 2018; (C) Disease cycle of Rhizoctonia solani, Image: Ajayi-Oyetunde and Bradley, 2018
Integrated management g⁄kg or thiram + carboxin at 2 g⁄kg seed (Gupta and Chauhan, 2005; Gupta et al., Charcoal rot disease can be controlled by 2012). organic amendments such as farmyard manure, neem and mustard cake (Rathore, In India, use of T. viride or Trichoderma 2000; Gupta et al., 2012). harzianum as a seed treatment (4–5 g⁄kg seed) has been recommended for the management Soil fumigation with sodium methyldithio of charcoal rot in soybean (Gupta and carbamate reduced populations of the Chauhan 2005). Seed treatment with pathogen on soybean residue and in the roots Pseudomonas aeruginosa reduced infection of plants grown in field plots (Kittle and of M. phaseolina by 14–100%, depending on Gray, 1982; Gupta et al., 2012). the strain of bacterium and the variety of soybean used (Ehteshamul-Haque et al., Seed treatment with captan at 3 g⁄kg or thiram 2007; Gupta et al., 2012). at 3 g⁄kg or thiram + carbendazim (2: 1) at 3
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Seed infection of M. phaseolina was pathogen survives on volunteer and winter- completely inhibited by dipping the seeds for sown soybean in southern India and then 5 min in ginger, garlic and neem extracts spreads to soybean in more northern areas (Hossain et al., 1999; Gupta et al., 2012). during the rainy season.
Future approaches in disease management The estimated reduction of yield in 2006 due to Soybean Rust in different countries are The role of RNA interference (RNAi) in the reported to be 45.3 (Argentina), development of disease-resistant varieties and 2000(Bolivia), 4720(Brazil), 6368.9(China), further suggested that such goal can be 78.4(India), 1.9(Paraguay), 24.59 (USA) in achieved in a more selective and robust thousand metric tonnes (Wrather et al., 2010). manner with the success of genetic engineering techniques. In this regard, RNAi Symptoms has emerged as a powerful tool to overcome the threats posed by viruses, fungi and The first symptoms of soybean rust caused by bacteria. Phakopsora pachyrhizi begin as very small brown or brick-red spots on leaves. Often the Possibilities may be explored to utilize RNA first lesions appear toward the base of the mediated gene silencing technology like leaflet near the petiole and leaf veins. This RNAi by supreesing the specific gene(s) part of the leaflet probably retains dew longer, governing susceptibility to charcoal rot in making conditions more favorable for soybean for successful management of the infection. Lesions remain small (2-5 mm in disease (Wani et al., 2010; Gupta et al., diameter), but increase in number as the 2012). disease progresses. Pustules, called uredinia, form in these lesions, mostly on the lower leaf Rust disease of soybean surface, and they can produce many urediniospores. Soybean rust urediniospores Soybean rust caused by P. pachyrhizi has are pale yellow-brown to colorless, with an been a serious disease in Asia for many echinulate (short spines) surface decades. It appeared in Africa in 1997, and in ornamentation. As more and more lesions the Americas in 2001 (Rupe and Sconyers, form on a leaflet, the affected area begins to 2008). yellow, and eventually the leaflet falls from the plant. Yield losses as high as 30 to 80% Soybean rust is one of the worst soybean have been reported, but the amount of loss diseases in India and may reduce yields up to depends on when the disease begins and how 100% depending on the time of infection, rapidly it progresses. Besides leaves, soybean variety planted, and climate. Initially, soybean rust can also appear on petioles, stems, and rust was restricted to the northeastern states of even cotyledons, but most rust lesions occur India and the hills of Uttar Pradesh and West on leaves (Rupe and Sconyers, 2008). Bengal prior to 1977 and caused little loss of soybean yield. Around 1993, it spread to other Causal organism areas such as Madhya Pradesh, Maharashtra, Rajasthan, Karnataka, Andhra Pradesh, The plant pathogenic basidiomycete fungi Himachal Pradesh, Tamil Nadu, and Kerala. It Phakopsora pachyrhizi and Phakopsora usually develops in India from the third week meibomiae cause rust disease in soybean of July to the last week of September. This plants. Phakopsora pachyrhizi originated in
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Asia–Australia, whereas the less aggressive P. Epidemiology meibomiae originated in Latin America The temperature in the range of 15-25˚ C in Domain Eukaryota; the presence of free moisture on the leaf Kingdom Fungi; surface is essential for the germination of Phylum Basidiomycota; uredospore. The maximum infection was Order Uredinales; found at 20-25˚C with 10-12 hours dew Class Urediniomycetes; period (Sharma and Gupta, 2006). Family Phakopsoraceae; Genus Phakopsora (Goellner et al., 2010). Generally, infection occurs when leaves are wet and temperatures are between 8°C and Disease cycle 28°C, with an optimum of 16°C to 28°C. At 25°C, some infection occurs in as little as 6 Interaction of P. pachyrhizi with its host hours of leaf wetness, but 12 hours are soybean and the nonhost plant Arabidopsis. a) optimal. After infection, lesions and pustules Upon infection P. pachyrhizi forms uredia with urediniospores can appear within 7 or 8 which are located mainly on the lower side of days, and the next infection cycle is set to the leaf. Newly formed uredospores are begin. Besides the environment, plant age dispersed by wind. b) Spores landing on affects soybean rust epidemics. leaves germinate and form an appressoria as depicted in the interference contrast Usually, rust lesions are not found on soybean micrograph. c) Intercellular hyphae form until flowering, unless there are high haustorial mother cells (hmc) from which inoculum levels early in the season. This may haustoria (hau) develop inside mesophyll be due to greater susceptibility of plants to cells. d) The life cycle of P. pachyrhizi is rust as the host enters the reproductive stages, completed with the formation of uredospores it may be because in lower parts of the canopy in uredia. e) In the nonhost interaction spores are more protected from UV radiation, between the fungus and Arabidopsis or it may be because conditions in the canopy uredospores germinate, form appressoria and become more humid as the canopy closes. In penetrate epidermal cells as known from the any event, lesions can form at any growth host type of interaction. stage, but major increases in disease do not occur until after flowering (Rupe and Similarly penetrated epidermal cells of host Sconyers, 2008). and nonhost plants die, as indicated after trypan‐blue staining. f) Fungal growth is Integrated management restricted at the mesophyll boundary. Pictures shown in e and f are optical sections from the There are three basic management tactics that same infection site focused either on the can play a role in reducing soybean rust epidermal or mesophyll layer. g) P. epidemics: fungicides, genetic resistance, and pachyrhizi is unable to complete its life cycle cultural practices. At present, fungicides are and does not sporulate on wild‐type the only highly effective tactic, but long-term Arabidopsis plants. sp, uredospore; app, management will probably depend more on appressorium; epi, epidermal cell; hau, resistance, in combination with fungicides haustorium; hmc, haustorial mother cell; and changes in cultural practices (Rupe and penh, penetration hypha; meso, mesophyll Sconyers, 2008). cell (Koch et al., 1983; Goellner et al., 2010).
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Future approaches in disease management Subclass: Agaricomycetidae Order: Polyporales Joint combination of systemic and multisite Family: Atheliaceae fungicides uses and genotypes with partial Genus: Athelia resistance, this strategy might be promising in Species: Atheliarolfsii (Teleomorph) future (Juliatti et al., 2017). At least two types of hyphae are produced. Biotechnological approaches like non host Coarse, straight, large cells (2-9um x 150- resistance, gene silencing are the other future 250um) have two clamp connections at each approaches for disease management (Godoy septation, but may exhibit branching in place et al., 2016). of one of the clamps. Branching is common in the slender hyphae (1.5-2.5um in diameter) Collar rot disease of soybean which tend to grow irregularly and lack clamp connections. Slender hyphae are often Root rot and collar rot are the important observed penetrating the substrate. diseases of soybean, in Vidarbha region of Maharashtra (Khodke and Raut, 2010). Sclerotia (0.5-2.0mm diameter) begin to develop after 4-7 days of mycelial growth. Collar rot of soybean caused by Initially a felty white appearance, sclerotia Sdewthimrolfsii, has attained the major status quickly melanize to a dark brown coloration in many soybean cultivating areas of northern (Fichtner, n.d.). Karnataka. Survey conducted in ten taluks of northern Karnataka during kharif 2002-03 Disease cycle indicated maximum disease incidence of 9.80% in Dharwad and traces in Bidar and When the cottony growth of the fungus comes Athani taluks (Prabhu, 2003). into contact with susceptible roots, leaves or stems, direct penetration occurs, but the Symptoms fungus can also infect through wounds. It produces chemicals that cause soft rots in 2-4 Infection occurs at or just below the soil days after infection. When the soft rots girdle surface. Yellowing or wilting of plants is the the stem, the foliage wilts and death of the first symptom. Leaves turn brown, dry and plant follows soon after. often cling to dead stem. Numerous tan to brown spherical sclerotia form on infected The fungal growth can easily be seen with the plant material (Borah, 2019). naked eye. About 7 days after infection, the cottony growth begins to form sclerotia. Causal organism These are 0.5-2 mm diameter and made up of tightly packed strands of the fungus. They are Collar rot caused by Sclerotium rofsii Sacc. white becoming light brown as they mature. (Anamorph) appears during seedling stage Sclerotia keep the fungus alive when there are no plants to infect. They remain alive for Domain: Eukaryota several years in soil or potting mix. Other Kingdom: Fungi than sclerotia, the fungus can survive between Phylum: Basidiomycota crops in the remains of plants. The life cycle Subphylum: Agaricomycotina is given below (Pestnet, n.d.). Class: Agaricomycetes
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Epidemiology were found effective in increasing seed germination and reducing pre and post Sclerotia serve as the principle overwintering emergence mortality. Maximum germination structures and primary inoculum for disease. was achieved due to seed treatment with Persisting near the soil surface, sclerotia may treatment T7 (Thiram+Carbendazim + exist free in the soil or in association with Trichoderma @ 3+1+4 g/kg) i.e. 89.15, 81.33 plant debris. Those buried deep in the soil and 83.14 per cent in consecutive three years may survive for a year or less, whereas those followed by seed treatment with Thiram + at the surface remain viable and may Carbendazim 3+1 g/kg (T-6) (Khodke and germinate in response to alcohols and other Raut, 2010). volatiles released from decomposing plant material. Thus, deep plowing serves as a Rhizoctonia root rot of soybean cultural control tactic by burying sclerotia deep in the soil. High temperatures and moist Economic importance of the disease (in conditions are associated with germination of India and abroad) sclerotia. High soil moisture, dense planting, and frequent irrigation promote infection Rhizoctonia root and hypocotyl rot, caused by (Fichtner, n.d.). Rhizoctonia solani Kuhn [teleomorph Thanatephorus cucumeris (Frank) Donk], is Integrated management an important disease of soybean [Glycine max (L.) Merr.] (Zhao et al., 2005). Deep ploughing in summer, crop rotation with maize or sorghum, Destroy infected stubble Rhizoctonia root and stem rot is a common (Kisan Suvidha). soybean disease that typically causes most damage to seedlings, but can also damage Belkar and Gade, 2013 reported that seed older plants. It can kill and stunt plants to treatment with Pseudomonas fluorescens @ result in significant yield losses, or the lesions 10g/kg of seed + Bradyrhizobium japonicum can be superficial and have minimal effects @ 20g/kg of seed + Pseudomonas striata @ on plant health. Rhizoctonia is a fungal 20 g/kg of seed was effective with minimum pathogen that infects many different plants in disease incidence i.e. 8.86%, 13.33%, 20.00% the northern U.S., but only some types of this at 20 DAS and 17.73%, 33.33% and 40.00% pathogen infect soybean (Malvick, 2018). at flowering, respectively. Symptoms Ansari, 2005 reported that from seed treatment with Trichoderma viride at 4 g/kg, Rusty-brown, dry sunken lesions on stems Pseudomonas fluorescens at 10 g/kg, and roots near the soil line are a characteristic recommended chemicals thiram+carbendazim symptom of Rhizoctonia infection. Lateral (2:1) at 3 g/kg, and an untreated control, roots may be decayed. Treatment with biological control agents produced more sturdy and vigorous plants Seedlings or older plants may develop these than those treated with chemicals and infections and become stunted, yellow, and untreated control. may wilt. The infections can be superficial and cause no clear damage to plants, or they Seed treatment and soil application of can girdle the stem and kill or stunt plants fungicides, bioagents and its combinations (Malvick, 2018).
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Causal organism Epidemiology
Rhizoctonia solani (a soilborne fungus). This Rhizoctonia root and stem rot occurs fungus has a wide host range that may include primarily in early to mid summer. Infected soybean, corn, alfalfa, and other crops; but plants typically appear in patches in a row or only some types of this pathogen infect field. Several different conditions can favor soybean. The most common strains of this this disease including, high soil moisture, pathogen (anastamosis groups also referred to warm soil temperatures, soil types with high as 'AG') that infect soybean are AG-2-2 and amounts of organic matter, and delayed AG-4. Different AG groups can have different emergence. Plant stress from herbicide or hail optimal conditions for growth and infection injury or the soybean cyst nematode (SCN) (Malvick, 2018). also may favor this disease (Malvick, 2018).
Hyphal branch originates from distal dolipore Integrated management septum with a characteristic constriction at the branching point. Conidia, clamp Planting resistant cultivars would be an connections, rhizomorphs, and cultural effective and environmentally sound strategy pigmentations other than brown are never to minimize economic losses from this observed. Basidiomal structure of sexual state disease (Zhao et al., 2005). is characterized by a vertically branching hymenium succeeded by layers of elongated Encourage seedling health with good basidia slightly wider than basal hyphae. agronomic practices and the use of high Domain Eukarya quality seed. Avoid or reduce plant stress, for Kingdom Fungi example from herbicide injury and SCN Subkingdom Dikarya infection. Crop rotation and tillage may be of Phylum Basidiomycota value where disease has been severe. Some Subphylum Agaricomycotina C seed treatment fungicides may reduce Class Agaricomycetes Rhizoctonia infection for a few weeks after Order Ceratobasidiaceae planting. Soybean cultivars may have Family Cantharellales different levels of tolerance, but none are Genus Rhizoctonia (Ajayi-Oyetunde and fully resistant to this disease (Malvick, 2018). Bradley, 2018) In conclusion: the correct identification and Disease cycle early detection are critical in the proper management of soybean diseases. We have Rhizoctonia solani isolates generally do not discussed about economic importance, produce vegetative or asexual spores, and the symptomatology, causal organism, disease role of basidiospores as an inoculum source cycle, epidemiology and integrated for the seedling diseases they incite on management of some economically important soybean is unknown. Its survival in the soil is fungal diseases of soybean viz. seed and aided by the formation of long-lived ‗nutrient- seedling diseases of soybean, Pod blight, independent propagules‘ called sclerotia. For Rhizoctonia aerial blight or web blight, most Rhizoctonia infections to occur, Charocal rot, Rust disease, collar rot and sclerotia must first germinate to form mycelia Rhizoctonia root rot disease of soybean. Seed that grow towards the host plant (Ajayi- and seedling diseases of soybean are more Oyetunde and Bradley,2018). prevalent when wet season follows planting.
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The disease can cause economic loss due to (Ludhiana), 20(2), 171-173. weak and less vigorous plants leading to poor Backman, P. A., Williams, J. C., and crop stand establishment. Rhizoctonia aerial Crawford, M. A. (1982). Yield losses in blight disease can cause significant yield loss soybeans from anthracnose caused by in soybean when conditions favor disease Colletotrichum truncatum. Plant development. The charcoal rot disease is more Disease, 66(11), 1032-1034. severe when plants are under stress from Belkar, Y. K., &Gade, R. M. (2013). moisture or nutrients, excessive plant Management of root rot and collar rot densities, soil compaction, improperly applied of soybean by antagonistic pesticides, nematodes or other pathogens. microorganism. Journal of Plant Although good progress in research on Disease Sciences, 8(1), 39-42. charcoal rot in soybean has been made during Borah, M. (2019). Identification of Soybean the past decade, still systematic studies are Diseases In Assam. Int J Recent Sci required to bridge the gap in knowledge of Res. 10(08), pp. 34154- physiological variability and pathogenicity. 34159. DOI: http://dx.doi.org/ Rust fungi, being a biotrphic pathogen, 10.24327/ijrsr.2019.1008.3832 requires integrated management approach, Bradley, C. A. (2008). Effect of fungicide owing to its high yield loss. If host is seed treatments on stand establishment, available, it can occur all the year round and it seedling disease, and yield of soybean occurs in major soybean producing regions of in North Dakota. Plant Disease, 92(1), the world. The fungus Colletotrichum 120-125. truncatum (Schwein.) causing pod blight Clemente, T. E., and Cahoon, E. B. (2009). causing severe economic loss as pods get Soybean oil: genetic approaches for heavily infested, which requires an integrated modification of functionality and total management approach. Rhizoctonia content. Plant physiology, 151(3), bataticola and Sclerotium rolfsii causes root 1030-1040. rot and collar rot in Soybean and is Crop Focus. (2013). Soybean Seed and considered as economically important Seedling Diseases. Retrieved from diseases of Soybean. http://www.compassagservices.com/wp - References content/uploads/2015/05/ais228_Crop_ Focus_Soybean_Seedling_Diseases.pdf Agarwal, D. K., Billore, S. D., Sharma, A. N., Crop Protection Network. (2015). Soybean Dupare, B. U., and Srivastava, S. K. Disease Management. Retrieved from (2013). Soybean: introduction, https://soybeanresearchinfo.com/pdf_do improvement, and utilization in India— cs/Soybean_Seedling_Diseases_CPN10 problems and prospects. Agricultural 08.pdf Research, 2(4), 293-300. De Silva, D. D., Crous, P. W., Ades, P. K., Ajayi‐Oyetunde, O. O., and Bradley, C. A. Hyde, K. D., and Taylor, P. W. (2017). (2018). Rhizoctonia solani: taxonomy, Life styles of Colletotrichum species population biology and management of and implications for plant biosecurity. rhizoctonia seedling disease of soybean. Fungal Biology Reviews, 31(3), 155- Plant pathology, 67(1), 3-17. 168. Ansari, M. M. (2005). Management of collar Do, E. S., and Paik, S. B. (1987). Effect of rot of soybean through biological Environmental Factors on agents. Plant Disease Research Appressorium Formation of
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How to cite this article:
Munmi Borah and Bishakha Deb. 2020. A Review on Symptomatology, Epidemiology and Integrated Management Strategies of Some Economically Important Fungal Diseases of Soybean (Glycine max). Int.J.Curr.Microbiol.App.Sci. 9(11): 1247-1267. doi: https://doi.org/10.20546/ijcmas.2020.911.147
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