Plant Pathology & Quarantine 10(1): 120–132 (2020) ISSN 2229-2217 Article www.ppqjournal.org Doi 10.5943/ppq/10/1/14 An annotated list of genus Pythium from India Dubey MK1,2*, Yadav M1 and Upadhyay RS1 1 Laboratory of Mycopathology and Microbial Technology, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi - 221005, Uttar Pradesh, India 2 Department of Life Sciences, School of Basic & Applied Sciences, Galgotias University, Greater Noida- 203201, Uttar Pradesh, India Dubey MK, Yadav M, Upadhyay RS 2020 – An annotated list of genus Pythium from India. Plant Pathology & Quarantine 10(1), 120–132, Doi 10.5943/PPQ/10/1/14 Abstract Up-to-date information is presented based on an intensive search of literature records on the identity, occurrence, nomenclature, substratum, host ranges, geographical distribution and literature references of the genus Pythium from India. All Pythium species published until 2020 are included in this list. The survey result of all forms of analyses revealed that India has 55 species of Pythium belonging to the phylum Oomycota indicating the presence of rich mycoflora. Distribution of these Pythium species reported so far from freshwater and terrestrial habitats of various Indian states are listed alphabetically. The most frequently collected species are Pythium aphanidermatum, P. spinosum, and P. ultimum. The majority of these species were found as a parasite on a wide range of plants in both freshwater and terrestrial environment. Overall, this systematic checklist provides the total count of Pythium species, currently known to occur in India and it is also a valued addition for comparing Pythium diversity in India as well as the world. Besides, it represents the first comprehensive overview of Pythium since 1996 from India. The knowledge generated by this working checklist comprising accepted taxa in Pythium from India is hoped to be beneficial in the progress of the systematics, diversity, ecology, plant protection, aquaculture, ichthyopathology, quarantine and many other diverse arrays of applied scientific disciplines in the country. Key words – Disease – distribution – ecology – parasitic – soil-borne pathogen – saprobes – systematic taxonomy Introduction The oomycete genus Pythium (Pythiaceae, Pythiales) is a large heterogeneous group currently placed under the kingdom Chromista or Heterokonta (also called Straminipila) in the supergroup Chromalveolates (Kirk et al. 2008, Beakes et al. 2014, Dubey et al. 2020a). This large genus of fungal-like organisms is characterized by profusely branched, well developed, filamentous (threadlike), coenocytic (non-septate) mycelium composed principally of cellulosic cell walls with filamentous to globose sporangia/zoosporangia like hyphal swellings containing asexually formed heterokont zoospores and sexually produced organs such as antheridia, oogonia and oospores (van der Plaats-Niterink 1981, Beakes et al. 2014). Currently, this cosmopolitan genus includes more than over 300 recorded species out of which 130 have been well-recognized (Dick 1990) with a wide range of life histories that includes many saprophytes, plant or animal pathogens and mycoparasites Submitted 16 August 2020, Accepted 9 October 2020, Published 28 October 2020 Corresponding Author: Manish Kumar Dubey – e-mail – mkmkdubey@gmail.com, manish.dubey@galgotiasuniversity.edu.in 120 in various types of soil and aquatic environments (Lévesque & de Cock 2004, Webster & Weber 2007, Mufunda et al. 2017). The Pythium comprises endophytes, saprobes and plant pathogens. However, most of the species in this largest oomycete genus often serve as obligate saprotrophs on animal and plant debris; significantly helping in maintaining the natural nutrient cycling and the energy budget of the freshwater and terrestrial ecosystem around the world (Dick 2001, Dubey et al. 2020a). However, under certain favorable conditions, Pythium spp. can parasitize a wide range of hosts including algae, crustacean, fish, insects or mosquito larvae, humans beings, even other fungi or Pythium species as mycoparasites and plants (van der Plaats-Niterink 1981, Kawamura et al. 2005, Weiland et al. 2012, Ho 2013). The species belonging to Pythium are the causal agents of rot and damping-off diseases of numerous wild as well as cultivated plants (Martin & Loper 1999, Villa et al. 2006, Broders et al. 2007). The Pythium, being obligate plant parasites, cause a variety of plant diseases or can damage to plant products, in most cases collectively accounts for multibillion-dollar losses due to the death of a large area of the world economically important cash crops (van West et al. 2003). Thus the knowledge of this most economically important group oomycete in a particular area is important concerning the biology, systematics and taxonomy as well as for phytopathological remediation purposes to prevent such diseases or reduce the losses they cause. To our knowledge, since the earliest record by Butler (1907), many Pythium specimens have been collected from India. The vast biodiversity and climatic conditions of India contribute to the vast diversity, distribution and host range of this group. However still, a large number of the representatives of this genus have not been reported and extensively studied from India. Further, the information pertaining to this genus and their host plant association is scattered and restricted to some regional studies in various plant pathological reports and some general fungal lists. Some publications provided lists of the Pythium from India (Rao 1963, Misra & Hall 1996), but these were incomplete, outdated and largely based on morphological data. Information regarding the occurrence and distribution of Pythium from India is difficult to obtain, primarily because literature is scattered and some of it is unavailable. Over the years with the advent of molecular biology, Pythium has undergone several taxonomic revisions, updates and a significant number of new records have been reported from India. The need for an up-to-date list is therefore evident. To remedy this, in the present contribution a comprehensive review of the species, host range and geographical distribution of Pythium in India is provided so that it will be more widely available to Indian phytopathologists and researchers interested in this ecological group. Moreover, data of earlier researchers are listed, to make this new checklist as complete as possible to serve as a baseline for future mycological studies. Materials & Methods All the previously published information relevant to the genus Pythium in India were surveyed and compiled (latest accessed 10/04/2020). The checklist was primarily based on an exhaustive bibliographic survey of the literature published in various national and international journals, online available digitized records of specimens, monographs, reports, books, book chapters and even magazines that included records of Pythium spp. from India. The different collections were compiled by disposing of each single species and subspecies/variety including the name of the species in alphabetical order and the authors’ epithets, host range/substrate, habitat or geographical distribution, and related recent references. Besides, from a phytopathological point of view, a family-wise list of the susceptible host plant for Pythium mediated diseases was prepared to assess their host range and variation in India. All species names were cross-checked for its validity and some preceding names as recorded in the cited publications have been substituted with their currently accepted scientific name according to the fungal nomenclature database MycoBank and Species Fungorum (http://www.mycobank.org, www.speciesfungorum.org, www.indexfungorum.org) website. Results A total of 55 species and 4 varieties of the genus Pythium are listed and arranged alphabetically in chronological order with their respective substrate/host range, places of collection, and related references from India (Table 1). The most frequently collected Pythium species are P. debaryanum, 121 P. aquatile, P. aphanidermatum, P. deliense, P. dissotocum, P. graminicola, P. intermedium, P. middletonii, P. myriotylum, P. spinosum, P. ultimum, and P. vexans. While the distribution of P. anguillulae-aceti, P. apleroticum, P. cucurbitacearum, P. drechsleri, P. echinogynum, P. elongatum, P. helicoides, P. hypogynum, P. indigoferae, P. kashmirense, P. lobatum, P. marsipium, P. monospermum, P. multisporum, P. parasiticum, P. periilum, P. periplocum, P. polytylum, P. pulchrum, P. rhizo-oryzae, P. rhizosaccharum, P. torulosum, P. stipitatum and P. campanulatum were found to be rare. Besides, over 46 Pythium taxa were recorded over the plants either as a parasite or saprophyte. The plants belonging to the family Malvaceae, Zingiberaceae, Solanaceae, Gramineae, Zygnemataceae, Cucurbitaceae, Papaveraceae, Araceae, Fabaceae, Apiaceae, Brassicaceae, Piperaceae, Anabantidae, Rosaceae, Geraniaceae and Cyprinidae are mostly prone to Pythium infection. After compilation of the literature records, it was noticed that most of the taxa were reported from South India followed by North India, East India and West India, respectively. In between them, most reports are available from Coimbatore (Tamil Nadu), Nainital (Uttarakhand), Varanasi, Gorakhpur (Uttar Pradesh) and Hyderabad (Telangana), respectively. Neither of the taxa has been ever recorded from Indian states such as Punjab, Goa, Andhra Pradesh, Orissa, Chhattisgarh, Jharkhand, Arunachal Pradesh, Manipur, Mizoram, Nagaland, and Tripura. Even though of the above results, about one-third of all Pythium species are more or less uniformly distributed throughout India. These ubiquitous species include P. graminicola, P. insidiosum, P. aphanidermatum, P. dissotocum, P. myriotylum, P. deliense, P. ultimum, P. catenulatum, P. debaryanum, P. dissotocum, P. intermedium, P. middletonii, P. spinosum and P. vexans. The Indian checklist contains several species that have importance to humans, such as important pathogens of crops (e.g., P. aphanidermatum, P. acanthophoron, P. aquatile, P. catenulatum, P. debaryanum, P. deliense, P. dissotocum, P. echinogynum, P. echinulatum and P. graminicola, etc), algae (P. carolinianum, P. catenulatum and P. cucurbitacearum), fishes (P. afertile and P. undulatum), Mosquito larva and human (e.g., P. insidiosum). Most of the India Pythium species were recorded from soil and water habitats whereas neither spp. was reported from the marine environment. P. acanthicum, P. apleroticum, P. drechsleri, P. elongatum, P. drechsleri, P. elongatum, P. kashmirense, P. lobatum, P. mamillatum, P. multisporum, P. parasiticum, P. periilum, P. pulchrum, P. rhizo-oryzae, P. rhizosaccharum were reported to be saprophytic in India. In contrast, P. acanthophoron, P. aphanidermatum, P. aquatile, P. carolinianum, P. catenulatum, P. debaryanum, P. deliense, P. dissotocum, P. echinulatum, P. helicoides, P. hydnosporum, P. indigoferae, P. irregular, P. middletonii, P. periplocum, P. spinosum, P. torulosum, P. vexansi, P. diclinum were parasitic as well as saprophytic in their mode of nutrition. In this sense, P. afertile, P. anguillulae-aceti, P. cucurbitacearum, P. echinogynum, P. graminicola, P. hypogynum, P. inflatum, P. insidiosum, P. intermedium, P. iwayamai, P. marsipium, P. monospermum, P. myriotylum, P. oedochilum, P. oligandrum, P. paroecandrum, P. polytylum, P. rostratum, P. splendens, P. ultimum, P. undulatum were parasitic in their mode of nutrition. The majority of the listed Pythium taxa were identified sorely based on the morphological features such as vegetative organs like the formation of hyphal swellings; asexual structures such as size and shape of zoosporangium/ heterokont zoospores, the formation of papilla/discharged tubes and patterns of their discharge; and reproductive organs including structure, production and mode of attachment of the antheridium, oogonium and oospores. However, in recent years, several Pythium spp. such as P. insidiosum, P. rhizosaccharum, P. aphanidermatum, P. dissotocum, P. myriotylum, P. deliense, P. rhizo-oryzae, P. graminicola, P. catenulatum, P. stipitatum, P. campanulatum and P. helicoides were subjected to morpho-molecular evaluation and identified largely based on molecular data. Discussion The current checklist is the first in a series of lists on the traditional zoosporic fungi recorded for India. The present publication aims to combine all earlier biodiversity explorations and their information pertaining to the genus Pythium in one list. The Pythium is considered one of the least explored ecological niches for oomycete remaining today in India. The research in this area has been primarily hampered by a confusing taxonomy largely dependent on nineteenth-century concepts and 122 exceedingly inadequate literature. However, these water mold being an important biodiversity component have the potential of impacting global food security and the human economy. Some species of this cosmopolitan oomycete listed herewith are considered to be an important pathogen of cash crops (e.g., P. aphanidermatum, P. myriotylum, P. arrhenomanes, P. dissotocum, P. elongatum, and P. spinosum) and have been reported to cause seedling damping-off and root rot (Khulbe 2001). Owing to their economic importance, the present insight is needed to prepare an outlook for the future. In this sense, past works (1907-2020) on Pythium spp. reported from India were studied to provide a compile data on an annotated alphabetical checklist of the genus herewith. Table 1 Pythium species recorded from India. Abbreviations: S: soil, W: water, PA: parasite, SA: saprotroph, MP: Madhya Pradesh, UP: Uttar Pradesh, KA: Karnataka, TN: Tamil Naidu, RA: Rajasthan, UK: Uttarakhand, AP: Andhra Pradesh, WB: West Bengal, GU: Gujrat, KE: Kerala, MS: Maharashtra, JK: Jammu and Kashmir, HP: Himachal Pradesh and ME: Meghalaya. S. No. 1 Pythium species 2 Type of sample S Substrates Nutrition Collection data Reference Agricultural soil SA Joshi & Chauhan 1982 P. acanthophoron Sideris S PA, SA 3 P. afertile Kanouse and Humphrey W, S Gossypium seed (Malvaceae) and Zingiber officinale (Zingiberaceae) rhizome Fish eggs, infected roots Hyderabad, Vakarabad (Telangana); Gwalior (MP); Banglore (KA) Coimbatore (TN); Udaipur (RA) PA Nainital (UK); Varanasi (UP) 4 P. anguillulae-aceti Sadebeck S PA Bomori, Haldwani (UK) 5 P. aphanidermatum (Edson) Fitzp S PA, SA Ubiquitous in nature throughout India Muthukumar 2010, Ashwathi et al. 2017 6 P. apleroticum Tokunaga P. aquatile Hohnk W Solanum melongena (Solanaceae) Reported on many monocotyledonous and dicotyledonous plants Plant debris Kiran et al. 1982, Khulbe 1977, Sati 1981 Bhatt 2000 SA Varanasi (UP) S, W Lycopersicon esculentum (Solanaceae) SA, PA Gorakhpur (UP); Hissar (Haryana); Hyderabad (AP) P. campanulatum Mathew, Singh, and Paul P. carolinianum Matthews S Rhizosphere of Zea mays (Gramineae) SA Gorakhpur (UP) Sarkar et al. 1981 Prabhuji & Srivastava 1978, Manoharachary & Rao 1978 Mathew et al. 2003 W, S Spirogyra species (Zygnemataceae) and Vegetable debris PA, SA Coimbatore (TN); Hyderabad (Telangana); Prayagraj, Chandauli (UP) 10 P. catenulatum Matthews W, S Spirogyra species (Zygnemataceae) and Saccharum officinarum (Poaceae) PA, SA Coimbatore (TN); Prayagraj, Chandauli (UP) 11 P. cucurbitacearum Takimoto S Trichosanthes dioica (Cucurbitaceae) PA Nadia (WB) 7 8 9 P. acanthicum Drechsler Lodha & Webster 1990 Balakrishnan 1948, Rajagopalan & Ramakrishnan 1964, 1971, Dubey 2018 Balakrishnan 1948, Srinivasan 1956, Chona 1958, Dubey 2018 Chaudhuri 1975 123 Table 1 Continued. S. No. 12 Pythium species 13 P. deliense Meurs S 14 P. diclinum Tokunaga 15 16 Substrates Nutrition Collection data Reference Reported on many monocotyledonous and dicotyledonous plants Reported on many dicotylednous plants PA, SA Ubiquitous in nature throughout India PA, SA Ubiquitous in nature throughout India S Reported on many monocot and dicot plants SA, PA Surat (GU); Dehradun (UK); Kolkata (WB) Butler 1907, 1913, Srivastava & Rao 1964, Kapoor 2008 Haware & Joshi 1974, Jooju 2005, Muthukumar 2010 Butler 1907 P. dissotocum Drechsler S, W Papaver somniferum (Papaveraceae) SA, PA P. drechsleri Rajagopalan and Ramakrishnan P. echinogynum Balghouthi, Jonathan, Gognies, Mliki and Belarbi P. echinulatum Matthews S Agricultural soil SA Barabanki, Lucknow (UP); New Delhi; Bangalore (KA); Kasargod (KE); Coimbatore (TN) Coimbatore (TN) S Turf grassroots (Poaceae) PA Nagpur (MS) S Triticum aestivum (Poaceae) SA, PA 19 P. elongatum Mathews W, S Moist soil SA 20 P. graminicola Subramaniam S Reported on many monocotyledonous and dicotyledonous plants PA Gorakhpur (UP); Nainital (UK); Vikarabad, Medak and Hyderabad (Telangana) Hyderabad (Telangana); Nainital (UK) Pusa (Bihar); New Delhi; Coimbatore, Chidambaram (TN); Jabalpur (MP); Chandauli (UP) 21 P. helicoides Drechsler S SA, PA Coimbatore (TN), Nadia (WB) 22 P. hydnosporum (Montagne) Schroter S, W Amorphophallus paeoniifolius (Araceae) Solanum tuberosum (Solanaceae) SA, PA Kolkata (WB); Khasi Hills (Assam); Coonoor (TN) 23 P. hypogynum Middleton P. indigoferae Butler S, W Triticum aestivum (Poaceae) Epiphyte on the leaves of Indigofera arrecta (Fabaceae) and Cucumis sativus (Cucurbitaceae) PA Udham Singh Nagar (UK) Kolkata (WB) 17 18 24 P. debaryanum Hesse Type of sample S S SA, PA Chowdhry & Agarwal 1980, 1981, Alam et al. 1996, Bajpai et al. 1999 Rajagopalan & Ramakrishnan 1971 Balghouthi et al. 2013 Rama Rao 1970, Verma 1987a Khulbe 1983 Subramaniam 1928, Ramakrishnan & Soumini 1955, Muthukumar 2010, Dubey et al. 2020a Guha Roy & Hong 2008 Sydow & Butler 1907, Chowdhry & Agarwal 1980 Verma 1984 Butler 1907 124 Table 1 Continued. S. No. 25 Pythium species 26 P. insidiosum De Cock W 27 P. intermedium De Bary S 28 P. irregulare Buisman S 29 P. iwayamai Ito S 30 P. kashmirense Paul 31 Substrates Nutrition Collection data Reference Oryza spp. (Poaceae) and Lycopersicon esculentum (Solanaceae) Mosquito larva, human PA Hyderabad (Telangana); Nainital (UP) Verma & Khulbe 1986, Verma 1987b PA Reported on many monocot and dicot plants Coriandrum sativum (Apiaceae) PA Pondicherry; Hyderabad (Telangana); Madurai (TN) Nagpur (MS); Bangalore (KA); Peechi (KE) Lucknow, Varanasi (UP); Bangalore (KA) Schurko et al. 2004, Kalra et al. 2018, Hasika et al. 2019 Ali & Nair 1989, Rao 1963 PA Bomori, Haldwani, Nainital, Rooshi (UK) S Lycopersicon esculentum and Solanum melongena (Solanaceae) Plant debris SA Reasi (JK) P. lobatum Rajagopalan and Ramakrishnan P. mamillatum Meurs S Moist soil SA Coimbatore (TN) S Moist soil SA 33 P. marsupium Drechsler S PA 34 P. middletonii Sparrow S, W 35 P. monospermum Pringsheim W 36 P. multisporum Poitras S Solanum melongena (Solanaceae) Reported on many dicotylednous plants Zingiber officinale (Zingiberaceae) and Lepidium sativum (Brassicaceae) Moist soil Chennai (TN); Pakhal, Medak and Hyderabad (Telangana) Bithoria, Haldwani (UK) 37 P. myriotylum Drechsler W, S 38 P. oedochilum Drechsler 39 40 32 P. inflatum Matthews Type of sample S SA, PA SA, PA Ubiquitous in nature throughout India PA Pusa (Bihar); Jabalpur (MP); Nainital (UK) SA Kushinagar (UP) Reported on many monocot and dicot plants PA Ubiquitous in nature throughout India S Brasssica oleracea var. botrytis (Brassicaceae) PA Annamalainagar and Coimbatore (TN) P. oligandrum Drechsler S PA Lucknow, Gorakhpur and Varanasi (UP) P. parasiticum Rajagopalan and Ramakrishnan S Piper betle (Piperaceae) and Anabas testudineus (Anabantidae) Agricultural soil SA Chennai (TN) Agnihotri 1969, Sharma & Basu Chaudhary 1981 Bhatt 2000 Paul & Bala 2008 Rajagopalan & Ramakrishnan 1971 Ramakrishnan 1955, Rao 1963, Rama Rao 1970 Bhatt 2000 Singh & Pavgi 1974, Khulbe & Bhargava 1977 Rao 1963, Khulbe & Bhargava 1977 Prabhuji & Srivastava 1978, Prabhuji & Sinha 1994 Devaki et al. 1991, Kumar et al. 2008, Geethu et al. 2013 Raghunathan 1968, Rajagopalan & Ramakrishnan 1964, 1971 Srivastava et al. 2017a, b Rajagopalan & Ramakrishnan 1971 125 Table 1 Continued. S. No. 41 Pythium species 42 P. periilum Drechsler S 43 P. periplocum Drechsler 44 Substrates Nutrition Collection data Reference PA SA Nainital and Nanakmatta (UK); Coimbatore (TN) - Balakrishnan 1948, Verma 1984 Plaats-Niterink 1981 S, W Phaseolus vulgaris (Fabaceae) Vegetable root Brassica oleracea var. capitata, Brassica oleracea var. botrytis (Brassicaceae) Agricultural soil SA, PA Coimbatore (TN) P. periplocum var. coimbatorense Balakrishnan P. polytylum Drechsler P. pulchrum Minden S Vegetable debris SA Coimbatore (TN) Balakrishnan 1948, Rajagopalan & Ramakrishnan 1964, 1971, Bisht et al. 1997 Balakrishnan 1948 S Vegetable debris PA S, W SA Verma & Khulbe 1985 Mer 1982 P. rhizo-oryzae Paul P. rhizosaccharum Singh, Mathew, Masih and Paul P. rostratum Butler S SA Gorakhpur (UP) Bala et al. 2006 SA Gorakhpur (UP) Singh et al. 2003 PA Pusa (Bihar); Nainital (UP) 50 P. spinosum Sawada S, W Malus sp. (Rosaceae), Crop field Hibiscus esculenta (Malvaceae) The rhizosphere of Oryza sativa (Poaceae) Saccharum officinarum (Poaceae) Triticum aestivum (Poaceae) Solan (HP); Nainital (UK) Nainital (UK) SA, PA Ubiquitous in nature throughout India 51 P. splendens Braun S PA 52 P. torulosum Coker and Patterson W Lucknow (UP); Hesaraghatta (KA); Shillong (ME); Sirmaur (HP) Varanasi (UP); Nainital (UK) 53 P. ultimum Trow S Reported on many monocotyledonous and dicotyledonous plants Pelargonium graveolens (Geraniaceae), Zingiber officinale (Zingiberaceae) Vegetable debris and Triticum aestivum (Poaceae) Butler 1907, Verma & Khulbe 1985 Rama Rao 1970, Manoharachary & Reddy 1975, Sati & Tiwari 1992 Shanmugam et al. 2010 PA Salon (HP); Parbhani (MH) 54 P. ultimum Trow var. ultimum S SA, PA Ubiquitous in nature throughout India 55 P. ultimum var. sporangiiferum Drechsler S Solanum lycopersicum (Solanaceae) and Glycine max (Fabaceae) Reported on many monocotyledonous and dicotyledonous plants PA Haldwani, Ramnagar, Ranikhet, Someshwar, Rooshi, Nainital (UK) 45 46 47 48 49 P. paroecandrum Drechsler Type of sample S, W S S SA, PA Khulbe & Verma 1983 Hudge & Deshpande 2014, Hudge et al. 2016, Kumar et al. 2018 Dohroo 1987, Muthukumar 2010 Bisht et al. 1997 126 Table 1 Continued. S. No. 56 Pythium species 57 Type of sample W Substrates Nutrition Collection data Reference Vegetable seedlings PA Nainital (UK) P. vexans de Bary S SA, PA Ubiquitous in nature throughout India 58 P. vexans var. minuta Mer and Khulbe S, W SA Nainital (UK) Mer & Khulbe 1983 59 Pythium stipitatum Karaca and Paul S Carassus auratus (Cyprinidae) and Brassica campestris (Solanaceae), Temperate fish Reported on many monocotyledonous and dicotyledonous plants Grass or Cyanodon dactylon roots (Poaceae) Khulbe & Bhargava 1977, Sati 1991, Sati & Tiwari 1992 Dastur 1935, Ramakrishnan 1949, Wilson & Rahim 1978 SA Nagpur (MH) Karaca et al. 2009 P. undulatum Petersen Research related to Pythium started in the early 19th century with collections made by Butler (1907) in India. Studies about Pythium in India were intensified between the years 1950-1990. A checklist of Indian Pythium taxa was published by Misra & Hall (1996) which included 40 species and included a survey of all known taxa and all relevant literature until that time. Since then, a large amount of new information on taxonomy, distribution, and to a lesser extent ecology, has been published. This information is contained in many papers in various journals and books, some of them not easily accessible so that a new survey is necessary. Moreover, the yearly output of publications on the subject was increasing rapidly, so that an updated version of the bibliography and a checklist seemed necessary. Most studies on Pythium in India have been conducted primarily from South India and Kumaon Himalayan region in North India (Khulbe 2001), and a total of 46 species have been recorded from these regions of the country. Moreover, the list also contains some saprophytes and some well-proven biological control agents among them. However, little research has been undertaken phytopathogenesis mediated negative attributes on the economy and food security by this necrotrophic generalistic pathogenic Pythium flora of fields worldwide, especially in India. It is therefore pertinent to understand the Pythium diversity and associated plant diseases, which will be helpful to develop relevant action plans for the future. Most of the Pythium were identified based on their morphological features whereas little were studied from the molecular identification point of view. Identifying the species of Pythium sorely based on morphological features has always been problematic due to various reasons, such as variations of a specific morphological feature, difficulty in isolating certain species and the lack of molecular identification data for species. Due to these reasons, identifying Pythium species based on morphological features has been a constant problem for even the most experienced mycologists (Lévesque & de Cock 2004). Therefore, during the last decade, molecular techniques have significantly assisted in the identification of unknown Pythium species and a large number of additional new species records and new species have been added based on it. Further, based on the data present in the list, it can be concluded that still large areas in India are unexplored relative to Pythium biodiversity and studies in this field have been hampered by grossly inadequate literature and a confused taxonomy based largely on nineteenth-century concepts. It is equally likely that a large number of species have not yet been described because newly explored areas always yield new taxa. Besides, according to the recent primarily checklist of fungi of Gujarat state, India, the genus Pythium is never been recorded in Gujarat (Rajput et al. 2015). However, our list provided supporting evidence that this genus was reported from Gujrat (Butler 1907). According to our results, this oomycete parasitized a large no. of the host plant and animal species in this country like other 127 members of Oomycota (Dubey et al. 2018, 2019, 2020b). However, it is expected that more collections and further taxonomic studies will substantially increase our knowledge and provide a better understanding of their biology, ecological aspects, host-specificity, origin and divergence as well as the application of this oomycete in biocontrol. Therefore, it seems a prerequisite to launch a full-scale survey of these biologically intriguing group of oomycete in other parts of India to complete at least a modicum of their checklist. After that plenty of knowledge can be accumulated that would be useful in the compilation of mycological diversity in India. Conclusion The current checklist facilities access to the scattered Indian literature on the topic that may not be readily available to the student of Indian mycology and the international community. Besides, the correctly identified checklist is essential, as it can assist in gathering information pertaining to the historical development in the study of Pythium and its diversity in India. The exact knowledge of this oomycete diversity is important because these water molds are the most-significant decomposers of plant and animal originated complex organic materials and normally comprise a major proportion of total microbial biomass. Nevertheless, the recent impact of global climate change and the betterknown role of mycobiota activities in the biogeochemical cycling of elements have enforced the importance of assessing the position of Indian mycobiota and its diversity. Further, the pathogenic species mentioned in the list can assist phytopathologists to confidently name disease causal agents, lead quarantine to put in place effective measures to prevent the entry of unwanted species, allow plant breeders to breed resistant varieties and biochemists to confidently put names to species producing novel chemicals. This shows clearly that the compilation of the checklist has fulfilled its purpose to encourage Indian mycologists to search for additional taxa. Besides, this checklist will help in making the evaluations of the oomycetes recorded in the country. Acknowledgments We thank the Head and Programme Coordinator, Department of Botany, Banaras Hindu University, Varanasi, Uttar Pradesh, India for providing library facilities. References Agnihotri VP. 1969 – Production and germination of appressoria in Pythium irregulare. Mycologia 61, 967–980. 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