pathogens Review Current Knowledge on Pathogenicity and Management of Stemphylium botryosum in Lentils (Lens culinaris ssp. culinaris Medik) Arpita Das 1, Subrata Dutta 1, Subhendu Jash 1, Ashis Roy Barman 1, Raju Das 1, Shiv Kumar 2,* and Sanjeev Gupta 3,* 1 Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal 741252, India; [email protected] (A.D.); [email protected] (S.D.); [email protected] (S.J.); [email protected] (A.R.B.); [email protected] (R.D.) 2 International Centre for Agricultural Research in the Dry Areas (ICARDA), Rabat- Institutes, B.P. 6299 Rabat, Morocco 3 All India Coordinated Research Project (AICRP) on MULLaRP, ICAR- Indian Institute of Pulses Research, Kanpur, Uttar Pradesh 208024, India * Correspondence: [email protected] (S.K.); saniipr@rediffmail.com (S.G.) Received: 4 September 2019; Accepted: 7 October 2019; Published: 8 November 2019 Abstract: Stemphylium blight (SB) caused by Ascomycete, Stemphylium botryosum Wallr. has been a serious threat to lentil cultivation, mainly in Bangladesh, Nepal, India, and Canada since its first outbreak in Bangladesh in 1986. The genus Stemphylium Wallr., a dematiaceous hyphomycete, comprises up to 150 species, and is pathogenic on a wide range of plants infecting leguminous as well as nonleguminous crops. In recent years, studies indicated overlapping in morphological characters among the different species under the genus Stemphylium, making the identification and description of species difficult. This necessitates different molecular phylogenetic analysis in species delimitation. Therefore, a detailed understanding of spatial diversity and population structure of the pathogen is pertinent for producing source material for resistance breeding. The role of different weather variables as predisposing factors for the rapid spread of the pathogen necessitates devising a disease predictive model for the judicial application of fungicides. A dearth of information regarding spore biology, epidemiology, race diversity, host-pathogen interaction, and holistic disease management approach necessitates immediate attention towards more intensive research efforts. This is the first comprehensive review on the current state of knowledge and research efforts being made for a better understanding of the SB resistance through cognizing biology, ecology, and epidemiology of S. botryosum and effective disease management strategies to prevent widespread outbreaks of SB. The information regarding the biology and epidemiology of S. botryosum is also crucial for strengthening the “Integrated Disease Management” (IDM) programme. The need for a regional research network is advocated where the disease is becoming endemic. Keywords: epidemiology; integrated disease management; lentil; Stemphylium botryosum 1. Introduction Lentil (Lens culinaris ssp. culinaris Medik.) is the world’s fifth largest pulse crop cultivated in more than 70 countries around the world, mainly in West Asia, North Africa, the Indian subcontinent, North America, and Australia [1]. Based on nutritional properties, it has been recognized as one of the five healthiest foods [2] as lentil grains are high in protein, fiber, micronutrients, and vitamins [3,4]. Stemphylium blight (SB) caused by the Ascomycete, Stemphylium botryosum Walr, once a minor disease with local significance in South Asia, is now a serious threat to lentil cultivation in many parts Pathogens 2019, 8, 225; doi:10.3390/pathogens8040225 www.mdpi.com/journal/pathogens Pathogens 2018, 7, x FOR PEER REVIEW 2 of 16 Pathogens 2019, 8, 225 2 of 16 Stemphylium blight (SB) caused by the Ascomycete, Stemphylium botryosum Walr, once a minor disease with local significance in South Asia, is now a serious threat to lentil cultivation in many ofparts the of world the world [5]. It is[5]. classified It is classified as a fungal as a fung diseaseal disease responsible responsible for large for scale large defoliation scale defoliation of plants, of causingplants, causing severe yield severe losses yield within losses a shortwithin period a short in conduciveperiod in conducive environments. environments. It has been reportedIt has been in lentilreported producing in lentil areas producing of Bangladesh, areas of India,Bangladesh, Nepal, theIndia, USA, Nepal, and Canadathe USA, [6 and,7]. TheCanada first appearance[6,7]. The first of SBappearance was observed of SB inwas Bangladesh observed in in Bangladesh 1986 [8], where in 1986 with [8], increased where with severity increased it caused severity up toit caused 80% yield up lossesto 80% [ 9yield,10]. losses The disease [9,10]. has The been disease on the has rise been in on frequency the rise andin frequency intensity and in India, intensity which in ranksIndia, firstwhich in lentilranks coveragefirst in lentil areas coverage globally. areas The globally. disease holdsThe disease the potential holds the for potential causing muchfor causing greater much losses greater once itlosses spreads once to it other spreads lentil to other producing lentil areasproducing with favorableareas with environmental favorable environmental conditions conditions for the pathogen. for the Thepathogen. potential The threat potential of its threat global of spread its global warrants spread immediate warrants attention immediate to understandattention to andunderstand manage thisand diseasemanage by this developing disease by a developing regional network a regional where network the disease where is the endemic. disease is endemic. SBSB cancan easilyeasily bebe distinguisheddistinguished fromfrom otherother blightsblights ofof lentillentil likelike AlternariaAlternaria blightblight andand AscochytaAscochyta blightblight basedbased onon symptoms,symptoms, the the severity severity of of infection, infection, and and morphology morphology of of pathogen. pathogen.Alternaria Alternariais closeris closer to Stemphyliumto Stemphylium, and, and often often mixed mixed infection infection of both of both is encountered is encountered on lentils. on lentils. Like SB,Like the SB, Ascochyta the Ascochyta blight andblight Alternaria and Alternaria blight generally blight generally appear in appear the field in during the field the floweringduring the stage flowering in a humid, stage cooler in a climatehumid, incooler the presenceclimate in of the prolonged presence leaf of prolonged wetness. The leaf initial wetness. symptom The initial of Ascochyta symptom Blight of Ascochyta is characterized Blight is bycharacterized the formation by the of whitishformation to grayishof whitish lesions to grayis on theh lesions stems on and the leaves stems that and turn leaves light that tan turn in color,light andtan in the color, mature and lesions the mature have darker lesions margins have darker with prominentmargins with black prominent pycnidia scatteredblack pycnidia throughout scattered the lesions.throughout On thethe contrary,lesions. On no the dark contrary, pycnidial no structure dark pycnidial is found structure in lesions is found caused in by lesions SB.SB caused produces by moreSB.SB pronounced produces more symptoms pronounced on leaves. symptoms on leaves. ToTo date,date, thethe diseasedisease isis poorlypoorly understoodunderstood andand veryvery fewfew studiesstudies were mademade onon the epidemiology ofof thethe fungus,fungus, thethe factorsfactors aaffectingffecting diseasedisease development,development, thethe racialracial structurestructure ofof thethe population,population, thethe interactionsinteractions withwith di ffdifferenterent hosts, hosts, and and genetics genetics of resistance. of resistance. An overview An overview of global researchof global concerning research variousconcerning aspects various of Stemphylium aspects of Stemphyliumas incitant of as SB incitant disease of of SB di ffdiseaseerent host of different plants published host plants and published indexed inand Web indexed of Science in Web (WoS) of Science for the period(WoS) offor 1998–2019 the period indicated of 1998–2019 that nearly indicated 770 articlesthat nearly were 770 published articles onwereStemphylium publishedon on di Stemphyliumfferent hosts, on of whichdifferent only hosts, 200 papers of which were on publishedly 200 papers on Stemphylium were published botryosum on. However,Stemphylium lentil botryosumStemphylium. However,covers onlylentil 4.6% Stemphylium of total global covers research, only 4.6% whereas, of total the pearglobalStemphylium research, pathosystemwhereas, the shares pear 12.6%,Stemphylium onion Stemphylium pathosystem10.4%, shares tomato 12.6%,Stemphylium onion Stemphylium8.6%, and garlic 10.4%,Stemphylium tomato coversStemphylium 4.8% of8.6%, global and research. garlic Stemphylium Moreover, it covers was found 4.8% thatof global nearly research. 43% of the Moreover, research it papers was found were onthat the nearly disease 43% management of the research approach papers were and littleon the has disease been management done on pathogenicity approach and and little breeding has been for resistancedone on pathogenicity against this disease and breeding (Figure1 ).for Therefore, resistance this against article this reviews disease the (Figure current knowledge1). Therefore, about this thearticle history, reviews etiology, the current epidemiology, knowledge variability, about and the host history, plant etiology, resistance, epidemiology, and discusses variability, the future need and forhost integrated plant resistance, disease and management discusses strategies.the future need for integrated disease management