Int.J.Curr.Microbiol.App.Sci (2020) 9(7): 472-481 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 9 Number 7 (2020) Journal homepage: http://www.ijcmas.com Original Research Article https://doi.org/10.20546/ijcmas.2020.907.052 Characterization of Cucurbit Powdery Mildews by Morphological and Microscopic Studies S. Priyanka1, L. Rajendran1, R. Anandham2 and T. Raguchander1* 1Department of Plant Pathology, 2Department of Agricultural Microbiology Tamil Nadu Agricultural University, Coimbatore – 641 003, India *Corresponding author ABSTRACT Powdery mildew of cucurbits is caused by two causal agents, Sphaerotheca fuliginea (Syn. Podosphaera xanthii) and Erysiphe cichoracearum (Syn. Golovinomyces cichoracearum). K e yw or ds To assess the distribution of powdery mildew in major cucurbit crops and also to identify peculiar characteristics of these causal agents, survey was conducted in various places of Cucurbits, diseases, Coimbatore and Dindigal districts of Tamil Nadu. The collected powdery mildew samples percent disease were examined for the presence of conidia and conidiophores. Conidial shapes, index (PDI) and conidiophore and conidial dimensions, presence of fibrosin bodies were established by powdery mildew microscopic studies. Based on the conidia and conidiophore characters, two different Article Info genera were observed in the samples collected. The conidial mean length of Podosphaera xanthii ranges from 30.51 to 40.88 µm whereas for Erysiphe cichoracearum ranges from Accepted: 32.08 to 46.87 µm but the conidial mean width of Podosphaera xanthii ranges from 21.28 05 June 2020 to 29.65 µm and for Erysiphe cichoracearum it ranges from 16.52 to 29.65 µm. For better Available Online: 10 July 2020 perception of host pathogen interaction, pathogenicity assay was proved by detached leaf assay in laboratory and glasshouse in vitro. This prelusive study would be beneficial for early disease discernment and effective management in coming times. Introduction cichoracearum) (Vakalounakis et al., 1994; Kristkova et al., 2000). The disease causes Cucurbits are economically important crops reduction in plant growth, premature that play a major role in vegetable production. defoliation and as a result, both yield and Among the different production constraints, quality of fruits gets reduced that ultimately the disease namely powdery mildew is the leads to major production problem (Lebeda et most common and serious fungal disease that al., 2010). arises both in field and greenhouse conditions all over the world. The disease is caused by Podosphaera xanthii occurs mostly in warmer two obligate biotrophs such as Sphaerotheca months (Rur et al., 2017) whereas Erysiphe fuliginea (Syn. Podosphaera xanthii) and cichoracearum in cooler spring and in early Erysiphe cichoracearum (Syn. Golovinomyces summer months (Aguiar et al., 2012). 472 Int.J.Curr.Microbiol.App.Sci (2020) 9(7): 472-481 The two obligate biotrophs produce which was described by Mc Kinney’s (1923). indistinguishable symptoms but can be easily Percent Disease Index was calculated by distinguished by light microscopic studies randomly selecting fifteen leaves and worked (Braun et al., 2002). The difference between out using the following formula the two species Podosphaera xanthii and Erysiphe cichoracearum can be made according to morphology of the conidia, the presence or absence of fibrosin bodies in interior of the conidia and the morphology of the germinative tube of conidia (Garcia et al., Microscopic studies 2010). The morphological characters of the causal Therefore, the objective of the study is to agents such as presence or absence of identify and characterize the powdery mildew conspicuous fibrosin bodies, the dimensions isolates from various hosts of cucurbit crops of conidia and conidiophore, shape of conidia, which will provide explicit information about type of mycelium and appresoria were the causal agents. This study also evaluates characterized by means of taking observation disease severity caused by both pathogens. under light microscope. Materials and Methods The image was captured using image analyser. The conidial numbers (25 conidia Survey with GPS coordinates per sample) were counted and out of these, the length and width of ten conidia was During 2019-20, powdery mildew infected measured. To study better structural aspects, leaf samples from various hosts of cucurbits the conidia and conidiophores has been were collected by conducting survey in stained with cotton blue in lactophenol. Coimbatore and Dindigal districts of Tamil Nadu, India. The samples were collected from Pathogenicity study various locations such as Poosaripalayam, Sattakalpudhur, PN Pudhur, Thondamuthur, To prove the pathogenicity of causal agents, Kinathukadavu, Vettaikaranpudhur, Koch’s postulates have been established. Arasampalayam of Coimbatore district and Pathogenicity assay was proved for powdery Sembatti, Paraipatti, Vellodu of Dindugal mildew of cucurbits caused by two causal district where cucurbits are largely cultivated. agents Podosphaera xanthii and Erysiphe During the survey, observations on disease cichoracearum in glasshouse and laboratory intensity, stage and variety of the crop and conditions. GPS coordinates of the locations were recorded. In glasshouse, cucumber (Japanese Long green) and bitter gourd (CO 1) have been Powdery mildew and its severity raised under controlled conditions in earthen pots containing the mixture of red soil, sand The disease intensity (percentage of leaf area and farm yard manure at the ratio of 2:1:1. infected) was assessed using disease score Diseased samples showing typical symptoms chart which includes 0-9 scales given by of powdery mildew caused by Podosphaera Jamadar and Desai (1997). The disease score xanthii in cucumber and Erysiphe was converted to Percent disease Index (PDI) cichoracearum in bitter gourd were collected. 473 Int.J.Curr.Microbiol.App.Sci (2020) 9(7): 472-481 The conidia of Podosphaera xanthii was Results and Discussion inoculated in 30 days old cucumber plant and the conidia of Erysiphe cichoracearum in 30 Survey and disease severity assessment days old bitter gourd plant by brushing the conidia onto the leaf by small camel’s brush The survey was conducted in various and control plant was maintained for each locations of Coimbatore and Dindugal district without inoculation of conidia. during the year 2019 – 2020. The cucurbits powdery mildew showing symptoms typically The plants were covered with polythene on both upper and lower surface of leaves and covers to maintain humidity for 24 to 48 later stage on petioles stems and fruits were hours. In laboratory conditions, healthy observed (Fig.1). detached leaves of cucumber and bitter gourd were collected and surface sterilized with The results showed that the severity for the 70% ethanol and then washed three times powdery mildew of cucurbits ranged from thoroughly with sterile distilled water. The 30.25 to 71.24 PDI. Maximum disease leaves were placed in petri dishes with three severity was noticed in ash gourd (71.24 PDI) layers of moistened sterile filter paper. collected from PN Pudur followed by snake gourd (69.12 PDI) collected from The leaves of cucumber were inoculated with Arasampalayam of Coimbatore district. sporulating colonies of Podosphaera xanthii onto the sites of leaf by slight brushing of The minimum disease severity was noticed in conidia. Likewise, the leaves of bitter gourd watermelon (30.25 PDI) collected from inoculated with Erysiphe cichoracearum. The Korapalayam of Dindugal district (Table 1). petriplates were wrapped with parafilm and Pathogenecity spectrum of disease is similar incubated at 250C with 16 hours of to other states in India. In a study conducted photoperiod. An observation on the growth of on cucurbits indicated that infection in plants powdery patches on leaves is recorded at in one or the other locality comprising of regular intervals. these districts were distinct. Statistical analysis Among the cucurbits, ash gourd was most severely affected. The species responsible for The microscopic study has been repeated for the disease in the state were identified as three times to capture the images and conidia Podoshaera xanthii and Golovinomyces length, breadth were measured. The cichoracearum (Khan and Khan., 1996; glasshouse study for the pathogenicity has Gupta et al., 2012;). The incidence and been carried out by using completely disease severity of powdery mildews in randomized design (CRD). Statistical analysis cucumber, bhendi and pea crops varied in were done using IRRISTAT version 92 different locations across the state which is developed by the International Rice Research similar to this present investigation Institute Biometrics unit, the Philippines (Parthasarathy et al., 2017; Rajalakshmi et al., (Gomez and Gomez, 1984) and the 2016; Parameshwar Naik et al., 2018). percentage values of the disease index were arcsine transformed. Data were subjected to Morphological and microscopic studies ANOVA at significant level (P < 0.05) and means were compared by Duncan’s multiple During the survey, twenty powdery mildew range test (DMRT). infected samples from major cucurbit crops 474 Int.J.Curr.Microbiol.App.Sci (2020) 9(7): 472-481 have been collected. The morphological Pathogenecity study examinations of the collected samples from various hosts of cucurbits were done using In pathogenecity assay, Podosphaera xanthii light microscope. With the help of image took initial infection