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Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 2074-2083 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 9 Number 11 (2020) Journal homepage: http://www.ijcmas.com Original Research Article https://doi.org/10.20546/ijcmas.2020.911.247 Studies on Induced Resistance by Chemicals against Papaya Ring Spot Virus (PRSV) in Papaya Hemlata Kshirsagar1* and Pankaj Deore2 1 Department of Plant Pathology, College of Agriculture Dhule, Maharashtra, India Mahatma Phule Agriculture University, Rahuri, Maharashtra, Maharashtra, India 2 *Corresponding author ABSTRACT Keywords Papaya ring spot virus, Induced résistance, Diffèrent chemicals, Incubation period, Disease incidence Article Info Accepted: 15 October 2020 Available Online: 10 November 2020 Papaya ring spot disease caused by papaya ringspot virus (PRSV) is the major limiting factor in papaya growing regions in Maharashtra. In these study chemicals inducing resistance was assessed in in vitro condition against PRSV. Eight chemicals which didn’t show any phytotoxicity (Chitosan, 6-Benzyladenine, Salicylic acid, IAA, IBA, NAA, Humic acid, Trisodium phosphate) inducing resistance were tested at different concentrations. The eight chemicals inducing resistance exhibited variable response in three modes of applications viz., seed soaking, pre inoculation spraying and post inoculation spraying. Among the chemicals tested, none was found efficient in inducing complete resistance against PRSV, but they increased the incubation period thereby delaying the symptom expression, as compared to control. The maximum incubation period was observed in spraying of Chitosan, at 72 hours prior to virus inoculation, which was most effective in reducing PRSV disease incidence in papaya. In seed soaking application, lowest PRSV incidence was recorded in Trisodium phosphate treatment while, by spraying of chemicals at 72 hrs. pre- and post-inoculation, the lowest PRSV incidence was recorded in humic acid treatment. All the chemical treatments delayed the symptoms expression as compared to control treatment. Pre-inoculation chemicals were the best gave the most effective control and Chitosan, 6-Benzyladenine, Salicylic acid, were the best treatments. Though all the chemical treatments enhanced the plant height of papaya, but with the chemicals viz., Salicylic acid, 6-Benzyladenine and Trisodium phosphate applied as seed treatment, there was no significant increase in plant height and same is the case with Naphthalene acetic acid and indole-3-acetic acid applied 72 hrs. prior and after inoculation. Introduction Benzyl-isothionate which has been reported as a germicide and insecticide (Olaya, 1985). Papaya, encompasses most of the desirable qualities of a whole as well as processed fruit (Amar Singh, 1996). Besides medicinal values, the seeds and unripe fruits of papaya are rich in sulphur containing chemicals like Papaya ringspot virus (PRSV) is the most economically important virus in papaya (Barbosa and Pagui, 1982) and has become a major constraint in papaya cultivation, in 2074 Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 2074-2083 India including Maharashtra (Kale, 1999). Symptoms consist of intense yellow mosaic on leaves, small shoestring-like new leaves along with dark green and slightly sunken rings on the fruit. Trees infected at a very young age remain stunted and never produce any fruit (Reddy et al., 2007). As, application of insecticides to control the insect vector is the only way to reduce the disease and biotechnological interventions are yet to be commercialized, alternate management controls are investigated. Plants possess a range of defenses that can be actively expressed in response to various pathogens and parasites, ranging from microscopic viruses to insect herbivores. Systemic acquired resistance (SAR) and induced systemic resistance (ISR) are two forms of induced resistance which is characterized by broad-spectrum disease resistance (Kessmann et al., 1994). The activated disease resistance is effective against both the inducing pathogen and other unrelated pathogens, which may be bacteria, viruses or fungi. Several investigators studied the effectiveness of chemical resistance inducers against root rot disease (Segarra et al., 2006) and hence this study was aimed to study the effect of chemically induced resistance in the management of PRSV in papaya. susceptible papaya variety i.e., Red Lady by mechanical sap inoculation in an insect free shade net house, which served as a source of virus for further studies. The aforementioned variety was used for subsequent studies. Phytotoxicity test of chemicals used in the study Eight treatments viz. Chitosan, 6Benzylaminopurine (6-BAP), Humic acid (HA), Salicylic acid(SA), Indole Acetic Acid (IAA), Indole Butyric Acid(IBA), Naphthalene acetic acid (NAA) and Trisodium phosphate(TSP) were used for the study. For the phytotoxicity test, papaya seedlings (var: Red lady) were used. Different doses of the treatments viz. Chitosan(10ppm, 50ppm, 100ppm and 250 ppm), 6-BAP (1ppm, 2.5 ppm, 5ppm and 10ppm), Humic and Salicylic acid(0.5ppm, 1ppm, 5ppm and 10ppm each) and IAA, IBA, NAA and Trisodium phosphate (50ppm, 100ppm, 250ppm and 500ppm each) were dissolved in their respective solvents and was used immediately for spraying. Phytotoxicity symptoms were recorded periodically and the highest dose/concentration of chemical not showing any phytotoxicity was selected for the further studies Induction of resistance through chemicals Materials and Methods Collection, isolation and maintenance of PRSV samples The papaya ring spot disease samples representing ideal symptoms were collected from the farmers’ fields of Dhule district (20.9042° N, 74.7749° E), Maharashtra. PRSV samples were collected separately in polyethylene bags and labeled. The collected samples of PRSV were established and maintained on highly The pot culture experiment was conducted to study the effect on induced resistance by chemicals against papaya ring spot virus (PRSV) in Papaya. For each of the test chemical, the highest dose/concentration of chemical not showing any phytotoxicity symptoms in phytotoxicity test was used. Nine treatments included Chitosan @250ppm, 6-BAP @ 10ppm, HA @ 10ppm, SA @ 10ppm, IAA @500ppm, IBA @ 500ppm, NAA @ 500ppm, TSP @ 500ppm along with an untreated virus inoculated control. The experiments were laid in completely 2075 Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 2074-2083 randomized design with three replications per treatment. Ten plants per treatment were considered for the study. The test chemicals were applied by the following methods Soaking of seeds The method of Lange (1961) with minor modifications was used. Fifteen healthy seeds per treatment were soaked in chemical solution for 60 minutes in sterilized beaker. The treated seeds were then raised in plastic polythene bags containing in insect proof shed net house. The fifty days old were sap inoculated at 6 to 8 leaf stage and the observations were recorded at 15 days interval. Pre inoculation spraying of chemicals Fifty days old seedlings at 6 to 8 leaf stage were sprayed with chemical solutions in their respective concentration as per the method of Hofgaard et al., (2010) with minor modifications, the sprayed seedlings were sap inoculated with the PRSV extract after 72 hrs. of application of chemicals and the observations were recorded at 15 days interval. b) Percent disease incidence (PDI) at 60 days after inoculation and calculated by the following formula as given by Chiang et al., (2017) Number of infected plants PDI = -------------------------------------------------- x 100 Total number of plants observed c) Incubation period i.e. Number of days required to produce the symptoms after inoculation. d) Symptoms of PRSV inoculated papaya plants viz. Vein clearing (vc), Chlorosis (c), Mosaic (m), Blistering (b), Leaf distortion (ld), Shoe stringing (ss) and Necrosis (n) e) Changes in plant height (cm) was observed 30 and 60days after inoculation of PRSV and finally calculated the per cent increase or decrease in the plant height, by applying the formula T-C Increase/ decrease in plant height (%) = ------------- x 100 T Where, T = Plant height in treated plants C = Plant height in inoculated untreated plants Statistical analysis Post inoculation spraying of chemicals The fifty days old seedlings at 6 to 8 leaf stage were sap inoculated with PRSV extract. The chemical solutions were prepared in requisite concentration and applied on the inoculated seedlings, 72 hrs. after inoculation. The observations were recorded at 15 days interval after inoculation. Observed parameters a) Phytotoxicity of the test chemicals, if any Statistical analysis was carried out as per the procedure given by Panse and Sukhatme (1995). To compare different numerical observations, the data was statistically analyzed by using CRD. Results and Discussion Collection, Isolation and maintenance of PRSV samples The PRSV infected papaya samples collected exhibited the symptoms viz., severe mosaic, 2076 Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 2074-2083 leaf distortion, shoe stringing and fruits with ringspot. All the inoculated papaya cv. Red lady seedlings showed the PRSV symptoms, which were used as a source of virus inoculum for further studies. Phytotoxicity test of chemicals The results obtained in phytotoxicity test are presented. It was observed that all the eight chemicals tested at four different concentrations did not show any phytotoxicity symptoms like chlorosis, epinasty, russeting, tip burning and necrosis on leaves up to ten days after spray. Hence, the final concentration of the chemicals viz., Chitosan (250ppm), 6-BAP (10ppm), Humic acid (10ppm), Salicylic acid (10ppm), IAA (500ppm), IBA (500ppm), NAA (500ppm) and Trisodium phosphate (500ppm) were used for further studies. Effect of the test chemicals on PRSV expression Effect on PRSV incidence In seeds soaked in chemicals the results (Table 2) revealed that there was minimum PRSV incidence with TSP (66.66%), as compared to untreated control followed by HA (73.33%) and SA treatment (76.66%) but they were all at par with each other. IAA, IBA and NAA (each 100%), did not have any effect on disease control. In pre-inoculation treatments, the most effective treatments were HA (70.00%), Chitosan (73.33%), SA (76.67%) and 6-BPA (83.33%) and they were all at par with each other. In this case also IAA, IBA and NAA recorded very high disease incidence. Finally, in post-inoculation also minimum per cent disease incidence was recorded in treatments with HA (73.33%), followed by SA (76.67%), Chitosan (80.00%) and 6-BPA (83.33%) treatments and they were statistically at par with each other. Like other two categories IAA, IBA and NAA recorded a disease incidence which was at par with untreated control. Effect on Incubation period Symptomatology on papaya plants There was a significant variation in incubation period (Table 1) of PRSV, in the three methods employed for the application of the chemicals. Minimum incubation period was recorded in untreated control (18 days) in all the three methods. Inseed soaked in chemicals, maximum incubation was observed with TSP treatment (26 days), which was at par with SA (25 days), In preinoculation treatments, maximum incubation period was recorded with Chitosan (28 days) but it was at par with HA (27 days) and 6BPA (27 days). In post-inoculation category, highest incubation period was recorded in HA and Chitosan treatments (each 26 days), and both were at par with SA treatment (25 days). When seeds were soaked in chemicals, 30 days after inoculation (DAI) only vein clearing was recorded in all the treatments; whereas, in untreated control there were severe symptoms of vein clearing, chlorosis, mosaic and leaf distortion (Table 3). At 60 days after inoculation, in inoculated untreated control more severe and pronounced symptoms were expressed along with shoestring symptoms. In Chitosan, HA, SA, and IAA treatments, chlorosis further progressed to mosaic and leaf distortion; while, in 6-BAP chlorosis progressed to mosaic only. In IBA and NAA treatments mosaic, leaf distortion, blistering and necrosis were observed. 2077 Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 2074-2083 In pre-inoculation studies, at 30 DAI no symptoms were recorded in Chitosan, 6 BAP and SA treatments. Only vein clearing was recorded in rest of the treatments except in untreated control, which recorded the severe symptoms viz., vein clearing, chlorosis, mosaic and leaf distortion (Table 3) At 60 days after inoculation, in inoculated untreated control the symptoms further progressed to shoe stringing. In chitosan, 6BPA, HA, and SA treatments the symptoms progressed to Chlorosis, vein clearing and leaf distortion, IBA and NAA had similar symptoms as untreated control. In post-inoculation, at 30 DAI, only vein clearing was recorded in all the treatments except untreated control, which expressed the severe symptoms viz., vein clearing, chlorosis, mosaic and leaf distortion. All other treatments had a mixed expression of different types of treatments (Table 3). Effect of chemicals on height of papaya plants The results (Table 4) indicated a significant difference in plant height at 60 DAI When seeds were soaked in chemicals,at 60 DAI, the maximum increase in plant height was recorded with IAA treatment (2.25cm) followed by SA (2.20cm), IBA (2.15cm), Chitosan (1.85cm) and NAA (1.20cm) treatments, all of which were at par. However, minimum increase in height was recorded with TSP treatment (0.20cm) followed by 6BPA (0.60cm), control (0.67cm), HA (0.90cm) and NAA (1.20cm) treatments, all of which were at par. Table.1 Effect of various chemicals on incubation period of PRSV Tr. No. 1 2 3 4 5 6 7 8 9 Conc. ppm Treatments Chitosan 6-BAP HA SA IAA IBA NAA TSP Control Seed soaking in chemicals 250 10 10 10 500 500 500 500 - 22 21 23 25 24 22 20 26 18 SE± CD @ 5 % 0.55 1.65 Incubation period (days) * Pre inoculation Post inoculation spraying of sprayingof chemicals chemicals 28 26 27 24 27 26 26 25 22 21 21 22 20 20 25 24 18 18 0.61 1.83 *: Mean of three replications 2078 0.53 1.58 Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 2074-2083 Table.2 Effect of various chemicals on incidence of PRSV at 60 Days after inoculation Tr. No. Chemicals Conc. ppm 1 Chitosan 250 2 6-BAP 10 3 HA 10 4 SA 10 5 IAA 500 6 IBA 500 7 NAA 500 8 TSP 500 9 Control SE± CD@5% Seed soaking in chemicals (PDI) 80.00 (63.93) 90.00 (68.86) 73.33 (59.00) 76.66 (61.22) 96.66 (83.86) 100.00 (90.00) 100.00 (90.00) 66.66 (54.78) 100.00 (90.00) 3.03 9.09 Mean PRSV incidence* (%) Pre inoculation spraying of chemicals(PDI) 73.33 (59.00) 83.33 (66.15) 70.00 (57.00) 76.67 (61.71) 96.67 (83.86) 93.33 (77.71) 96.67 (83.86) 96.67 (83.86) 100 (90.00) 3.61 10.83 Post inoculation spraying of chemicals(PDI) 80.00 (63.93) 83.33 (66.15) 73.33 (59.00) 76.67 (61.22) 96.67 (83.86) 96.67 (83.86) 100 (90.00) 93.33 (77.71) 100 (90.00) 3.82 11.44 *: Mean of three replications, figures in parentheses arc sine values DI: Disease Incidence PDI: Per cent disease incidence Table.3 Reactions of PRSV at various intervals on Papaya cv. Red Lady Tr. Chemicals No. Conc. ppm Seed soaking in chemicals 1 Chitosan 250 30 DAI vc 60 DAI vc,c, m,lld vc,c,m 2 6-BAP 10 vc 3 HA 10 vc 4 SA 10 vc 5 IAA 500 vc 6 IBA 500 vc 7 NAA 500 vc 8 TSP 500 vc vc,c, m,lld vc,c, ,lld vc,c, ,lld vc,c,m, lld,b,n vc,c,m, lld,b,n vc,c, 9 Control - vc,c, m,lld vc,c,m,lld, b,n,ss DAI: Days After Inoculation 2079 Pre inoculation spraying of chemicals 30 60 DAI DAI vc,c, ,lld vc,c, ,lld vc vc,c, ,lld vc,c, ,lld vc vc,c, ,lld vc vc,c,m, lld,b,n vc vc,c,m, lld,b,n vc vc,c, , lld,b vc,c, vc,c,m, m,lld lld,b,n,ss Post inoculation spraying of chemicals 30 60 DAI DAI Vc vc,c,lld Vc vc,c,lld Vc vc,c, m,lld vc,c,lld Vc Vc Vc Vc Vc vc,c, m,lld vc,c, ,n vc,c, , lld,n vc,c, , lld,n vc,c, , lld,n vc,c,m,lld, b,n,ss Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 2074-2083 Table.4 Sr. No. Treatment Conc. ppm 1 2 3 4 5 6 7 8 9 Chitosan 6-BAP HA SA IAA IBA NAA TSP Control 250 10 10 10 500 500 500 500 - SE± CD @5% Height of papaya plants (cm) Seed soaking in Pre inoculation Post inoculation chemicals (Mean) spraying of spraying of chemicals (Mean) chemicals (Mean) ATI 60 DAI ATI 60 DAI ATI 60 DAI 23.07 24.92 30.5 32.9 29.1 30.55 22.3 22.9 27.3 28.35 29.1 30.8 25.78 26.68 33.95 35.8 32.2 36.1 24.17 26.37 27.4 28.75 32.8 34.3 25.5 27.75 23.75 25.4 22.7 24.2 27.4 29.55 24.25 25.65 22.35 24.3 30.4 31.6 25.05 25.4 16.8 17.55 29.1 29.3 26.95 29.5 27.35 29.75 23.15 23.82 23.15 23.82 23.15 23.82 0.42 1.26 0.72 2.14 0.57 1.7 0.67 2 0.57 1.71 0.67 2 ATI: Height of papaya plants (cm) at the time of inoculation (50 days old seedlings) DAI: Days after Inoculation In pre-inoculation, at 60 DAI, the maximum increase in plant height was recorded with TSP treatment (2.55cm) but it was at par with all the treatments except NAA (0.35cm), control (0.67cm) and 6-BPA (1.05cm) treatments. However, minimum increase in height was recorded with NAA treatment (0.35cm) but it was at par with control (0.67cm), 6-BPA (1.05cm), SA (1.35cm) and IBA (1.40cm) treatments. In post-inoculation, at 60 DAI, the maximum increase in plant height was recorded with HA treatment (3.90cm) followed by TSP treatment (2.40cm), both the treatments were at par with each other. However, minimum increase in height was recorded with control treatment (0.67cm) but it was at par with all the treatments except TSP (2.40cm) and HA (3.90cm) treatments. The papaya specimens showing typical virus infected symptoms were collected and identified on the basis of symptoms as papaya ring spot virus. The symptoms observed were compared with the symptoms described by Sta. Cruz et al., (2009), Tripathi et al., (2008) and Verma et al., (2007), and were found similar. The phytotoxicity test attempted with the test chemicals at three concentrations revealed that all the test chemicals were nonphytotoxic to papaya, and on this basis their highest concentration were selected for further studies. This was in accordance with the findings of Spletzer and Enyedi (1999) who reported that 200 mM SA when added in MS medium to the hydroponically grown tomato plants caused no change in leaf turgor or signs of phytotoxicity on the foliage. Le (2006) tested chemical inducers like the salicylic acid for controlling anthracnose in chilli and no phytotoxicity was reported at higher concentrations. In all the treatments significant variations were observed in respect of incubation period 2080 Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 2074-2083 of PRSV. However, minimum incubation period was observed in control treatment (18 days), followed by NAA (20 days); whereas, it was maximum with Chitosan (28 days), followed by 6-BPA (27 days) and HA (27 days). It was also observed that due to the chemical treatments there was increase in incubation period as compared to control among all three applications. However, there was a significant variation in incubation period when applied in different manner or applied at different times of inoculation. Similar findings were reported by Gandhi et al., (2009) and Reddy et al., (2006) who opined salicylic acid was responsible for delaying the virus infection on blackgram and urdbean respectively. As chemicals can prolong the incubation period it can play a significant role in the management of PRSV. Among the three application methods of the test chemicals, spraying of chemicals at 72 hrs. prior to PRSV inoculation was found most effective in reducing PRSV disease incidence in papaya. In seed soaking application, lowest PRSV incidence was recorded in TSP treatment (6.67%) but the same treatment in other applications recorded higher disease incidence; In chemical application by spraying at 72 hrs. prior and 72 hrs. after PRSV inoculation, the lowest PRSV incidence was recorded in HA treatment. In similar studies, Yang et al., (2011) reported that the resistance inducing agents polypeptide and 3-acetonyl-3hydroxyoxindole (AHO) delayed the TMV incident in tobacco. Madhusudhan (2008)also observed that Acibenzolar-Smethyl (ASM; S-methylbenzo (1,2,3) thiadiazole-7-carbothiate) pretreatment to tomato and tobacco plants reduced the concentration of Tomato mosaic tobamovirus (ToMV) and Tobacco mosaic tobamovirus (TMV) in tomato and bell pepper seedlings, respectively. Elsharkawy and Mousa (2015) reported Silicon nanopowder treated cucumber plants had reduced severity of PRSV as compared with the control due to strong activations of peroxidases (POX) and phenylalanine ammonialyase (PAL) genes. All three methods of the chemicals applications delayed the symptoms expression, as compared to control treatment, which indicated that time and type of application of chemicals inducing resistance play important role in PRSV symptom expression. However, pre-application of chemicals was found to be the best for Chitosan, 6-BPA and SA. Deya et al., (2008) reported that SA applied to the leaves of Vicia faba prior to Bean Yellow Mosaic Virus (BYMV) inoculation had enhanced the plant resistance against BYMV which was manifested by reduction in percentage of infected plants and decrease in disease severity The results obtained indicated that the entire test chemicals applied by either of the method significantly enhanced the height of papaya plants but same chemical showed variation in increase height of papaya plant when applied in different manner or different time of inoculation. It was also observed chemicals viz., SA, 6-BPA and TSP when applied as seed treatment reported increase in plant height less than control same is the case with NAA applied 72 hrs. prior to inoculation and for IAA and NAA applied 72 hrs. after inoculation. From this it is pointed out that some chemicals have deleterious effect on papaya plant height when plants were inoculated with PRSV and so time of chemical application and way of chemical application is important factor while using chemicals for inducing resistance. 2081 Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 2074-2083 Le et al., (2012) reported that the SAR chemicals (oxalic acid) when applied as seed soaking to protect rice crop against grassy stunt virus disease, had enhanced the plant height, reduced the disease incidence and also increased the grain yield in rice and this finding is in tandem with the present finding. Thus the above findings revealed that none of the test chemical was effective in inducing complete resistance in papaya against PRSV, but they delayed the incubation period and symptoms production, as compared to control. 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Molecular Plant Pathology 9: 269-280. Verma, R., Ram, R.D., Tomer, S.P.S., 2007. Survey and surveillance of papaya ring spot virus disease in India. J. Maharashtra Agric. Univ, 32(2): 277278. Yang, S., Park, M., Kim, I., Kim, Y., Yang, J., Ryu, C.M., 2011. 2-aminobenzoic acid of Bacillus sp. Bs107 as an ISR determinant against Pectobacterium carotovorum sub sp carotovotrum Scc1 in tobacco. European J. Pl. Pathol., 129: 371-378. How to cite this article: Hemlata Kshirsagar and Pankaj Deore. 2020. Studies on Induced Resistance by Chemicals against Papaya Ring Spot Virus (PRSV) in Papaya. Int.J.Curr.Microbiol.App.Sci. 9(11): 20742083. doi: https://doi.org/10.20546/ijcmas.2020.911.247 2083