INTRODUCTION Brinjal (Solanum melongena L.) is one of the important vegetable crops of our own country and belongs to the family Solanaceae. It features on the menu of virtually every household in India, irrespective of food preference, income level or social status. Successful cultivation of the brinjal crop has been hindered by several insect pests and devastating diseases. Among the diseases, bacterial wilt caused by Ralstonia solanacearum (Yabucchi et al, 1995) is a major limiting factor. This has been the most ubiquitous and serious bacterial disease throughout tropical, sub-tropical and temperate regions of the world (Hayward, 1991). In India, this disease is of a major concern and is serious in parts of Karnataka, Kerala, Orissa, Maharashtra, Madhya Pradesh and West Bengal (Rao et al, 1976). Yield losses ranging from 65 to 70% have been reported in brinjal (Das and Chattopadhyay, 1953). The disease is characterized by sudden wilting of the plant at flowering stage, by yellowing of foliage and stunted plant growth (Kelman, 1953; Rai et al, 1975) and an initial, brownish discoloration of vascular tissues occassionally accompanied by browning and rotting of tissues inside vascular bundles (Smith, 1920). Evaluation of brinjal genotypes against bacterial wilt caused by Ralstonia solanacearum H.M. Santhosha, K.M. Indiresh, C. Gopalakrishnan1 and T.H.Singh1 University of Horticultural Sciences, Bagalkot, India 1ICAR-Indian Institute of Horticultural Research Hesaraghatta Lake Post, Bengaluru – 560089, India E-mail: san3070@gmail.com ABSTRACT Forty brinjal genotypes were screened by artificial inoculation using Ralstonia solanacearum inoculum at a concentration of 1.0 X 108 cfu/ml (O.D600 = 0.3). Genotypes Arka Nidhi, Haritha, Swetha, Surya, IIHR-3, IIHR-555, WCGR, R-2588, WL-2230, L-3261, L-3270, L-3272 and Arka Anand were found to be resistant to bacterial wilt, whereas, IIHR-7, L-3263, L-3268 and L-3269 were moderately resistant. Genotypes R-2584, R-2586, R- 2592, L-3260, L-3262, L-3264, L-3266 and L-3267 were moderately susceptible, and genotypes R-2580, R-2582, R-2587, R-2591, R- 2593 and R- 2595 were found to be susceptible. Lastly, genotypes R-2581, R- 2594, R-2589, R-2590, WL-2232, Pusa hybrid-6, Arka Shirish, R-2585 and R-2583 were found to be highly susceptible to bacterial wilt. Resistant and moderately resistant genotypes showed longer incubation period. Key words: Brinjal, bacterial wilt, Ralstonia solanacearum, genotypes J. Hortl. Sci. Vol. 10(1):74-78, 2015 For management of bacterial wilt in the field, various control measures like crop rotation (cultural practice), use of antagonistic organisms (biological method) and application of chemicals (chemical control) are suggested. As the pathogen can survive or persist in the soil for several years, it is very difficult to control bacterial wilt by chemical applications, using antagonistic organisms or by cultural practices. Therefore, mitigation of the disease using appropriate farming practices needs further development and adaptation (Grimault and Prior, 1990). Therefore, search for resistant sources and incorporating those genes in commercial cultivars is a sound approach to the problem. MATERIAL AND METHODS The experimental material consisting of 40 genotypes was maintained in a homozygous state at the vegetable block, Post-Graduation Centre, UHS Campus, Bengaluru. Seeds of these genotypes were sown in protrays in the 1st week of August 2011. The experiment was laid out in Randomized Complete Block Design (RCBD), with three replications. A row consisting of 15 plants constituted a replication under each treatment. The 40 genotypes, including resistant (Arka Anand) and susceptible check (Pusa Hybrid-6) were 75 subjected to artificial inoculation which made on seedlings in portrays, a day prior to transplantation into the main field. A slight injury was made to the root with a sterile knife before inoculating while withholding irrigation for a day. Three ml volume of the inoculum at a concentration of 1.0 X 108 cfu/ml (O.D600 = 0.3) was poured into the root zone. Thereafter, the seedlings were transplanted into the main field. Ten days after inoculation, symptoms of wilting were seen. Observations were made as per the scale suggested by Zakir Hussain et al (2005). Observations on (i) days to 50% bacterial wilt, (ii) bacterial wilt at different stages of plant growth, and (iii) cumulative bacterial wilt incidence at 50 days after inoculation were recorded. Observations were recorded at intervals of 10 days, with the last observation made at 50 days after inoculation. RESULTS AND DISCUSSION Any breeding programme, including any that involves host-plant resistance to a pathogen, must begin with an extensive screening of germplasm. Success in finding resistance to bacterial wilt is directly related to availability of resistant genotypes in the germplasm. Development of varieties/ hybrids with suitable horticultural traits is a slow process, despite availability of sources of resistance. This is due to the unstable nature of resistance under different environmental conditions, which has necessitated the breeder to explore better sources of resistance in the cultivated brinjal for breeding bacterial wilt resistance. The 40 genotypes were screened against Race-I, Biovar 3. Genotypes Arka Nidhi, Haritha, Shwetha, Surya, IIHR-3, IIHR-7, IIHR-555, WCGR, R-2588, R- 2592, WL- 2230, L-3260, L-3261, L-3262, L-3263, L-3268, L-3269, L- 3270, L-3272 and Arka Anand (Resistant check) showed no 50% wilt even at 50 DAI. However, most genotypes like Pusa Hybrid-6, L-3267, R-2581, R-2589, R- 2593 and R- 2583 took the least number of days to show 50% wilt incidence. Genotypes R-2586, L-3266 and R-2584 took the maximum number of days to express 50% wilt. Least number of days taken to express 50% wilt in a genotype shows occurrence of a shorter incubation period, and, such genotypes were highly susceptible to Ralstonia solanacearum under field conditions; while, in some genotypes, no 50% wilt even at 50 DAI shows occurrence of a longer incubation period. Therefore, these genotypes are able to withstand attack from Ralstonia solanacearum under field conditions, without any great loss in economic yield. Results of the present study are in agreement with those of Zakir Hussain et al (2005) (Table 1). Genotypes Pusa Hybrid-6 (at 0-10 and 11-20 DAI), followed by R- 2595 (at 0-10 DAI), R- 2593 (at 11-20 DAI) and R-2591 (at 11-20 DAI) recorded comparatively higher wilt incidence, indicating that it was the stage that was critical for genotypes becoming susceptible to bacterial wilt. Compare this to the genotypes Shwetha, Surya, IIHR-3, IIHR-7, IIHR-555, WL-2230, L-3261, L-3270 and WCGR, where none, or very low, wilt-incidence was recorded. At 21-30, 31-40 and 41-50 DAI, most genotypes showed medium to low level of wilt. Most of the susceptible genotypes showed a susceptible reaction in their early stages of growth (0-10 and 11-20 DAI). Similarly, Hoque et al (1981) recorded higher incidence of wilt in tomato in the early stage of crop growth, i.e., the first symptom of wilt was observed by them on the 15th day from inoculation. Data on wilting collected by them at 43 days after inoculation varied from 13.3% to 100%. Significant difference was observed for cumulative bacterial wilt incidence at 50 DAI among the eggplant genotypes studied. Highest incidence was recorded in WL- 2232, followed by R-2590, Arka Shirish and Pusa Hybrid-6. Lowest incidence was recorded in the genotypes Surya, IIHR-3 and L-3270. In the present study, during screening of the genotypes, air temperature and relative humidity recorded were 19-28°C and 51-94%, respectively. These factors, together with impact from soil moisture and soil temperature, may have influenced resistance reaction of the genotypes. Among the various genotypes used in this trial, only Arka Nidhi, Haritha, Shwetha, Surya, IIHR-3, IIHR-555, WCGR, R-2588, WL-2230,L-3261, L-3270, L-3272 and Arka Anand were resistant to bacterial wilt; IIHR-7, L-3263, L- 3268 and L-3269 were found to be moderately resistant. Vasse et al (2005) reported that resistance exhibited by various genotypes may be due to the secondary metabolism of polyphenols, and the higher concentration of steroidal glycoalkaloids present in resistant plants, thereby preventing bacterial movement into the vicinity of the plant system (by their action as a repellent). Further, Prior et al (1994) reported that inhibitor extracts, tyloses and gums in resistant plants act like filters, thereby preventing bacterial movement within a plant system. Among the genotypes used in our experiment, Arka Nidhi, Haritha, Shwetha, Surya, IIHR-3, IIHR-555, WCGR, R-2588, WL-2230, L-3261, L-3270, L-3272 and Arka Anand graded as resistant to bacterial wilt, whereas, IIHR-7, L- J. Hortl. Sci. Vol. 10(1):74-78, 2015 Evaluation of brinjal genotypes against bacterial wilt 76 Table 1. Reaction of eggplant genotypes at different stages of plant growth to bacterial wilt pathogen (%) under field conditions Sl. Genotype Days Bacterial wilt incidence (%) Cumulative Disease No. to 50% 0-10 DAI 11-20 DAI 21-30 DAI 31-40 DAI 41-50 DAI bacterial reaction bacterial wilt wilt incidence at 50 DAI (%) 1 Arka - 5 (12.63) 2.5 (9.09) 5 (12.92) 2.5 (9.09) 0 15.00 (22.73) Resistant Nidhi 2 Haritha - 2.5 (9.09) 0 0 12.5 (20.63) 1.66 (4.31) 16.67 (23.93) Resistant 3 Shwetha - 0 0 0 5 (12.92) 0 5.00 (12.92) Resistant 4 Surya - 0 0 0 0.83 (3.03) 1.66 (4.31) 2.50 (7.34) Resistant 5 IIHR-3 - 0 0 0 0 2.5 (9.09) 2.50 (9.09) Resistant 6 IIHR-7 - 0 0 0 15 (22.59) 10 (18.04) 25.00 (29.91) Moderately resistant 7 Arka 18 36.04 (36.86) 25 (29.97) 13.63 (21.60) 0.83 (3.03) 12.5 (20.63) 88.00 (70.17) Highly Shirish susceptible 8 IIHR-555 - 0 0 0 0 20 (26.44) 20.00 (26.44) Resistant 9 WCGR - 2.5 (9.09) 0 2.5 (9.09) 0 0 5.00 (12.92) Resistant 10 R-2580 26 5 (10.45) 25 (29.91) 25 (29.91) 15 (22.59) 2.5 (7.34) 72.50 (58.89) Susceptible 11 R-2581 12 35 (36.22) 37.5 (37.74) 7.5 (15.89) 0 2.5 (9.09) 82.50 (65.59) Highly susceptible 12 R-2582 24 20 (26.53) 27.5 (31.60) 15 (22.73) 1.66 (4.31) 0 64.17 (53.23) Susceptible 13 R-2585 18 27.5 (31.60) 35 (36.26) 20 (26.44) 2.5 (9.09) 0.83 (3.03) 85.83 (68.63) Highly susceptible 14 R-2583 15 22.62 (28.36) 33.28 (35.20) 13.79 (21.73) 12.04 (19.19) 0 81.74 (63.94) Highly susceptible 15 R-2584 36 0.93 (3.20) 27.59 (31.66) 19.48 (26.15) 5.52 (13.34) 0 53.52 (47.01) Moderately susceptible 16 R-2586 50 2.5 (9.09) 15 (22.73) 10 (18.43) 17.33 (24.43) 5 (12.92) 49.83 (44.89) Moderately susceptible 17 R-2587 19 7.38 (15.61) 42.62 (40.73) 14.06 (21.97) 0 0 64.06 (53.15) Susceptible 18 R-2588 - 7.5 (15.23) 5 (12.63) 0 0.83 (3.03) 0 13.33 (20.75) Resistant 19 R- 2592 - 3.57 (6.36) 7.04 (15.29) 21.47 (27.57) 10.23 (18.56) 0 42.33 (40.54) Moderately susceptible 20 R-2589 14 35 (36.26) 27.5 (31.60) 15 (22.78) 2.5 (9.09) 1.66 (4.31) 81.67 (64.63) Highly susceptible 21 R-2590 16 26.49 (30.93) 23.18 (28.76) 26.49 (30.95) 6.29 (14.40) 5.62(13.36) 88.07 (69.88) Highly susceptible 22 R-2591 19 5.29 (13.00) 47.02 (43.27) 8.77 (17.09) 0 14.73(22.50) 75.82 (60.65) Susceptible 23 R- 2593 14 12.5 (20.70) 50.34 (45.17) 9.46 (17.81) 6.08 (14.14) 0 78.38 (62.29) Susceptible 24 R- 2594 30 12.5 (20.63) 25.34 (30.20) 15 (22.78) 15 (22.73) 13.5 (20.63) 81.33 (63.68) Highly susceptible 25 L-3261 - 0 5 (12.63) 0 0 0 5.00 (12.63) Resistant 26 R- 2595 20 38.25 (38.19) 15.75 (23.37) 11.08 (19.23) 1.5 (4.08) 1.85 (4.54) 68.44 (55.84) Susceptible 27 WL-2230 - 0 7.5 (15.74) 5 (12.63) 5 (10.45) 0 17.50 (24.07) Resistant 28 WL-2232 18 28.12 (32.05) 35.09 (36.28) 11.25 (19.54) 17.54 (24.72) 0 92.09 (73.78) Highly susceptible 29 L-3260 - 2.9 (9.80) 17.53 (24.71) 0 14.9 (22.65) 11.25(19.39) 46.59 (43.02) Moderately susceptible 30 L-3262 - 5 (12.92) 17.5 (24.68) 10 (18.04) 10 (18.04) 5 (12.63) 47.50 (43.54) Moderately susceptible 31 L-3269 - 2.54 (7.40) 15.4 (23.04) 7.63 (15.88) 0.86 (3.09) 5.03(12.69) 31.46 (34.10) Moderately resistant 32 L-3263 - 5 (12.63) 20 (26.55) 0.83 (3.03) 0 0.83 (3.03) 26.67 (31.07) Moderately resistant 33 L-3264 26 22.5 (28.28) 25 (29.97) 5 (12.92) 1.66 (4.31) 0.83 (3.03) 55.00 (47.85) Moderately susceptible Santhosha et al J. Hortl. Sci. Vol. 10(1):74-78, 2015 77 3263, L-3268 and L-3269 graded as moderately resistant to bacterial wilt. However, further research is needed to evaluate level of resistance of the genotypes under different agro-climatic zones of the country, to study the stability of resistance to various races of Ralstonia solanacearum. ACKNOWLEDGEMENT Santhosha, H.M. is grateful to Department of Science and Technology, Govt. of India, New Delhi, for awarding INSPIRE fellowship (2010–2013) to pursue this work at College of Horticulture (Bengaluru Campus), University of Horticultural Sciences, Bagalkot REFERENCES Grimault, V. and Prior, P. 1990. Approach des mecanismes de resistance a fletrissement bactarian (Pseudomonas solanacearum E.F. Smith) Chez la tomato. In: Society Franchaise de phytopahologie, Zenus congress de la SFP, Montpellier, pp. 28-30 Das, C.R. and Chattopadhyay, S.B. 1953. Bacterial wilt on eggplant. Indian Phytopathol., 8:130-135 Hayward, A.C. 1991. 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Sci., 3:61-64 Smith, E.F. 1920. Brown rot of Pseudomonas solanacearum. An introduction to bacterial diseases Table 1. Contd... Sl. Genotype Days Bacterial wilt incidence (%) Cumulative Disease No. to 50% 0-10 DAI 11-20 DAI 21-30 DAI 31-40 DAI 41-50 DAI bacterial reaction bacterial wilt wilt incidence at 50 DAI (%) 34 L-3266 42 13.38 (21.42) 26.25 (30.80) 6.52 (14.72) 4.45 (11.84) 2.39 (8.89) 52.99 (46.70) Moderately susceptible 35 L-3267 12 27.5 (31.60) 31 (33.81) 0 1.13 (3.54) 0 59.63 (50.55) Moderately susceptible 36 L-3268 - 1.94 (4.64) 14.56 (22.38) 11.58 (19.82) 0 0 28.09 (31.89) Moderately resistant 37 L-3270 - 0 2.5 (9.09) 0 0 0 2.50 (9.09) Resistant 38 L-3272 - 2.5 (9.09) 5 (12.92) 0.83 (3.03) 0 2.5 (9.09) 10.83 (19.18) Resistant 39 Arka - 5 (12.63) 2.5 (9.09) 0 0 0 7.50 (15.74) Resistant Anand (Resistant Check) 40 Pusa 11 47 (43.26) 38.25 (38.18) 2.56 (7.46) 0 0 87.81 (69.69) Highly susceptible hybrid-6 (Susceptible check) Level of ** ** ** ** ** ** Significance SEm± 1.14 0.93 1.22 0.93 0.56 2.03 CD @ 5% 3.21 2.64 3.45 2.64 1.58 5.72 CV (%) 12.21 7.35 16.59 18.65 15.66 8.47 DAI – Days after inoculation; Figures in parentheses are angular transformed values J. Hortl. Sci. Vol. 10(1):74-78, 2015 Evaluation of brinjal genotypes against bacterial wilt 78 of plants. W.B. Saunder Co., Phildelphia, U.S.A., pp. 177-201 Vasse, J., Danoun, S. and Trigalet, A. 2005. Microscopic studies of root infection in resistant tomato cultivar Hawaii 7996. In: Allen, C., Prior, P. and Hayward, A.C. (eds.). Bacterial wilt disease and the Ralstonia solanacearum species complex. APS Press, St. Paul, Minnesota, USA, 285 p. Yabucchi, Y., Ikuya, Y., Hisako, H. and Yukiko, N, 1995. Transfer of two Burkholderia and an Alacaligenes species to Ralstonia genome. Microbiol – Immunol., 39:897-904 Zakir Hussain, M., Rahman, M.A. and Bashar, M.A. 2005. Screening of brinjal accessions for bacterial wilt caused by Ralstonia solanacearum. Bangladesh J. Bot., 34:53-58 (MS Received 12 April 2014, Revised 18 May 2015, Accepted 26 May 2015) J. Hortl. Sci. Vol. 10(1):74-78, 2015 Santhosha et al