Participatory Evaluation of Some Tomato Genotypes for Resistance to Bacterial Wilt

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1 Nepal Agri. Res. J. Vol. 8, Partiipatory Evaluation of Some Tomato Genotypes for Resistane to Baterial Wilt Ram D. Timila* and Sharada Joshi Plant Pathology Division, Nepal Agriultural Researh Counil, Khumaltar, Lalitpur, Nepal ABSTRACT Baterial wilt aused by Ralstonia solanaearum E.F. Smith is one of the destrutive diseases of tomato. Experiments were onduted to onfirm the resistane and to evaluate varieties reeived from Asian Vegetable Researh and Development Center against baterial wilt disease in the farmers baterial wilt sik fields at Thaiba and at Panhkhal during 1999 and respetively. A total of five varieties suh as 2026 C, 2026 D, 1466 J, 1466 P and suseptible hek Lapsigede or L 390 were inluded in the experiments. Randomized omplete blok design with 4 repliations was ommened at both the loations. In terms of disease inidene and yield parameters as well as onsumers preferene on the fruit size, 2026 C was found the best variety followed by 2026 D. Wilt inidene was signifiantly lower in those varieties showing resistant reation than in suseptible hek. However, the marketable fruit yields were signifiantly higher with low wilt inidenes in 1466 P and 1466 J also ompared to suseptible hek. But the large fruit size of those varieties was not aeptable to the onsumers and the growers. Thus, 2026 C and 2026 D ould be used as resistant variety to minimize rop losses from baterial wilt disease. Key words: Baterial wilt, Ralstonia solanaearum, resistant variety, Tomato INTRODUCTION Baterial wilt aused by Ralstonia solanaearum E.F. Smith (RS) is widely distributed disease in the world. It is one of the limiting fators to the suessful ultivation of solnaeous vegetables throughout the world, where warm and humid limate is prevalent (Kelman 1953, Vawdrey and Gounder 1993). In Nepal, Tomato (Lyopersion esulentum L.) is one of the fruit vegetables grown extensively in terai, foothills and valleys of Nepal. After late blight, baterial wilt is onsidered to be the seond most important disease in tomato. In Nepal, it was first reorded in 1978 in tomato rop (Shrestha 1990) and proved to be one of the limiting fators for suessful ultivation in lowlands, foothills and valleys. Its inidene was reported as high as 80% ausing onsiderable yield losses in tomato growing areas of Nepal (Timila et al 1997). The primary soure of inoulum for the ourrene and spread of the pathogen is onsidered to be infested soil, plant debris and weeds (Kelman 1953). Baterial wilt is diffiult to ontrol, one established in the field beause of soil borne nature of the pathogen, and having wide host range, wide spread distribution and vast geneti variability of the pathogen (Hayward 1991). In reent years, RS is reported to be apable of infeting more than 50 botanial families with more than 200 plant speies (Maro et al 2005). Due to the limited effiay of urrent integrated management strategies of baterial wilt, this disease is ontinued to be eonomially important (Pradhananga et al 2003). Wide use of pestiides has favored the development of pathogen resistane towards pestiides. Conerns for human health and the environment have pushed the rop prodution to redued use of pestiides. Host resistane plays an important role in the development of novel strategies to ontrol baterial wilt disease. Planting resistant varieties is the most effetive and simplest methods for ontrolling baterial wilt disease and also environmentally sound. Virulene differenes among pathogen strains and bioti and abioti fators an ause resistane instability in host (Hayward 1991). The least aggressive strain affets least on the resistant ultivars. Instability in host resistane appeared to be a major problem in using resistant lines (Wang et al 1997). However, effetive and

2 Nepal Agri. Res. J. Vol. 8, long-term disease ontrol ould be ahieved with resistant or tolerant varieties as a part of integrated disease management strategies (Saddler 2005). So, the experiments were onduted in the farmers field to evaluate the varieties and to verify their resistane to baterial wilt that was previously reported to be resistant at Asian Vegetable Researh and Development Center (AVRDC). MATERIALS AND METHODS Seeds of the five tomato varieties ( 2026 D, 2026 C, 1466 P, 1466 J supposed to be resistant and suseptible hek, L 390 were reeived from AVRDC, Taiwan under South Asian Vegetable Researh Network (SAVERNET). In the year 1999, the experiment was onduted at Thaiba, Lalitpur (1350 masl) in naturally infested farmers field. Five varieties from AVRDC and one of the popular hybrid variety (NS 815) in that loatons in addition to suseptible hek from AVRDC were inluded in the trial. In the following onseutive years (2000 and 2001), experiments were onduted at Panhkhal of Kavrepalanhowk (850 masl) distrit in naturally infested farmers field. In both the loations, the experimental fields were hosen with uniform distribution of baterial wilt disease in previous season. The basis for determining uniform distribution of baterial wilt disease was uniform distribution of wilted tomato plants (whih showed baterial ooze in water from the ut surfae) during previous season in the fields. Above five genotypes inluding loal Lapsigede (suseptible hek) were inluded in the experiment. Seedlings were raised under sreenhouse onditions at Plant Pathology Division using steam sterilized soil to make sure of seedlings free from disease. The experimental design was randomized omplete blok with four repliations. The number of plants per repliation of eah variety was 20. Plant to plant and row to row spaing were 30 and 60 respetively. Chemial fertilizer applied was 85:20:50 kg NPK/ha in addition to 10mt/h of ompost. One month old seedlings were transplanted during first and third week of August at Thaiba and Panhkhal respetively. Agronomial praties were given as per need. Wilt inidene was reorded based on the survival of the plants every 7 days interval until disease beame stable. Ripened fruits were harvested by hand pluking and alulated in terms of t/h. Marketable and unmarketable fruit yield due to late blight were separated. For determining the size of the fruit, average of 10 fruits were taken. Three sprays of 0.15% Krilaxyl (metalaxyl 8% plus manozeb 64%) were given to save plants from Late Blight disease. Area under disease progress urve (AUDPC) for promising varieties at Panhkhal were alulated aording to Shanner and Finney (1977) using following formula. n AUDPC = Σ [(y i+1 +y i )/2] [x i+1 - x i ] i=1 where, yi = disease index or inidene at the i th observation, xi = time at the i th observation, and n = total number of observations. For assessing resistane level of the genotypes ategorization was followed aording to Mew and Ho (1976) as given below. The data were analyzed using MSTATC after transformation whenever neessary. Resistant = less than 20% wilt inidene Moderately resistant = 21-40% wilt inidene Moderately suseptible = 41-60% wilt inidene Suseptible = % wilt inidene. RESULTS At Thaiba, the varieties 2026 C and 1466 J were resistant with wilt inidenes, 12.8% and 24, 3% respetively. Varieties, 2026 D and 1466 P were moderately resistant with

3 Nepal Agri. Res. J. Vol. 8, wilt inidenes, 21% and 30.6% respetively. Those all varieties were signifiantly better and are at par in response to baterial wilt (Figure 1). Yield ould not be taken due to severe infetion of late blight inspite of Krilaxyl spray. However the farmers at the loation were highly impressed by the higher perentage of survival (less wilt inidene) of the plants ompared to suseptible hek variety, L 390 (90%) or Pusa Ruby (65%) and popular ommerial variety, NS 815 (57%) of that loation a 80 Wilt inidene, % a b D 2026 C 1466 J 1466 P Pusa Ruby NS 815 L390 Tomato varieties Figure 1. Onfarm evaluation of tomato varieties against baterial wilt in the farmers' field at Thaiba, (CV = 26.6%. Column with same letter are not signifiantly different at P 0.05 using DMRT) Wilting of the tomato plants were started two weeks after transplanting in suseptible hek, loal Lapsigede variety in both the years at Panhkhal. In the year 2000, disease inidene was found least in 2026 C followed by 1466 J, 1466 P and 2026 D based on terminal disease inidene. The latest variety was statistially different from 2026 C (Table 1). Hundred perent wilt inidene was found in loal suseptible hek variety, Lapsigede before fruiting stage. Regarding yield parameter, highest marketable fruit yield was found in the variety 1466 P in Other three varieties 2026 C, 2026 D, and 1466 J were not statistially different in marketable fruit yield. In fruit size, 2026 C and 2026 D, and 1466 P and 1466 J were at par. Lesser unmarketable fruit yield due to late bight infetion was found in 1466 J. Similarly in the year 2001, same trend of disease inidenes were found in the test varieties. All test varieties from AVRDC were statistially similar but different from the loal suseptible hek in wilt reation (wilt inidene). The disease inidene was higher in 2000 than in the year 2001, it ould be due to slightly higher temperature in 2000 (more than 30 o C). Similarly in the year 2001, highest fruit yield was found in 2026 C and it was statistially different from other rest of the tested varieties. Size of the fruit was found better in the varieties 2026 C and 2026 D with medium sizes, whih were loser to loal Lapsigede variety (Table 1). Table 1. Response of some promising tomato genotypes to baterial wilt disease and yield parameters at Panhkhal during 2000 and 2001 S Varieties N Wilt Yield, t/h Wilt Yield, t/h inidene, % Marketable Unmarketable Fruit size, g/fruit inidene, % Marketable Unmarketable Fruit size, g/fruit D b 7.25 b b b b b C ,25 b b b a b J b b a b 8.92 b a P b a a b b a 5 Lapsigede suseptible a a 8.18 b loal hek CV, %

4 Nepal Agri. Res. J. Vol. 8, Mean in the olumn with same letter are not signifiantly different at P 0.05 using DMRT. Disease progress was muh faster in loal suseptible hek than in other varieties. Disease inidene reahed nearly 90% within 4 weeks where as, the inidene was less than 25% in 2026 C during that period (Figure 2). The disease progress muh slower in other varieties ompared to loal suseptible hek. Same trend of disease progress was found in the year 2001 also, however, disease progress urves were not drawn for that year. ANOVA showed that there was no signifiant differene among those varieties from AVRDC in AUDPC values. Those varieties were signifiantly different from the loal suseptible hek in terms of wilt inidene. The AUDPC values for 2026 C was very low and it was very high in loal Lapsigede C was at par with 1466 P and J but different from 2026 D in their AUDPC values (Figure 3) Wilt inidene,% w eeks 4 Weeks 6 Weeks 8 Weeks 10 w eeks Weeks after transplanting 2026D 2026C 1466J 1466P Lapsigede Figure 2. Disease progress urves of baterial wilt of different promising tomato varieties at Panhkhal, Kavrepalanhowk, DISCUSSION Tomato is number one fruit vegetable grown in terai, foothills and the valleys of Nepal. The rop is attaked by Ralstonia solanaearum ausing wilting of the plants in warm and humid onditions. The farmers experiened onsiderable eonomi losses due to this disease. Beause of soil borne nature, loation speifi strain, wide host range with wide spread distribution and vast geneti variability (Hayward 1991), baterial wilt disease is diffiult to ontrol one established in the field. Use of resistant variety is the most effetive and simplest methods of ontrolling baterial wilt (Monma and Sakata 1983), however, the geneti basis of resistane breaks down due to the hanges in the host or pathogen under ondition of high temperature (Mew and Ho 1977). Four promising varieties with resistane to baterial wilt from AVRDC were tested at Panhkhal of Kavrepalanhowk, whih is one of the most baterial wilt prone areas and at Thaiba of Lalipur where outbreak of baterial wilt ourred in reent years. Our results showed that the varieties 2026 C and 2026 D were better than other varieties in terms of disease and yield parameters. These varieties were preferred by the farmers and the onsumers as well. However, 1466 J also showed better performane. But the limitation with this variety was bigger fruit size, whih do not preferred by the onsumers. Conerning fruit harateristis same type of observation was found by

5 Nepal Agri. Res. J. Vol. 8, Budhathoki and Ahamad (2001). However, the yield and fruit size of Lapsigede ould not be ompared with the test varieties due to 100% wilt before fruiting during Better fruit yield in 2026 C and 2026 D were also reported by Budhathoki et al (2004) under plasti house onditions, thus suitable for off season ultivation. In Nepal previously, the variety CL 1131 (now NCL 1) was resistane to baterial wilt but its resistane was found to be broken at Panhkhal area (Timila and Shrestha 2001) a AUDPC Values b b b D 2026C 1466J 1466P Lapsigede Tomato varieties Figure 3. Area under disease progress urve (AUDPC) values for different tomato varieties at Panhkhal, 2000 (Bar indiates the standard error of the mean). CV = 24.9% Mean in the olumn with same letter are not signifiantly different at P 0.05 using DMRT. The variety 2026 C and 2026 D observed to be promising in all respet, however the fruit test may not replae the loal variety, suh as Lapsigede whih is highly preferred by the onsumers. Loal variety get higher prie than the bigger sized fruits. The later get good prie only when the supply of loal tomato is less in the market. But in absene of other resistant varieties these ould be ultivated as an alternative to other suseptible varieties in disease prone loations to over ome the losses aused by baterial wilt disease. ACKNOWLEDGEMENTS We thank Dr SK Shrestha, Former Chief Plant Pathologist, Plant Pathology Division, NARC for valuable suggestions during the oarse of experiments. Sinere thank goes to Dr JF Wang, Assoiate Professor, AVRDC for supplying seed and the tehnial suggestions. Finanial supports from SAVERNET program of AVRDC is also highly aknowledged. We also express our thanks to the farmers, Mr Damodar Adhikari of Panhkhal and Mr Madhav Khadka of Thaiba for their partiipation, helps and availing fields for the experiments. REFERENCES Budhathoki K and S Ahamad Evaluation of tomato ultivars for normal and off-season ultivation for the hills and plain onditions of Nepal. Nepal. In: Proeedings of the South Asia Vegetable Researh Network (SAVERNET II) Final Workshop, 3-8 June 2001, Bangkok, Thailand. Pp Budhathoki K, NG Pradhan HN Regmi and PR Bhurtyal Evaluation of tomato ultivars for off-season prodution under polyhouse and open field onditions. In: Proeedings of the fourth National Workshop on Hortiulture. NARI and HRD, NARC, Kathmandu. Pp Hayward AC Biology and epidemiology of baterial wilt aused by Pseudomonas solanaearum. Annul. Rev. Phytopatho. 29:65-67.

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