EFFICACY OF SUBSTRATES USED TO FORMULATE TRICHODERMA HARZIANUM BASED BIO-FUNGICIDE TO CONTROL FOOT AND ROOT ROT DISEASE (SCLEROTIUM ROLFSII) OF CABBAGE
Efficacy of three organic substrates viz. rice bran, wheat bran, grasspea bran and their combinations with or without supplement with mustard oilcake (MOC) to formulate Trichoderma harzianum based bio-fungicides to control foot and root rot disease of cabbage caused by Sclerotium rolfsii in the seedbed soil. The seedbed soil was inoculated with the foot and root rot causing fungal pathogen S. rolfsii colonized on barley grain before treatment with T. harzianum based bio-fungicides. The results from a series of experiments revealed that T. harzianum based bio-fungicides effectively reduced pre-emergence and post-emergence mortality of cabbage seedling. Besides, vegetative growth of cabbage seedlings viz. shoot length, shoot weight, root length and root weight were enhanced significantly by the different substrates based T. harzianum bio-fungicides in S. rolfsii sick seedbed condition. The individual used of different substrates viz. rice bran, wheat bran, grass pea bran and combination of different substrates viz. rice bran + wheat bran, rice bran + mustard oilcake, rice bran + wheat bran + MOC and wheat bran + grass pea bran + MOC were equally suitable for effective formulation of T. harzianum bio-fungicides against foot and root rot disease of cabbage in seedbed condition.
Among the vegetables grown and consumed in Bangladesh, cabbage (Brassica oleracea) is the most popular one. The crop is attacked by several soil borne diseases mostly caused by fungi. Among the diseases germination failure, seedling mortality, foot and root-rot caused by the most common soil borne fungal pathogen, S. rolfsii is the major constraints for seedling production of vegetable crops especially in seedbed (Najar et al. 2011). The soil borne pathogen can survive in soil under adverse environmental conditions for long time and it is very difficult to control this soil borne pathogen through conventional method such as application of fungicides or cultural methods (Mondal et al. 1996). Resistant variety of cabbage against the soil borne pathogen has not yet been developed and released in Bangladesh. Soil solarization, application of organic soil amendments and chemical fungicides have been used to control the disease but the success is not considerable (Brown and Hendrix 1980, Punja et. al. 1982). Biological control methods, on the other hand may be considered as economical, sustainable and a potentially powerful alternative methods for the management of soil borne pathogens (Kulkarni et al. 2007, Anand and Reddy 2009). About 90% of the beneficial microbes used as biological agents and effectively control soil borne plant pathogens are different strains of T. harzianum, T. virens, T. viride (Elad et al. 1983, Roy et al. 1989, Benítez et al. 2004). The fungus Trichoderma possesses different mechanisms to combat the targeted pathogen such as mycoparasitism, competition for space and nutrients, secretion of antibiotics and fungal cell wall degrading enzymes for the inhibition of growth and reproduction of phytopathogens (Kubicek et al. 2001, Howell 2003, Benítez et al. 2004, Harman et al. 2004). Moreover, Trichoderma have a stimulatory effect on plant growth as a result of modification of soil conditions (Naseby et al. 2000). The native bio-control agents usually remain in low population density in most of the agricultural soil, so up-scaling of their density to a higher stability level in soil through artificial inoculation is necessary for successful management of soil borne pathogens like S. rolfsii in seedbed. The major limitation is the lack of appropriate mass culturing techniques and inadequate information on the suitable substrate materials of T. harzianum (Harman et al., 1991). Several research reports reveal that T. harzianum has been formulated as bio-fungicides on various substrates including wheat bran, rice bran, maize bran, sawdust (Das et al., 1997); rice straw, chickpea bran, grass pea bran, rice course powder, black gram bran (Shamsuzzaman et al. 2003); cow dung, poultry manure, ground nut shell, black ash, coir waste, spent straw from mushroom bed, talc, vermiculite (Rettinassababady and Ramadoss 2000); and jaggery, groundnut cake, neem cake, niger cake, pongamia (Shamarao et al. 1998). All of these substrate materials are available in Bangladesh but their potentialities to use in the formulation of T. harzianum bio-fungicide have not yet been studied in the country.
Therefore, the present study was undertaken to find out the effective local substrates to formulate T. harzianum based bio-fungicides against foot and root rot disease of cabbage seedling in seedbed caused by S. rolfsii.
MATERIALS AND METHODS
Efficacy of three organic substrates viz. rice bran, wheat bran, grasspea bran and their combinations mixed with or without mustard oilcake (MOC) was evaluated to formulate T. harzianum based bio-fungicides to control foot and root rot disease of cabbage seedlings in seedbed caused by S. rolfsii. The experiment was conducted in the seedbed of Plant Pathology Division, Bangladesh Agricultural Research Institute (BARl), Gazipur during three consecutive years from 2011-12 to 2013-14 under pothouse conditions. The seedbed soils were inoculated with the fungal isolate S. rolfsii multiplied on the barley grains @ 100g/m2 soil. The pathogen was allowed to colonize the soil in seedbed for 10 days. A pure culture of T. harzianum (TM7) isolated from the native soil was grown in potato dextrose agar (PDA) medium which was used as inocula for preparation bio-fungicides. The substrates were rice bran, wheat bran, grasspea bran, Rice bran + wheat bran (1:1), rice bran + grasspea bran (1:1), rice bran + mustard oilcake (1:1), rice bran + wheat bran + MOC (1:1:1), rice bran + grasspea bran + MOC (1:1:1), rice bran + wheat bran + grasspea bran (1:1:1) and rice bran + wheat bran + grasspea bran+ MOC(1:1:1:1). Six hundred gram of individual or combination of substrate materials were poured into 1000 ml Erlenmeyer flask, sterilized in an autoclave at 121C for 15 min and cooled down to make it ready for inoculation. The sterilized substrates were inoculated individually with 5 mm diameter mycelial disc of five-day old culture of T. harzianum grown on PDA and incubated at room temperature (25±2C) for 15 days. After incubation the colonized substrates were removed from the flasks, air dried and finally preserved in refrigerator at 10C. Each of the colonized substrate was considered as a treatment. Seed treatment with Provax-200 WP (Carboxin+Thiram) (2.5%) and control were considered two additional treatments for comparison.
The T. harzianum based Bio-fungicides were incorporated to the previously S. rolfsii inoculated seedbed soils @ 100 g/m2 soil and kept for 7 days maintaining proper soil moisture to establish T. harzianum in the soils. The control bed did not receive any colonized substrate of T. harzianum except the inoculum of S. rolfsii. The seeds of cabbage variety Atlas were sown in the seedbed @ 200 seeds per treatment. The initial germination of the seeds was 99% as per blotter test. The emergence of seedling was calculated on the basis of initial germination status of the seeds. The experiment was laid out in completely randomized design with four replications. Proper weeding, irrigation and intercultural operations were done for proper growth of cabbage seedlings in the seedbed.
Data were collected on seedling emergence after 15 days of seed sowing. Data on seedling mortality was recorded at an interval of 7 days starting from seedling emergence and it was continued up to 35 days of seedling age. The length and weight of shoot and root of cabbage seedlings were recorded at 35 days of seedling age. The percent data were converted into arcsine transformation values before statistical analysis. Data were analyzed statistically by using the MSTATC program. The treatment effects were compared following least significant difference (LSD) test (P=0.05).
RESULTS AND DISCUSSION
Seedling emergence of cabbage was 45.67, 62.33 and 67.00% under control during first, second and third year, respectively. It was increased to 53.00-69.00, 74.00-80.00 and 74.00-92.00% in first, second and third year due to treatment of seedbed soils with T. harzianum based bio-fungicides multiplied on different organic substrates materials and Provax-200 WP. The differences in seedling emergence under various treatments were not considerable in every year’s trials (Table 1).
Pre-emergence and Post-emergence mortality
In control treatment, the pre-mergence seedling mortality was 54.33, 37.67 and 33.00% in first, second and third year, respectively. The pre-emergence seedling mortality was reduced to 13.49-50.91, 30.98-50.44 and 21.21-75.76% in first, second and third year trials, respectively due to treatments of seed with Provax-200 WP or seedbed soils with various T. harzianum based bio-fungicides. However, efficacy of all bio-fungicides was more or less similar to improve seedling emergence and to reduce pre-emergence mortality (Table 1).
Application of Provax-200 WP or various T. harzianum based bio-fungicides significantly reduced post emergence seedling mortality of cabbage in S. rolfsii inoculated seedbed soil under pothouse conditions. In control treatment the post emergence mortality was 23.67, 30.33 and 20.33% in first, second and third year, respectively. Treatment of inoculated seedbed soils with T. harzianum based bio-fungicides or seed treatment with Provax-200 WP reduced the disease incidence of cabbage seedling by 50.02-69.63, 66.94-72.16 and 65.90-75.01%, respectively in three consecutive years. The efficacy of different treatments with bio-fungicides and Provax-200 WP was not significantly different in all years (Table 2).
Length and weight of shoot
Under control, shoot length was 13.43, 4.50 and 14.20 cm, and shoot weight was 5.74, 3.38 and 7.67 g plant-1 in first, second and third year, respectively. Treatment of S. rolfsii inoculated seedbed soils with T. harzianum based bio-fungicides multiplied on different substrates or seed treatment with Provax-200 WP increased the shoot length to 17.47-20.13, 6.63-10.57 and 18.33-22.90 cm, and shoot weight to 9.44-9.95, 4.82-8.58 and 10.70 g plant-1 in first, second and third year, respectively. Every year, the increase in shoot growth was significant compared to control and rice bran along with wheat bran, grasspea bran and MOC for formulation of T. harzianum based bio-fungicides gave the maximum shoot growth of cabbage than other treatments (Table 3).
Length and weight of root
The range in root length was 6.37-7.60 cm in first year, 6.73-8.20 cm in second year and 5.00-6.10 cm in third year under treatments with T. harzianum based bio-fungicides. The corresponding root length under control was 5.30, 4.00 and 3.67 cm, respectively and 6.17, 4.70 and 4.53 cm, respectively in Provax-200 WP treatment. The increase of root length was significant compared to control in each year. Every year, significant increase in root weight was achieved with all treatments with bio-fungicides compared to control and efficacy of all bio-fungicides to increase root weight was statistically similar. Effectiveness of Provax-200 WP was lower than bio-fungicides (Table 4).
Results of the present investigation clearly show that treatment of S. rolfsii infested
seedbed soils with T. harzianum based bio-fungicides multiplied on rice bran, wheat bran, grasspea bran and mustard oil cake in different combinations and alone are effective to control pre-emergence as well as post-emergence mortality of cabbage seedlings. The treatments increase seed germination and seedling growth effectively. Many other investigators reported similar results. The potentiality of Trichoderma species as bio-control agents for enhancing seed germination and seedling growth in addition to suppression of soil-borne plant pathogenic fungi like Phytophthora, Pythium, Sclerotium, Botrytis, Rhizoctonia and Fusarium of various crops have been recorded by Benitez et al. (2004), Celar and Valic (2005), Dubey et al. (2007) and Rojo et al. (2007). Significant increase in seedling emergence and suppression of pre-emergence mortality of cabbage seedling have also been reported by Mishra and Sinha (2000), Prasad and Anes (2008) and Mukhtar (2008). Podder et al. (2004) and Rojo et al. (2007) recorded the efficacy of Trichoderma spp. as bio-control agents to formulate bio-fungicides after colonization on organic materials. Findings of the present investigation have also been in agreement with findings of other researchers (Begum et al. 1999, Chowdhury et al. 2000, Hossain and Samsuzzaman 2003, Yeasmin 2004, Hossain and Naznin 2005, Hermosa et al. 2012, Samolski et al. 2012).
Based on findings of the present investigation, it may be concluded that treatment of seedbed soil with T. harzianum based bio-fungicides multiplied on rice bran, wheat bran and grasspea bran alone or in combinations may be effective to control foot and root rot of cabbage seedling caused by S. rolfsii.
The authors thankfully acknowledged BAS-USDA who provided financial support and Bangladesh Agricultural Research Institute, Gazipur for extending necessary logistic support for implementation of the research project. Special thanks to Dr. M. A. Rahman, former Chief Scientific Officer Plant Pathology Division, BARI for his fruitful counseling’s and directives. Thanks also go to the Scientific Assistant Mr. Md. Abdur Razzak and Mr. Zamil Akter for their sincere assistance in the work.
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Table-1. Effect of soil treatment with T. harzianum based bio-fungicides multiplied on different substrates on emergence and mortality of cabbage seedling grown in S. rolfsii inoculated soils of seedbed
Table-2. Effect of soil treatment with T. harzianum based bio-fungicides multiplied on different substrates on post emergence mortality of cabbage seedling grown in S. rolfsii inoculated soils of seedbed
Table 3. Effect of soil treatment with T. harzianum based bio-fungicides multiplied on shoot growth of cabbage seedling grown in S. rolfsii inoculated soils of seedbed
Table 4. Effect of soil treatment with T. harzianum based bio-fungicides multiplied on root growth of cabbage seedling grown in S. rolfsii inoculated soils of seedbed