Management of Root Rot (Rhizoctonia solani) of Mothbean through Bio-Agents

India grows a variety of pulse crops under a wide range of agro-ecological conditions and is recognized globally as a major player in pulse production contributing 25.4% of the global production. The compound growth rate of yield of pulses (0.67) is lower as compared to that of the cereals (2.15). This has resulted in the decline in per capita availability of pulses from 71 g in 1955 to 41.8 g in 2008 necessitating their import to meet the domestic demands. To alleviate protein and energy malnutrition, a minimum of 50 g pulses/capita/day should be available in addition to other sources of protein. Thus, to make the nation pulse sufficient, average yield level has to increase substantially up to 1200 kg/ha by 2020 (Pooniya et al., 2015). To achieve this, more than 4.0% growth rate in pulse production is required. The per cent contribution of pulses in total food grain production in India has declined during the last three decades owing to low-endowed land and biotic constraints. Besides this, around 8-10% production is lost annually because of the ravages of diseases alone costing nearly Rs. 10,000 million (Vishwadhar and Chaudhary, 2001).
        
Mothbean [Vigna aconitifolia (Jacq.) Marechal] is an important pulse crop of dry and semi dry areas of India and some countries of Asia. Among Kharif pulses, it has the maximum capacity to resist drought conditions. Plants cover large area on the surface, conserve moisture and also protect the soil from erosion. Mothbean is mainly used as ‘Dal, Pappad and Bhujia’ preparations. Green pods are used as vegetable. India has the major area under mothbean in the world. In India, mothbean is mainly grown in Rajasthan and Gujarat which covers an area of about 0.92 M ha which yields about 0.26 MT annually with the productivity of 388 kg/ha (Anonymous, 2014). Mothbean is generally grown on poor light textured soil. However, light loam soil is best suited for its cultivation. It is cultivated in Kharif season mainly in low rainfall areas. Mothbean can be included in any cropping system in the rainy season. It can be grown as mixed/ intercrop with maize, sorghum, pearl millet, cotton etc.
        
Mothbean is prone to many diseases including root rot caused by Rhizoctonia solani Kuhn, which is considered as one of the factors for low productivity of mothbean. The pathogen which attacks roots causing damping-off and root rot diseases. The disease causes substantial loss to mothbean crop. Rhizoctonia solani Kuhn [teleomorph- Thanatephorus cucumeris (Fr.) Donk] is a destructive soil-borne plant pathogen (Saksena and Dwivedi, 1973) infecting a wide range of agricultural and horticultural crops, including legumes and worldwide causing several diseases (Kataria and Grover; 1977; Gonzalez et al., 2006). The pathogen also causes considerable yield loss in mungbean and urdbean in India (Dubey, 2003). Yield loss up to 57% in mungbean was reported from Iran (Kaiser, 1970). Control of R. solani is difficult because of wide host range and its ability to survive through sclerotia under adverse environmental conditions. In practice, control of diseases caused by R. solani relies mainly on fungicides (Kataria and Gisi, 1996).
        
There is a rising demand for intervention of ecologically safe and sound, environmentally compatible techniques in crop production which will provide global food security and    improved agricultural produces. To accomplish this goal, application of agriculturally beneficial microorganisms is a potential alternative to traditional agricultural techniques which have severely damaged the agro-ecosystem (Abhilash et al., 2016). Beneficial microorganisms including biological control agents (BCAs), plant growth promoting rhizobacteria (PGPRs) and fungi (PGPFs) and endophytes play a crucial role in sustainable crop production. These microorganisms provide growth promotion, crop protection and abiotic stress mitigation by the direct application. Hence, the present investigation was undertaken using different combinations of bio-control agents against root rot disease of mothbean.

Field experiment was under taken at Agricultural Research Station, Swami Keshwanand Rajasthan Agricultural University, Bikaner, Rajasthan during three consecutive kharif   seasons of 2014 to 2016. A most popular mothbean cultivar Rajathan Mothbean-225 (RMO - 225) was used in the experiment. In this experiment. six different combination treatments of bio-agents were evaluated. These were T₁: Trichoderma harzianum seed  treatment (8 g/kg seed),T₂: T. harzianum seed treatment (8 g/kg seed) + soil application of   T. harzianum   (2.5 kg in 100 kg FYM/ha), T₃:  T. harzianum + Pseudomonas  fluorescens seed treatment (4+4 g/kg seed), T₄: T. harzianum + P. fluorescens seed  treatment (4+4 g/kg seed) + soil application  of T. harzianum + P. fluorescens (1.25 +1.25 kg in 50 kg FYM for each/ha), T₅: P. fluorescens seed treatment (8 g/kg seed), T₆: P. fluorescens seed treatment (8 g/kg seed) + soil application of P. fluorescens (2.5 kg in 100 kg FYM/ha) and T₇: untreated control. Pre-sowing seed dressing treatments were done. The treatments were applied immediately before planting of the seed in field. The bio-agents were mixed in moist FYM 15 days before sowing every year and keep in shade. The treated seeds were sown by drilling method keeping seed rate 15 kg/ha. The treatments were assigned to randomized block design (RBD) and replicated four times. The crop was planted at 45 cm row to row and 10 cm plant to plant spacing. The gross plot size was 3.0 × 2.7 m². All other recommended practices required for cultivation of the crop were followed. Bio formulations T. harzianum and Pseudomonas fluorescens contained 1 × 10⁷ and 2 × 10⁶ c.f.u./g, respectively. The data for disease incidence (%) of mothbean from each treatment were recorded. Grain yield (q/ha) and economics of each treatment were computed. The statistical analysis of data was done as per procedure suggested by Panse and Sukhatme (1967).
        
Bio-agents (Trichoderma harzianum and Pseudomonas fluorescens) were received from bio-agent lab, Department of Plant Pathology, College of Agriculture, SKRAU, Bikaner to conduct the experiment.

The application of bio-agents caused significant reduction in root rot incidence in all the years (Table 1). However, amongst the different bio-agents tested, treatment combination of T. harzianum + P. fluorescens seed treatment (4+4 g/kg seed) + soil application of T. harzianum + P. fluorescens (1.25 +1.25 kg in 50 kg FYM for each/ha) found most effective in controlling root rot in all the years and had 19.00, 20.33 and 26.00 per cent root rot during 2014, 2015 and 2016, respectively. Averaged across the years, this treatment had lowest incidence (21.78%) among all the treatments.This treatment caused 55.65 per cent reduction in root rot incidence as compared to untreated control plots. Treatment T₂, i.e. T. harzianum seed treatment 8 g/kg seed + soil application of T. harzianum 2.5 kg in 100 kg FYM/ha found next best option.. It has reduced 47.95 per cent root rot incidence as compare to untreated control plots. Treatment T₅ i.e. seed treatment with P. fluorescens @ 8 g/kg seed found least effective against  root rot in allthe years. The maximum root rot incidence of 48.33 per cent, 48.67 per cent and 50.33per cent were recorded in control plot of respective consecutive years.
 

        
The application of bio-agents treatments had significant effects on grain yield (Table 1) and all the treatments were found effective in enhancing grain yield than contol. The  highest grain yield 10.56 q/ha was recorded in the treatment T₄ i.e., treatment combination of T. harzianum + P. fluorescens seed treatment (4+4 g/kg seed) + soil application  of T. harzianum + P. fluorescens (1.25 +1.25 kg in 50 kg FYM for each/ha), which had significantly higher grain yield compared to all other treatments, followed by T₂ i.e. T. harzianum seed treatment 8 g/kg seed + soil application of T. harzianum 2.5 kg in 100 kg FYM/ha (9, 42 q/ha). This treatment had 3.61 q/ha greater grain yield than control. This treatment enhanced 34.19 per cent increased the grain yield as compare to untreatred control plots.The least grain yield was obtained in treatment T₅ i.e. seed treatment with P. fluorescens @ 8 g/kg seed (7.35 q/ha).
        
The economics computed on various treatments revealed that the treatment combination of T. harzianum + P. fluorescens seed treatment (4+4g/kg seed) + soil application of T. harzianum + P. fluorescens (1.25+1.25 kg in 50 kg FYM for each/ha) gave highest gross return  Rs 44,352/ha when treatment cost was Rs 824/ha as compare to control (Rs 29,190/ha) which gave an additional income of  Rs. 15,162/ha and net gain of  Rs 14,338/ha (Table 2).  Antagonists applied to seeds before planting colonies the rhizosphere of seedlings and thus are present at or near the pathogen’s infection court, where they act by producing antifungal or antibiotic compounds, through hyperparasitism, or by competitively colonising spermosphere and rhizosphere substrates (Taylor and Harman 1990). Seed treatment is an attractive delivery system of fungal bioprotectants (Wright et al., 2003). Bioprotectants applied to seeds may not only protect seeds (Sivan and Chet 1986) but also may colonise and protect roots and may increase plant growth. It is evident that the antagonistic bio-agent can affect the plant’s resistance to a pathogen either by inducing the basal level of defense reactions immediately after treatment or by enhancing a capacity for rapid and effective activation of cellular defence responses (Conrath et al., 2002). Lorito et al., (1996) reported that fungal pathogens are killed by the release of toxic compounds i.e. antibiotics gliotoxin, gliovirin and peptabiols and a battery of lytic enzymes, mainly chitinases, glucanases and proteases produced by species of Trichoderma. These enzymes facilitate penetration into the host and utilization of host nutrients. Antibiotic production, mycoparasitism, the production of cell wall degrading enzymes and competition for nutrient or space are considered as the action involved in biocontrol of pathogens during mycoparasitic interaction between Trichoderma and fungal pathogens (Zeilinger and Omann, 2007 and Vinale et al., 2008). Similarly, Benhamou and Chet (1993) illustrated many interactions of Trichoderma with pathogens Rhizoctonia and Pythium. Various species of bacteria including Pseudomonas, Bacillus, Azospirillum, etc. have been reported as potential biocontrol agents, biofertilizers and biostimulants (Keswani et al., 2014, 2015a).   They suppress plant pathogens in soil through production of antibiotics and siderophores and suppress plant diseases through induction of defense response (Bisen et al., 2015; Keswani et al., 2015b; Singh, 2014). Earlier workers also reported that the genus Trichoderma is highly effective against several phytopathogenic fungi including R. solani causing seed and soil-borne diseases of several economically important crops (Howell 2003). The potential of Trichoderma  species in managing diseases caused by R. solani has been demonstrated in soybean (Raguchander et al., 1998), mungbean (Dubey and Patel 2001, Singh and Chand 2006), potato (Ishtiaq and Raziq 2006), faba bean (El-Mougy and Abdel-Kader 2008), tomato (Montealegre et al., 2010), bean (Abd-El-Khair et al., 2010) and chickpea (Dubey et al., 2012).
 

In recent years cultivation of mothbean has been decreased due to major constraint of root rot disease. In our study, in mothbean cv. RMO-225, seed biopriming with a combination of T. harzianum + P. fluorescens seed treatment (4+4 g/kg seed) along with soil application of T. harzianum + P. fluorescens (1.25 +1.25 kg in 50 kg FYM for each/ha) was observed to be an effective treatment which reduced root rot incidence and increased grain yield as compared to other treatment as well as untreated control under field conditions.  It can be recommended to the cultivaters of mothbean for enhancing the yield.

The authors are vary much thankful to Head, Department of Plant Pathology, College of Agriculture, SKRAU, Bikaner to provide bio- agents to conduct the experiment.