0 Views
M. MAHENDRA, M. REDDI KUMAR*, C.P.D. RAJAN AND P. SUMATHI
Department of Plant Pathology, S.V. Agricultural College, ANGRAU, Tirupati – 517 502, Chittoor Dt., Andhra Pradesh
Six isolates of Trichoderma spp. were tested for their antagonist potential against four isolates of M. phaseolina, incitant of groundnut dry root rot by following dual culture technique in vitro. Among all the isolates of Trichoderma, GRT5 shown highest (59.48%) mean inhibition followed by GRT2 (59.38%), GRT1 (59.27%) and GRT4 (58.96%). From the above study top four isolates of Trichoderma spp. which showed maximum mean inhibition per cent when dual cultured with four isolates of M. phaseolina viz., GRT5, GRT2, GRT1 and GRT4 were considered as effective Trichoderma isolates and one isolate of patho-gen i.e., SmMp was considered as a more virulent pathogen which exhibited lowest mean percent inhibition (56.81%) in dual culture.
Tricoderma spp. M. Phaseolina, Dual culture, Inhibition percent and Dry root rot.
Groundnut is a major oil seed crop in India covering an area of 4.59 M ha with a production of 6.73 M t averaging a productivity of 1.46 t ha-1. In Andhra Pradesh, it is grown over an area of 0.77 M ha with a production of 0.80 M t and productivity of 1.03 t ha-1 (Commodity Market of India, 2016). In Andhra Pradesh, majority of groundnut crop is cultivated during kharif in Anantapuramu, Chittoor, Kurnool, Kadapa districts occupying 97.42 per cent area of the total groundnut growing area in Andhra Pradesh (Anonymous, 2014-15).
Several factors such as water stress, pests, and diseases are responsible for the low productivity of groundnut in A.P (1.03 t ha-1) compared with national average (1.46 t ha-1). Diseases such as late leaf spot (Phaeoisariopsis personata), collar rot (Aspergillus niger), stem rot (Sclerotium rolfsii) and dry root rot (M. phaseolina) are of major concern among fungal diseases.
In groundnut, M. phaseolina is known to cause root, stem, peg and pod rots and leaf spots on seedlings and on older plants. It also causes seedling blight, root rot and charcoal rot diseases on more than 500 plant species from more than 100 families distributed worldwide. The disease appears in hot and dry weather when soil temperature is 80-95°F (27-35°C) for 2-3 weeks. The disease control is inefficient or difficult by using the chemical fungicides.
The fungus is a facultative parasite capable of living saprophytically on dead organic tissue, particularly on many of its natural hosts producing sclerotial bodies. The fungus is mainly a soil dweller and spreads from plant to plant through irrigation water and implements and cultural operation. The sclerotia and pycniospore may also become air borne and cause further spread of the pathogen (Rangaswami and Mahadevan, 2008).
Biological control seems to offer a practicable approach. As biological control has several advantages (when applied either alone or in combination with other management practices) like ecofriendly, effective against soilborne diseases and having growth promoting activity which cannot be possible by chemicals.
Biocontrol agents like Pseudomonas fluorescens and Trichoderma spp. have been assessed for their efficacy against M. phaseolina and S. rolfsii (Ganasen and Sekar, 2012; Monali et al., 2016).
Application of two different biocontrol agents or two strains of the same biocontrol agent with different mechanisms of action gives the advantage of complementing each other in nullifying the deleterious effect of plant pathogens (Mishra et al., 2013; Rajasekhar et al., 2016).
Screening of Trichoderma isolates for their antagonistic potential against M. phaseolina was done using dual culture method (Morton and Straube, 1955).
For finding the potential fungal antagonist against test pathogen, 5 mm mycelial disc of fungal antagonist was placed at 1 cm away from the periphery of 9 cm sterile Petri plate containing 20 ml of sterile PDA. Then, 5mm mycelial disc of the test pathogen was placed opposite to the mycelial disc of fungal antagonist at 1cm away from the periphery of Petri plate. The plates were kept in incubator at 25 ± 2oc for incubation. Readings were recorded when the pathogen in the monoculture grown fully.
Per cent inhibition of mycelial growth of test pathogen over control was calculated by the formula given by Vincent (1927).
I CCT X100
where,
I = Per cent reduction in growth of test pathogen.
C = Radial growth (mm) in monocultured check.
T = Radial growth (mm) in dual cultured plates.
Six isolates of Trichoderma spp. were tested for their antagonist potential against four isolates of M. phaseolina, incitant of groundnut dry root rot following dual culture technique in vitro. The results were analysed using two factorial CRD and were represented in Table 3. 1.
Among the six isolates of Trichoderma spp. tested against the four isolates of M. phaseolina, maximum mean inhibition per cent (59.48%) was observed with the GRT5 isolate followed by GRT2 (59.38%), GRT1 (59.27%), GRT4 (58.96%) and GRT6 (58.13%). The isolate GRT5 significantly differed with GRT6 and GRT3 isolates and on par with GRT2, GRT1 and GRT4 isolates. Lowest mean inhibition per cent (58.02%) was observed with the GRT3 isolate, which significantly differed with the GRT5, GRT2 and GRT1 isolates, insignificant with the GRT4 and GRT6 isolates.
Interaction effects between RgMp isolate of pathogen dual cultured with the all the six isolates of Trichoderma spp. revealed that maximum inhibition per cent (67.92%) was observed with the GRT5 isolate followed by GRT2 (62.92%), GRT4 (61.67%), GRT3 (60.42%), GRT1(58.75%) and GRT6 (57.50%) isolates. The isolate GRT5 significantly differed with the all the remaining isolates. Lowest inhibition per cent (57.50%) was observed with GRT6 isolate, which significantly differed with all the remaining isolates of Trichoderma spp. except isolate GRT1.
When TpMp isolate of pathogen dual cultured with all the six isolates of Trichoderma spp. maximum inhibition per cent (61.25%) was observed with the isolate GRT6 followed by GRT1 (58.75%), GRT5 (58.33%), GRT4 (57.92%) and GRT3 (56.67%) isolates. The isolate GRT6 significantly differed with all the remaining isolates of Trichoderma spp. The lowest inhibition per cent (55.42%) was observed with the isolate GRT2, which significantly differed with the other remaining isolates except isolate GRT3.
Interaction effects between SgMp and all the six isolates of Trichoderma spp. revealed that maximum inhibition per cent (60.42%) was observed with GRT1, GRT2 and GRT4 isolates of Trichoderma which insignificantly differed among them and also with other remaining isolates of Trichoderma spp. except GRT5 (55.83%). Lowest inhibition per cent (55.83%) was observed with the isolate GRT5, which significantly differed with the all the remaining isolates of Trichoderma spp.
Results from dual culture interaction studies in case of SmMp isolate and six isolates of Trichoderma spp., revealed that maximum inhibition per cent (59.17%) was observed with isolate GRT1 followed by GRT2 (58.75%), GRT3 (56.67%), GRT4 (55.83%) and GRT5 (55.83%). Lowest inhibition per cent (54.58%) was observed with isolate GRT6.
From the above study top four isolates of Trichoderma spp. which showed maximum mean inhibition per cent when dual cultured with four isolates of M. phaseolina viz., GRT5, GRT2, GRT1 and GRT4 were considered as effective Trichoderma isolates. Besides the one isolate of pathogen which showed lowest mean per cent inhibition (56.81%) in dual culture i.e., SmMp was considered as virulent pathogen.
The results were in agreement with the findings of Karthikeyan et al. (2006) who reported that T. viride (Tv1) and T. harzianum were most effective in reducing the mycelial growth and sclerotial formation of M. phaseolina causing dry root rot of groundnut. They also reported that volatiles of Tv1 had shown greater fungistatic effect on M. phaseolina under in vitro conditions.
Ramezani (2008) studied efficacy of four fungal bioagents viz., T. hamatum, T. harzianum, T. polysporum and T. viride under in vitro conditions against the brinjal root rot pathogen, M. phaseolina. He reported that T. harzianum produced the maximum inhibition zone of 18.20 per cent compared to the minimum of 7.30 per cent by T. hamatum.
Among the six Trichoderma isolates tested against four isolates of M. phaseolina, isolate GRT5 was superior with highest (59.48%) mean inhibition followed by GRT2 (59.38%), GRT1 (59.27%) and GRT4 (58.96%) isolates which were on par with each other. From the above results top four isolates of Trichoderma spp. which showed maximum mean inhibition per cent when dual cultured with four isolates of M. phaseolina viz., GRT5, GRT2, GRT1 and GRT4 were considered as effective Trichoderma isolates. Besides this one isolate of pathogen i.e., SmMp was considered as a more virulent pathogen which showed lowest mean percent inhibition (56.81%) in dual culture.