Someshwar Bhagat

Isolation and Characterization of Trichoderma spp. for Antagonistic Activity Against Root Rot and Foliar Pathogens

Trichoderma, soil-borne filamentous fungi, are capable of parasitising several plant pathogenic fungi. Twelve isolates of Trichoderma spp. isolated from different locations of South Andaman were characterized for their cultural, morphological and antagonistic activity against soil borne and foliar borne pathogens. The sequencing of these isolates showed seven different species. The isolates revealed differential reaction patterns against the test pathogens viz., Sclerotium rolfsii, Colletotrichum gloeosporioides and C. capsici. However, the isolates, TND1, TWN1, TWC1, TGD1 and TSD1 were most effective in percentage inhibition of mycelial growth of test pathogens. Significant chitinase and β-1,3-glucanase activities of all Trichoderma isolates has been recorded in growth medium. T. viride was found with highest chitinase whereas T. harzianum was recorded with highest β-1,3-glucanase activities.

Genetic and physiological relatedness of antagonistic Trichoderma isolates against soil borne plant pathogenic fungi

In this study, the in vitro potential of 42 Trichoderma spp. were evaluated against four isolates of soil borne phytopathogenic fungi viz., Rhizoctonia solani, Macrophomina sp., Sclerotium rolfsii and Pythium aphanidermatum in dual culture techniques and through production of volatile and non-volatile inhibitors. In vitro screening results showed that the proportion of isolates with antagonistic activities was highest for the S. rolfsii followed by R. solani, Macrophomina sp. and P. aphanidermatum, respectively. The isolates TNT1, TNP2 and TWP1 showed consistent results in volatile and non-volatile activity in vitro against any of the two pathogens tested. Based on genomic finger prints, potential isolates showed no particular correlation between the origin of the isolates and the Random Amplified Polymorphic DNA (RAPD) groups could not be established. However, the polymorphism shown by the isolates did not correlate to their level of antagonism. Whereas, in physiology studies using BIOLOG (microbial identification system), three groups were formed, one group consists with 14 different Trichoderma species and two groups with two isolates each comprised of only T. koningii and T. viride.

Management of Soft Rot (Pythium spp.) and Wilt (Ralstonia solanacearum) of Ginger (Zingiber officinale) in Andamans

Five isolates of Trichoderma and one isolate of Pseudomonas fluorescens were evaluated against Pythium and Ralstonia solanacearum in vitro and in vivo with different combinations with some chemical fungicides and neem cake. The results indicated that all isolates of Trichoderma, lone isolates of Pseudomonas fluorescens and fungicides alone significantly inhibited both pathogens in vitro. The biocontrol agent, Trichoderma spp and isolate of Pseudomonas fluorescens were comparable to each other in their ability to inhibit both the pathogens. The combination of cultural practices, chemical pesticides at low concentration, biocontrol agents with optimum population (cfu/g) along with neem cake have been found most effective in reducing the disease incidence of both soft rot and wilt of ginger and corresponding yield increase in the year 2008–09 and 2009–10. Furthermore, seed + soil application of biofungicides and chemical fungicides resulted into lowest incidences of soft rot and wilt diseases, highest rhizosphere population of biocontrol agents at all the dates observed and highest yield of ginger.

Integrated disease management for tomato in island ecosystem of Andaman

Integrated disease management modules were developed for the management of disease complex in tomato during 2008–09, 2009–10 and 2010–11, under Island ecosystem of Andaman and Nicobar Islands. All isolates of biocontrol agents significantly parasitized the test pathogens in vitro but the isolate Tv-CARI-73 was most effective against all the pathogens, viz., Pythium sp., Phytophthora sp., Rhizoctonia solani, Sclerotium rolfsii and Fusarium oxysporum f.sp. lycopersici followed by Th-CARI-50, Tv-CARI-85 and Th-CARI-70. In IDM module - I, T10 (combination of seed treatment + seedling dip + soil application of biocontrol agents) treatment was most effective in reduction of disease incidences in tomato (except bacterial wilt) followed by T11, T12, T11 and T9. This treatment was also recorded with highest yield (227.5 q/ha). In IDM module - II, T7 (integration of bioagents with the fungicides)treatment was recorded with highest percent reduction in incidence of all diseases (86.0% bacterial wilt, 56.2% leaf curl, 76.4% basal stem rot and 74.8% fusarial wilt) and increase in yield (75.3%) followed by T1, T9, T8, T13 and T14. Similarly, T2 treatment in IDM module - III, was most effective in reduction of disease incidence (89.9% bacterial wilt, 56.5% leaf curl, 77.0% basal stem rot and 75.7% fusarial wilt) and corresponding yield increase (83.6%) of tomato, followed by T3, T4 and T1 treatments.

Plant Disease Management: Prospects of Pesticides of Plant Origin

The indiscriminate use of chemical fungicides led to pesticide residues in food products, risk of development of new pathotypes and pollution of soil and water ecosystem. This resulted in several ill effects on human beings, flora and fauna. To overcome the ill effects of chemical pesticides, attention had been paid to explore into products of higher plants for developing novel biopesticides in plant disease management. Our ancestors had been using these botanicals for the management of plant diseases, before the era of conventional fungicides. But the popularity of pesticides of plant origin has again been increasing due to its potential fungicidal action against several plant pathogens without any deleterious effect to the crop plants as well as environment. Several plants have been identified for antimicrobial properties which can suppress the growth and multiplication of plant pathogens, reduction in storage decay and spoilage of food products. The potential plant origin pesticides, viz. neem (Azadirachta indica), garlic bulb (Allium sativum), eucalyptus (Eucalyptus globulus), turmeric (Curcuma longa), tobacco (Nicotiana tabacum), ginger (Zingiber officinale), etc., have been successfully used for the management of several plant diseases. Moreover, seed treatment + foliar spray of freshly prepared garlic bulb extract has resulted into the reduction of Alternaria blight (35.6 %), white rust (50.4 %), powdery mildew (67.7 %) and Sclerotinia rot (80.3 %) in mustard with 27.3 % increase in yield over untreated control. These pesticides can suitably fit in any integrated pest management framework as well as in organic farming system which is a necessity in the current situation. Keeping in view the ever-increasing demand for safe food, pesticides of plant origin have a pivotal role to play in the management of plant diseases in comparison to the conventional chemical pesticides. These pesticides are not only useful to the developing countries due to their easy availability, being relatively cheap, easy sustenance in any crop protection programme and having direct relevance to the developed countries for healthy and quality produce of foodstuffs.

DNA Fingerprinting of Bio-control Isolates of Trichoderma spp. Isolated From Different Crop Rhizosphere of Andaman Islands

The biocontrol fungi, Trichoderma spp. are the most important biocontrol agent and have been used extensively worldwide for the management of various plant pathogens. Twenty isolates of Trichoderma (T. harzianum, T. viride and T. hamatum) were isolated from rhizosphere of different crops and location of Andaman district, Andaman and Nicobar Island and tested in vitro against sclerotium rolfsii causing stem rot of brinjal. In vitro test of these antagonist against test pathogen under non-volatile condition revealed that all isolates significantly inhibited the S. rolfsii in vitro (>80% inhibition), but the isolates Th-CARI1 to Th-CARI5 was most effective in parasitizing the test pathogen with >90% inhibition. Under volatile condition there was a significant variation in the percentage inhibition (16.7% - 61%). PCR-RFLP amplified fragments with ITS1 and ITS4 primer of these isolates showed clear difference among the Trichoderma isolates with overall 69% similarity. However the Trichoderma isolates Thr-1, Tv-3, GH4-1 and Thr 1(2) \ were found 90% similarity.