Biocontrol Of Tea Diseases

Role of Biocontrol Agents for Disease Management in Sustainable Agriculture pp. 223–230 © Research India Publications

Biological Control of Tea Diseases- A Review R. Premkumar, D. Ajay and N. Muraleedharan UPASI Tea Research Institute, Valparai – 642 127, Tamil Nadu

Introduction Tea is one of the most common and cheapest beverages in the world. Tea is manufactured from the crop shoots comprising two to three leaves and a bud of a perennial shrub which belongs to camellia genus of the theaceae family. It is commercially grown in more than 30 countries, predominantly grown in Asia followed by Africa and to a very small extent in Europe, South America and Australia. India has more than 4,40,000 ha under tea cultivation and is the largest producer and consumer of black tea in the world. Tea is attacked by a number of pests and diseases, which is the major limiting factor in crop productivity. A majority of tea diseases are of fungal origin and more than 300 species of fungi are reported to affect different parts of the tea plant (Agnihothrudu, 1964, Chen and Chen, 1990). Being a foliage crop, leaf diseases are of most concern as it leads to direct crop loss and quality deterioration of the final produce (Baby et al. 1998). The important foliar diseases of tea are blister blight and grey blight. The major stem diseases are collar canker and thorny stem blight and major root diseases are red root and brown root. Chemical control measures are effective in controlling tea diseases (Premkumar and Baby, 2005). However, concerns on environmental safety, pesticide residues in made tea, and escalating cost of fungicides, an alternative to chemical control, is the need of the hour. Being ecofriendly, economical and sustainable, biological control can be an alternative to fungicides or they can form an important component in integrated management of diseases where the chemical application is done when it is absolutely necessary. Here we give a brief account of some of the important work done on biological control of certain diseases of tea. Foliar Diseases Blister blight is caused by an obligate parasitic fungus Exobasidium vexans. The disease symptom initially appears as a pale yellow translucent spot on young crop shoots (3 leaves and a bud). The spot gradually enlarges to a lesion with a bulge on the lower surface of the leaf, thus forming the characteristic blister (Plate 1a). The disease attains epidemic proportion during monsoon months (June-Dec) and causes a crop loss as high as 50%. Earlier attempts on biological control of blister blight were made with popular antagonists like Trichoderma harzianum, Gliocladium virens, Serratia marcescens, Pseudomonas fluorescens and Bacillus subtilis (Premkumar, 2001, 2002). These were applied as formulations based on talc/vermicompost but the results were not encouraging. Balasubramanian et al (2006) reported lower efficacy with diluted sprays of vermicompost based Trichoderma. In case of Pseudomonas fluorescens and Bacillus subtilis applied as liquid culture, addition of nutrients like (NH4) 2 SO4 and salicylic acid improved its bioefficacy especially when the disease incidence is low (Premkumar, 2003). Under natural

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conditions in southern India, Glomerella cingulata, the causal agent of brown blight disease of tea was found to antagonize sporulating blister lesions (Plate 1b&c). Work done in Sri Lanka with fungal extracts of Glomerella cingulata resulted in remarkable inhibition of spore germination of E.vexans (Balasuriya and Kalaichelvan, 2000). Field experiments on pilot scale with liquid culture of Glomerella cingulata (coded as BB 2) was effective in controlling blister blight (Premkumar, 2001) but was ineffective when used as bioformulation based on talc (Premkumar, 2002). However, being a pathogen that causes brown blight of tea, its usage could not be promoted.

Plate 1: Colonisation of Glomerella cingulata over Exobasidium vexans under natural conditions. a. Sporulating lesions of E.vexan. b. Colonisation of G. cingulata on lesions of E.vexans – Initial stage. c. Complete colonisation of G. cingulata over blister lesions. All the above factors led to explore native antagonistic microbes on the tea phylloplane, especially, bacteria (Premkumar, 2003, Baby et al, 2004). These microbes were isolated from tea plantations located in different agroclimatic zones of southern India. A total of 889 bacteria were isolated of which Bacillus spp (8 Nos.) were found to be promising. Evaluation of the selected strains under greenhouse and field conditions revealed that the blister blight control achieved with strains CPB 77, MPB 138, WPB 104 under greenhouse and with APB 78, WPB 104, 109, NLB 12 under field condition was fairly good compared to unsprayed control and type cultures of B.subtilis and P. fluorescens (Baby et al, 2004). In North East India, B. subtilis and two strains of actinomycetes (MM AC/02 & 05) were found to give satisfactory control for the disease. The disease protection achieved with B. subtilis was 40% (Barthakur, 2002, Sarmah, 2005) and with actinomycetes strains (Sarmah, 2005) above 50% when compared to 84% protection achieved with standard COC treatment. Grey blight of tea caused by Pestalotiopsis theae is another important foliar pathogen. Talc based commercial formulations of Trichoderma and Pseudomonas was evaluated under field conditions to control grey blight, but they were ineffective (Sanjay, 2005). Trichoderma performed well when vermicompost was used as the carrier. Premkumar et al (2005) reported some strains of Bacillus spp isolated from tea phylloplane showing good antagonism to Pestalotiopsis under in vitro conditions (Plate 2). Under glasshouse conditions, strains, APB 78 and WPB 104 provided excellent control of the disease and were superior to type cultures of B.subtilis and P.fluorescens. In China, endophytic strain of Bacillus subtilis (TL2) showed strong antagonism under in vitro conditions against P. theae (Hong yong-cong, 2005).

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Plate 2. Antagonism of tea phylloplane bacteria to Pestalotiopsis under in vitro conditions (Note: Lytic zones around bacterial colonies in plates fully covered by Pestalotiopsis) Black rot, another foliar disease of tea caused by Corticium invisum/theae was successfully controlled by spraying two days old culture of Bacillus subtilis, diluted to 10% in water (Barthakur, et al, 1993, Sarmah, 2005). The percent control achieved was 68 when compared to 75% achieved with COC sprays. Chakraborty et al (1995), reported phyllosphere microorganisms of tea and their interactions with Glomerella cingulata, the causal agent for brown blight of tea. The bacterium Micrococcus luteus showed good antagonism to G. cingulata and an antigfungal compound extracted from M. luteus inhibited growth of G. cingulata and Pestalotiopsis theae (Chakraborty et al, 1998).

Stem Diseases Stem diseases are reported to cause yield stagnation in tea plantations. The pathogens gain entry through wounds caused on the tea stem due to cultural practices. The practice of pruning tea bushes expose the woody stems to many parasitic fungi and dry weather pruning exposes the frame to sunscorch injuries (Premkumar and Baby, 2005). The major stem diseases of tea are wood rot (Hypoxylon serpens/Nimania diffusa), collar canker (Phompsis theae), branch canker (Macrophoma theicola, Poria hypobrunnea) and thorny stem blight (Tunstallia aculeata) In Sri Lanka, naturally occurring fungi, Aspergillus niger, Trichoderma viride, Penicillium sp. and a species of Bacillus showed antagonism to stem rot caused by Nimania diffusa (Balasuriya, 1998). But inoculation of these organisms on wood caused wood decay, which was marginally high when compared to Nemania diffusa inoculated alone (Balasuriya, 1999). Protection of pruned cuts by applying a paste of talc formulation of Trichoderma and soil application of Trichoderma (1kg/bush) around the bush is effective in protecting stem diseases of tea including Hypoxyoln serpens (Premkumar, 2005) In vitro interaction between collar canker pathogen Phomopsis theae and fungal antagonists like T. harzianum and G. virens revealed that the establishment of pathogen was inhibited by the antagonists through the mechanisms of antibiosis and hyperparasitism (Ponmurugan and Baby, 2003). In case of pathogen grown on tea stem bits, pre-inoculation and simultaneous inoculation of antagonists prevented complete development of pathogen whereas antagonist could not inhibit growth of pathogen already established since there was normal development of pycnidia followed by exudation of cirrhus (spore mass). Field efficacy of T. harzianum and G. virens in controlling collar canker is reported (Ponmurugan et al, 2002). Talc based formulation of biocontrol agents was made into a paste and dressed on cankers as well as on pruned cuts along with soil application of either biocontrol agents (2kg/bush) or fungicide solution (0.5%). The results showed that wound healing (reduction in canker size) was high in the case of biocontrol treatments applied both

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on the wounds as well in soil. These bioagents survived well in soil and also on pruned cuts. (Table 1). Biocontrol agents

Colony forming units Soil (x 104g-1 soil dry wt.)

Wood (x 103g-1 soil dry wt.)

Months after treatment Initial 6

12

18

24

Initial 6

12

18

24

Trichoderma

18.4

5.6

3.7

2.8

0.4

1.8

1.3

3.2

2.4

0.7

Gliocladium

20.6

6.2

3.2

3.1

0.7

1.4

1.8

2.5

2.3

0.7

Root Diseases Among root diseases of tea, red root (Poria hypolateritia), brown root (Fomes noxius, Fomes lamaoensis) and charcoal stump rot or root? (Ustulina zonata) are common in occurrence. Unlike foliar or stem diseases, the root diseases can lead to death of bushes and hence cause serious concern. Most often the symptoms are noticed after the death of bushes and hence curing a diseased plant seems to be impossible. Since the pathogens are soil borne in nature, the treatment is aimed at curing the ‘sick soil’ before replanting the area. A number of antagonistic microbes have been tried under gnotobiotic conditions against major root pathogens of tea. They were Trichoderma spp (Baby and Chandra Mouli, 1996, Hazarika et al, 2000, Balasuriya, 2001, Sarmah, 2005,), Gliocladium virens (Baby and Chandra Mouli, 1996, Hazarika et al, 2000), Bacillus pumilis, Bacillus megaterium, Serratia marcescens and Ochrobactrum anthropi (Chakraborty and Chakraborty, 2005), strains of fluorescent Pseudomonas (Hazarika et al, 2000, Dileep Kumar et al, 2005) and nonfluorescent Pseudomonas (Dileep Kumar et al, 2005), Bacillus subtilis (Hazarika et al, 2000) and strains of actinomycetes (Sarmah, 2005). Field experiments on red root disease showed that biocontrol agents like T. harzianum and Gliocladium virens were effective in controlling the disease in new planting area as there was no casualty in young plants (Baby et al ,2004). They were applied as bioformulation based on coir pith at the rate of 4 tonnes/ha as in furrow application or in planting pits (100g/pit). There was mild incidence of casualty among new plants in chemical treated plots and interestingly in chemical treatments where biocontrol agents were given as sub treatments no casualty was noticed. Similar observations were reported from Sri Lanka, with T. harzianum (5g/lit), which gave good control of Poria root disease (Balasuriya, 2005). In Northeast India, biocontrol of brown root and charcoal stump rot with Trichoderma (Barthakur, 2002, Sarmah, 2005) was effective as there was no mortality in treated plots in the replanted areas without rehabilitation. Application of bioformulations of bacterial antagonists like Psuedomonas fluorescens and Bacillus subtilis at the rate of 100g/planting pit is also equally effective to Trichoderma in controlling primary root diseases of tea (Premkumar and Baby, 2005) Hazarika et al (2000), used spore suspensions (108ml-1) of antagonistic microbes like T. harzianum, T. viride, G. virens, B. subtilis and P. fluorescens on potted tea plants artificially inoculated with Ustulina zonata. He observed that all the antagonists gave disease control comparable to carbendazim treatment. Soil drenching was superior compared to

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seedling root dip in reducing the mortality of the plants. In another experiment with Ustulina zonata (Hazarika and Phookan, 2003), a consortium of Psuedomonas, Trichoderma and VAM fungi Glomus fasciculatum was used and the level of disease control achieved was significantly superior to the application of individual components. The success of biocontrol agents under field conditions depends on certain factors like carrier materials and organic matter status in the soil. Among different carrier materials tested for shelf life in UPASI TRI for Trichoderma, composted coir pith was the best followed by vermicompost (Ajay et al, 2004). The population of Trichoderma was as high as 0.32 x 108 even at 14 months. Soil organic matter also plays an important role as it is the chief source of energy for the introduced organism. The population of introduced Trichoderma was high in tea soils with higher organic matter content (Barthakur, 2002, Ajay et al, 2005) Future Works Much work has to be done with improved bioformulations especially in case of foliar disease control. Liquid formulations can have an edge over carrier based formulations both in terms of bioefficacy and extended shelf life. Usage of a consortium of biocontrol agents instead of single organism to control tea diseases has to be tried. Improving bioefficacy of bioagents by increasing its population size in the niche environment through the addition of nutrients in the spray fluid is another area. Biocontrol agents with high tolerance to fungicides has to be developed either by screening of natural isolates or by random screening after mutagenesis or through genetic manipulation. This will help us to design an integrated management strategy to control tea diseases more effectively.

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