Symptomological Variations in Tea caused by Six Isolates of the Root Lesion Nematode, Pratylenchus Loosi in Sri Lanka

The root lesion nematode, Pratylenchus loosi is the major nematode species causing significant above-ground and below-ground stress symptoms in tea. Unusual spread and damage levels of P. loosi were evident in all tea growing regions in the recent past and warranted in-depth studies on symptomology and pathogenicity caused by different P. loosi populations. Hence, a series of studies was conducted to assess the pathogenicity and symptomology of different P. loosi populations under controlled conditions and in P. loosi infested fields in six locations in Sri Lanka i.e. Cicilton (Balangoda), Delmar (Ragala), Hapugastenna (Ratnapura), Mahadowa (Passara), Nawalapitiya and Richiland (Deniyaya).  
The data revealed six different P. loosi populations causing damage to tea with significantly different virulence and pathogenicity levels and causing varying symptoms. Cicilton population seemed highly virulent at soil temperature 24 oC showing significantly higher reduction in plant height (52.3%) and root weight (42.6%). However, Richiland (Deniyaya) population caused significantly higher reduction (58.67%) in shoot weight. Data also confirmed significantly different virulence and pathogenicity levels of P. loosi triggered by changing soil temperatures.  Overall, the six isolates of P. loosi showed irreversible damage to tea at different magnitudes in different agro ecological regions and elevations.  Stunting of plants, root lesions, fall of feeder roots/fragments, flowering and fruiting as triggered through hormonal imbalances and dry matter production were symptoms in tea.  These warranted appropriate isolate/location specific nematode management and mitigation strategies in different tea growing regions.