MSc

Tomato is one of the popular and widely grown vegetables in the world.
Occurrence of diseases acts as the major constraint in the cultivation of tomato in
Kerala. Recently, tomato leaf curl, a whitefly vectored gemini virus, has emerged as a
serious threat to tomato cultivation.

Considering the importance of tomato leaf curl disease (ToLCD) in the state,
Kerala Agricultural University has initiated research on developing resistant varieties
against this disease. The present study was undertaken, giving emphasis on the
molecular variability, and disease management aspects.

Survey undertaken to record the incidence of ToLCV in Palakkad and
Vellanikkara revealed that, the incidence varied from location to location and also
from season to season. Disease incidence was less during September to December
and severe in summer season recording 74 to cent per cent in Palakkad and 64- 83 per
cent in Vellanikkara.

Four different types of symptoms were seen associated with ToLCV affected
plants. In transmission studies, grafting and the vector, Bemisia tabaci were able to
transmit the disease with production of all the types of symptoms on healthy plants.

Serological studies using DAC – ELISA revealed close relationship of ToLCV
with African cassava mosaic virus and thus confirmed the association of gemini virus
in the four different types of symptoms understudy. The protocol suggested by Rogers
and Bendich (1994) with slight modification was found to be best for extracting the
DNA from ToLCV infected plants.
The presence of ToLCV in the four types of symptoms under investigation
was confirmed with the PCR amplification with primers CRv301F and CRc 1152R.
The coat protein gene from the samples were amplified and sequenced. The
phylogenetic analysis of the four sequences revealed, differences in nucleotide
sequence`. Yellowing and curling and curling with purple tint types symptom
producing strains were found identical to the reported strains of ToLCVK3 and
ToLCVK5 with DNA-A component. The upward curling and cupping type and
curling and rolling type showed homology to Ageratum yellow vein mosaic virus and
Pepper (Chilli) leaf curl Pakistan virus respectively with respect to the coat protein
region.

In the management studies, all treatments were superior to control. Among
the 16 treatments, the combined spray of imidacloprid and the botanical, Perfekt
showed 80.84 per cent disease reduction and highest yield. In addition, imidacloprid
alone, Perfekt alone and Pseudomonas fluorescens + Perfekt were also effective.


Thus, the present study augmented our understanding of the various aspects
of tomato leaf curl disease in Kerala specifically, the symptomatology, molecular
characterization and disease management strategies.