MSc.

The study entitled ‘Etiology and management of mosaic disease in ginger
(Zingiber officinale Roscoe)’ was conducted at the Department of Plant Pathology,
College of Agriculture, Vellayani during 2015-2018 with the objectives to
identify, characterize and sequence the genes of Ginger mosaic virus infecting
ginger along with the management of the disease. As part of the study, the
symptoms produced by the virus in ginger plants collected from the field and
grown in glass house were observed. The symptoms on the leaves appeared as
small light green flecks. These flecks eventually increased in size and formed
streaks. The streaks were arranged parallel to the veins. The appearance of too
many streaks on the leaves led to severe chlorosis and the leaves showed necrotic
symptoms in the advanced stage.
Transmission of the virus was tested in rhizome (seed material collected from
infected plants) and mechanical inoculation was done using infected leaf sap to
the healthy plants. The infected rhizomes resulted in 100% transmission and
mechanical transmission failed to transmit the virus.
Changes in total carbohydrates, chlorophyll, phenol, total soluble proteins
and defense related enzymes namely peroxidase, polyphenol oxidase and
phenylalanine ammonialyase were carried out at 30, 60, 90 and 120 days after
infection. The study revealed an increase in the content of phenols and defense
related enzymes in infected plants. An increase in carbohydrates, chlorophyll and
protein in healthy plants was also observed. Protein profile study using sodium
dodecyl sulphate- polyacrylamide gel electrophoresis (SDS- PAGE) indicated the
presence of a novel protein with molecular weight of 20 kDa in the infected plant
sample.
The immunological detection techniques direct antigen coating- enzyme
linked immunosorbant assay (DAC- ELISA) and dot immunobinding assay
(DIBA) were carried out. Since the etiology of the virus was unknown, seven
suspected viruses were tested in DAC- ELISA and antibodies specific to two
viruses namely Banana bract mosaic virus (BBrMV), Cucumber mosaic virus
(CMV) gave an absorbance value of 0.15 and 0.19 respectively which was three
times more than the absorbance shown by the healthy leaf (0.05 and 0.07). The
infected leaf tested for the presence of African cassava mosaic virus (ACMV) by
triple antibody sandwich ELISA (TAS-ELISA) gave an absorbance of 0.0425
while the healthy gave an absorbance of 0.017. DIBA analysis gave positive
reaction to BBrMV.
Polymerase chain reaction ( PCR) was carried out with both total DNA
and RNA isolated from infected ginger leaf sample. The PCR experiment was
positive to Begomoviruses and negative to PVY (Potato virus Y) and BBrMV
isolates. An amplicon of size 550 bp was obtained for the sample DNA using
begomo degenerate primer. The sequence was subjected to BLAST analysis
which indicated 74 per cent similarity to Tomato leaf curl virus Bangalore isolate.
The management studies were conducted with antiviral principles like
botanicals, chemicals and that of microbial origin against the virus. The
experiment was conducted in completely randomized design (CRD) with 13
treatments and three replications. Karthika was the variety used for the study.
Perfekt (a botanical extract-76%) at 0.5 ml L-1 and 1ml L-1, chemicals namely
aspirin, salicylic acid, barium chloride, at 100 and 150 ppm concentrations and
botanicals namely ten per cent leaf extracts of Mirabilis jalapa and Bougainvillea
spectabilis, two per cent neem oil garlic emulsion and two per cent PGPR mix II
were used in the experiment. The treatments were given at fortnightly interval.
Before each spray the efficacy of the treatments were evaluated using
Vulnerability Index (V.I) developed by Bos (1982). The treatments with Perfekt at
the rate of 0.5 ml L-1 and 1.0 ml L-1 and ten per cent leaf extract of Mirabilis
jalapa were found effective for the management of the disease.
The study indicates that the mosaic disease in ginger is transmitted
through rhizomes, the virus has been molecularly characterized and shows only
74% identity with Tomato leaf curl virus (TLCV) and management of the disease
can be done by application of Perfekt at 0.5 ml L-1 or 10% leaf extract of Mirabilis
jalapa at fortnightly interval.