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The present study entitled ‘Survival and genetic diversity of geminivirus infecting
okra (Abelmoschus esculentus (L.) Moench) and bitter gourd (Momordica charantia L.)’ was
conducted at Department of Plant Pathology, College of Agriculture, Vellayani during 2016 -
18 , with the objective to identify the genetic variability in geminivirus isolates infecting okra
and bitter gourd and their dissemination in the associated weeds. Survey was conducted in
three taluks of Thiruvanathapuram districts viz. Neyyattinkkara, Neumangad and
Chirayinkeezh. During the survey majority of the fields had yellow vein mosaic disease of
okra and mosaic disease of bitter gourd. Chirayinkeezh area recorded the highest disease
incidence and vulnerability index (78.2 in okra and 52.8 in bitter gourd) for bhendi yellow
vein mosaic as well as for bitter gourd mosaic. From nearby areas of okra and bitter gourd
fields, nineteen weeds expressing yellow vein and mosaic symptoms were collected.
Symptoms of both the diseases were studied.
Okra yellow vein mosaic appeared as initial vein clearing which later turn to complete
yellowing of veins and leaves. In severe cases fruits were malformed and bleached in
appearance. Symptoms of mosaic disease in bitter gourd started as yellow specks on foliage
which later turn to mosaic and complete chlorosis of leaf. Reduction in fruit size and
hairiness of vines were prominent symptoms at fruit setting stage. Among nineteen weeds
collected, five weeds exhibited typical vein clearing and fourteen exhibited mosaic symptom.
Some other weeds expressed puckering and curling of leaf along with mosaic symptoms.
Transmission studies by wedge grafting recorded 70 and 80 percent transmission of
geminivirus in okra and bitter gourd respectively. Through whitefly (Bemisia tabaci
Gennadius), 80 percent transmission was observed in both okra and bitter gourd.
Immunological detection studies revealed that geminivirus isolates infecting okra were
serologically related to Sri lankan cassava mosaic virus (SLCMV) and that of bitter gourd to
African cassava mosaic virus (ACMV). Acalypha indica L., Ageratum conyzoides L.,
Centrosema pubescens Benth., Croton sparsiflorus L., Desmodium gyrans (L.) DC., Emilia
sonchifolia (L.) DC., Euphorbia geniculata Ortega, Hemidesmus indicus (L.) R. Br,
Phyllanthus niruri L., Richardia scabra L., Synedrella nodiflora (L.) Gaertn., Tephrosia
purpurea (L. ) Pers. showed positive serological relation to ACMV. Acalypha indica L.,
Emilia sonchifolia (L.) DC., Hemidesmus indicus (L.) R.Br. Sida rhombifolia L. Sida
cordifolia L. were serologically related to SLCMV.
Geminivirus infecting okra, bitter gourd and associated weeds were partially
characterized using two primers specific to geminivirus. Okra isolates of geminivirus showed
maximum similarity to the Okra enation leaf curl virus (>90 %) and bitter gourd isolates of
geminivirus showed maximum identity with Tomato leaf curl virus (>90 %) and Chilli Leaf
curl virus (>90 %). Among the nineteen weed species tested, only ten weeds viz. A. indica, A.
conyzoides., C. sparsiflorus E. sonchifolia, E. geniculata, H. indicus, S. cordifolia, S.
rhombifolia, S. nodiflora and T. purpurea gave amplification with geminivirus specific
primers and were characterized as geminivirus.
Phylogenetic study and genetic diversity of geminiviral isolates of okra, bitter gourd
and associated weeds was undertaken. Phylogeny tree analysis showed that okra isolates of
geminivirus have a common cluster which diverged from the cluster of bitter gourd
geminivirus isolates. S. cordifolia (vein clearing), S. rhombifolia (mosaic) and C. sparsiflorus
(vein clearing) isolates of geminivirus shared more similarity with the cluster of okra isolates
of geminivirus (vein clearing). Geminivirus infecting A. conyzoides (vein clearing), S.
nodiflora (vein clearing), E. sonchifolia (vein clearing) and T. purpurea (mosaic) aggregated
in one cluster which showed more similarity to the okra isolates of geminivirus (vein
clearing).. H. indicus strain of geminivirus (mosaic) and E. geniculata strain of geminivirus
(mosaic) have a close relation with bitter gourd geminivirus isolates (mosaic). Geminivirus
strain of A. indica (mosaic) form a separate cluster which shared more similarity with the
separate cluster of bitter gourd geminivirus isolates (mosaic). In phylogeny study weeds
showing vein clearing symptoms recorded close relationship with geminivirus infecting okra
with vein clearing symptoms except for T. purpurea and S. rhombifolia in which mosaic
symptoms were observed. Weeds with mosaic symptoms showed close relationship to the
geminivirus infecting bitter gourd with mosaic symptoms. Genetic distance between
geminiviral isolates of okra, bitter gourd and weeds was less, indicating less divergence
between the isolates that suggest a possibility of transmission of geminivirus from crops to
weeds and vice versa.
Present study indicated that all the ten weeds have close relation to the geminivirus
infecting okra and bittergourd and can act as collateral host for these viruses. Future studies
should undertake for characterizing the geminivirus infecting weeds completely for
formulating better management practices against geminivirus.