Experimental and natural host range studies of Tobacco streak virus (TSV) isolates of Blackgram and Greengram of Telangana using DAC-ELISA

Introduction

Among pulses, Blackgram (urdbean -Vigna mungo L. Hepper) and Greengram (mungbean -Vigna radiata L. Wilczek) are major grain legumes and are cultivated in both upland and rice fallows in India. Tobacco streak virus (TSV) has been reported to be a cause of leaf curl symptoms on Blackgram (Prasada Rao et al., 2003; Ladhalakshmi et al., 2005) [4,5] and Greengram (Bhat et al., 2002; Prasada Rao et al., 2003) [2,5] paving confusion in field diagnosis to assess the disease incidence among other viral diseases attacking. In the present study, the TSVV isolates of Blackgram and Greengram were tested on a different crop and weed species to determine experimental and natural host range as knowledge of the sources of the virus inoculum plays a crucial role in plant virus disease management.

Materials and Methods

Experimental host range under glasshouse conditions

Crop and weed species belonging to different families were tested under glasshouse conditions by mechanical inoculation with the four isolates viz., TSV-BG and TSVV-GG. Ten plants (2 plants/pot) of each species were sap inoculated. Cucurbits and legumes were inoculated at the primary leaf stage and others at 2-4 leaf stage.

The plants were kept under observation for symptom expression. Development of local and systemic symptoms was recorded up to 30 days. Irrespective of symptoms produced, all inoculated and newly emerged leaves were indexed back on local lesion assay host (cowpea cv. C-152) and tested also by DAC-ELISA with respective antiserum.

Natural host range under field conditions

Crop and weed species samples were collected randomly from the fields of Anantapur and experimental fields of NBPGR-RS, Hyderabad. The samples collected were tested by DAC-ELISA using both PBNV antiserum.

Results

Experimental host range

The studies on experimental host range of TSV-BG and TSV-GG isolates under glasshouse conditions by mechanical inoculation revealed that 25 plant as well as weed species could be infected out of 36 tested (Table 1). Symptoms expressed on the experimental host plants ranged from chlorotic, necrotic lesions/rings, chlorotic, necrotic concentric rings, leaf and stem necrosis, chlorotic spots, leaf curl, smalling of leaves, stunting, mosaic mottling, apical necrosis to death with both the TSV isolates inoculations (Fig. 1 &2). Leaf necrosis, veinal necrosis, stem and apical necrosis leading to death was observed on groundnut test plants inoculated with TSV isolates while no infection was recorded on tomato with TSV-BG as well as TSV-GG isolates.

Both the, TSV isolates produced localized necrotic lesions on the inoculated leaves of Gossypium spp. followed by no systemic infection. TSV isolates could infect the plant species like Abelmoschus esculentum., Helianthus annuus cv.PAC-36, Trigonella foenumgraecum, Gossypium herbaceum, Crossandra infundibuliformis, Tagetes patula, Amaranthus spp., Croton sparsiflorus with varied symptoms. TSV-BG and TSV-GG isolates produced only localized necrotic lesions on the inoculated leaves of G. herbaceum followed by no systemic infection while C. infundibuliformis L. and Tagetes patula developed only systemic symptoms. [6] , Prasada Rao et al. (2003) [5] and Arun Kumar (2006) [1] . Both local and systemic symptoms observed on A. esculentum confirming the result of Prasada Rao et al. (2003b) [5] , whereas Arunkumar (2006) [1] reported only local symptoms. V. radiata. cv. K-851, V. mungo developed both local and systemic symptoms in the present study in contrast to the findings of Prasada Rao et al.

(2003) [5] , whereas local and systemic symptoms reported in V. radiata. by Reddy et al. (2002) [6] and Arun Kumar (2006) [1] and in V. mungo by Reddy et al. (2002) [6] . N. glutinosa, N. rustica, N. tabacum cv. Samsun, recorded with both local and systemic symptoms confirming the findings of Reddy et al. (2002) [6] and Arunkumar (2006) [1] , whereas no TSV infection found by Prasada Rao et al. (2003) [5] . S. melongena L. developed both local and systemic symptoms in agreement with the finding of Arunkumar (2006) [1] . Both local and systemic symptoms were observed in D. stramonium in contrast to the finding of Arunkumar (2006) [1] where only local symptoms reported, whereas no TSV infection was found by Prasada Rao et al.

(2003) [5] . Vicia faba L. developed both local and systemic symptoms strengthening the results of Reddy et al. (2002) [6] and Arunkumar (2006) [1] . G. herbaceum developed only local symptoms, and the ornamental crops, C. infundibularis and T. patuala Cav. showed only systemic symptoms in agreement with Arunkumar (2006) [1] , whereas local and systemic symptoms were reported in G. hirsutum by Reddy et al. (2002) [6] . TSV isolates of Blackgram and Greengram symptomlessly infected Amaranthus viridis, Commelina bengalensis, P. hysterophorus in the present study which is strengthening the findings of Prasada Rao et al. (2003) [5] . T. procumbense also recorded with symptomless infection of TSV in the present study which is confirming the finding of Arun Kumar (2006) [1] , whereas no TSV infection was found by Prasada Rao et al.

(2003) [5] . No infection was found in Cucumis sativus, C. tetragonaloba, Lagenaria cineraria, L. esculentum which is in accordance with findings of Prasada Rao et al. (2003) [5] and Arun Kumar (2006) [1] . [1] , whereas TSV was not detected in T. procumbens and C. sparsiflorus by Prasada Rao et al. (2003) [5] . TSV was found in V. mungo which is in agreement with Ladhalakshmi et al.

Natural host range

(2006) [4] . In addition [5] . However, TSV infection was found in C. annuum by Jain et al. (2005) [3] .

Conclusion

This study demonstrated that Tobacco streak virus (TSV) isolates from Blackgram and Greengram successfully infected 25 of 36 tested plant species, displaying both local and systemic symptoms. Notable hosts included Arachis hypogaea, Cajanus cajan, and Vigna unguiculata, aligning with previous research. Some species exhibited symptomless infections, reinforcing earlier findings. Furthermore, TSV was detected in 19 out of 44 plant species tested via DAC-ELISA, confirming its presence in economically significant crops and various weeds. This highlights the complex host range of TSV and the necessity for ongoing monitoring in agricultural settings.

References

1. Bhat AI, Jain RK, Chaudhary V, Krishnareddy M, Ramaiah M, Chattannavar SN. Sequence conservation in the coat protein gene of Tobacco streak virus isolates causing necrosis disease in cotton, mungbean, sunflower and sunnhemp in India. Indian Journal of Biotechnology. 2002;1:350-356.
2. Jain RK, Bag S, Awasthi LP. First report of natural infection of Capsicum annuum by Tobacco streak virus in India. Plant Pathology. 2005;54:257.
3. Ladhalakshmi D, Ramaiah M, Ganapathy T, Krishnareddy M, Khabbaj SE, Babu M. First report of natural occurrence of Tobacco streak virus on Blackgram (Vigna mungo). Plant Pathology. 2006;55:1395.
4. Prasada Rao RDVJ, Reddy AS, Reddy SV, Thirumala Devi K, Chander Rao S. The host range of Tobacco streak virus in India and transmission by thrips. Annals of Applied Biology. 2003;142:365-368.
5. Reddy AS, Prasada Rao RDVJ, Thirumala Devi K, Reddy SV, Mayo MA, Roberts I. Occurrence of Tobacco streak virus on peanut (Arachis hypogea) in India. Plant Disease. 2002;86:173-178.