Evaluation of Solanum species for resistance to Tomato leaf curl New Delhi virus using chip grafting assay.
Tomato leaf curl disease (ToLCD) caused by a complex of whitefly-transmitted begomoviruses is a serious threat to tomato crop worldwide. Involvement of Tomato leaf curl New Delhi virus (ToLCNDV) with ToLCD is considered as an emerging threat to tomato production in Pakistan. Use of resistant variety is one of options to control this ToLCD. To date, information on tomato resistance against ToLCNDV is very meager. In the present study, a simple, cost effective, reliable and rapid chip graft inoculation assay (CGIA) that result in 100% transmission rate of ToLCNDV have been described for the first time. Using CGIA 170 tomato genotypes belonging to different Solanum species were evaluated against ToLCNDV. Following CGIA, resistance to ToLCNDV was found in 5 wild and 13 accessions of tomato containing Ty genes. Grafted plants of these accessions showed delayed latent period, mild symptoms with low virus accumulation as compared those found in susceptible genotypes. However, none of accessions can be used directly for general cultivation because of their unacceptable horticultural characteristics. In conclusion, current finding shows that CGIA is suitable for efficient assessment of resistance to ToLCNDV across a range of tomato germplasm. Furthermore, it will also be useful to study the underlying mechanisms of pathogenicity in ToLCD and other important virus diseases of tomato. Moreover, ToLCNDV-resistant accessions carrying Ty genes that belong to Solanum lycopersicum, can easily be used for breeding commercial tomato hybrids/genotypes.