Quantification of Sugarcane Yellow Leaf Virus in In Vitro Plantlets and Asymptomatic Plants of Sugarcane by RT-qPCR

Yellow leaf caused by Sugarcane yellow leaf virus (SCYLV) is a serious viral disease affecting production and productivity in many ruling sugarcane varieties in India. Usually the characteristic disease symptoms appear during maturity phases of the crop; also many of the infected varieties do not exhibit disease symptoms and disease expression is influenced by virus titre and other factors, including the prevailing climate. The present study was taken up to quantify and compare SCYLV in meristem-derived tissue culture raised in vitro plantlets and asymptomatic sugarcane plants in RT-qPCR by relative standard curve method. The standard curve was prepared with serial dilutions of plasmid standards from 3 × 10⁷ to 3 × 10³ copy numbers of virus target gene. In this assay, copy number of virus population in in vitro plantlets and asymptomatic plants was estimated from 20,314.58 to 4,330.87 and from 8.96 to 0.27 million copies of viruses respectively. Relative expression level of the virus between in vitro plantlets and asymptomatic plants was in the ratio 73.7 : 243,393.1 based on 2^{-(Δ ΔCt). The results clearly established that meristem-derived tissue culture significantly reduced SCYLV population and it is concluded that the relative standard curve method efficiently detects the copy numbers of the target virus in different sugarcane samples.}