RT-PCR and quantitative real-time RT-PCR detection of Sugarcane Yellow Leaf Virus (SCYLV) in symptomatic and asymptomatic plants of Hawaiian sugarcane cultivars and the correlation of SCYLV titre to yield

Sugarcane yellow leaf virus (SCYLV) has been reported worldwide to infect sugarcane and to cause significant yield losses. Current detection methods include tissue blot immunoassay (TBIA), reverse transcription-polymerase chain reaction (RT-PCR) and quantitative real-time RT-PCR assay (qRT-PCR). In this paper, we report the use and comparison of these detection methods for the study of SCYLV in Hawaiian cultivars. We observed positive RT-PCR and qRT-PCR reactions in cultivars previously thought (based on TBIA) to be immune to virus infection. The semi-quantitative virus titre in these cultivars was however at least 10(6)-fold lower than in the cultivars which were known to be SCYLV-susceptible. The RT-PCR methods also revealed that plants of the cultivar H65-7052, which were previously shown to vary strongly between TBIA-positive and TBIA-negative, indeed exhibited fluctuating SCYLV-titres in a range of 10(3)-10(4)-fold. The virus titre was carried through to the next vegetative generation, i. e. plants grown from seed pieces with low virus titre had low virus titre and plants grown from seed pieces with high virus titre contained high virus titre. A small field trial comparing plants of cv. H65-7052 of low and high SCYLV-titre showed that the field plots with plants of high virus titre developed Yellow Leaf symptoms and yielded only 54-60% of cane and sugar tonnage compared to plots with plants of low virus titre.