Resistance to wheat streak mosaic virus in transgenic wheat expressing the viral replicase (NIb) gene

Wheat (Triticum aestivum L. cv. Hi-Line) immature embryos were transformed with the replicase gene (NIb) of wheat streak mosaic virus (WSMV) by the biolistic method. Six independent transgenic plant lines were analyzed for transgene expression and for resistance to mechanical inoculation of WSMV at R3 or R4 generation. Four out of the six lines showed various degree of resistance to WSMV. These lines had initially milder symptoms than controls, and the new growth ranged from milder symptoms, a substantial delay in symptom development, or asymptomatic. Two lines displayed higher resistance with very mild virus symptoms after inoculation and the new growth of 72% and 32% plants from these lines were asymptomatic and had no detectable virus through the plant life cycle. Interestingly, five out of the six transgenic lines had no detectable transgene mRNA expression by RNA gel blot hybridization. The only line that had detectable transgene mRNA did not show delay in the symptom development but had overall milder symptom to the virus.