Small RNAs regulate a large set of gene expression in all plants and constitute a natural immunity against viruses. Small RNA based genetic engineering (SRGE) technology had been explored for crop protection against viruses for nearly 30 years. Viral resistance has been developed in diverse crops with SRGE technology and a few viral resistant crops have been approved for commercial release. In this review we summarized the efforts generating viral resistance with SRGE in different crops, analyzed the evolution of the technology, its efficacy in different crops for different viruses and its application status in different crops. The challenge and potential solution for application of SRGE in crop protection are also discussed.

No abstract

No abstract

2 Foliar urea application is considered an important factor affecting phenology, growth, yield, and yield components of maize. A field experiment was conducted to study effects of urea spray on Azam variety of maize (Zea mays L.) in Mardan district of the North West Frontier Province (NWFP) of Pakistan during 2005-06. The 5 × 4 factorial experiment was designed with five urea levels (U 0 = control, U 1 = 2, U 2 = 4, U 3 = 6 and U 4 = 8% urea) applied to main plots and four application timings (T 1 = at V9, T 2 = V12, T 3 = VT and T 4 = R1 stages) assigned to subplots. Days to tasseling, silking, and maturity were delayed significantly when urea was applied at the rate of 6% and when applied at the V12 stage. Earlier tasseling, silking, and maturity were observed in urea control plots and in plots that received urea at the V9 stage. Plant height, leaf area, number of grains per cob and per line as well as (1000) grain weight, and grain and stover yields increased significantly up to the 6% urea level. Maize yield and yield components were higher when urea was applied at the V12 and VT stages than at the V9 and R1 stages. It is concluded that urea spray at the rate of 6% during the V12 stage would improve the grain yield and yield components of maize in the study area and contribute significantly to increased production.