Isolated polynucleotides and polypeptides and methods of using same for increasing plant yield, biomass, growth rate, vigor, oil content, abiotic stress tolerance of plants and nitrogen use efficiency

A method of increasing leaf number, growth rate of plot coverage and/or growth rate of rosette diameter of a plant, comprising:

• (a) over-expressing within the plant a polypeptide comprising an amino acid sequence at least 87% identical to SEQ ID NO:
• 638, wherein said over-expressing of said polypeptide is effected by transforming a cell of the plant with an exogenous polynucleotide comprising a nucleic acid sequence encoding said polypeptide, and
• (b) selecting said plant over-expressing said polypeptide for an increased trait selected from the group consisting of:
• leaf number, growth rate of plot coverage and growth rate of rosette diameter as compared to a native plant of the same species under the same growth conditions,
• thereby increasing the leaf number, growth rate of plot coverage and growth rate of rosette diameter of the plant.