When a diploid female plant is crossed with a tetraploid male, the...

Female parent genotype $=2 \mathrm{~N}=2 \mathrm{~A}$ Male Gamete formed $=\mathrm{N}=\mathrm{A}$ Male parent genotype $=2 \mathrm{~N}=4 \mathrm{~A}$ Male Gamete formed $=\mathrm{N}=2 \mathrm{~A}$ Endosperm is formed by the fusion of 2 polar nuclei (from female gamete) and 1 male gamete. Thus, the ploidy of endosperm = $3 \mathrm{~N}=\mathrm{A}+\mathrm{A}+2 \mathrm{~A}=4 \mathrm{~A}$ (tetraploid)