The correct answer is option 2: Test cross.

In genetics, a test cross is used to determine the genotype of an individual with a dominant phenotype. It involves crossing the individual with a known homozygous recessive individual.

Here, the cross is between a homozygous recessive plant (both alleles are recessive) and a heterozygous plant (one allele is dominant and the other is recessive). The purpose of this cross is to determine if the heterozygous plant is homozygous dominant or heterozygous recessive.

In a test cross, if all offspring show the dominant phenotype, the unknown individual is homozygous dominant. If some offspring show the recessive phenotype, it means the unknown individual is heterozygous.

So, the cross between the homozygous recessive and heterozygous plant is a test cross.