Answer: For the first question about which greenhouse flower to use, it's the white ones. For the second question about wild genotype, it's heterozygous (probably).
Explanation: White flowers for the test cross because test crosses always use the genotypes with two recessive alleles. And the wild roses must be heterozygous because they produced half white flowers. The only way to produce more rr genotypes after a cross is if the other is also rr or is heterozygous.