Nicotiana sylvestris flowers only during long days and N.tabacum flowers only during short days. If raised in the laboratory under different photoperiods, they can be indued to flower at the same time and can be cross-fertilized to produce self-fertile offspring. What is the best reason considering N . sylvestris and N.tabocum to be separate species ?

Step-by-step solution

According to biological species concept, a species is a natural inbreeding group which may have essentially similar morphological traits but they are genetically distinct and reproductively isolated from others. As under laboratory conditions, N. tabacum and N . sylvestris cannot produce selffertile offspring, so they are not reproductively isolated. They are considered as separate species because since their flowering periods are different so cross pollination is not possible between them naturally. This makes the