Cross-compatibility of Petunia exserta with other Petunia taxa

Cross-compatibility of Petunia exserta, a natural species having red flowers, with 46 taxa of Petunia sensu Jussieu (20 taxa of Petunia sensu Wijsman plus 27 taxa of Calibrachoa) was examined to obtain basic information for the breeding of garden petunias. Petunia exserta completely failed to set capsules when crossed with any species of Calibrachoa. Petunia exserta exhibited unilateral interspecific incompatibility with 15 taxa of Petunia sensu Wijsman: As a seed parent, it could be crossed with all taxa of Petunia except P. occidentalis, but the reciprocal crossings were successful with only five taxa. In the F₂ generation of P. exserta hybrid crossed with P. axillaris subsp. axillaris having white flower, individuals having red flowers segregated. F₂ progenies contained delphinidin glycosides as the major floral anthocyanin similar to P. exserta. The use of P. exserta as an additional gene resource for improving red flowered garden petunias is discussed.