The genetic basis of self-incompatibilitiy in Capsicum pubescens and C. cardenasii was studied. Self-incompatibility was discovered for the first time in the normally self-compatible, cultivated species C. pubescens. All strains of C. cardenasii studied were self-incompatible.

Diallel matings of F₁ plants from intraspecific (Capsicum cardenasii) and interspecific (C. pubescens × C. cardenasii) crosses indicated a gametophytic system of incompatibility of the Nicotiana type in both species. Each F₁ progeny, regardless of the direction of the cross, constituted four intrasterile, interfertile groups. When self-incompatible C. pubescens or C. cardenasii plants were crossed with self-compatible C. pubescens, all F₁ and F₂ plants were self-compatible. F₁ plants accepted pollen readily from either parent. In contrast to Nicotiana, however, the self-incompatible strains accepted pollen readily from self-compatible plants.

The number of pollen-grain nuclei and the site of inhibition of pollen-tube growth substantiated the gametophytic interpretation of incompatibility in Capsicum.