The intermorph breeding system is responsible for reproductive success in heterostylous Nyctanthes arbor‐tristis L.

Abstract

AbstractHeterostyly is a specialized reproductive system associated with self‐ and intramorph incompatibility. It reinforces the intermorph breeding system in heterostylous plant species. However, distyly has not been comprehensively studied in Nyctanthes arbor‐tristis. The present study demonstrates the floral traits, breeding system, fruit and seed set, and morph ratio in distylous N. arbor‐tristis. The length of style and filament showed reciprocal herkogamy between long style (L‐morph) and short style (S‐morph). Flower size, corolla tube size, stamen and anther length, ovary length, and pollen diameter were larger in S‐morph. However, the style was longer in L‐morph. Our results demonstrated strongly incompatible self‐ and intramorph pollination combinations. The intermorph pollination was compatible, showing normal pollen tube growth throughout the style and ovary. The embryo formation was also higher in intermorph interaction. Moreover, the fruit setting was higher when the intermorph plants grew in the vicinity of natural conditions. Collectively, all data indicate that N. arbor‐tristis is a distylous species with a self‐incompatible breeding system, resulting in less seed formation in nature.