Papillar integrity as an indicator of stigmatic receptivity in kiwifruit (Actinidia deliciosa)

Stigmatic receptivity is a major factor limiting fruit set in kiwifruit (Actinidia deliciosa). The aim of this work was to know what determines the cessation of stigmatic receptivity in this species. Stigmatic receptivity has been analysed in kiwifruit through the capacity of the stigma to sustain pollen germination and has been related to stigmatic development and degeneration.The stigma of kiwifruit flowers has a papillate surface which from anthesis is covered with an abundant exudate. Papillae are unicellular and contain a number of phenolic deposits. During the lifetime of the flower these papillae gradually lose turgidity, while stigmatic secretion increases until 5 d after anthesis when papillae start rupturing and the papillar content is liberated into the germination medium. Stigmatic receptivity is high at anthesis and lasts for the next 4 d. However, it drastically decreases 5 d after anthesis and it is nil 2 d later. The pattern of stigmatic receptivity closely fits that of papillar integrity, indicating that stigmatic receptivity relies on this integrity. Since papillar integrity can easily be evaluated in stigmatic arms, this criterion can be used as a quick method to estimate stigmatic receptivity.