Asynchronous development of stigmatic receptivity in the pear (Pyrus communis; Rosaceae) flower

Abstract

While stigma anatomy is well documented for a good number of species, little information is available on the acquisition and cessation of stigmatic receptivity. The aim of this work is to characterize the development of stigma receptivity, from anthesis to stigma degeneration, in the pentacarpellar pear (Pyrus communis) flower. Stigma development and stigmatic receptivity were monitored over two consecutive years, as the capacity of the stigmas to offer support for pollen germination and pollen tube growth. In an experiment where hand pollinations were delayed for specified times after anthesis, three different stigmatic developmental stages could be observed: (1) immature stigmas, which allow pollen adhesion but not hydration; (2) receptive stigmas, which allow proper pollen hydration and germination; and (3) degenerated stigmas, in which pollen hydrates and germinates properly, but pollen tube growth is impaired soon after germination. This developmental characterization showed that stigmas in different developmental stages coexist within a flower and that the acquisition and cessation of stigmatic receptivity by each carpel occur in a sequential manner. In this way, while the duration of stigmatic receptivity for each carpel is rather short, the flower has an expanded receptive period. This asynchronous period of receptivity for the different stigmas of a single flower is discussed as a strategy that could serve to maximize pollination resources under unreliable pollination conditions.

Pollinizer Efficacy of Several ‘Ingeborg’ Pear Pollinizers in Hardanger, Norway, Examined Using Microsatellite Markers

“…Although this is a trait common for pear cultivars, 'Ingeborg' fruit set and yield seem to be especially affected depending on season and possibly microclimate, as shown by stark differences in yield between orchards in the same region. Furthermore, Sanzol et al (2003) demonstrated clearly that asynchronous maturation of the both stigmas and ovules within a single ovary in the same pear flower can occur and varies between years. This probably means that EPP is long enough to ensure the pollination and fertilization in pears.…”

“…This probably means that EPP is long enough to ensure the pollination and fertilization in pears. According to Sanzol et al (2003), this aspect is even more pronounced in populations where pollinator efficiency is low, unreliable pollination conditions exist, or both. This certainly appears to be the case in the Hardanger region.…”

Pistil Factors Controlling Pollination

“…For example, on immature stigmas of pear flowers, mature pollen can adhere but do not hydrate and germinate. On a degenerating stigma, pollen can adhere, hydrate, and germinate, but pollen tube growth arrests abruptly (Sanzol et al, 2003). A cuticle of varying thickness is deposited on most stigmas above the epidermis, and compatible pollen deposited on a heavily cutinized surface never germinates (HeslopHarrison, 2000).…”

Assessment of effective pollination period in olive (Olea europaea) by means of fluorescence microscopy and plant response to sequential pollinations: limitations and drawbacks of current methodologies

“…As in the current study, stigma receptivity was monitored in pear as the capacity to offer support for pollen germination and pollen tube growth (Sanzol et al 2003b). Immature pear flowers' stigmas can support adhesion of pollen on their surface, but cannot provide a substrate for pollen hydration and germination (Sanzol et al 2003b), which confirms that pollen germination is a more appropriate measure of pollen receptivity. Olive flowers exhibited early stigma receptivity, showing high percentages of pollen germination at anthesis (Table 1).…”