Post-pollination hybridization barriers in Nicotiana section Alatae

Abstract

Nicotiana section Alatae contains eight species with variable flower sizes and morphologies. Section members readily hybridize in the glasshouse, but no hybrids have been observed in natural sympatric and parapatric populations. To investigate interspecific crossing relationships with respect to mechanisms preventing hybridization, all members of section Alatae were intercrossed in a complete diallel. We found positive correlation between the pistil length of the pollen donor and interspecific seed set relative to the conspecific cross. Pollen tube growth rate and pollen donor pistil length were positively correlated as well. Furthermore, pollen from short-pistil members of section Alatae could only grow a maximum distance proportional to, but greater than, their own pistil lengths. Our results show that pollen tube growth capacity (i.e., rate and distance), provides a hybridization barrier in long-pistil species 9 short-pistil species crosses. We also found another hybridization barrier not specifically related to pollen tube growth capacity in short-pistil species 9 long-pistil species. Taken together, these barriers can generally be described by a 'pistil-length mismatch' rule; in section Alatae, pollen has the most success fertilizing ovules from species with pistil lengths similar to their own. This rule could contribute to hybridization barriers in Section Alatae because the species display dramatically different pistil lengths.

Production and characterisation of the intergeneric hybrids between Dendranthema morifolium and Artemisia vulgaris exhibiting enhanced resistance to chrysanthemum aphid (Macrosiphoniella sanbourni)

“…10 days after pollination, only a few developed to globular stage and aborted thereafter. Thus there are evidently severely post-zygotic barriers preventing the hybridization of chrysanthemum 'Zhongshanjingui' and mugwort 'Variegata', just as affect many wide crosses (Weiblen and Brehm 1996;Lee et al 2008;Tang et al 2009). However, the ability of some hybrid embryos to develop normally up to the globular stage indicated that there was a possibility of overcoming the cross barriers using ovule culture (Li and Chen 2004;Tang et al 2009).…”

Interspecific reproductive barriers in the tomato clade: opportunities to decipher mechanisms of reproductive isolation

“…However, as Darwin concluded (1884), there are many exceptions to this tenet, both within heterostyled species where pollen grain size can be identical in the two morphotypes, and between species wherein pollen grains are similarly sized but must grow greatly varying distances in styles. While style length does not vary as much in the tomato clade as in some other taxa (Lee et al 2008), there is more than twofold variation in style length, from 5.35 to 11.76 mm, and threefold variation in pollen size (volume), from 4,419 to 13,388 lm 3 (Fig. 2).…”

A Pollen Protein, NaPCCP, That Binds Pistil Arabinogalactan Proteins Also Binds Phosphatidylinositol 3-Phosphate and Associates with the Pollen Tube Endomembrane System

“…4D, 5A, and 6, A, E, F, and I). Perhaps, pollen tubes growing in planta may have a more extended growth region because of their much faster growth rates Lee et al, 2008a). Nevertheless, culture-grown tubes expressing NaPCCP::GFP displayed similar patterns to tubes grown in planta (Fig.…”

“…Pollen tubes attain remarkable growth rates in planta, as high as 250 nm s 21 in lily (Messerli et al, 2000) and 400 nm s 21 in N. alata (Lee et al, 2008a), rates much faster than growth in culture. Thus, the pistil promotes rapid pollen tube growth.…”