Pollen Competition and Paternal Contribution during Artificially Controlled Pollination of Black Locust (Robinia pseudoacacia L.) without Castration

Yuhan Sun,Ruiyang Hu,Chao Han,Peiyao Han,Jiankang Li,Yingming Fan,Xiuyu Li,Saleem Uddin,Qi Guo,Yun Li,Cui Long,Sen Cao,Zijie Zhang,Li Dong

doi:10.3390/f12101416

Abstract

(1) Background: Considering the serious damage caused by castration and the extremely high outcrossing rate in nature, we hypothesized that artificial controlled pollination of black locust without castration could be conducted for hybridization breeding. (2) Methods: The study conducted controlled pollination on 20 mating combinations of black locust without castration using a single or mixed male parent. Offspring of different developmental stages and the leaves of parents were collected to extract DNA and perform paternity analysis using SSR molecular markers. (3) Results: The contribution rate of each male parent differed according to developmental stage after pollination using different pollens mixed in equal proportions. There were significant correlations between the genetic similarity between each male parent and female parent and contribution rate of each male parent at three different developmental stages after pollination. (4) Conclusions: The composition of offspring pollen donors showed no bias toward selfing or outcrossing when artificially pollinated without castration. Hybrid breeding of black locust by artificially controlled pollination without castration may not be feasible, given that our manual method resulted in a large number of abortive and abnormal offspring. Introduction of honeybees in a limited space to conduct controlled pollination of black locust for hybrid breeding may be feasible.

Highlights

Considering the damage caused by castration and the extremely high outcrossing rate in nature, we hypothesized that artificial controlled pollination of black locust without castration could be conducted for hybridization breeding
These results indicate that the ambient temperature after pollination affects the development of black locust seeds, and high temperatures accelerate their development
For abnormal and abortive seeds at maturity, the outcrossing rate of five of eight cross combinations exceeded 50%. These results suggest that black locust has a mixed mating system—both self-crossing and outcrossing

Summary

Introduction

It is adaptable and tolerates a wide range of soils including sandy or nearly barren soils [1,2]. It fixes nitrogen and produces good wood suitable for poles, beams, and firewood, as well as scented flowers for bees [1,2]. Compared with Populus [3,4], Eucommia [5], Eucalyptus [6], and other tree species, hybrid breeding of black locust is in its infancy. Hybrid breeding can make better use of genetic variation among individuals for genetic improvement of black locust. The low seed-setting rate of black locust and the damage caused by castration hamper its hybridization [9,10]

Methods

Results

Discussion

Conclusion