Is floral structure a reliable indicator of breeding system in the Brassicaceae?

Abstract

This study investigated the usefulness of floral characters as a potential indicator of breeding system in the Brassicaceae. Initially, pod set, seed set and pollen tube growth experiments were carried out to confirm the breeding systems of 53 lines representing 25 different cultivated and weedy species from the Brassicaceae. The results of the pod set tests clearly differentiated between self-compatible and self-incompatible species. Floral characters were then evaluated on one or more lines of each of the 25 species. Fourteen floral characters were evaluated including, flower diameter, Cruden’s outcrossing index, timing and direction of dehiscence and pollen-ovule ratio. Significant differences between species were evident in all of the floral characteristics evaluated. Flower diameter was generally larger in self-incompatible species than self-compatible species and pollen/ovule ratio was generally higher in self-incompatible species than self-compatible species. However, none of the floral characteristics was able to clearly differentiate the self-compatible and self-incompatible species and allow prediction of the breeding system with absolute confidence. The floral characteristic which was most effective at differentiating the two groups was anther direction at dehiscence.

Floral structure and genetical differences of sandalwood variants in Gunung Sewu (Java, Indonesia), and its effects on breeding systems and reproductive ability

“…Flowers of Tetracentron chinense grew in the same region are very small-sized, hermaphrodite without any separation of sexes, having OCI score less than 3, and were proven to have mixed mating with selfing preference (Gan et al 2013). Study on several Brassicaceae in Australia showed that species with larger flower and separation of sexes, which could be both spatially or temporally, scored higher OCI and tended to be more outcrossing (Salisbury et al 2017). Similarly, other studies also revealed that the size of corolla, length of filament and anthers, and the position of sexual organs, all were positively correlated to the quality of pollen transferred; hence the heterostylous and heteranthery flowers tended to be more outcrosser.…”

“…Total N = 30 single flowers x 3 variants x 4 sites = 360 single flowers. Cruden's Outcrossing Index (Salisbury et al 2017) was measured by totalling the score of these three characters: (i) Flower diameter: < 1 mm = 0; 1-2 mm = 1; 2-6 mm = 2; > 6 mm = 3; (ii) Temporal separation of maturity between male and female sexual organs: concurrently = 0; mature at different time = 1; (iii) Spatial separation between male and female sexual organs: pistil and stamen are not separated, located within a similar position with a possibility to inter-mate = 0; pistil and stamen are spatially separated = 1. Plant is classified into outcrossing taxa when the value of Cruden's Outcrossing Index is equal to more than 3.…”

“…Reproductive failure might exist as a result of genetic mechanisms, such as self-incompatibility, which might occur in mating between relatives (Rao et al 2007;Salisbury et al 2017;Yang et al 2017). Reproductive failure might also occurred as a result of mating barriers due to the differences on floral structures and biology among individuals within population, that in turn lead to a mating incompatibility (Rughkla et al 2006;Barrett 2011;Tamla et al 2012;Gan et al 2013;Salisbury et al 2017;Yang et al 2017).…”

“…Reproductive failure might exist as a result of genetic mechanisms, such as self-incompatibility, which might occur in mating between relatives (Rao et al 2007;Salisbury et al 2017;Yang et al 2017). Reproductive failure might also occurred as a result of mating barriers due to the differences on floral structures and biology among individuals within population, that in turn lead to a mating incompatibility (Rughkla et al 2006;Barrett 2011;Tamla et al 2012;Gan et al 2013;Salisbury et al 2017;Yang et al 2017). In such cases, pollination barrier occurred due to the differences on the length of stylus and/or filament, structures of corolla, stigma-anthers position (Rughkla et al 2006;Fernandez et al 2009;Tamla et al 2012), pistil dysfunction, male sterility (Sindhu-Vereendra and Anantha-Padmanabha 1996; Warburton et al 2000) and/or flowering asynchrony (Ratnaningrum et al 2016(Ratnaningrum et al , 2017b(Ratnaningrum et al , 2018.…”

“…Several methods which correlate floral characters with the plant preference to outcross or inbreed, are the Index of Self Incompatibility (ISI) and Cruden's Outcrossing Index (OCI) methods. The breeding system estimation based on ISI and OCI values has reported in Schima superba (Yang et al 2017) and Tetracentron chinense (Gan et al 2013) in the tropical Southern China region, and several Brassicaceae in Australia (Salisbury et al 2017).…”