Sex expression and inbreeding depression in progeny derived from an extraordinary hermaphrodite of Salix subfragilis.

Teruyoshi Nagamitsu,Norihiro Futamura

doi:10.1186/1999-3110-55-3

Teruyoshi Nagamitsu, Norihiro Futamura

Open Access

https://doi.org/10.1186/1999-3110-55-3

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Abstract

BackgroundAn extraordinary hermaphrodite of dioecious willows provides us an opportunity to examine the inheritance of sex expression and the magnitude of inbreeding depression using a progeny assay of the hermaphrodite.ResultsWe indentified 165 progeny of an open-pollinated hermaphrodite of Salix subfragilis as siblings selfed (Self) or crossed with another hermaphrodite (Cross_H) or a male (Cross_M) using microsatellite genotypes. There were more selfed progeny (110 in Self) than outcrossed progeny (31 in Cross_H and 24 in Cross_M), suggesting the absence of barriers to selfing in the maternal hermaphrodite. The sex ratio (female:male:hermaphrodite) of the progeny differed among the sibling groups (27:17:66 in Self, 3:16:12 in Cross_H and 9:8:7 in Cross_M). Nearly half of the selfed progeny were hermaphrodites, suggesting that an identical combination of parental alleles in progeny reproduced the hermaphroditism of the parent. We measured fitness components of growth (stem height and basal area), survival and fertility (pollen germination proportion, number of ovules and seed set). The magnitudes of inbreeding depression in growth and survival (0.29-0.70) were higher than those in fertility (0.00-0.16).ConclusionsThe findings suggest a genetic basis of extraordinary hermaphroditism and substantial inbreeding depression in survival and growth in the dieocious S. subfragilis.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-55-3) contains supplementary material, which is available to authorized users.

Highlights

An extraordinary hermaphrodite of dioecious willows provides us an opportunity to examine the inheritance of sex expression and the magnitude of inbreeding depression using a progeny assay of the hermaphrodite
We investigated the inheritance of sex expression and the magnitude of inbreeding depression using selfed and outcrossed progeny of an extraordinary hermaphrodite discovered in S. subfragilis
We evaluated inbreeding depression for fitness components from mean measurements of selfed progeny Ws and those from progeny crossed with a hermaphrodite Woh or those from progeny crossed with a male Wom in the following form: δh 1⁄4 1−W s=W ohðW s ≤ W ohÞ; W oh=W s − 1 ðW s > W ohÞ; δm 1⁄4 1−W s=W omðW s ≤ W omÞ; W om=W s − 1 ðW s > W omÞ: The magnitude of inbreeding depression δh, in comparison with the progeny derived from outcrossing with a hermaphrodite, would be underestimated because the hermaphroditic parents were siblings (Kurahashi and Kimura, 2002)

Summary

Introduction

An extraordinary hermaphrodite of dioecious willows provides us an opportunity to examine the inheritance of sex expression and the magnitude of inbreeding depression using a progeny assay of the hermaphrodite. Willows (genus Salix, Salicaceae) are promising materials for short-rotation forestry for renewable energy. Breeding programs for willows require a basic knowledge of the reproduction and genetics of the genus Salix (Karp et al, 2011). Extraordinary polygamy has been found in some individuals, which bear catkins of both female and male flowers in various compositions (Smith, 1940; Mosseler and Zsuffa, 1989; Falinski, 1998; Rottenberg, 2007). Hermaphroditic flowers with pistils and stamens were discovered in S. martiana (Rohwer and Kubitzki, 1984). Such bisexual individuals provide us an opportunity to investigate the

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