Reproductive behaviour of tetraploid alfalfa plants obtained by unilateral and bilateral sexual polyploidization |
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Authors: | Gianni Barcaccia Daniele Rosellini Mario Falcinelli Fabio Veronesi |
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Institution: | (1) Istituto di Miglioramento Genetico Vegetale, Facoltàdi Agraria, Università degli Studi di Perugia, Borgo XX Giugno, 06121 Perugia, Italy |
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Abstract: | The objective of the present study was to evaluate the fertility of tetraploid plants obtained from diploid mutants that produced
2n gametes via bilateral (BSP) and unilateral sexual polyploidization (USP) schemes. Controlled matings between selected plants
from BSP and USP were carried out according to a complete diallel. The level of male and female fertility of each plant was
estimated within full-sib, half-sib and non-inbred crosses. Crosses with unrelated self-fertile and male-sterile testers were
also performed. Pollen size and stainability were determined by acetocarmine staining. The number of ovules per ovary was
counted and the callose deposition within ovules examined to evaluate embryo sac fecundity. Cross-fertility was generally
much higher for USP than BSP plants (on average, 0.3 vs. 0.03 seeds per flower pollinated). Both male and female fertility
were inversely related to the inbreeding level of cross combinations. The in vitro pollen germinability was positively correlated
to male fertility of BSP plants. The level of in vivo embryo sac sterility was not correlated to female fertility in either
BSP or USP plants. Female fertility was restored in both BSP and USP groups when plants were crossed with unrelated tetraploid
testers. Male fertility also increased in USP plants but remained rather low in the BSP plants. Scaling up the ploidy level
by means of 2n gamete union resulted in tetraploid plants with low fertility. In particular, the BSP process yielded virtually
self-sterile and highly cross-sterile plants. The well documented positive effect of sexual tetraploidization on forage yield
was accompanied by worsening of fertility traits.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | alfalfa breeding Medicago spp 2n gametes pollen germinability embryo sac fecundity self- and cross-fertility |
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