Use of secondary somatic embryos improves genetic fidelity of cocoa (Theobroma cacao L.) following cryopreservation

in International Symposium (poster summary), 國際研討會(摘要海報發表)
標題Use of secondary somatic embryos improves genetic fidelity of cocoa (Theobroma cacao L.) following cryopreservation
AuthorsRodriguez-Lopez Carlos, 無中文, Adu-Gyamfi Raphael 無中文姓名, Jong-Yi Fang 方中宜, & Emanuel Necas 無
出版日期Nov 10 2007 12:0

A drought this year in the Ivory Coast, the world’s largest cocoa producer, has sent futures in the crop to their highest levels since 2003. Other factors contributing to the price climb include the spread of cocoa swollen shoot virus in West Africa and a growing taste for dark chocolate, which has a higher concentration of cocoa solids. Such pressures for improved yield and stress and disease resistance highlight the importance of securely preserving the diversity of the species for future breeding goals. Because of the recalcitrant nature of cocoa seed and the insecurity of field collections it is a priority to establish a replicated cryopreserved base collection of existing cocoa germplasm. Thus approximately 600 accessions of cocoa are being cryopreserved at Reading University through the encapsulation-dehydration of floral-derived somatic embryos (SEs) [1]. This vitrification-based procedure involves the rapid cooling of the prolific secondary SEs obtained from cultured cotyledonary explants of primary SEs. Due to concern about somaclonal variation arising through the protracted callus phase involved in the generation of these propagules, their genetic fidelity has been tested and primary SEs have been found to exhibit a significant mutation frequency [2]. In this study nuclear microsatellite-based screening has been applied to each of the cocoa linkage groups in SEs sampled from sequential stages of the cryopreservation procedure (ie following culture, sucrose pretreatment, dehydration over silica and thawing after storage in liquid nitrogen) and compared with profiles for the donor tree. For all 48 regenerants tested in duplicate none exhibited aberrant profiles with respect to the donor tree for any of the 12 microsatellites screened. We conclude that, within the limits of this test population, no gross chromosomal changes occurred during cryopreservation and that, until an efficient means of apical shoot culture is established for cocoa, secondary SEs constitute an acceptable target tissue for germplasm conservation.

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