Morphological and cytological study in a new type of cytoplasmic male-sterile line CMS-GIG2 in sunflower (Helianthus annuus).

Abstract Cytoplasmic male sterility (CMS) is essential for sunﬂower hybridproduction. CMS-GIG2, a new sunﬂower CMS type, was furtherconﬁrmed by crossing with the maintainer and restorer lines for theCMS-PET1, both of which maintain the male sterility of CMS-GIG2.Meiotic division in CMS-GIG2 was observed with 4¢6-diamidino-2-phenylindole dihydrochloride staining, indicating that microsporeformation was disrupted before the meiotic cytokinesis was com-pleted. Light microscopy observation showed that both middle layerand tapetal cells expand radially rather than degrade over time,followed by failure to form tetrads and normal microspores. Thismorphological defect leading to male sterility in CMS-GIG2 diﬀersfrom that observed in the PET1 CMS type. CMS-GIG2 will certainlyprovide additional genetic diversity for sunﬂower hybrid breedingprogrammes. Key words: Helianthus annuus L. — cytoplasmic male sterility— microsporogenesis — meiotic divisionCytoplasmic male sterility (CMS) is a maternally inheritedtrait that has been described in more than 150 plant species,and is characterized by the inability to produce functionalpollen grains, but both vegetative and female development areunaﬀected (Kaul 1988). The FAO Technical Consultation ofthe European Cooperative Research Network on Sunﬂowerreported 72 male-sterile sunﬂower sources of diﬀerent origins(Serieys 2005), including (i) mutants spontaneously occurringin nature, such as ANN1, ANN2, ANN3 and ANN4(Serieys 1984); (ii) interspeciﬁc cross progeny such as ARG3(Christov 1992), CMG1, CMG2 and CMG3 (Whelan andDedio 1980); (iii) intraspeciﬁc crosses progeny such as ANT1(Vranceanu et al. 1986), ANL2 (Heiser 1982) and ANL1(Anashchenko et al. 1974) and (iv) MUT1 and MUT2 frommutagenesis of two maintainer lines for the PET1 cytoplasm(Christov 1993). SunﬂowerCMS-PET1wasﬁrstidentiﬁedintheprogeny of the interspeciﬁc cross Helianthus petiolaris ·Helianthus annuus (Leclercq 1969), which is the only sourceextensively used in oilseed hybrid production. In addition toidentifying new sources of CMS and corresponding fertilityrestorers to broaden the genetic diversity of hybrid seedproduction, more research work has been focused on theabortionmechanismaswellasthechimericgenesrelatedtoCMS.The observation of microsporogenesis development inCMS-PET1, with the cytoplasm of H. petiolaris and nucleusof H. annuus, indicates that the anther abortion is due totapetum degeneration and disintegration after meiosis II(Horner 1977, Laveau et al. 1989). In some crops, such asPennisetum glaucum L. , Triticum aestivum L. , Brassica napus L.and Zea mays L. , diﬀerent CMS cytoplasm genotypes with thesame nuclear genotype display various abortion stages,abortion process of microspore development or abnormaltapetum (Li and Sun 1996, Chhabra et al. 1997, Zhou et al.1997, Long et al. 2005). Therefore, the observation ofmicrospore development in diﬀerent sunﬂower CMS typeswill extend our knowledge of the important cytoplasmic eﬀectsoccurring during pollen production.The objectives of this study were to compare the antherdevelopment of CMS-GIG2 with HA 89, a public oilseedsunﬂower inbred maintainer line to conﬁrm the abortion stageof the new CMS, meanwhile, we can primarily identify a newCMS type diﬀerent from PETl (H. petiolaris cytoplasm andH. annuus nucleus) based on its diﬀerent reﬂects in themicrospore abortion as well as cross with some identiﬁed linesfor PET1.