Spontaneous versus colchicine-induced chromosome doubling in maize anther culture

The range of genetic variation of spontaneous chromosome doubling frequency of maize haploid plantlets derived from in vitro anther culture was evaluated. When regeneration is obtained by direct embryo-genesis, bypassing the callus phase, it appears that the frequency of spontaneous doubling may exceed 40 of the regenerated plantlets. This high frequency may be one consequence of the use of doubled haploid lines derived from anther culture and spontaneous chromosome doubling. We also report an increase, by more than 50, of the productivity of diploid fertile regenerated plantlets produced by colchicine supplemented medium during the cold shock pretreatment of the microspores inside the anthers. Optimization of the treatments and the anther culture procedure are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Segregation distortion at marker loci: variation during microspore embryogenesis in maize

In the present study, we analyzed the segregation distortions of markers during in vitro androgenesis in maize. This was based on four segregating populations derived from the A188×DH7 one-way-cross. These populations consisted of very young androgenetic embryos, well-developed calluses, haploid regenerated plantlets and spontaneous diploid plantlets. These structures all represented different developmental stages, from that of microspores to the regenerated plantlets. This study complemented a previous one by Murigneux et al. 1994, where distorted segregations of RFLP markers were detected in a single-seed-descent population and in a doubled-haploid population derived from the same cross. The weakly biased SSD maize genetic map was used as a reference to locate 145 AFLP loci whose allelic segregations were also analyzed in the androgenetic segregating populations. Segregation distortions were determined based on chi-square analysis (P<0.01 and P<0.001). Regions on chromosomes 2 and 8 showed distortions from the beginning of embryo formation, with large effects throughout the process. Regions on chromosomes 3, 4, 6 and 10 could control callus formation from microspores. Other deviations of marker genotypes on chromosomes 1, 4, 6 and 10 could be associated with the regeneration phase. Moreover, the statistical method of Cheng et al. for mapping a lethal factor locus inside segments of linked distorted markers was used to estimate the position of seven partial lethal androgenetic factors on chromosomes 1, 2, 8 and 10. These factors could represent selective genes actively involved in maize androgenesis. Received: 31 July 2000 / Accepted: 2 January 2001     

Genetic improvement of anther culture response in maize: relationships with molecular, Mendelian and agronomic traits

 Two cycles of androgenetic in vitro doubled haploid (DH) plant production and intermating were implemented in an experimental synthetic population of maize. In vitro traits, including androgenetic embryo production, the regeneration potential and the frequency of spontaneous chromosome doubling, were studied. The success of the regenerated plants to self pollinate was also observed. Impressive genetic progress is reported for all the steps of the androgenetic process including seed set. Differential genetic progress is recorded according to the trait measured. Using a set of Mendelian and molecular markers that mapped to the different maize chromosomes, we were able to characterize the variation in the genetic variability in the population. Progress in the in vitro response was not found to be associated with any noticeable decline in global genetic variability. In addition, the QTL chromosomic regions tested, which were involved in androgenetic response, were not found to be subjected to a strong variation during the breeding experiment. Some phenotypical and morphological traits were also evaluated, and these showed that there was no depreciation effect in the agronomic value of the population. DH plant production and intermating the regenerated plants may be considered for the introduction and use of androgenesis in material which responds poorly. Received: 3 October 1997 / Accepted: 25 November 1997