Abstract
RAPD markers were used to assess the potential five inbreeding methods have to release genetic variability. These methods were employed until family selection in the F 5 generation, plus the parents Carioca and Flor de Mayo, and the test cultivar Perola. DNA was extracted from 16 plants per family for RAPD reaction. Twenty-two primers amplified DNA fragments linked to a number of grain yield loci, weight of 100 seeds, number of days to flowering, and reaction to the oidium and angular leaf spot. To estimate genetic similarities between every genotype pair in each inbreeding method 42 polymorphic bands amplified among the families and parents were used. Genetic similarities were UPGMA-clustered and grouped by multidimensional scaling. The bulk method was most efficient to release genetic variability, followed by bulk in F 2 families, SSD, bulk in F3 families, and pedigree. The bulk method created families with higher similarities close to the Carioca, which is one of the regionally most grown cultivars.
Highlights
Success in common bean breeding by hybridization depends on the trait mean and variability magnitude generated by segregant populations
Two hundred and ninety-two families were used along with their two parents, Carioca and Flor de Mayo, and a control, the Pérola cultivar, evaluated in a trial carried out by Raposo (1999). This author conducted the segregant population by different methods to the F4 generation when 100 to 121 plants were sampled randomly, the families assessed in F5 for grain yield, and the 64 most productive of each inbreeding method selected for comparison
Bulk method within F3 families, and 36 by Single Seed Descent (SSD). These numbers were obtained from the dendrograms constructed for each inbreeding method, and an example is shown in Figure 1 for the population method
Summary
Success in common bean breeding by hybridization depends on the trait mean and variability magnitude generated by segregant populations. The magnitude of this variability is determined by the parental genetic diversity as well as the selfpollinated inbreeding methods of segregant populations. The most efficient conduction for segregant population can be selected by assessing the line variability after the advance of the population over several generations. This procedure does assess the real variability, released by different conduction procedures and for each trait of interest, it has the disadvantage of requiring a lot of experimental work. An alternative is to assess the variability released by conduction procedures, which make use of genetic diversity among lines
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