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CROP BREEDING & GENETICS

Marker-Facilitated Selection for a Major QTL Associated with Root Rot Resistance in Snap Bean (Phaseolus vulgaris L.)

Dep. of Horticulture, Univ. of Wisconsin, 1575 Linden Drive, Madison, WI 53706

^* Corresponding author (nienhuis{at}wisc.edu).

The use of molecular markers associated with quantitative trait loci (QTL) can improve the efficiency of breeding programs. In previous research, randomly amplified polymorphic DNA marker alleles AD9.950⁺ derived from the root rot resistant snap bean (Phaseolus vulgaris L.) cultivar Puebla 152 and S18.1500^– derived from the susceptible cultivar Eagle were linked in repulsion phase and mapped to the same locus. The alleles were associated with a major QTL that explained 25 and 49% of the variation for the root rot complex for plant vigor and plant biomass, respectively. The objective of the current study was to estimate the average effect of allelic substitution in BC₁F₃ families that were indirectly selected for root rot resistance or susceptibility based on the AD9.950 and S18.1500 marker phenotypes. Four BC₁F₃ inbred backcross populations were developed by crossing two susceptible snap bean cultivars (Hercules and Nicelo) with two root rot resistant donor inbred lines. When evaluated in a field with high levels of root rot inocula, families carrying the AD9.950⁺/S18.1500^– marker alleles had a mean plant vigor of 3.95 ± 0.96 and mean plant biomass of 25.09 ± 0.89 g plant^–1 compared with 7.01 ± 0.96 and 7.05 ± 0.90, respectively, in families that lacked these alleles. Realized gains in plant biomass and plant vigor validate the effectiveness of substituting the AD9.950⁺ and the S18.1500^– marker alleles to introgress root rot resistance into susceptible genetic backgrounds.

Abbreviations: EEP, (Eagle x Puebla) x Eagle • EPH, (Eagle x Puebla) x Hystyle • H, heterozygous • MAS, marker-assisted selection • PCR, polymerase chain reaction • QTL, quantitative trait locus/loci • R, resistant • RAPD, randomly amplified polymorphic DNA • REML, restricted maximum likelihood • S, susceptible