V. A. Ragagnin

Use of molecular markers to accelerate the breeding of common bean lines resistant to rust and anthracnose

The main goal of this work was to introduce resistance genes for rust, caused by Uromyces appendiculatus, and anthracnose, caused by Colletotrichum lindemuthianum, in an adapted common bean cultivar through marker-assisted backcrossing. DNA fingerprinting was used to select plants genetically closer to the recurrent parent which were also resistant to rust and to race 89 of C. lindemuthianum. DNA samples extracted from the resistant parent (cv. Ouro Negro), the recurrent parent (cv. Rudá), and from BC1, BC2 and BC3 resistant plants were amplified by the RAPD technique. The relative genetic distances in relation to the recurrent parent varied between 9 and 59% for BC1, 7 and 33% for BC2, and 0 and 7% for BC3 resistant plants. After only three backcrosses, five lines resistant to rust and anthracnose with, approximately, 0% genetic distance in relation to the recurrent parent were obtained. These lines underwent field yield tests in two consecutive growing seasons and three of them presented a good yield performance, surpassing in that sense their parents and most of the reference cultivars tested.

RAPD markers linked to a block of genes conferring rust resistance to the common bean

Abstract Rust, caused by the fungus Uromyces appendiculatus , may cause a significant loss to common bean ( Phaseolus vulgaris L.) yield.RAPD markers tightly linked to the resistance genes may be used in breeding programs to aid the development of rust-resistant b eancultivars. In this sense, the objective of the present work was to identify RAPD markers linked to a rust resistance gene block present inthe cultivar Ouro Negro. Two hundred and fourteen F 2 individuals from a cross between the resistant cultivar Ouro Negro and thesusceptible cultivar US Pinto 111 were inoculated with a mixture of eight races of U. appendiculatus . The segregation ratio obtainedsuggested that resistance is monogenic and dominant. Bulked segregant analysis was used in conjunction with the RAPD technique tosearch for markers linked to rust resistance genes. Two molecular markers flanking the rust resistance gene block were identifi ed, one at5.8 ± 1.6 cM (OX11 630 ) and the other at 7.7 ± 1.7 cM (OF10