Termos de indexação: feijão, nutrição de plantas, micronutrientes, nitrogênio.

No abstract

The pathogenic variability of the fungus Colletotrichum lindemuthianum represents an obstacle for the creation of resistant common bean (Phaseolus vulgaris L.) varieties. Gene pyramiding is an alternative strategy for the development of varieties with durable resistance. RAPD markers have been proposed as a means to facilitate pyramiding of resistance genes without the need for multiple inoculations of the pathogens. The main aims of this work were to define the inheritance pattern of resistance present in common bean cultivar AB 136 in segregating populations derived from crosses with cultivar Rudá (susceptible to most C. lindemuthianum races) and to identify RAPD markers linked to anthracnose resistance. The two progenitors, populations F1 and F2, F2:3 families and backcross-derived plants were inoculated with race 89 of C. lindemuthianum under environmentally controlled greenhouse conditions. The results indicate that a single dominant gene, Co-6, controls common bean resistance to this race, giving a segregation ratio between resistant and susceptible plants of 3:1 in the F2, 1:0 in the backcrosses to AB 136 and 1:1 in the backcross to Rudá. The segregation ratio of F2:3 families derived from F2 resistant plants was 1:2 (homozygous to heterozygous resistant). Molecular marker analyses in the F2 population identified a DNA band of approximately 940 base pairs (OPAZ20(940)), linked in coupling phase at 7.1 cM of the Co-6 gene. This marker is being used in our backcross breeding program to develop Rudá-derived common bean cultivars resistant to anthracnose and adapted to central Brazil.
A antracnose do feijoeiro, causada por Colletotrichum lindemuthianum, é uma doença que ocasiona severas perdas, estando amplamente distribuída no Brasil. Trabalhos anteriores têm demonstrado que o cultivar AB 136, possuidor do gene Co-6, é uma importante fonte de resistência à antracnose no Brasil, uma vez que todos os patótipos identificados no país até o momento são incompatíveis com esse cultivar. O objetivo deste trabalho foi identificar um marcador RAPD ligado ao gene de resistência Co-6 presente no cultivar AB 136. Para este fim, foi utilizada uma população do cruzamento entre o progenitor Rudá, suscetível à raça 89 de C. lindemuthianum, e o cultivar AB 136. Nas populações F2 e F3 deste cruzamento observou-se uma segregação de 3 plantas resistentes para 1 suscetível, e 1 planta homozigota para 2 heterozigotas, respectivamente, sugerindo que a resistência é determinada pela ação de um único gene. Na população F2, foi identificado um marcador, de aproximadamente 940 pb (OPAZ20), ligado em fase de acoplamento a 7,1 cM do gene Co-6. Este marcador está sendo utilizado em nosso programa de melhoramento para desenvolver cultivares de feijoeiro derivados de Rudá resistentes à antracnose e adaptados ao Brasil Central

New cultivars of the common bean (Phaseolus vulgaris) with durable resistance to anthracnose can be developed by pyramiding major resistance genes using marker-assisted selection. To this end, it is necessary to identify sources of resistance and molecular markers tightly linked to the resistance genes. The objectives of this work were to study the inheritance of resistance to anthracnose in the cultivar TO (carrying the Co-4 gene), to identify random amplified polymorphic DNA (RAPD) markers linked to Co-4, and to introgress this gene in the cultivar Rudá. Populations F(1), F(2), F(2:3), BC(1)s, and BC(1)r from the cross Rudá x TO were inoculated with race 65 of Colletotrichum lindemuthianum, causal agent of bean anthracnose. The phenotypic ratios (resistant/susceptible) were 3:1 in the F(2) population, 1:1 in the BC(1)s, and 1:0 in the BC(1)r, confirming that resistance to anthracnose in the cultivar TO was monogenic and dominant. Six RAPD markers linked to the Co-4 gene were identified, four in the coupling phase: OPY20(830C) (0.0 centimorgan [cM]), OPC08(900C) (9.7 cM), OPI16(850C) (14.3 cM), and OPJ01(1,380C) (18.1 cM); and two in the repulsion phase: OPB03(1,800T) (3.7 cM) and OPA18(830T) (17.4 cM). OPY20(830C) and OPB03(1,800T), used in association as a codominant pair, allowed the identification of the three genotypic classes with a high degree of confidence. Marker OPY20(830C), which is tightly linked to Co-4, is being used to assist in breeding for resistance to anthracnose.