Fernando José Correa Victoria

Comparison of rice lines derived through anther culture and the pedigree method in relation to blast (Pyricularia grisea Sacc.) resistance

Crosses were made between Fanny (highly susceptible to blast) and 11 cultivars differing in blast resistance. Using the pedigree method (PM) segregating generations were evaluated and selected for blast resistance. Via anther culture (AC), doubled-haploids were obtained from F1 plants and from F2 blast-susceptible plants. Pedigree and anther culture-derived lines were planted together and evaluated for blast resistance under rainfed conditions at the Santa Rosa Experiment Station, Villavicencio, Colombia. The principal objective was to compare PM and AC in terms of their efficiency in producing rice lines resistant to blast. Results of a stratified analysis showed an association between method and blast resistance. Results of the logit-model analysis showed that AC produced a significantly (P=0.0001) higher proportion of lines with initial blast resistance (leaf- and neck-blast reaction ≤4) than did PM across all cross types. Stable blast resistance was assessed based on field performance over 3 years. AC was superior to PM in generating stable resistance for only some cross types. Consequently, with a few exceptions, AC can be used as effectively as PM to develop rice cultivars resistant to blast, with savings in time and labor. Additionally, blast-resistant lines were obtained either by the pedigree method or by anther culture from crosses between blast-susceptible cultivars (Fanny/CICA4 and Fanny/Colombial). This excludes somaclonal variation as a possible mechanism responsible for this resistance and suggests that a recombination of minor genes could have occurred and was fixed through either method. However, the stability of the resistance was greater in pedigree-derived lines. The implications of these findings for rice blast-resistance breeding are discussed.

Breeding Rice Cultivars with Durable Blast Resistance in Colombia

Rice blast disease (Pyricularia grisea) is the most important rice production constraint in Latin America. One strategy to improve the durability of blast resistance is to pyramid resistance genes. To do this, we have conducted extensive studies on the genetic structure of blast pathogen populations in Colombia and Latin America; determined composition, distribution and frequency of the avirulences that underlie race variation; identified and incorporated resistance gene combinations into commercial rice cultivars using genetic markers; and continuously evaluated and selected breeding lines under high disease pressure and pathogen diversity. Rice differentials with known blast resistance genes have been used to study avirulence gene composition and frequency in the blast pathogen and to identify relevant resistance genes. The combination of the blast resistance genes (Pi-1, Pi-2, Pi-33) for which their corresponding avirulence genes are highly conserved in blast pathogen populations in Colombia has proven to confer stable blast resistance after several years of testing under high blast pressure in the field and greenhouse inoculations. Additional pathogen characterization of spontaneous mutations of the blast pathogen allowed the identification of the blast resistance genes Pi-b, Pi-9 and Pi-ta 2, which will be needed for protecting rice cultivars from potential future changes in the avirulence/virulence genes in the blast pathogen population. Microsatellite markers highly linked to these blast resistance genes have been found from public databases facilitating the introgression and pyramiding of each of these six blast resistance genes into Latin American rice cultivars and elite lines derived from rice breeding programs aiming at developing rice cultivars with durable blast resistance.