Targeted mapping of a sugarcane rust resistance gene (Bru1) using bulked segregant analysis and AFLP markers.

The presence of a major resistance gene (Bru1) for brown rust in the sugarcane cultivar R570 (2n about 115) was confirmed by analyzing segregation of rust resistance in a large population of 658 individuals, derived from selfing of clone R570. A subset of this population was analyzed with AFLP and bulked segregant analysis (BSA) to develop a detailed genetic map around the resistance gene. Four hundred and forty three primer pairs were used resulting in the identification of eight AFLP markers surrounding the resistance gene in an interval of 10 cM, with the closest markers located at 1.9 and 2.2 cM on each side of the gene. Efficiency of the AFLP/BSA applied to the complex polyploid genome of sugarcane is discussed, as well as the potential of the newly identified AFLP markers for developing a map-based cloning approach exploiting, synteny conservation with sorghum.

Resistance of Sugarcane Cultivar R 570 to Puccinia melanocephala Isolatesfrom Different Geographic Locations.

Two different inoculation techniques were investigated before studying the reaction of the major rust resistance gene of sugarcane cultivar R 570 against isolates of Puccinia melanocephala from different geographic locations. Cultivar R 570 exhibited severe rust symptoms when in vitro plantlets were inoculated with a rust isolate from Réunion Island, but a good correlation with field resistance was observed when detached leaves were inoculated with the pathogen. This latter technique was then used to inoculate R 570 and a sample of its self progeny with rust isolates from Brazil, Colombia, Florida (three isolates), Guadeloupe, Réunion Island, and Zimbabwe. R 570 was resistant to all isolates of P. melanocephala, and the segregation of resistance in the progeny did not change with the isolates, suggesting that a single gene, or a single chromosomic region, was involved in the resistance against all tested isolates. This major resistance gene has, therefore, potential value to improve resistance to rust in various geographic regions.