Résumé
Brown rust, caused by
Puccinia
melanocephala
, has had devastating effects on sugarcane (
Saccharum
spp.) breeding programs and commercial production. The discovery of
Bru
1, a major gene conferring resistance to brown rust, represented a substantial breakthrough. Markers for
Bru
1 are the first available for sugarcane molecular breeding. The contribution of
Bru
1 towards brown rust resistance in the Canal Point (CP) sugarcane breeding program was determined as a means of directing future breeding strategies.
Bru
1 was detected in 285 of 1,072 (27 %) clones used for crossing; this germplasm represents the genetic base for cultivar development in Florida. The frequency of
Bru
1 was greatest in CP clones (42 %) and lowest among Louisiana clones (6 %).
Bru
1 was not detected in clones with year assignments before 1953. However,
Bru
1 frequency increased from 15 % (assignments 1975–1985) to 47 % in the current decade. The increase coincided with the introduction of brown rust to Florida.
Bru
1 was detected in 155 (32 %) of 485 parental clones tested for brown rust susceptibility at two field locations. Of clones classed resistant to brown rust, 154 (59 %) contained
Bru
1, yet none of 100 susceptible clones contained the gene.
Bru
1 was detected in 667 (44 %) clones in the second clonal stage of selection, 87 % of which were free of brown rust symptoms.
Bru
1 is the predominant source of resistance in the Florida sugarcane genetic base. Efforts to identify and integrate new brown rust resistance genes must be pursued to minimize risks associated with a future breakdown in major gene resistance provided by
Bru
1.