Occurrence and Impact of a New Leaf Rust Race on Durum Wheat in Northwestern Mexico from 2001 to 2003

Abstract

Durum wheat (Triticum turgidum var. durum) is the main irrigated winter crop in northwestern Mexico. Historically, leaf rust, caused by Puccinia triticina, had not induced significant losses to durum production in the area until 2001. That year, a new race, designated as BBG/BN, was detected that caused the most widely grown cultivar, Altar C84, which had remained resistant for 16 years, to become susceptible. Other recommended cultivars also became either moderately susceptible or susceptible. Detailed characterization of avirulence/virulence characteristics on Lr genes indicated that this race possibly did not evolve from the older races, but may have been introduced. Rust epidemics during the 2000-2001, 2001-2002, and 2002-2003 crop seasons have caused estimated losses of at least US$32 million. Although a majority of cultivars from 31 different countries, including the United States and Canada, and most of CIMMYT's durum wheat germ plasm were highly susceptible, diversity for both race-specific resistance and moderate levels of slow rusting resistance were identified. Jupare C2001, a resistant cultivar released in 2001, showed high levels of resistance and negligible losses in grain yield in a trial where Altar C84 suffered over 27% losses.

Molecular characterization of durum and common wheat recombinant lines carrying leaf rust resistance (Lr19) and yellow pigment (Y) genes from Lophopyrum ponticum

“…However, results from this study showed that Lr19 is still effective against the new leaf rust race detected in Mexico and California (Singh et al 2004), which is highly virulent to durum wheat. Introgression of Lr19 into durum wheat germplasm might still be a valuable breeding objective for durum breeding programs in this region, at least in the near future.…”

“…Isolates CA 2.1 and MX 11.1 are highly virulent to durum wheat cultivars and are classified as BBB-10, 14b, 20, 23, 33, 41 (Long and Kolmer 1989), based on virulence to isogenic lines of Thatcher wheat, which differ for single-leaf rust resistance genes. These isolates belong to the same race collected in Mexico and that was previously described by Singh et al (2004). This new leaf rust race is virulent on most of the current California durum wheat cultivars, including the backcross recurrent parent UC1113.…”

“…Virulence tests of isolates from 243 fields determined that the same race was present on all the susceptible durum wheat analyzed during these three years (Singh et al 2004). A major concern about this new race is that most of the durum cultivars from the United States, Canada, and several other countries are highly susceptible.…”

“…The new durum leaf rust race that appeared in northwestern Mexico has caused estimated loses of US $32 million between 2001(Singh et al 2004. Virulence tests of isolates from 243 fields determined that the same race was present on all the susceptible durum wheat analyzed during these three years (Singh et al 2004).…”

“…A major concern about this new race is that most of the durum cultivars from the United States, Canada, and several other countries are highly susceptible. In addition, most of the CIMMYT elite durum germplasm (93% of 1,160 accessions) were also highly susceptible to this leaf rust race (Singh et al 2004).…”