Ultrastructural Changes in the Interaction Between Puccinia striiformis and Wheat Cultivar with Slow-Rusting Resistance

Ultrastructural changes in both pathogen and host cells in the interaction between Puccinia striiformis and wheat cultivar （Libellula） with slow-rusting resistance were observed by transmission electron microscopy. Observations revealed marked changes in ultrastructure of both pathogen and host cells. In the pathogen respect, there were many vesicles appeared in the intercellular hyphae and gradually fused into bigger vacuoles, a number of fat drops and electron-dense granules accumulated, mitochondria became swollen and some of them degraded into vesicles, and the plasmalemma of intercellular hyphae became dark. In the haustoria, the cytoplasm degraded gradually and developed a vacuole in the center, fat drops increased, the extrahaustorial matrix widened with a great amount of electron-dense fibrillar and granular materials, and most of the haustoria died with in conjunction with the disappearance of fat drops and other organelles. Structural defense of the host, including formation of cell wall apposition, collar and papilla, occurred in the host respect. Host resistance expression and cytological features occurring in the slow-rusting resistance were discussed.

Ultrastructure of Slow-Rusting Expression of Wheat to Stripe Rust

The ultrastructure of wheat cultivars with slow-rusting resistance expression to the stripe rust, Puccinia striiformis, wasstudied through TEM. The results show that slow-rusting has the same hypersensitive response characters with the lowinfection type resistance, but the mesophyll cell necrotized less in number, thereby only partially inhibiting the extensionof rust fungus, and the fungus being inhibited and necrosed slighter in degree. Apart from the occurrence ofhypersensitiveness, the response of the host cells in slow-rusting wheat cultivars to the infection of fungus also producesstructural materials associated with defense reaction, but distinctly less than that in resistant cultivar. Thus, it is suggestedthat the slow-rusting resistance might have a similar mechanism with the low infection type resistance of race specificity,but with lower intensity.

Identification and Validation of a Major Quantitative Trait Locus for Slow-rusting Resistance to Stripe Rust in Wheat

Stripe （yellow） rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks （Pst）, is one of the most important wheat （Triticum aestivum L.） diseases and causes significant yield losses. A recombinant inbred （RI） population derived from a cross between Yanzhan 1 and Xichang 76-9 cultivars was evaluated for resistance to wheat stripe rust strain CYR32 at both the seedling and adult plant stages. Four resistance quantitative trait loci （QTLs） were detected in this population, in which the major one, designated as Yrql, was mapped on chromosome 2DS. The strategy of using the Brachypodium distachyon genome, wheat expressed sequence tags and a draft DNA sequences （scaffolds） of the D-genome （Aegilops tauschfi Coss.） for the development of simple sequence repeat （SSR） markers was successfully used to identify 147 SSRs in hexaploid wheat. Of the 19 polymorphic SSRs in the RI population, 17 SSRs were mapped in the homeologous group 2 chromosomes near Yrql region and eight SSRs were genetically mapped in the 2.7 cM region of Yrql, providing abundant DNA markers for fine-mapping of Yrql and marker-assisted selection in wheat breeding program. The effectiveness of Yrql was validated in an independent population, indicating that this resistance QTL can be successfully transferred into a susceptible cultivar for improvement of stripe rust resistance.