Seeding And Adult-Plant Resistance To Pomdery Mildew In Bread Wheat And QTL Analysis Of Pomdery Mildew Resistance In Bainong 64

Powdery mildew is one of the major diseases in wheat. Resistant cultivars offer an effective, economical, and environmentally safe way to control powdery mildew. The adult-plant resistance (APR) shows moderately resistant to powdery mildew at adult plant stage by retarding infection, growth and reproduction of the pathogen, and more durable than race-specific resistance. The objectives of this study were to evaluate the effectiveness of some Pm-genes in China, identify genes that confer seedling resistance to powdery mildew in 35 Chinese bread wheat cultivars and 85 introductions used by breeding programs in China, and evaluate APR of 76 cultivars in the field. A genetic linkage map was constructed by using 218 F2:3 lines derived from the cross between a APR cultivar Bainong 64 and a powdery mildew susceptible cultivar Jingshuang16 and QTL analysis was performed. The results were presented below: 1. Genotypes carrying Pm12 and Pm16 were highly resistant to all powdery mildew isolates tested. Genotypes carrying Pm20, Pm2+6, Pm2+mld, Pm2+Ta, Pm4a, Pm4b and Pm4+8 were also effective to powdery mildew, whereas, those carrying Pm1, Pm3e, Pm5, Pm7, Pm3a, Pm3d, Pm3f, Pm6, Pm8 and Pm17 were susceptible to most powdery mildew isolates tested. 2. Totally, 42 out of 120 tested wheat cultivars and lines carried one or more resistance genes to powdery mildew. Thirty cultivars contained unknown Pm genes. There were 26 cultivars carrying Pm8 and its complex. Pm8 was the most common resistance gene, followed by Pm3d, Pm6, Pm4b and Pm2. 3.　The　frequency　of　1B/1R　translocation　was　48%　in　the　cultivars　tested.　All　genotypes　carrying　Pm8　were　1B/1R　translocation.　However,　only　29.4%　and　51.2　of　1B/1R　translocation　lines　showed　the　Pm8　reaction　pattern　in　Chinese　cultivars　and　introduction　lines,　respectively.　4.　Twenty-five　cultivars　and　lines　showed　APR　to　powdery　mildew　according　to　cluster　analysis　based　on　R1　(rate　of　ID),　R2　(rate　of　severity　on　penultimate　leaves),　AUDPC　(area　under　the　disease　progress　curve),　DI　(disease　index)　and　MDS(maximum　disease　severity　on　penultimate)　and　LSD　analysis,　in　combination　with　the　postulation　of　Pm　genes　at　seedling　stage.　Thirteen　lines　were　typical　of　APR　that　were　susceptible　to　all　powdery　mildew　isolates　tested　at　seeding　stage　but　moderately　resistant　to　powdery　mildew　in　adult　plants.　Twelve　lines　in　which　major-gene　resistance　has　been　overcome　and　showed　moderately　resistant　to　powdery　mildew　in　adult　plant.　5.　APR　lines　were　characterized　with　lower　AUDPC　and　MSD　(between　11.9　to　99.7　and　1.0%　to　8.0%,　respectively)　in　comparsion　with　highly　susceptible　check　cultivar　Jingshuang　16　(AUDPC　and　MDS　was　913.5　and　95.0%,　respectively).　They　showed　little　conidia　production,　small　colony　size,　and　low　disease　severity.　Results　for　APR　identification　based　on　MDS　were　siminar　to　the　combined　cluster　analysis　based　on　R1,　R2,　AUDPC,　DI　and　MDS.　Therefore,　MDS　was　a　simple　parameter　for　APR　identification.　6.　A　total　of　158　markers　including　100　SSRs　and　58　AFLPs　were　mapped　on　20　linkage　groups　covering　3114　cM,　with　an　average　distance　of　19.7　cM.　Twelve　SSR　markers　unmapped　previously　were　placed　onto　the　genetic　linkage　map.　7.　Five　QTL　named　QPm-2B,　QPm-2D,　QPm-5A,　QPm-7A　and　QPm-7D,　respectively　were　associated　with　APR.　The　QTL　QPm-2B,　QPm-2D　and　QPm-7D　explained　20%~21.3%,　15.5%~18%　and　27.7%~28%　of　phenotypic　variance,　respectively.　Two　minor　QTL　QPm-5A　and　QPm-7A　accounted　for　7.5%~10.7%　and　5.4%~6%　of　phenotypic　variance,　respectively.　QTL　associated　with　APR　showed　mainly　additive　effect.　The　negative　additive　value　indicated　that　the　QTL　was　from　Bainong　64　conferring　resistance　to　powdery　mildew.