Hybrid Necrosis and Resistance Levels.
Plant material is described in genotype labels and diagrams (columns 1 to 3). Hybrid necrosis symptoms are described as quantity of necrotic lesions at macroscopical and microscopical level and as retarded growth (columns 4 to 6). Resistance levels are described as relative area under disease progress curve (rAUDPC) and infection severity (IS) against B. lactucae races Bl:14 and Bl:16 at two temperatures (columns 7 to 12). Letters in common within a column indicate that the values are not significantly different (α = 0.05, Tukey honestly significant difference [HSD] procedure). N.D., not determined. a, Percentage of necrotic leaf area. Two leaf segments × three plants per genotype were examined. b, Seedling gets completely necrotic and shrivels after several days. c, Dry weight in grams from the shoots of 11-week-old plants grown in the greenhouse (n = 7). d, Relative AUDPC from YDT in climate chamber calculated from observations for infection severity at 8, 10, and 12 d after inoculation (DAI). L. sativa cv Olof was set at 1.00. e, Relative AUDPC from YDT in greenhouse calculated from observations for infection severity at 8, 9, 10, and 11 DAI. L. sativa cv Olof was set at 1.00. f, Similar results were observed in disease tests with race Bl:14 on cotyledons of these genotypes. g, Similar results were observed in four disease tests with races Bl:14 and Bl:16 on detached leaf discs from 9- and 12-week-old plants of these genotypes. h, In the climate chamber with day/night cycles of 19/12°C (block intervals) and an average temperature of 17°C. i, In the greenhouse with an average temperature of 19°C, minimal night temperature of 15°C, and the day temperature was 6 h above 24°C and 12 h above 22°C. j, Average infection severity level of downy mildew at 11 DAI on young plants (YDT) scored as percentage of leaf area showing sporangiophores. k, sat = homozygous L. sativa, sal = homozygous L. saligna, and het = heterozygous. m, graphical genotype of C6 and C9; white means L. sativa allele, and black means L. saligna allele. The C6 and C9 introgressions are 40 and 11 cM long, respectively.