Chromosomal location of genes encoding for resistance to septoria tritici blotch (Mycosphaerella graminicola) in substitution lines of wheat

Chromosomal location of resistance to Mycosphaerella graminicola was studied in substitution lines of resistant Triticum genotypes into the (susceptible) cultivar Chinese Spring (T. aestivum). (Moderately) resistant genotypes for which substitution lines were available were tested in a first screening. We selected a synthetic hexaploid wheat (Synthetic 6x; T. dicoccoides x T. tauschii), T. spelta and the wheat (T. aestivum) cultivars Cheyenne and Cappelle-Desprez. In a second screening the most suitable Argentinian isolates were identified. We decided to use the isolate IPO 92067 (all sets of substitution lines), IPO 93014 (substitution lines of Synthetic 6x, Cappelle-Desprez and T. spelta) and IPO 92064 (substitution lines of Cheyenne). In the final experiments, substitution lines of the selected genotypes into Chinese Spring were grown in two different environments and inoculated with the selected isolates at the seedling stage (lines of all four selected genotypes) or the adult stage (lines of Synthetic 6x and Cheyenne). Resistance was expressed as (reduction in) necrosis percentage or pycnidial coverage percentage; the two measures were highly (linearly) correlated. When tested in the seedling stage, all chromosomes seemed to carry genes effective against M. graminicola. Many genes were effective against only one isolate or in only one environment or their effects only showed in one resistance parameter. Often these effects were minor. Only chromosome 7D of Synthetic 6x was found with a major effect against both isolates tested. When tested in the adult stage, all lines but the one carrying chromosome 4B from the resistant parent seemed to show genes effective against M. graminicola. The line carrying chromosome 7D from Synthetic 6x showed a level of resistance similar to the resistant parent for isolate IPO 92067, but not for isolate IPO 93014. Major genes, effective against both isolates, were also found on chromosomes 5A and 5D from Synthetic 6x. Lines carrying chromosome 1B, 5D or 6D from Cheyenne showed major effects against isolate IPO 92064. For both necrosis percentage and pycnidial coverage percentage, highly significant linear correlations were found between resistance in the seedling stage and resistance in the adult stage. However, the variance accounted for was only small (20¿24%; n = 184)

Influence of plant height and heading date on the expression of the resistance to Septoria tritici blotch in near isogenic lines of wheat

The effects of plant height and heading date on the expression of the resistance to Septoria tritici blotch, which is caused by the fungus Mycosphaerella graminicola (Fuckel) Schroeter, in Cohn (Septoria tritici Rob. ex Desm.), were investigated in wheat (Triticum aestivum L.) near isogenic lines in the Mercia and Cappelle-Desprez background and differing in dwarfing genes (Rht) or in genes for insensitivity to photoperiod (Ppd). The experimental design was a randomized block design with four replications conducted over 2 yr. Necrosis percentage at boot (growth stage GS 49), milk (GS 73), and dough stage (GS 85); area under disease progress curve (AUDPC); plant height; and heading date were recorded. The shortest lines, Mercia Rht12, Mercia Rht3, and Cappelle-Desprez Rht3, showed higher necrosis percentage and AUDPC values than their respective controls. Mercia lines with Ppd1 and Cappelle-Desprez Ppd1 and Ppd2, the earliest heading lines, showed lower necrosis values than their respective controls. Multiple regression models including plant height and heading date accounted for 44.3 to 99.1% of the variation in necrosis percentage and were statistically significant in most cases. Reduced plant height was usually associated with more necrosis because of the highest necrosis percentage of the shortest lines. Late heading date was not associated or positively associated with more necrosis because of favorable weather conditions for late heading cultivars. When weather variables were included in the models, several of them replaced days to heading, suggesting that the positive relationship between necrosis and days to heading was caused by environmental conditions. Corrections of disease severity values for heading date and plant height should be done in breeding programs when selecting for resistance

Effects of temperature on the establishment potential of the predatory mite Amblyseius californicus McGregor (Acari: Phytoseiidae) in the UK

Amblyseius californicus was introduced into the UK in the early 1990s as a biocontrol agent against glasshouse red spider mite Tetranychus urticae. This study investigated the effects of temperature on the establishment potential of A. californicus in the UK in the light of recent reports of their successful overwintering outside of glasshouse environments. The developmental thresholds were 9.9 and 8.6 degreesC respectively using simple and weighted linear regression. Using the day-degree requirement per generation calculated by weighted regression (143 day-degrees) in combination with climate data, it was estimated that up to seven generations would be possible annually outdoors in the UK. Non-diapausing adult females froze at -22 degreesC, with 100% mortality after reaching their freezing temperature. Up to 90% of mites died before freezing after short exposures to low temperatures. Significant acclimation responses occurred; 90% of acclimated individuals survived 26 days exposure at 0 degreesC and 11 days at -5 degreesC (acclimated mites were reared at 19 degreesC, 6L:18D followed by I week at 10 degreesC, 12L:12D). Non-diapausing adult females survived over 3 months outdoors in winter under sheltered conditions and oviposition was observed. The experimental protocol used in this study is discussed as a pre-release screen for the establishment potential of other Amblyseius species, and similar non-native biocontrol agents

Inheritance of resistance of wheat to eyespot at the adult stage

International audienc

Chromosomal location of resistance to Septoria tritici in seedlings of a synthetic hexaploid wheat, Triticum spelta and two cultivars of Triticum aestivum

Chromosomal location of resistance to two virulent Argentinean isolatesofSeptoria triticiwas studied in two wheat (Triticum aestivumL.) cultivars (Cappelle-Desprez & Cheyenne), a synthetic hexaploid(Synthetic 6x) andTriticum speltain seedlings. Substitution lines of these(resistant or moderately resistant) genotypes into (susceptible)ChineseSpringwere selected from a previous screening. For Synthetic 6x,resistance was clearly located in chromosome 7D. Chinese Spring with the7D chromosome substituted by Synthetic 6x showed almost completeresistance, similar to the level of Synthetic 6x. For the substitutions withCappelle-Desprez, Cheyenne, andT.speltathere were no lines with abehaviour similar to the resistant parent. However, some substitutions weremore resistant than the susceptible parent suggesting that severalchromosomes could be involved in the resistance of these genotypes toSeptoria leaf blotch