Phenotypic and molecular genetic characterization indicate no major race‐specific interactions between Xanthomonas translucens pv. graminis and Lolium multiflorum

Abstract

Bacterial wilt of forage grasses, caused by the pathogen Xanthomonas translucens pv. graminis (Xtg), is a major disease of forage grasses such as Italian ryegrass (Lolium multiflorum). The plant genotype-bacterial isolate interaction was analysed to elucidate the existence of race-specific responses and to assist the identification of plant disease resistance genes. In a greenhouse experiment, 62 selected plant genotypes were artificially inoculated with six different bacterial isolates. Significant differences in resistance were observed among L. multiflorum genotypes (P < 0AE001) and in virulence (intensity of disease symptoms) among Xtg isolates (P < 0AE001) using the area under the disease progress curve (AUDPC). No significant genotype-isolate interaction (P > 0AE05) could be observed using linear regression modelling. However, additive main effects and multiplicative interaction effects (AMMI) analysis revealed five genotypes which did not cluster close to the origin of the biplot, indicating specific interactions between these genotypes and some bacterial isolates. Simple sequence repeat (SSR) markers were used to identify marker-resistance associations using the same plant genotypes and bacterial isolates. The SSR marker NFA027 located on linkage group (LG) 5 was significantly associated with bacterial wilt resistance across all six bacterial isolates and explained up to 37AE4% of the total variance of AUDPC values. Neither the inoculation experiment nor the SSR analyses revealed major host genotype-pathogen isolate interactions, thus suggesting that Xtg resistance, observed so far, is effective across a broad range of different bacterial isolates and plant genotypes.

The noncanonical type III secretion system of Xanthomonas translucens pv. graminis is essential for forage grass infection

“…In a needle inoculation experiment using resistant L. multiflorum genotypes and the wild‐type Xtg 29 isolate, we failed to observe HR symptoms (data not shown). The lack of HR could be a further explanation for the absence of race specificity reported previously for the interaction of different Xtg isolates with Italian ryegrass genotypes (Wichmann et al ., ). However, this needs to be clarified in further studies targeting directly the translocation of effector proteins into the host cell using immunochemical approaches.…”

Breeding for Resistance to Bacterial Wilt in Ryegrass: Insights into the Genetic Control of Plant Resistance and Pathogen Virulence

“…The major QTL on LG 4 (Studer et al 2006) could not be confirmed in the F 2 progeny derived from the initial mapping population. This may be due to insufficient linkage between the SSR markers used and the QTL and the small number of parental alleles observed in the investigated individuals (Wichmann et al 2011b). Neither the inoculation experiment nor the SSR analyses revealed major host genotype-pathogen isolate interactions, thus suggesting that Xtg resistance, so far observed, is effective across a broad range of different bacterial isolates and plant genotypes.…”

“…Phenotypic traits that result in the identification of one single QTL explaining such a high percentage of the total observed phenotypic variance have often been shown to be controlled by one or only a few major R-genes (Mutlu et al 2006). In order to investigate whether Xtg resistance was based on a major, race-specific resistance gene, 62 selected plant genotypes were artificially inoculated in the greenhouse with six different bacterial isolates (Wichmann et al 2011b). Significant differences in resistance among L. multiflorum genotypes (p < 0.001) and in virulence among Xtg isolates (p < 0.001) were observed using the area under the disease progress curve (AUDPC).…”

Comparative genomics of host adaptive traits in Xanthomonas translucens pv. graminis

“…All six Xtg strains listed in Table 1 were verified for pathogenicity on the Italian ryegrass ( Lolium multiflorum ) genotype LmK-01 [43] using four weeks old, clonally propagated plants with five to ten tillers each. The bacteria were grown over night in liquid medium containing 2% ( w / v ) glucose and 0.5% ( w / v ) yeast extract at 28 °C and 200 rpm.…”

“…Per treatment, four pots with one plant each were inoculated. Assessment of symptoms development was performed 28 days post inoculation (dpi) and was based on a scoring system of nine indices representing disease severity in ascending order from no symptoms (1), over quantitative increasing wilting symptoms on leaves and tillers to finally dead plants (9) [43]. Analysis of variance and predefined contrasts implemented in R statistical software [44] were used to test for significant differences between the control treatment and the bacterial strains.…”