Genetic Variation for Virulence and Resistance in the Wheat-Mycosphaerella graminicola Pathosystem III. Comparative Seedling and Adult Plant Experiments

Abstract

Fourteen Dutch Mycosphaerella graminicola isolates were studied for their virulence to 22 wheat cultivars in the seedling stage in an experiment set up as a completely randomized block design with three repetitions. Isolate x cultivar interactions were highly significant. Cluster analyses were applied to select three isolates with significantly different virulence characteristics for both disease parameters. These were retested in the seedling stage and used to inoculate two field experiments that were planted according to a split plot design in 1992 and 1995. Overhead inoculations were conducted after flowering to avoid the effects of plant height; hence, these experiments were intended as monocyclic tests for virulence differences between the isolates. Significant isolate x cultivar interactions were detected in each experiment, demonstrating specificity in the wheat-M. graminicola pathosystem in the adult plant stage under field conditions. The reproducibility of the adult plant data was high. Genetic differences among the isolates were additionally demonstrated by randomly amplified polymorphic DNA (RAPD) patterns, which also showed that no significant contamination of the inoculated plots with the natural M. graminicola population had occurred. Rank correlations between seedling and adult plant data were significant for M. graminicola isolates IPO323 and IPO290, but not for isolate IPO001. Hence, evaluation of resistance and virulence may require seedling, as well as adult plant, tests.

Fusion of two divergent fungal individuals led to the recent emergence of a unique widespread pathogen species

“…Experimental inoculation of both Z. tritici and Z. pseudotritici on different host species including wheat, Elymus repens and Lolium perenne, demonstrates that both species can infect and propagate asexually on multiple hosts. Different isolates, however, show a large variability in their degree of virulence, and in both species significant differences in virulence between isolates have been observed (11,23). This suggests specialization to occur not only at the species level but also at the population level.…”

Septoria Leaf Blotch and Yellow Rust Control By: Fungicide Application Opportunity and Genetic Response of Bread Wheat Varieties

“…In Portugal only the asexual state of fungal life cycle is known; the primary and subsequent infections are caused by pycniospores (from pycnia). The symptoms of infection on wheat leaves are expressed as irregular pale brown necrotic lesions with small dark fungal bodies (pycnidia) inside (Kema et al, 1996). Minimum temperatures of 8°C and maximum temperatures between 15°C and 25°C, relative humidity higher than 80% and long periods of leaf wetness are considered as the optimal environmental conditions to disease development.…”

Aggressiveness and physiological specialization of Septoria tritici Rob. isolates

“…The USA 00005 isolate proved to be virulent on cultivars that carry the Stb1 (Bulgaria 88), Stb2 (Veranopolis), and Stb4 (Tadinia) resistance genes. Kema et al (1996b) and Kema & Van Silfhout (1997), also found differential interactions between wheat genotypes and Septoria tritici isolates. Gene-to-gene interactions between wheat genotypes and Septoria tritici isolates, suggesting the presence of a strain-specific type of resistance, were reported by McCartney et al (2002) and Brading et al (2002).…”