Assessment of quantitative traits of aggressiveness in Mycosphaerella graminicola on adult wheat plants

Abstract

Septoria tritici blotch, caused by Mycosphaerella graminicola, is a major foliar disease of wheat. The quantitative traits of pathogenicity are not comprehensively described in this pathosystem. The objective of this study was to identify and quantify the most relevant variables to describe traits of aggressiveness. Four wheat cultivars were inoculated in a greenhouse with four isolates. Inoculation was performed on a limited surface of the two uppermost leaves of adult plants. The dynamics of chlorotic, necrotic and sporulating areas were assessed twice a week. Pycnidia were counted at the same time. A Gompertz model was fitted to the resulting curves. Parameter combinations with easily interpreted biological relevance were examined further as descriptors of aggressiveness. Within each category of descriptor, those which were the most pairwise correlated and which explained the largest part of the variance were retained: incubation and latent period, development rate of sporulating area, maximal sporulating area, pycnidial density, and sporulation capacity. Correlations between these variables were discussed, assuming they reflect biological relationships between the corresponding aggressiveness quantitative traits. It is suggested that the selected variables, providing a good measure of M. graminicola fitness, can be used to estimate quantitative resistance of wheat to septoria tritici blotch, to characterize differences among isolates within a pathogen population, and to study quantitative adaptation of the pathogen to its host and to its environment.

Seasonal Changes Drive Short-Term Selection for Fitness Traits in the Wheat Pathogen Zymoseptoria tritici

“…(i) In planta assessment. Four quantitative fitness traits of the plant-pathogen interaction were selected as the most relevant for our study, based on our previous knowledge of their impact on epidemic development (12). The maximum sporulating area (SPOmax) was estimated by the maximum percentage of the area covered by fruiting bodies (pycnidia).…”

“…Such a difference probably had no effect, since Z. tritici can usually be stored for several years in this way without any change in its ability to grow (this was the case, e.g., for Z. tritici isolates IPO323 and IPO94269, isolated in 1984 and 1994 [28]). Aqueous suspensions (10 5 conidia ml Ϫ1 ), prepared as described by Suffert et al (12), were applied using a paintbrush along 25-mm-long sections of the upper sides of the F1 and F2 leaves of each main tiller of the adult plants and along 70-mm-long sections of the upper sides of the third leaves of the seedlings. To promote infection, the inoculated plant material was enclosed for 72 h in a sealed transparent polyethylene bag moistened with distilled water.…”

“…Pathogen populations are characterized by high phenotypic plasticity with signs of thermal adaptation (10). Variation in quantitative fitness traits (also considered to be quantitative traits of pathogenicity or components of aggressiveness by plant pathologists [11]) was shown to be accurate enough to establish differences in phenotypic expression in planta (12). During the epidemic period (from late autumn to early summer in the Northern Hemisphere), pathogen populations are exposed to large seasonal changes in thermal amplitude.…”

Response of selected winter wheat cultivars to inoculation with different Mycosphaerella graminicola isolates

“…The relatively highest affection of grain number per spike by this isolate (20.8%; average: 16.0%), besides 1039 (20.2%), may indicate an early outbreak of the disease and probably a relatively shorter incubation period. Suffert et al (2013) suggested incubation and latent periods, development rate of sporulating area, maximum sporulating area, pycnidial density, and sporulation capacity as the most important aggressiveness variables. The second lowest aggressiveness was detected in 1081.…”

WHEAT Triticum L.) CULTIVARS FROM GRIN COLLECTION (USA) SELECTED FOR DURABLE RESISTANCE TO Septoria tritici AND Stagonospora nodorum BLOTCH

“…The greatest harmfulness of the disease was noted in France, Great Britain, Germany, Poland, Belgium, Czech Republic, the Netherlands, in Scandinavian countries (Norway, Sweden, and Finland), Lithuania, and Latvia [3][4][5][6][7]. Cases of Septoria blotch were recorded in North Africa (Tunisia, Algeria, Morocco, Ethiopia) and Australia, Northern Caucasia (Georgia), North America (the USA, Canada) and South America (Mexico, Argentina) [8][9][10][11][12][13][14][15].…”