تحديد بعض عوامل شراسة و وبائية مرض تبقع أوارق القمح السبتوري

Abstract EN

Wheat Septoria leaf blotch caused by Zymoseptoria tritici is considered to be one of the most important fungal diseases on wheat worldwide, with around 50% yield losses.

Although the disease appears every year in most wheat fields in Syria, there are few studies conducted on it in this country.

The objective of this study was to better understand the relationship between Z.

tritici isolates morphological and colonies properties and their virulence.

The results obtained showed that 66% of the fields were infected with this disease during 2014 growing season.

Reaction types varied in planted cultivars between resistant (Cham7 and Cham9), moderately resistant (Cham5, Acsad 65 and Cham 4), and very susceptible (Cham 1 and Doma 1).

When 27 Z.

tritici isolates were studied for their biological characters, they varied in colony color, and their ability to change their color to black when grown on PDA medium.

Conidial spores formed on PDA were different in size and shape, and some of them were not divided.

There was a high negative correlation (r=-0.92) between length of incubation period and period required to change colony color to black, and high positive correlation (r=0.93) between period to change color to black and the percentage of leaf area covered with lesions.

Isolates were divided into three virulence levels; virulent isolates (ZTB 5, 10, 13) which attacked more than 60% of leaf area, and needed 11days to end incubation period, weakly virulent isolates (ZTB 26, 2, 19, 3) with long incubation period of 18 days, and the rest of the isolates being moderately virulent.

Cluster analysis of 27 isolates of Z.

tritici grouped the isolates in two major groups; the first one included 9 virulent isolates distributed into two subgroups, differentiated by the shape of conidial spores.

The isolates with moderate and weak virulence were in the second main group, and were divided into many sub-groups with undefined relationship among them.

These results showed that digital image analysis in studying the percentage of leaf area covered by lesions (PLACL) provides a powerful tool for measuring differences in virulence among isolates of Z.

tritici.

Furthermore, the study showed that the period required for changing colony color to black on PDA medium can be considered an important indicator for Z.

tritici virulenc