The Effect of two Bioclimatic Stages on the Area Under Disease Progress Curve (AUDPC) to assess reaction of durum wheat varieties to Zymoseptoria tritici in Tunisia

Abstract

Zymoseptoria tritici >is currently one of the most serious foliar diseases of durum wheat (Triticum turgidum var. durum L.) in different regions of Tunisia characterized by favorable temperature and high humidity during growing season. Four wheat genotypes with different resistance levels were evaluated in natural conditions for their reaction to Z. tritici attack during 2014-2015 season at two locations in North Western Tunisia representing sub-humid (Beja) and semi-arid (Oued Mliz) climatic conditions. The assessments of Septoria tritici blotch (STB) symptoms were made using double digit scale at four different crop stages, and the different agronomic parameters (Straw height (SH), Ear tiller number/plant (ET), Aerial biomass/plant (AB) and the thousand Kernel Weight (TKW)) were measured. Disease rating was eventually visually recorded by using Area under Disease Progress Curve (AUDPC) for each wheat cultivar evaluated. There was a relationship between genotype susceptibility and AUDPC since the most susceptible wheat cultivar (Karim) exhibited higher AUDPC values in both locations. Preliminary results indicated that the highest AUDPC values were recorded in semi-arid climatic condition for all genotypes. However, disease severity increased by 28% for Karim and by 65% for Salim, between Oued Mliz and Oued Beja locations. The decrease in thousand kernel weights was associated with important disease severity level for each durum wheat cultivar in both locations. Similarly, AUDPC were negatively and highly correlated with SH, ET and AB. These results suggest that the AUDPC can be an efficient tool to evaluate the epidemic development of foliar pathogen considering each genotype susceptibility in different bioclimatic stages. The contribution of the approach described above for general epidemiology showed that the season fluctuation and bioclimatic regions may play an important role in shaping variability of disease severity and incidence in the field.