Outbreak of Wheat Yellow Rust disease under Moroccan conditions during 2016-2017 cropping season
Wheat rusts, notably yellow rust, are amongst the most damaging diseases on wheat in Morocco. The objective of this survey was to assess the incidence and severity of wheat rust diseases across Morocco. The survey was carried out during April-May 2017 where growth stage of wheat ranged from anthesis to physiological maturity. The severity and response rating for the adult plant field reaction to rusts were based on the modified Cobb scale. A total of 117 bread wheat fields were inspected. The survey revealed that the most prevalent disease was yellow rust (96 out of 117 fields). Leaf rust, SLD (Septoria Like Diseases) and to some extent root rot complex were less prevalent. Leaf rust was only observed in 8 out of 117 inspected fields and exhibited low severity. Stem rust was observed in only one field. Following the drought of 2016, the 2017 growing season was an epidemic year for yellow rust in Morocco. It was detected across all regions and 50% of inspected fields were highly infected. Those that were lightly or not infected were sprayed with fungicides up to two times. Almost all commercial bread wheat cultivars in Morocco are highly susceptible to yellow rust. Appearance of new virulent races is leading to the breakdown of resistance in major cultivars e.g., Arrihan, which had very few pustules of yellow rust in 2013 was highly susceptible in the last three years. Samples of yellow rust from 2016 revealed a new virulent race in all samples, temporarily designated Pst (new) [virulence pattern: [Yr-,2,3,-,-,6,7,8,9,-,-,17,-,25,-,32,Sp,AvS,-]. Thirty-four samples submitted to GRRC in 2017 were all of the same genotype, identical to the new race already detected in 2016. The results demonstrate that surveillance and genotyping/race phenotyping of samples may be important for early-warning and anticipatory breeding strategies.