Susceptibility of winter Triticale cultivars to Rhizoctonia cerealis (sharp eyespot) and R. solani

In the field study period from 2006 to 2010, the incidence and severity of sharp eyespot caused by Rhizoctonia were recorded on 36 cultivars of triticale at the milk ripe growth stage. Four localities in north-central Poland were included: Chrząstowo, Dębina, Kończewice and Minikowo. The susceptibility of the seedlings of 30 cultivars of triticale to R. cerealis (AG-D subgroup I) and R. solani (AG-5) was studied in the laboratory. There was much variation in incidence and severity of sharp eyespot between years and locations. The disease was most intense at Chrząstowo. At this location, the mean percentage of diseased stems on 28 cultivars was 2.6-35.7 (-55.0), and the mean disease index was 0.7-15.6 (-24.5), with the lowest and highest values in 2008 and 2009, respectively. At Minikowo, the disease was least intense. At this location, the mean percentage of diseased stems on 23 cultivars was 1.0-4.6 (-18.0), and the mean disease index was 0.3-1.4 (-6.3), with the lowest and highest values in 2006 and 2007, respectively. The cultivars with least intense disease were Tulus and Atletico (Chrząstowo), Grenado and Zorro (Dębina), Krakowiak and Tornado (Kończewice), and Woltario and Constans (Minikowo). The cultivars with most intense disease were Alekto (Chrząstowo), Baltiko (Dębina), Pawo (Kończewice) and Borwo (Minikowo). Mostly R. cerealis was isolated from the diseased stems; R. solani was isolated only sporadically. There was a wide variation in the susceptibility of triticale cultivars to Rhizoctonia. Most triticale seedlings inoculated with R. cerealis produced symptoms typical of sharp eyespot. Seedlings inoculated with R. solani formed extended lesions with no defined borders. Most symptoms developed on coleoptiles, with less symptoms on the leaves and the least on the roots. There was much variation in susceptibility of triticale cultivars to both Rhizoctonia species. Cultivars were grouped into six categories according to the intensity of seedling infection. Categories 1, 2 and 3, representing low, moderate and high susceptibility to R. cerealis, included 17, 10 and 3 cultivars, respectively. Categories 4, 5 and 6, representing low, moderate and high susceptibility to R. solani, included 3, 12 and 15 cultivars, respectively. Cultivars Baltiko and Zorro had low, and cv. Cultivo had high susceptibility to both Rhizoctonia species. No cultivar was resistant to Rhizoctonia. There was a positive correlation between infection by R. cerealis and R. solani. Infection of coleoptiles by R. cerealis or R. solani was significantly correlated with infection of leaves. No correlation between intensity of sharp eyespot on triticale plants in the field and on seedlings in controlled conditions was found.