Evaluation of different disease inoculation techniques for banded leaf and sheath blight disease of maize (Zea mays L.) In Sri Lanka

Banded leaf and sheath blight disease, caused by Rhizoctonia solani, is a serious disease in maize cultivation. Identification of disease resistant/tolerant germplasm/varieties is the primary and essential component of a successful breeding programme. In Sri Lanka, screening for this disease has been done by the detached leaf disk method. However, this is not practical as the leaf disks become yellow and dry before scoring. An experiment was conducted during Maha 2012/13, Yala 2013, Maha 2013/14, and Maha 2014/15 seasons at the Field Crops Research and Development Institute, Mahailluppallama, with the objective of identifying a nondestructive, accurate, and rapid screening technique for the disease using three maize varieties. Five inoculation methods, namely spraying mycelium suspension into soil, incorporation of sclerotia into soil, injecting mycelium suspension into sheath, inserting sclerotia into sheath, and the detached leaf disk method, were practiced in the first two seasons. Thereafter, four inoculation methods, namely inserting sclerotia into the sheath, inserting culture grown on paddy straw, inserting culture grown on sorghum grain, and the floating leaf disk method, were practiced in the next seasons. Number of days taken to appear symptoms, disease incidence, and disease severity index were recorded. According to the results, inserting sclerotia into the sheath showed rapid symptom development in all the varieties. However, the disease incidence and disease severity index of the inbred variety Ruwan were greater than other local and exotic hybrids used. Among the tested methods, inserting sclerotia into the sheath is significantly (p<0.05) superior to other methods tested and can be adopted as a rapid varietal screening technique for banded leaf and sheath blight disease in Sri Lanka.