Hema Kasinathan Thesis May 1 2012.pdf - Atrium - University of ...

Assessments of clubroot symptoms were conducted at 6 weeks after sowing ortransplanting. The roots were washed and assessed for clubroot incidence (%) and placedinto severity classes using a 0–3 scale where 0 = no clubbing, 1 < 1/3 of root with clubsymptoms, 2 = 1/3 to 2/3 of root clubbed, and 3 > 2/3 of root clubbed (Buczacki et al.1975). These ratings were converted to a disease severity index (DSI) from 0–100 usingthe following equation (Kobriger and Hagedorn 1983).DSI =∑ [(class no.)(no. of plants in each class)](total no. plants per sample)(no. classes -1)x 100In the canola field trials, 25 plants per experimental unit were pulled andexamined for clubroot symptoms for the first two seeding date treatments (assessed 02July and 23 July in 2010). For the third seeding of the study in 2010 (13 August, 2010)and the single seeding in 2011 (29 July, 2011), 50 plants per unit were assessed. Thischange was made to improve the precision of treatment comparisons in statisticalanalysis.For shoot and root weight assessment, the individual plants were pulled, separatedinto shoot and root portions at the soil line, and the total weight of shoots and roots wererecorded per experimental unit. In each of the canola field trials in 2010, the root weightof 25 or 50 canola plants from each experimental unit were recorded, but shoot weightswere not recorded because there were no difference in growth stages based on visualobservation. In 2011, the shoot and root weight of 10 individual canola plants wererecorded.68