Performance of three tolerant air-cured tobacco cultivars when infected by black shank and root-knot nematode in Golestan province

Soil-borne fungi and root-knot nematodes are distributed all over the world and cause great economic loss to tobacco. The best managing method to these diseases is using resistant cultivars. This research was performed to determine the effect of black shank and root-knot nematode on quality and yield of tolerant air-cured tobacco cultivars in Golestan province during 2014-2015 with 4 treatments and 3 replications. Three tolerant (K17, Burley Geel3 and BCE) and a susceptible tobacco cultivar (Burley 21 as control) were planted and grown on 5 × 8 m2 plots in a randomized complete block design (RCBD) as coupled plots in a field that was naturally infested with both pathogens in Valeshabad village of Gorgan. Black shank (Phytophthora nicotianae) severity on tobacco plants was determined weekly based on 1 to 5 index. Evaluation of root-knot nematode infection was performed based on gall index (0-10 scoring system), number of egg masses, and average number of eggs per egg mass at the end of season. Important morphological, agronomical and qualitative traits were determined. Mean comparison of qualitative traits showed that in the terms of nicotine content, BCE had the highest and Burley 21 had the lowest amount. For potassium level, BCE had the highest and K17 had the lowest amount. For total nitrogen, Burley 21 had the highest and Burley Geel3 had the lowest content. Reaction of air-cured tobacco varieties to soil-borne pathogenic agents showed significant differences at P≤1% or 5%. In terms of all agronomic traits, yield and disease amount, BCE cultivar was superior and showed lowest disease incidence and infection percent. The susceptible control cultivar (Burley 21) showed the highest rate of infection to soil-borne diseases and was the poorest in agronomic traits and yield.