Host resistance and bio-management of tobacco root-rot caused by Pythium aphanidermatum

In view of the harmful effect of chemical pesticides, alternative approaches like host resistance and biocontrol were evaluated to develop an operative and sustainable option for the management of root-rot disease of tobacco incited by Pythium aphanidermatum . For host resistance, three tobacco cultivars viz., RK-10 P3, RK-18 P8 and RK-12 P3 were evaluated under pot conditions for their relative susceptibility to P. aphanidermatum . The effects of host reaction on total phenol (TP) and salicylic acid (SA) synthesis, as well as their impact on disease aetiology, were investigated. The increase in TP and SA showed negative correlations with the root-rot index. The highest increase in the TP (31%) and SA (20%) contents of the leaf was noted in cv. RK-12 P3, whereas the lowest increase was recorded in cultivar RK-10 P3 (6% TP and 7% SA). Further, the effects of two multi-facial biocontrol agents, Trichoderma harzianum AMUTH-1 and Pseudomonas fluorescens AMUPF-1 against P. aphanidermatum were investigated on all three tobacco cultivars. Soil application of these two biocontrol agents was also compared with the fungicide, carbendazim. Inoculation of P. aphanidermatum caused severe root-rot in cv. RK-10 P3 and cv. RK-18 P8 with a 7–15% decrease in plant growth and 15–20% in chlorophyll and carotenoid contents. However, soil application of BCA and fungicides significantly improved the plant growth variables, chlorophyll and carotenoid contents, and reduced the disease severity. The highest reduction in the root-rot index was recorded with T. harzianum and carbendazim over control. The most significant improvement in the plant growth and biomass production of tobacco was seen in cv. RK-10 P3 with T. harzianum (11–16%), followed by carbendazim (9–14%). The study found that cv. RK-12 P3 expressed resistant reaction to P. aphanidermatum and may be cultivated in the disease prone areas, and T. harzianum may be used in place of fungicide in root-rot-infested fields to increase the tobacco yield.