Effects of Php Gene-Associated versus Induced Resistance to Tobacco Cyst Nematode in Flue-Cured Tobacco

Effects of the systemic acquired resistance (SAR)-inducing compound acibenzolar-S-methyl (ASM) and the plant-growth promoting rhizobacterial mixture Bacillus subtilis A13 and B. amyloliquefaciens IN937a (GB99+GB122) were assessed on the reproduction of a tobacco cyst nematode (TCN- Globodera tabacum solanacearum) tinder greenhouse conditions. Two sets of two independent experiments were conducted, each involving soil or root sampling. Soil sample experiments included flue-cured tobacco cultivars with (Ph-p+: NC71 and NC102) and without (Ph-p-: K326 and 1(346) a gene (Ph-p) suppressing TCN parasitism. Root. sample experiments examined TCN root parasitism of NC71 and K326. Cultivars possessing the Ph-p gene (Ph-p+) were compared with Ph-p- cultivars to assess the effects of resistance mediated via Ph-p gene vs. induced resistance to TCN. GB99+GB122 consistently reduced nematode reproductive ratio on both Ph-p+ and Ph-p- cultivars, but similar effects of ASM across Ph-p- cultivars were less consistent. In addition, ASM application resulted in leaf yellowing and reduced root weight. GB99+GB122 consistently reduced nematode development in roots of both Ph-p+ and Ph-p- cultivars, while similar effects of ASM were frequently less consistent. The results of this study indicate that GB99+GB122 consistently reduced TCN reproduction in all flue-cured tobacco cultivars tested, while the effects of ASM were only consistent in Ph-p+ cultivars. Under most circumstances, GB99+GB122 suppressed nematode reproduction more consistently than ASM compared to the untreated control.