Characterizing resistance in flue-cured tobacco to Globodera tabacum solanacearum

Resistance to Globodera tabacum solanacearum in flue-cured tobacco was characterized in vitro, in the greenhouse, and field. The objectives of this study included evaluation of hatching of G. t. solanacearum as stimulated by root exudate, penetration and development of G. t. solanacearum on roots, and the effects of G. t. solanacearum on growth, yield, and quality of flue-cured tobacco.

Root exudate from resistant (NC 567) and susceptible (K 326) flue cured tobacco cultivars had similar effects on hatching of G. t. solanacearum. Dilution of root exudate reduced hatching and hatching appeared to increase with increased temperature. More swollen and flask shaped nematodes developed in roots of K 326 than those of NC 567. Resistance reduced development of vermiform juveniles to swollen nematodes in NC 567. However, development of swollen nematodes to flask shaped nematodes was similar for both cultivars. Resistance to G. t. solanacearum was effective at 17, 22, 27, and 31°C. Infection by G. t. solanacearum suppressed number of leaves, plant height, fresh weight of leaves, and feeder roots. Reduction in fresh leaf weight at 11 weeks after transplanting was greater for the susceptible cultivar, K 326, than for the resistant cultivar, NC 567. However reduction in fresh feeder root weight and increases in the ratio of leaf weight to feeder root weight at 11 weeks after transplanting between both cultivars. Yield and grade index of cured leaves were negatively correlated with area under curves of total nematode population densities per gram of feeder root. The rate parameters of regression models suggested that the two cultivars responded similarly to infection by G. t. solanacearum in yield and quality reduction. However, K 326 had a higher yield potential in the absence of nematodes.