Three species of root-knot nematodes (Meloidogyne incognita, M. arenaria, and M. javanica) have long been a problem in tobacco production around the world. Meloidogyne incognita has historically been the most economically significant root-knot nematode species on tobacco in Virginia. However, with most commercial varieties now containing a resistance gene to races 1 and 3 of M. incognita (Rk1), M. arenaria has emerged as the most common root-knot nematode pathogen in Virginia tobacco fields. The objective of this study is to determine if homozygosity for both Rk1 and Rk2 increases resistance to M. arenaria compared to the presence of either gene alone. Six tobacco cultivars were used: C371G (susceptible), NC 95 and SC 72 (homozygous for Rk1), T-15-1-1 (homozygous for Rk2), and STNCB-2-28 and NOD 8 (homozygous for both Rk1 and Rk2). Six plants of each variety were grown in a greenhouse and inoculated with 5,000 M. arenaria eggs. Egg mass counts, egg counts, and a gall rating by weight were obtained from roots 60 days after inoculation. Plants with Rk1 alone, and Rk1 and Rk2 together significantly reduced root galling, egg masses, and eggs than the control variety. Combining Rk1 and Rk2 genes further reduced galling (significantly in 1 of 4 trials), egg masses (significantly in 2 of 4 trials), and eggs (significantly in 1 of 3 trials). A better understanding of the specific effects of Rk1 and Rk2 on root-knot nematode parasitism could help plant breeders improve tobacco resistance to M. arenaria. (Reprinted with permission)