Abstract
Chemical controls for root-knot nematodes are increasingly restricted due to environmental and human health concerns. Host resistance to these nematodes is key to flue-cured tobacco production in Virginia. Resistance to Meloidogyne incognita races 1 and 3, and race 1 of M. arenaria is imparted by the gene Rk1, which is widely available in commercial flue-cured tobacco. Rk2 imparts increased resistance to M. javanica when stacked with Rk1 and is becoming commercially available. The efficacy of Rk2 against M. arenaria race 2, which is increasingly prevalent in Virginia, is unclear. Greenhouse trials were conducted in 2017 to determine how potential resistance derived from N. repanda compares to the root-knot nematode resistance afforded by Rk1 and Rk2. Trials were arranged in a completely randomized block design and included an entry with traits derived from N. repanda, a susceptible entry and entries possessing Rk1 and/or Rk2. Data collected after 60 days included percent root galling, egg mass counts, and egg counts. Root galling and reproduction were significantly lower on the entry possessing traits derived from N. repanda relative to other entries, suggesting that the N. repanda species may hold a novel source of root-knot nematode resistance for commercial flue-cured tobacco cultivars.
Highlights
Tobacco (Nicotiana tabacum L.) is a valuable agri cultural commodity cultivated around the world, with the value of unprocessed tobacco globally estimated at over 17 billion dollars in 2018 (FAO, 2018)
Rk1 may have some inhibitory effect on the reproduction of M. javanicaon flue-cured tobacco (Ternouth et al, 1986) but contradicting research suggests that Rk1 imparts minimal or no resistance to M. javanica, M. incognita host races 2 and 4, M. arenaria race 2, and M. hapla Chitwood (1949) (Ng’ambi et al, 1999b)
Four greenhouse experiments were conducted in 2017 to evaluate the impact of a putative source of resistance to root-knot nematodes derived from N. repanda on the reproductive capacity of a population of M. arenaria race 2 on a panel of seven flue-cured tobacco entries: Hicks; K326; T-15-1-1; CC 13; STNCB-2-28; BAG 29-15-3-32-1; and 81-R-617A
Summary
Tobacco (Nicotiana tabacum L.) is a valuable agri cultural commodity cultivated around the world, with the value of unprocessed tobacco globally estimated at over 17 billion dollars in 2018 (FAO, 2018). Root-knot nematode resistance first became commercially available in Zimbabwe in 1961 with the introduction of a cultivar possessing a gene, Rk, originally discovered in N. tomentosa Ruis and Pav (Yi et al, 1998) This gene, known as Rk1, is widely available in commercial flue-cured tobacco cultivars and imparts what has been described as some level of resistance to M. incognita (Kofoid and White) Chitwood (1949) host races 1 and 3 and M. arenaria (Neal) Chitwood (1949) host race 1 (Ng’ambi et al, 1999b; Schneider, 1991). In 1993, another root-knot nematode resistance gene, known as Rk2, was introduced into a cultivar commercially available in Zimbabwe, Kutsaga RK26, stacked with Rk1 (Jack, 2001; Jack and Lyle, 1999; Way, 1994a) This gene, originally known as ‘T,’ was discovered in 1950 in N. tabacum plants in subsistence gardens along the Zambezi river in Zimbabwe. A 2004 survey of 170 Virginia tobacco fields found 43.5% of surveyed fields were infested with root-knot nematodes, with M. arenaria present in 56.7% of infested fields and
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