Registration of `Metacomet' Tobacco.
The tobacco cyst nematode was first described from Hazardville, CT, in the early 1950s (1) and is now widely distributed in shade production areas in the Connecticut River Valley of Connecticut and Massachusetts. All previous Connecticut shade and broadleaf cultivars tested were susceptible to G. t. tabacum (2). Nematode infection of roots can cause dramatic stunting, reduced leaf weight, and also reduced leaf quality. Losses can exceed 40% at high nematode densities (3). Fluecured tobacco lines with resistance to G. t. solanacearum (Miller and Gray) were identified as resistant to G. t. tabacum (4) and crosses to Connecticut shade tobacco were first made in 1987.
Metacomet is an inbred derived from a cross between the nematode-susceptible Connecticut shade tobacco cultivar O-30, which was developed as a commercial production line by Windsor Shade Tobacco, Inc., and the G. t. solanacearum resistant flue-cured line VA 81. Cyst nematode resistance in VA 81 was most likely derived from TL 106. Resistance to G. t. tabacum is conferred by a single dominant gene (2). Resistance to G. t. tabacum and G. t. solanacearum may be linked to wildfire [caused by Pseudomonas syringae pv. tabaci (Wolf & Foster) Young et al.] resistance (5), transferred from N. longiflora Cavanilles to the breeding line TL 106 (6). Nicotiana longiflora was resistant to G. t. solanacearum in pot experiments (7).
The pedigree breeding system was used. The experimental designation of CT 21-2A was used during cultivar development. Metacomet was selected as a selfed inbred over 12 generations of field evaluation for agronomic characteristics and greenhouse evaluation for G. t. tabacum resistance. Individual plants in the [F.sub.4] and [F.sub.6] generations were selected with cyst nematode resistance using a greenhouse seedling assay (2). Progeny testing was performed in 1993 to select plants homozygous for G. t. tabacum resistance.
Metacomet was selected under field conditions for growth and yield characteristics in the presence of damaging population levels of G. t. tabacum to avoid severe intolerance to nematode infection. Metacomet was also selected for the hypersensitive gene for resistance to tobacco mosaic virus derived from N. glutinosa L. and for reduced sensitivity to weather fleck.
The effects of nematode resistance on G. t. tabacum populations were determined in field plots in a cloth-covered shade tent at the Experiment Station Valley Laboratory in Windsor in 1993, 1994, and 1997. Nematode population densities were reduced by 83, 74, and 72%, respectively, at the same time that the susceptible cultivar increased populations by more than 200%. The population reduction resulting from the season-long production of a resistant cultivar is comparable with growing a nematode-susceptible cultivar with soil fumigation.
Leaf yield and quality of Metacomet and the nematode-susceptible O-40 were compared in field plots infested with 120 to 250 infective G. t. tabacum juveniles per cubic centimeter of soil. Fresh weight yields were 759.6 and 614.7 g [plant.sup.-1] for Metacomet and O-40, respectively. Cured leaf quality was determined by industry evaluation. Economic value, determined by percentage weight in each grade and percentage weight in each cured leaf grade in 1993, was $42,27 [kg.sup-1] for Metacomet and $24.20 for the O-40 standard. Metacomet demonstrated higher leaf yields per plant than another cyst nematode resistant cultivar, `Poquonock', averaging 753 and 732 g [plant.sup.-1], respectively. While not significantly different, Metacomet also had a greater impact on tobacco cyst nematode populations than Poquonock, averaging 76.3 and 65.0% population reductions per year, respectively.
Metacomet shade tobacco will allow the production of high quality shade tobacco in fields infested with G. t. tabacum. This cultivar allows growers to produce a tobacco crop while reducing cyst nematode populations in a manner comparable with a fumigant nematicide.
Breeder seed of Metacomet will be maintained and distributed by the Connecticut Agricultural Experiment Station Valley Laboratory, 153 Cook Hill Rd., Windsor, CT 06095. U.S. plant variety protection for Metacomet will not be applied for.
J.A. LAMONDIA(*) (8)
References and Notes
(1.) Lownsbery, B.F., and J.W. Lownsbery. 1954. Heterodera tabacum n. sp., a parasite of solanaceous plants in Connecticut. Proc. Helminthol. So. Wash. 21:42-47.
(2.) LaMondia, J.A. 1991. Genetics of tobacco resistance to Globodera tabacum tabacum. Plant Dis. 75:453-454.
(3.) LaMondia, J.A. 1995. Shade tobacco yield loss and Globodera tabacum tabacum population changes in relation to initial nematode density. J. Nematol. 27:114-119.
(4.) LaMondia, J.A. 1988. Tobacco resistance to Globodera tabacum. Ann. Appl. Nematol. 2:77-80.
(5.) Spasoff, L., J.A. Fox, and L.I. Miller. 1971. Multigenic inheritance of resistance to Osborne's cyst nematode. J. Nematol. 3:329-330.
(6.) Clayton, E.E. 1947. A wildfire resistant tobacco. J. Hered. 38:35-40.
(7.) Balaawy, H.A., and J.A. Fox. 1971. Resistance to Osborne's cyst nematode in selected Nicotiana species. J. Nematol. 3:395-398.
(8.) J.A. LaMondia, Connecticut Agric. Exp. Stn., Valley Lab, P.O. Box 248, Windsor, CT 06095. Registration by CSSA. Accepted 30 Apr. 2000. (*) Corresponding author
Published in Crop Sci. 40:1504-1505 (2000).