Registration of `Poquonock' Tobacco.
The tobacco cyst nematode is widely distributed in shade production areas in Connecticut and Massachusetts. All previous Connecticut shade cultivars evaluated were susceptible to G. t. tabacum (1). Cyst nematode infection may cause leaf quality reduction, dramatic early season stunting, and fresh leaf weight losses exceeding 40% at high nematode densities (2). Flue-cured tobacco lines with resistance to G. t. solanacearum (Miller & Gray) Behrens were also resistant to G. t. tabacum (3). Resistance to G. t. tabacum is conferred by a single dominant gene (1). Resistance to G. t. tabacum and G. t. solanacearum may be linked to wildfire [Pseudomonas syringae pv. tabaci (Wolf & Foster) Young et al.] resistance (4). Wildfire resistance was transferred from N. longiflora Cavanilles to the breeding line TL 106, which had a pair of chromosomes from the wild species (5), and eventually to VA 81. Nicotiana longiflora was resistant to G. t. solanacearum in pot experiments (6).
Poquonock is an inbred derived from an initial cross made in 1987 between the nematode-susceptible Connecticut shade tobacco cultivar O-30 and the G. t. solanacearum resistant flue-cured line VA 81. The pedigree system of breeding was used. Poquonock was selected from the [F.sub.2] generation of the O-30 and VA 81 cross, back-crossed to O-30 twice, then to the nematode-susceptible shade cultivar O-40 twice, then crossed again to a selfed inbred (three generations) from the cross of O-30 by VA 81. Both O-30 and O-40 were developed and commercially grown by Windsor Shade Tobacco, Inc. Resulting selections were selfed to homogeneity for six generations. Individual plants in the second and fourth selfed generations were selected with cyst nematode resistance using a greenhouse seedling assay (1). Progeny testing was performed in 1993 to identify plants homozygous for G. t. tabacum resistance. The experimental designation CT-107 was used during development.
Poquonock was selected for growth and yield characteristics under field conditions. Selection was done in the presence of damaging population levels of G. t. tabacum to avoid severe intolerance to nematode infection. Poquonock was also selected for the dominant hypersensitive gene for resistance to tobacco mosaic virus derived from Nicotiana glutinosa L. and for reduced sensitivity to weather fleck, caused by ozone.
Poquonock reduced cyst nematode population densities by 67% in 1994 and 63% in 1997 in field plots in a cloth-covered shade tent at the Experiment Station Valley Laboratory in Windsor. In comparison, the susceptible cultivar O-40 increased G. t. tabacum populations by more than 200% annually. Production of Poquonock shade tobacco reduced cyst nematode populations in a manner similar to soil fumigation after production of a susceptible cultivar.
Leaf yield and quality of Poquonock and the nematode-susceptible O-40 were compared in field plots infested with 120 to 250 infective G. t. tabacum juveniles per cubic centimeter soil. Yields were similar or greater for Poquonock than the O-40 standard. Average fresh weight leaf yield of Poquonock and the susceptible O-40 was 731.9 and 614.7 g [plant.sup.-1], respectively. Cured leaf quality was determined by industry evaluation, Economic value, determined by leaf yields and percentage weight in each cured leaf quality grade in 1993, was $44.00 [kg.sup-1] for Poquonock and $24.20 [kg.sup-1] for the nematode-susceptible O-40 standard. Poquonock produces higher quality leaf grades than `Metacomet', which has the advantage of higher leaf weights (6).
Poquonock shade tobacco will allow the production of high-quality shade tobacco in fields infested with damaging populations of G. t. tabacum. This cultivar allows growers a nonchemical nematode control tactic that can reduce nematode populations comparable with a fumigant nematicide.
Breeder seed of Poquonock 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 Poquonock will not be applied for.
J.A. LAMONDIA(*) (8)
References and Notes
(1.) LaMondia, J.A. 1991. Genetics of tobacco resistance to Globodera tabacum tabacum. Plant Dis. 75:453-454.
(2.) 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.
(3.) LaMondia, J.A. 1988. Tobacco resistance to Globodera tabacum. Ann. Appl. Nematol. 2:77-80.
(4.) Spasoff, L., J.A. Fox, and L.I. Miller. 1971. Multigenic inheritance of resistance to Osborne's cyst nematode. J. Nematol. 3:329-330.
(5.) Clayton, E.E. 1947. A wildfire resistant tobacco. J. Hered. 38:35-40.
(6.) LaMondia, J.A. 2000. Registration of `Metacomet' Tobacco. Crop Sci. 40:1510 (this issue).
(7.) 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. 40:1505-1506 (2000).