CT92 is a high yielding flue-cured tobacco with resistance to the soil borne fungus Black Root Rot Chalara elegans Nag Rag and Kendrick (synonym: Thielaviopsis basicola (Berk and Broome) Ferraris). CT92 has a grade index that is comparable to the check CTH14 and showed a higher potential to provide greater economic returns than the check.
La variété à haut rendement de tabac jaune CT92 résiste au pourridié noir causé par le champignon Chalara elegans Nag Rag and Kendrick [Syn. : Thielaviopsis basicola (Berk and Broome) Ferraris]. Avec un indice qualité comparable à celui du cultivar témoin CTH14, le nouveau cultivar pourrait rapporter davantage aux producteurs. [Traduit par la Rédaction]
Introduction
CT92, a new flue-cured tobacco (Nicotiana tabacum L.) developed by the Canadian Tobacco Research Foundation, has been recommended for registration by the Ontario Recommending Committee for Flue-Cured Tobacco (ORCFCT), based on trials conducted at three locations in the tobacco growing regions of Southwestern Ontario in 2019 and 2020. The Canadian Food Inspection Agency, Seed Division, Variety Registration Office issued the registration number 9414 for CT92 on 16 July 2021.
Breeding method
CT92, tested in trials as 16DA9-2, has the pedigree “CT681/20KA15-2//CT572”. In 2012, a cross was made between CT681 and 20KA15-2 in a field at Tillsonburg, Ontario. The following year, a single plant of the resulting F1 was crossed as the female to CT572. CT681 (Haji et al. 2000) is a Black Root Rot resistant variety that was registered in Canada in 2000, 20KA15-2 is a breeding line with a Black Root Rot resistance genetic background, and CT572 (Haji et al. 2002) is a popular Canadian commercial cultivar with improved leaf quality.
The F1 seed from the second cross was grown in a greenhouse in the Fall 2013 and one plant was selfed to produce F2 seed that was grown in a field in 2014. Subsequent selection procedures and performance testing were similar to those previously described for the cultivar CT652 (Amankwa et al. 2009). Briefly, several plants were selected from this population based on physical, agronomic, and chemical characteristics, and the seeds were bulked to grow an F3 population in 2015 in a seed nursery at Tillsonburg, Ontario. A number of F3 plants were harvested individually, based on the same criteria used earlier, to plant F4 head rows in 2016. In 2017, the F5 seed of an F4 plant selection (with the designation 16DA9-2) was evaluated for reaction to Black Root Rot, under controlled conditions using a modification test developed by Litton (1983). The selection was found to possess improved resistance to the pathogen. The same year, the F5 line also was tested in a replicated, preliminary trial together with other selections. F6 seed was bulked and used to evaluate the line in a Strain Trial in 2018 at Delhi, Ontario, and also tested for reaction to Black Rot under controlled conditions.
16DA9-2 was entered in a registration trial conducted at Simcoe, Delhi, and Aylmer, Ontario, Canada, in 2019 (F4:7) and 2020 (F4:8). Black Root Rot resistance screening under controlled conditions was continued in both 2019 and 2020. F8 seed collected from several uniform plants in an F7 row in 2019 will be used for further breeder seed production. In February 2021, 16DA9-2 was supported for registration and named as CT92 by the ORCFCT.
Performance
The 2 year registration trial was conducted based on protocols approved by the ORCFCT, and CT92 was compared with the check CTH14, a commercially available tobacco cultivar, for various economic, agronomic, and chemical traits (Tables 1 and 2). Plots were topped (the stem apex including flower buds and some top leaves were removed to improve leaf development) when 50% of the plants had stretched terminal buds with one or two flowers opened. The crop was harvested over a period of 5–7 weeks. Yield and leaf quality in 2019 were based on all the locations but in 2020 the final harvest at Delhi, Ontario, could not be done due to frost damage that occurred on 19 September; therefore, two locations were used for yield and quality assessment that year. CT92 yielded higher than the check each year with a grade index that was comparable to the check, and as a result, CT92 showed a higher potential to provide greater economic returns. On visual company evaluation of usability, from a scale of 0 to 100 (0 = unusable and 100 = excellent), CT92 was rated 75 and did seem comparable to the check (76). CT92 flowered 2 days earlier than the check and was topped approximately 3 cm higher than the check. CT92 showed a slightly wider leaf spacing on the topped plant, which is considered desirable in machine harvesting; now the common practice in Ontario.
Table 1.
Yield, grade index, and grade index returns of CT92 compared to CTH14 in the 2019 and 2020 tobacco registration trial conducted at three locations, Ontario.
Table 2.
Agronomic, physical, and chemical characteristics of CT92 compared to CTH14 in the 2019 and 2020 tobacco registration trial conducted at three locations, Ontario.
Ground sucker weight was similar between CT92 and the check. The average width of the eighth leaf (mid plant) was 35 cm, compared to 30 cm found on the check. The average length of the eighth leaf was similar to that found on the check. The average area of the three tip leaves was greater than CTH14 and the eighth leaf area was also greater than CTH14. Percent leaf lamina for CT92 was higher than that of CTH14. CT92 showed improved resistance to Black Root Rot, different from the check (susceptible), which will be advantageous for growers where the disease is a major problem.
Acknowledgement
Special thanks go to our on-farm co-operators at Aylmer, Delhi, and Simcoe for allowing us to conduct the variety trials on their farms.
