HAROLD H. SMITH 



Cornell Universify 



Chapter 10 



Fixing Tronsgressive Vigor 

 in Nicofiona Rustica 



Hybrid vigor has been observed to varying degrees among certain inter- 

 varietal hybrids of the self-pollinated cultivated species Nicotiana rustica L. 

 (Bolsunow, 1944; East, 1921). In experiments undertaken to obtain a larger 

 ;V. rustica plant giving increased yield of nicotine, it was reported (Smith 

 and Bacon, 1941) that inbred lines derived as selections from hybrids among 

 three varieties exceeded the parents and Fi's in plant height, number of 

 leaves, or size of the largest leaf. 



The general experience of breeders of self-pollinated plants has been that 

 improved varieties can be developed through hybridization followed by selec- 

 tion and inbreeding, to fix desirable transgressive characteristics. Yet it is 

 difficult to find data from which quantitative relationships of parents, Fi, and 

 transgressive inbred can be adequately evaluated; as from replicated and 

 randomized experiments in which the generations have been grown at the 

 same time under comparable conditions. In view of the increasing number 

 of reports on hybrid vigor in self-pollinated crop plants and its suggested 

 utilization (Ash ton, 1946), it was considered opportune to present relevant 

 data accumulated on N. rustica. 



Since methods of partitioning phenotypic variance have become generally 

 available there was additional interest in making further study of the iV. 

 rustica material. Breeding results obtained in advanced selections could be 

 related to the heritability estimated from data on early generations. 



MATERIALS AND METHODS 



Four varieties of Nicotiana rustica were used in these experiments. Three 



of them — hrasilia strain 34753, Olson 68, and tall type have been described 



* Published as Paper No. 261 , Department of Plant Breeding, Cornell University, Ithaca 

 New York. 



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