Breeding/Hybridizing Louisiana Irises

ABSTRACT: Goals and methods of a program designed not to yield immediate introductions but instead to expand the genetic variability of tetraploid Louisiana iris strains include an attempt to directly convert, through chemical treatment, seedlings of Louisiana iris species as well as the treatment of seedlings resulting from (species X diploid hybrid) crosses. One season's hybridizing involved the use of colchicine treatments, with unknown results; seedlings from this batch should bloom in 1992. The current season's work involved herbicide treatments of 100 (species X diploid hybrid) crosses, using the method described by Dr. Kevin Vaughn elsewhere in this newsletter. 

By Joseph K. Mertzweiller 
ABSTRACT: Tetraploid Louisiana iris pioneer Joseph K Mertzweiller is now involved in a complex process called interploidy hybridizing - the attempt to produce new tetraploids through diploid X tetraploid crosses. Although complicated, this is the process used by bearded iris hybridizers to convert that class of plants to tetraploids earlier in this century. Results of the author's program thus far indicate that seed production is extremely difficult and germination is poor. Offsetting the difficulties, however, is the possibility of including new diploid-originated genetic material into tetraploid strains. 

by Kevin C. Vaughn*, PhD
Louisiana Irises and Comments on Existing Cultivars
ABSTRACT: The herbicides trifluralin (TREFlAN) and oryzalin (SURFLAN) were selected as chemical compounds likely to increase ploidy levels in Louisiana irises. The compounds, while not as .toxic to animals, affect the development of plant tubulin protein in the same way as colchicine. Two batches of seedlings in two years have received the treatments. The first group (with some seedlings set aside as a control) was treated for 4-24 hours with herbicide solutions of 2-10 ppm. Seedlings were then thoroughly rinsed and planted into a sterile, soil-less mix. Club-shaped swelling was noted on the roots, and the treated seedlings showed stomate size approximately 50 percent larger than the control group. Of 12 treated seedlings, o~e appears to be a sectorial chimera, but 11 appear to be tetraploids. All but one of the seedlings in this group should bloom during Spring 1992. A second group of seedlings from diploid crosses was treated this year, and the same high conversion rate was noted. Attempts to produce tetraploids by tetraploid X tetraploid crosses, however, has proved disappointing. The article concludes with comments on existing tetraploid cultivars. 

ABSTRACT: The tetraploid breeding program of Mr. Norris includes both clonal and seedling treatment with colchicine, an alkaloid found in the autumn crocus, Colchicum autumnale. Clonal treatment involves injecting O.5cc of a 0.4% colchicine solution into the plant fan just above the growing point, concentrating on offsets which would be expected to bloom the following year. Chimeras normally are produced instead of tetraploids, and seed is obtained through crosses of chimera X chimera or chimera X tetraploid. Treatment of seedling iris involves a 12-hour soak in a .075% colchicine solution followed by a 12-hour waiting period in moist vermiculite then a 3-4 day soak in ice water. The seedlings are then planted. Evaluation of ploidy level is made by microscopic examination of stomata size. Chimera or tetraploid cells display a stomata size of 45-50 microns over the long direction, rather than the 35-40 microns normally observed in diploid cells. Pollen size also is an indication of ploidy levels, with diploid pollen averaging lIS microns and tetraploid pollen ranging from 125-150 microns. Chimeras may not be produced until two or three vegetative generations following treatInent. 

By Joseph K. Mertzweiller 
ABSTRACT: Based on observations of his own work over the last 15 years, the author identifies four main contemporary problems faced by tetraploid hybridizers of Louisiana irises. The problems include: (1) Limited fertility, including problems of sterility and seed set, which impedes the production of a broad genetic base among tetraploid cultivars; (2) Limited genetic variability, caused by the limited parentage of existing tetraploid cultivars; (3) Incomplete opening of blooms, which is observed in many tetraploid Louisianas; and (4) Reduced hardiness to cold, which has been observed in several cultivars for reasons not readily apparent. The best solution to these problems, the author suggests, is the production of a breeding stock which is more genetically varied and which includes light-colored cultivars, The expanded breeding stock ideally will come mostly from new conversions of tetraploid cultivars from existing diploid cultivars through the use of three possible methods.


Terry Aitken reports on a variagated Louisiana iris  in his nursery in Vancouver, Washington and speculates what may have caused this to occur.

'Red Dazzler' was hybridized by P. Hale in 1969

One of my first experiences with Louisiana irises was when I was a teenager in Massachusetts, growing a rather large collection of them on the protected west side of my parents house and heavily mulched for the winter with leaves and pine boughs. Two of the most impressive ones in that group were two brilliant reds: William McGarvey's 'Devil'sAdvocate' (1972) and Preston Hale's 'Red Dazzler' (1969). Although 'Red Dazzler' is still available, I would love to find 'Devil'sAdvocate' as it had marvelously round petals, much better than any other fulvas I have seen since, and it also rebloomed in October in Mass. Maybe one of our readers still grows the plant? Anyway, these reds were like nothing else in irisdom and they were very intriguing to me. Unfortunately, academics and career prevented me from capitalizing on these as hybridizing objects.

Over the past several years the late Samuel Norris of Kentucky and I have tried every trick in the book to get a higher number of tetraploid Louisiana iris seedlings. The two main obstacles seem to be poor seed set during bloom season and low germination of the few seed that are produced.