Induction of Tetraploidy and a Rapid Field Method of Detecting Induced Tetraploidy in Pensacola Bahiagrass 1

D I P L O I D Pensacola bahiagrass (2n = 20) , Paspalum ,?otd,tum var. saurae Parodi, is sexual, more winterhardy and productive of forage, but narrower leafed and less palatable than most naturally occurring tetraploid bahiagrass in the breeding program at Tifton, Georgia. These natural tetraploids are apomictic and diploid x tetraploid hybrids (and their reciprocals) are apomictic. It was hoped that induced autotetraploid Pensacola could be used in genetic, cytological, and growth-response studies, which would provide fundamental information on apomixis, the cytogenetic nature of natural tetraploidy, and the effects of autotetraploidy p e r se on growth response and reproduction in bahiagrass. Seeds of a superior experimental clonal cross ( 1 x 108) were treated with 0, 0.1, 0.2, 0.4, and 0.8% aqueous colchicine for 6, 24, 48, and 96 hours at room temperature in November 1953. Duplicate lots of 40 seeds each were placed in Petri dishes on filter paper moistened with the solutions listed. After treatment the seeds were rinsed in tap water and allowed to continue to grow in fresh Petri dishes on filter papers kept moist with tap water. All colchicine treatments reduced growth of the seedlings and most of them produced abnormal growth, i.e., stunted roots and shoots, in part of the seedlings. Many of the abnormal seedlings died. As soon as the seedlings had sufficiently long roots to give them a good chance to survive, they were transplanted to steam-sterilized soil in thumb pots in the greenhouse. More abnormal plants died in the greenhouse. In April 1954, the 117 seedling survivors were transplanted to the field. Morphological variability present in this highly crosspollinated grass discouraged attempts to screen the seedlings for tetraploid plants on the basis of size differences of plant parts. During 1954, chromosome counts of roottip samples from part of the population resulted in the detection of one completely tetraploid plant. The tetraploid plant set seed in only 0.3% of its florets. This result indicated that a rapid field method of detecting induced tetraploidy that used high sterility as a criterion might be practicable. The entire population was screened for the high sterility character in July 1955. Five mature seedheads, evenly spaced around the perimeter of each seedling, were analyzed for seed set in the field by biting the florets to detect empty ones. If one or more heads on a seedling appeared to be highly sterile, all the heads on the plant were analyzed and the corresponding seed culms were appropriately tagged (Figure 1) so that the suspected diploid and tetraploid sectors of chimeral plants were defined with red and green tags, respectively. Sub-cultures of tillers were recovered from the centers of the sectors thus defined. Chromo-