| Doubling chromosome numbers of wheat-rye amphiploids
with colchicine, DMSO, and cold treatment K.D. BEATTY1), E.A. RUPERT2) and Nancy DEHGAN Department of Agronomy and Range Science University of California, Davis California, U.S.A. 95616 The introduction of diversity into triticale (x Triticosecale WITTMACK) from the extensive genetic variability found among wheat and rye cultivars has been limited by difficulties in synthesizing new primary hybrids. For a fertile hexaploid triticale hybrid to be obtained, successful pollinations should be followed by 1) culture of embryos on synthetic media and 2) subsequent doubling of the chromosome number of the sterile amphiploid plants. Conventional methods of colchicine treatment yield approximately 3 to 15% fertile plants (LARTER, TSUCHIYA and EVANS 1968). Some specific parental combinations produce seed only after persistent repetition of the various steps from pollination to seed production. BELL (1950) and SIDDIQUI(1971) have reviewed methods of colchicine chromosome number doubling among interspecific and intergeneric cereal hybrids. Bell's capping method of application has been generally the most effective method for cereals, allowing repeated treatments and resulting in lowered mortality rates. Capping introduces colchicine into the meristem of the crown through a cut tiller; subsequent development and differentiation of polyploid tissue is influenced by temperature, turgidity, vigor and the genetic constitution of the individual plant. Since low temperatures and short days during early developmental stages frequently increase the number of tillers per plant among cereals, it seemed possible that a combination of chemical and cold treatment could increase the production of fertile alloploid spikes. This report describes observations on triticale development that resulted in a higher frequency of amphidiploid production following colchicine treatment than has been noted in previous work. Materials and Methods Cultures of embryos germinated on synthetic media (NORSTOG 1973) yielded 111 amphiploid seedlings of Triticum turgidum L. (durum group) x Secale cereale L. and 124 seedlings of T. aestivum L. em. THELL. (vulgare group) x S. cereale. These 235 hybrids originated from 10 tetraploid and 5 hexaploid wheats pollinated by various diploid rye lines. Amphiploid plants were removed from agar medium in test tubes and placed in small peat pots containing a 1 : 1 : 1 mixture of peat moss, vermiculite and soil. The plants were placed in a cool (20 to 22C) greenhouse, suitable fertilizer was added and time was allowed for the development of three or more vigorous tillers about 10 cm tall. Plant numbers can be increased by separating tillers at the crown but time to resume vigorous growth should be allowed before further treatment. The main tiller was cut 2 cm from the crown and a vial containing 0.1% colchicine in an aqueous 2.0% dimethyl sulfonate (DMSO) solution was inverted over the cut stem. Vials were prepared by cutting 5 mm glass tubing into 5 cm lengths, sealing one end with floral clay and attaching the glass tube vial to wooden pot labels with floral caly. Absorption of colchicine seemed to be increased if the pots were kept slightly dry during treatment. If leakage occurred from the inverted vial the plants were watered thoroughly to wash the colchicine from the root system and the vial was not refilled for a few days. Care was taken to avoid skin contact during handling of the DMSO and dolchicine. The vials were refilled one or more times on alternate days. Swelling at the base of the treated tiller, leaf tip-burn and/or intensification of color in the leaves indicated that colchicine was absorbed into the tissues. One to three days of thorough watering allowed recovery after the colchicine applicator was removed from the plant. Following colchicine application the plants were placed for 2 to 5 weeks in a vernalization chamber or growth cabinet at 5C with 12 hr light (both fluorescent and incandenscent). Two weeks were sufficient for hybrids from spring habit parents ; five or more weeks were required for simultaneous treatment and vernalization of hybrids from winter habit parents. The plants were returned to a greenhouse and lighted for 12 hr per day until strong vegetative growth was initiated. After a vigorous vegetative plant had been produced the light period was extended to 16 hr to stimulate rapid flowering. |
| 1) Northeast Branch Experiment station, University of Arkansas, Keiser,
Arkansas, U.S.A. 72351. 2) Department of Agronomy and Soils, clemson University, clemson, South Carolina, U.S.A 29631. |
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