GROWTH AND DEVELOPMENT IN AN OAT MUTANT EXPRESSING GIANTISM

Sources of germplasm for a forage oat (Avena sativa L.) program are li mited. A recently isolated mutant oat, PI546363, exhibits characterist ics (late maturity, tallness, leafiness, and low grain/straw ratio) th at are desirable in a forage oat cultivar. As part of an investigation into the genetic/physiological basis for the mutant characteristics, a morphological and anatomical comparison was made between the mutant and its parents (two standard oat cultivars Tibor and OT745) during gr owth and development. The mutant and its parents were grown in a contr olled-environment chamber (21/17 degrees C, day/night temperature; 16- h photoperiod; approximately 400 mol m(-2) s(-1) photosynthetic photon flux at canopy height). Measurements of height, tillering, and leaf s tage were made, and tissue samples were collected at weekly intervals until panicle emergence. Panicle emergence occurred after 16 wk (1568 heat units) for the mutant, and 6 wk (588 heat units) for the parents. At panicle emergence, the mutant averaged 17 leaves compared with eig ht leaves for the parents; the height of the mutant was approximately 195 cm compared with 96 cm for the parents; and the number of live til lers was similar for both. The shift of the apex from vegetative to re productive growth occurred at approximately 8 wk in the mutant and at 2 to 3 wk in the parents. The apex of the mutant was longer and larger (i.e., it had increased amounts of parenchymatous tissue), and produc ed more leaf primordia than its parents. Because of the delay in flowe ring and the increased vegetative growth, the mutant may be a useful s ource of germplasm in the development of superior forage oat cultivars .