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Determination of Physiological Maturity in Oat¹

In studying various ecological and physiological factors affecting the yield of the several small grains, it is important to be able to define the length of the grain fill period, that is the period from anthesis to physiological maturity. Unfortunately, the various small grain crops do not develop a readily recognizable indicator, such as the ‘black layer’ in corn, Zea mays L., and tested methods to evaluate physiological maturity in small grains seem to be lacking. Our objective was to evaluate several techniques for determining when physiological maturity occurs in spring oat, Avena sativa L. In this study, five methods of determining physiological maturity were evaluated. Field grown plants of ‘Astro,’ ‘Noble,’ and ‘Otee’ spring oat were tagged when the spikelets at the second node from the base of the panicle were at anthesis. Plants were grown on a Murrill fine silty loam (a mixed, mesic Typic Hapludults.). Beginning 15 days after anthesis for each cultivar, spikelets at the tagged node were sampled daily, and an evaluation made of color changes in certain panicle parts, the uptake of a red, water-soluble dye, and the uptake of¹⁴C-sucrose. The groats were then weighed, freeze-dried, and reweighed to secure dry weight and fresh moisture content. Lack of dry weight changes significant at p 0.05 was used as the standard method to define physiological maturity and the other techniques compared to this. When half of the glume tips no longer took up the red dye and approximately 75% of the glume surface was yellow it provided a useful, nondestructive estimation of physiological maturity as defined by the dry weight method. Small amounts of ¹⁴C-sucrose were taken up for a few additional days, but dry weight changes were not significant at p 0.05. Groat and grain moisture content did not satisfactorily indicate physiological maturity. Observations of color changes in the glumes and cessation of dye uptake, either alone or in combination, provide a method of comparing the length of the oat fill period under various cultural and environmental conditions and for various genotypes.

Key Words: ¹⁴C-sucrose • ³H₂O • Water-soluble-dye • Groat weight • Moisture conten • Avenu sativa L. • Fill period • Carbon translocation • Glume yellowing • Anthesis

² Former graduate assistant, agronomy professor, and associate professor of crop physiology, respectively, The Pennsylvania State Univ. Dr. Lee is now assistant professor of agronomy, Seoul National Univ., Suweon, Korea 170.

Received for publication April 7, 1978.