Paper No. 9 



MORPHOGENESIS AND MANAGEMENT OF PERENNIAL GRASSES IN 



THE UNITED STATES 



By D. N. Hyder 1 



Abstract 



Elevation of root and shoot primordia increases 

 the susceptibility of perennial grasses to unfav- 

 orable conditions and treatments. All grass seed- 

 lings may exhibit some elevation of crowns, but 

 elongation of the sub-coleoptile internode (meso- 

 cotyl) typically places the crown near the soil 

 surface. Problems in seedling establishment and 

 expansion by tillering might be solved by burying 

 the crowns soon after emergence. The process 

 of tillering from axillary buds on the crown can 

 elevate successive tiller crowns and eventually can 

 result in dead centers. Excessive elevation of 

 crowns through the process of tillering might be 

 prevented by mechanical or grazing treatments. 

 Grasses have culmed or culmless vegetative 

 shoots, some of which become reproductive. The 

 time and amount of elevation of shoot apices and 

 inflorescences affects resistance to grazing and the 

 leaf replacement potential after defoliation. Thus, 

 strategies for grazing management should con- 

 sider morphogenetic characteristics. 



Additional key words: Grass seedling morphol- 

 ogy; vegetative shoot morphology 



Introduction 



Morphogenesis is defined as the structural 

 changes during the development of an organism. 

 These structural changes of plants suggest man- 

 agement practices and sometimes create manage- 

 ment problems. Nevertheless, the subject of mor- 

 phogenesis, as it relates to management, is scarce- 

 ly developed beyond its importance in seed pro- 

 duction. My objective is to describe some forms 



1 Range Scientist, Plant Science Research Division, 

 Agricultural Research Service, U.S. Department of Agri- 

 culture, Fort Collins, Colo. 80521. 



of growth pertinent to grass management, partic- 

 ularly the ways in which the elevation of root 

 and shoot primordia influences the susceptibility 

 of perennial grasses to unfavorable conditions 

 and treatments and affects the capacity of grasses 

 for production of adventitious roots and leaves 

 which are critically essential for plant survival 

 and growth. 



Root Morphogenesis 



The grass root system consists of seminal 

 (seed) roots and adventitious roots. The seminal - 

 root system typically consists of one to five 

 roots — the primary root (radicle) and two pairs 

 of lateral roots, which arise in the same plane 

 from the scutellar node. The scutellum, located 

 adjacent to the endosperm of the seed, is the 

 cotyledon (4) . In addition, a single root may arise 

 opposite the scutellum (4, 18). All seminal roots 

 are slender and branched, and usually die in a 

 few months (40). 



The adventitious-root system consists of whorls 

 of roots arising from the coleoptilar node and 

 the nodes of shoots, and sometimes from culm 

 internodes (4). Secondary shoots (tillers) are 

 rooted less substantially than the seminal (pri- 

 mary) shoot, because they lack the seminal roots 

 and their adventitious whorls consist of fewer 

 roots (18). This rooting deficiency of tillers, 

 among other factors, may cause declining yields 

 of a seeded strand in the first two or three 

 years. Yields of seeded stands on semiarid range- 

 land typically reach a maximum in one to three 

 years. Yields of seeded stands on semiarid range- 

 {24). Breeding and selection programs should 

 include, among other things, emphasis on su- 

 perior rooting characteristics, and management 

 practices should be designed to minimize undesir- 

 able rooting phenomena. 



89 



