PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



55 



number remains stable. Removing tillers at vari- 

 ous stages of development or heights has pro- 

 nounced effects on tillering response. However, 

 such management practices likely exert their in- 

 fluence on development of existing tiller initials 

 rather than on tiller formation. Environmental 

 factors would affect both tiller formation (activa- 

 tion of the axillary buds) as well as tiller develop- 

 ment. 



Templeton and others (19) found that the tiller 

 number of fall fescue (Festuca arundinacea 

 Schreb.) plants, growing in the field, increased 

 throughout the winter even though weekly mean 

 temperatures were near 0°. As mean weekly 

 temperatures increased (mid-March) rate of tiller 

 appearance increased markedly so that by mid- 

 April the tiller number was approximately 3.5 

 times what it had been only 38 days earlier. Fol- 

 lowing this rapid tillering, the rate of tiller ap- 

 pearance decreased and remained low until early 

 June. 



Under controlled conditions, tillering was fa- 

 vored by a period of daily exposure to a tempera- 

 ture of 2°C (table 4). In all but one treatment 

 combination, plants grown under an 8-hour photo- 

 period had a greater number of tillers than plants 

 grown under a 16-hour photoperiod. Ryle (17) 

 reported similar observations. In his studies, the 

 number . of tillers per plant of orchardgrass, 

 meadow fescue (Festuca pratensis Huds.), and 

 perennial ryegrass (Lolium perene L.) decreased 

 as day length was increased from 8 to 24 hours 



(table 5). The smaller number of tillers noted 

 for plants grown under the long photoperiod 

 was due to lack of axillary bud development at 

 the lower nodes and to a longer time interval 

 between the appearance of a leaf and the appear- 

 ance of a tiller in its axil. 



Literature on the influence of light intensity 

 on tiller formation is somewhat contradictory. 

 Horrocks and Washko (11) found that the num- 

 ber of tillers of both timothy (Phleum pratense 

 L.) and reed canarygrass (Phalaris arundinacea 

 L.) was greater on plants grown under shaded 

 conditions compared to plants grown at full in- 

 tensity (fig. 7). Full light intensity was 73 or 80 

 milliwatts cm. -2 min. -1 . Reduction in number 

 of tillers was most pronounced for the timothy 

 plants. Others have reported that any change 

 in the light regime that decreased energy avail- 

 able to the plants reduced their rate of tillering. 

 Sato and Ito (18) reported that short days 

 (8-hour photoperiods) and cool night tempera- 

 tures (15°) were most favorable for tillering 

 of orchardgrass. The ratio of dormant buds to 

 total tillers per plant increased as temperatures 

 under which the plants were grown increased. 

 Sato and Ito suggested that tillering capacity 

 is closely related to the nonstructural carbohy- 

 drate and nonprotein nitrogen content of the leaf- 

 sheath and stem tissue. In their experiments, 

 when growth of the shoot was reduced under 

 lower temperatures and shorter day lengths, non- 

 structural carbohydrate and labile nitrogenous 



Table 4. — -Tiller number of tall fescue plants grown under con- 

 trolled environments (19) 



Number of tillers grown under 

 :emperatures and photoperiods of — 



Age of plants 



when treatment 



began, weeks 



23° C. 



23° C. — 2° C. 2 



Duration, 

 weeks 



8hr. 



16 hr. 8hr. 



16 hr. 



7 



6 



7.1 



5.1 



16.4 



17.5 



7 



3 



4.3 



4.0 



7.2 



6.5 



4 



6 



4.3 



2.7 



9.2 



8.2 



4 



3 



2.4 



1.5 



3.3 



2.9 



Mean 





4.5 



3.3 



il.M 



8.8 



temperature was 23° C. during the 8-hour, high illumination period 

 and 2° C. for 16 hours of darkness, or 8 hours of low illumination plus 8 

 hours of darkness. 



