GROWTH ASPECTS OF PLANT VIRUS INFECTIONS 



645 



centration in the case of turnip-mosaic virus in rape under diflFerent 

 photoperiods (Pound and Garces, 1959). When rape plants are grown 

 under 4-, 8-, 12-, and 16-hour photoperiods, both virus concentration 

 and host growth increase with increased photoperiod, regardless of the 

 time interval after inoculation (Figure 9). Shortly after inoculation, 

 virus synthesis is more affected by photoperiod than is host growth, but 

 in later assays the two are closely parallel. Since there are no reversals 

 in concentration patterns, it is suggested that in this host-virus combi- 

 nation, virus synthesis and host growth are in a balance which is not 

 upset by photoperiod or by temperature. 



Summary and general conclusions 



Virus synthesis in plants obviously results from an aberration of 

 the cellular metabolism of the host, since viruses do not have the neces- 

 sary enzymes for their own self-duplication. The virus nucleic acid 



4hr. ehr. I2hr. I6hr. 



7 DAYS 



4hr, ehr. I2hr. I6hr. 4hr. 8hr. I2hr.l6h'. dhr. 6hr. I2hr. I6hr. 



14 DAYS 



21 DAYS 



28 DAYS 



Figure 9. Effect of photoperiod on host growth and concentration of turnip 

 mosaic virus in rape. (After Pound and Carlos Garces-Orejuela. ) 



