INFLUENCE OF CUCUMBER MOSAIC-VIRUS INFECTION ON THE GROWTH-RESPONSE OF PORTULACA-OLERACEA (PURSLANE) AND STELLARIA-MEDIA (CHICKWEED) TO NITROGEN AVAILABILITY

The study characterized the influence of cucumber mosaic virus (CMV) o n the growth response of two annual weeds to nitrogen. Plants were gro wn individually along a N gradient from 4 to 32 mmol l(-1) and data we re interpreted using growth analysis. Plant biomass increased with N c oncentration and was significantly higher for healthy than infected pl ants at the two highest N concentrations. Healthy plants of Portulaca oleracea L. were characterized by lower biomass allocation to leaves a nd higher biomass allocation to roots than infected plants; no change in biomass allocation was recorded for Stellaria media Vill. Relative growth rate (RGR), net assimilation rate (NAR) and specific leaf area (SLA) of plants increased with increasing N concentration. Healthy pla nts of P. oleracea were characterized by a higher RGR and NAR and a lo wer SLA than infected plants, whereas healthy S. media had a higher RG R but a similar NAR and SLA or leaf weight ratio (LWR) compared with i nfected plants. The consequences of these results on the population dy namics of weeds and virus spread are discussed.