Effect of infections with barley yellow dwarf virus and Fusarium spp. on assimilation of 14CO2 by flag leaves and translocation of photosynthates in wheat

The effects of infections of Barley yellow dwarf virus (BYDV), Fusarium culmorum and F. graminearum alone as well as double infections of BYDV and Fusarium spp. on assimilation of (CO2)-C-14 by flag leaves and translocation of photosynthates in winter wheat cultivars 'Agent' (susceptible to Fusarium head blight (FHB)) and 'Petrus' (moderately resistant to FHB) were studied in outdoor pot experiments in 2001 and 2002. Wheat plants were inoculated with BYDV-PAV strain by Rhopalosiphum padi at growth stage (GS) 51 in 2001 and at GS 39 in 2002. Control plants were inoculated with virus free aphids. In the middle part of spikes single florets of wheat plants of both cvs were inoculated at GS 65 with conidia suspensions of F. culmorum in 2001 and F graminearum in 2002. Exposure of flag leaves with (CO2)-C-14 revealed that photosynthetic fixation was most pronounced at GS 71 and declined from GS 75 to GS 85. F. culmorum infections diminished absorption of (CO2)-C-14 by flag leaves in cv. 'Agent' and very low percentages of photosynthates were transported into the middle and upper head parts, while absorption of (CO2)-C-14 in cv. 'Petrus' was only slightly reduced and high proportions of C-14 assimilates were translocated also into the middle and upper spike sections. BYDV infections markedly reduced (CO2)-C-14 assimilation by flag leaves and export of photosynthates into wheat spikes of both cvs, especially in cv. 'Petrus'. In double infected plants (BYDV and Fusarium spp.), photosynthetic fixation by flag leaves of both cvs at the first and second exposure times corresponded with that of BYDV-infected plants. However, export of assimilates in spikes was more effectively reduced in cv. 'Agent' than in cv. 'Petrus'. Preinfestation with R. padi slightly reduced assimilation of (CO2)-C-14 in both cvs. In cv. 'Agent', translocation of C-14 assimilates into the upper spike section was more impaired than in cv. 'Petrus'. Assimilation of (CO2)-C-14 and distribution pattern of C-14 assimilates in R. padi-preinfested plus Fusarium-infected plants of both cvs resembled that of fungus-infected plants at the first two exposure times. Absorption of (CO2)-C-14 by flag leaves and translocation of assimilates into spikes was markedly affected by severity of virus infection. The earlier BYDV inoculation in 2002 at GS 39 resulted in more severe virus infection and, therefore, drastically diminished (CO2)-C-14 absorption by flag leaves and translocation of photosynthates into spikes compared to 2001 when wheat plants were inoculated at GS 51. The differential translocation of photosynthates into Fusarium-infected spikes of the two cvs 'Agent' and 'Petrus' reflects the varying susceptibility of both cvs to FHB. The studies also revealed severe effects of BYD-disease on FHB development. This interaction may result in practical consequences.