Gas exchange measurements were made on healthy and rose bloom infected branches of cranberry on 31 May 1991 during the middle of the sporing period. CO2 assimilation rates of infected branches were reduced 89% on a leaf area basis and 95% on a dry weight basis compared to healthy tissue. Stomatal conductance was 12× higher in infected tissue, while mesophyll conductance was reduced by 92%. Transpiration was 4× higher in diseased tissue reducing water use efficiency by 96%.
Total chlorophyll content of diseased tissue was 81% less than that of healthy tissue but chlorophyll a/b was unchanged. Fourth derivative profiles of chlorophyll action spectra were altered in diseased tissue. Rose bloom leaves were found to lack stomata and have no discernable mesophyll layer.