Resumen de Berry cracking caused by powdery mildew (uncinula necator) infection to 'fujiminori' grapevines (vitis sp.)
Powdery mildew (Uncinula necator) is one of the common grape diseases in protected rain-shelter cultivation in Korea. Wounds from disease infection may provide the starting point of cracking in susceptible tetraploid grapevines. To find out the effect of U. necator infection on berry cracking, morphological and histological observations were conducted using the cracking susceptible ?Fujiminori? grape cultivar. The intact berry rate was lower after inoculation (85.8%) than in the control vines (89.3%). Cluster weight and numbers of berries per cluster in inoculated vines was significantly lower, with 722.6 g and 38.6 compared with 842.2 g and 40.2 in controls. Inoculation with powdery mildew reduced the firmness of pericarp to 1.11 kg?5 mm-1 ? from 1.31 kg?5 mm-1 ? with the controls. The berry cracking rate under critical turgor pressure was also decreased from 18.0 to 29.0% after inoculation with U. necator. The degree of cell wall degradation was measured by cell wall content from 10 g of pericarp tissue. The cell wall content of inoculated ?Fujiminori? was reduced 31.3% with collection of 311.7 mg compared with untreated vines of 453.7 mg. Polygalacturonase, one of the major enzymes inducing cell wall degradation, activity was increased from 0.143 to 0.204 units?ml-1 in U. necator infected berries. In the results from powdery mildew inoculation, the invasion of hypha in early berry growth stages before veraison promotes cell breakdown between the sub-epidermal and the epidermal layer by secretion of cell wall degradation enzymes even without any visible disease symptom in the berry.
