Analysis of the spatial spread of esca in some Tuscan Vineyards (Italy)

Four vineyards in Tuscany [GTFI at Gambassi Terme, cv. Sangiovese; CBSI-1, 2, 3 at Castelnuovo Berardenga, cv. Sangiovese (1), cv. Trebbiano (2) and various cultivars (3)] were examined for esca over periods of 4 (CBSI-1, 2, 3) or 6 years (GTFI). A high level of discontinuity in the symptoms expression of each diseased plant was observed from year to year. The cumulated disease incidence, calculated by counting all plants exhibiting symptoms at least once during the entire 4 to 6 year test period, was 49.09% at Gambassi Terme and an average of 13% for the 3 vineyards at Castelnuovo Berardenga. Analysis of the field data by three indices of dispersion (Lloyd’s index of patchiness, variance-to-mean ratio and Morisita’s index) and ordinary runs tests showed occasional aggregation of diseased vines only in vineyards with higher disease incidence (GTFI and CBSI-3). The results of two-dimensional distance class and correlation analyses (2DCLASS and 2DCORR) indicated a significant spatial correlation of infected- infected plant pairs in the GTFI vineyard both along and across columns. For CBSI-3 (19 columns, one cultivar for column), however, the results indicated a tendency for infected vines to be aggregated along columns. The remaining 2 vineyards (CBSI-1 and 2) consistently exhibited a random spatial pattern of diseased vines. This result suggests that the down-column contagion found for CBSI-3 may merely be a byproduct of cultivar dependent susceptibility to disease. On the whole, the results obtained suggest that in the vineyards examined esca was spread by airborne spores from distant and/or internal sources rather then by contaminated pruning tools along the vine columns.