Bunch compactness, rot incidence, and stenospermocarpy gradient: a five-year evaluation of six Pinot blanc clones in northeast Italy

In viticulture, bunch rot is considered a major issue due to the elevated intrinsic varietal susceptibility, leading to significant yield and quality losses. Pinot blanc can be severely affected by late-season bunch rot, primarily due to its characteristically compact bunch structure. While several vineyard management practices can induce looser bunch architecture, clonal selection offers the potential to identify individuals with naturally less compact bunches without major penalties on yield or juice chemical parameters. In this study, six Pinot blanc clones (namely, ersa140, 141, and 142; Lb16 and 18; and SMA102), trained to “pergola semplice”, were evaluated over five years in an experimental vineyard in the Trentino region. The evaluation focused on traits associated with yield and its components, bunch compactness, juice chemical parameters, and bunch rot incidence. The results revealed contrasting traits among clones, with a gradient in yield and related components across the tested material. Although differences in bunch compactness were observed—expressed as the ratio between bunch weight and rachis length (ranging from 6 to 15 g/cm)—the loose bunch trait was primarily associated with reduced yield and was linearly related to an increased number of stenospermocarpic berries. Clones with looser bunches exhibited higher °Brix and pH levels, likely due to berry dehydration (potentially driven by accelerated ripening following an unbalanced leaf-to-fruit ratio) and increased potassium uptake, respectively. Bunch rot frequency and the number of bunches exhibiting high rot incidence varied among clones, potentially due to two non-mutually exclusive mechanisms: (i) looser bunch architecture and (ii) specific properties of the berry skin. This study provides evidence of a strong relationship between bunch characteristics and yield potential in the six Pinot blanc clones evaluated, which should be considered in future vineyard planning. Intermediate clones, such as Lb18 and especially SMA102, were characterised by moderate vine productivity levels (~3 kg per vine) combined with good tolerance to bunch rot, suggesting their suitability for environments with moderate disease pressure without incurring severe yield penalties