Impact assessment of apple replant disease (ARD) by indication at single tree level in orchards

U. Cavael, K. Diehl, P. Lentzsch
Apple replant disease (ARD) is a serious risk affecting newly planted apple trees after consecutive planting of apple in the same field. It is a soil-based production constraint that constitutes a widespread impediment to achieving profitability in fruit production. ARD-effects are reflected in a characteristic decline of tree growth, root necrosis and yield reduction. A pilot study including two orchards in Brandenburg (Germany) had the objective to develop a tree-specific assessment of ARD-related effects. A methodological approach was developed by projecting crown volume on crown area by photographic imaging. Crown area was calculated based on software (Krypten, Herolab GmbH) and related to trunk cross sectional area (CSA), resulting in a strong correlation between both vegetative parameters. Further, soil-borne microorganisms, particularly fungi, are commonly assumed as causal organisms of ARD. Abundances of Alternaria group (Ag), expressed in logarithmic scale, and CSA differed significantly between no-replant soil and replant soil. Analysis of data over both soil-variants (replant/no-replant) resulted in a significant medium correlation coefficient (r2 = 0.4) between ln(Ag) and CSA. Based on this relation, ARD-effects were assessed at the level of the individual tree by scoring the calculated ratio of CSA and ln(Ag) per tree. Each score indicated the tree-specific impact of ARD, which in turn could be applied to estimate the reduction of vegetative growth and consequently yields as compared to no-replant trees. The mean yield of trees amounts to the ARD-effect at field-level. The results reflected reports on yield depression by fruit producers in Brandenburg. Further attention should be given to the high variability of ARD-effects within a production-site, e.g., the assessment of management effects at single tree-level.
Cavael, U., Diehl, K. and Lentzsch, P. (2020). Impact assessment of apple replant disease (ARD) by indication at single tree level in orchards. Acta Hortic. 1270, 281-294
DOI: 10.17660/ActaHortic.2020.1270.34
soil-borne microorganisms, apple production, indicator

Acta Horticulturae