Investigation into pomegranate dieback in Australia

O.F. Rad, M.R. Vazifeshenas
This investigation was carried out to identify a possible correlation between waterlogging and Australian pomegranate dieback; to address whether it is biotic or abiotic? Over several years, various pomegranate trials were conducted on 14 trial sites with markedly different topography and environmental conditions. In one part, a minimum of six specimens from multiple pomegranate (Punica granatum L.) accessions were planted at each site. Compound site analyses were undertaken originally to determine the phenological variance among different accessions planted in regions with different environmental factors. All plants were originally propagated under controlled conditions using cuttings obtained from a single parent plant of each cultivar. Once these plants were two years old, they were planted at various trial sites. The rate and volume of vegetative growth, leaf and flower formation, and regional and climatic characteristics were observed to compare plant behaviour from one cultivar and region to another. Relative humidity, annual rainfall, weather patterns, site soil composition, altitude, and proximity to sea/ocean exhibit direct correlations with variations in phenological observations between trial sites. However, the most striking, and at first incidental, finding from the trials pointed to waterlogging as a possible cause of the dieback. A direct correlation existed between dieback and waterlogging, chiefly observed in areas with most silt and clay in the soil. Notably, the volume or frequency of rainfall, either daily or annually, had little or no direct effect on the trees in regions with much lower silt and/or clay in the soil. These findings led to the design and rollout of a pot trial under controlled conditions not only to validate the findings relevant to the dieback but also to identify several accessions with a certain degree of tolerance toward waterlogging and hence the pomegranate dieback. The implication of this study is not simply that Punica is susceptible to waterlogging, as are many other fruiting plants, but rather not knowing what disease, if any, was behind the dieback. There, now, exists a good body of evidence pointing to abiotic, waterlogging rather than biotic cause(s). There is additional evidence of cultivars that exhibit greater tolerance for waterlogging, rendering them suitable for use as rootstock and future plant breeding for building resilience into current commercial cultivars.
Rad, O.F. and Vazifeshenas, M.R. (2022). Investigation into pomegranate dieback in Australia. Acta Hortic. 1349, 123-132
DOI: 10.17660/ActaHortic.2022.1349.17
pomegranate, dieback, soil composition, phenological, waterlogging

Acta Horticulturae