A Field Screening of a Pomegranate ( Punica granatum ) Ex-Situ Germplasm Collection for Resistance against the False Spider Mite ( Tenuipalpus punicae )

Mite management is a major problem in pomegranate ( Punica granatum L.) cultivation in the arid and semi-arid regions of India and other Asian countries. The aim of this work was to investigate the susceptibility to the false spider mite ( Tenuipalpus punicae ) in a germplasm collection of Indian pomegranates. A field screening of 73 accessions allowed to define different classes of susceptibility (from very low to very high) based on the percentage of infested leaves. Twenty-two accessions, representative of the empirically identified five susceptibility classes, were further tested. The field screening against the mite, extended to another two years, showed that the infestation level did not display a significant interaction with the growing season, and highly correlated between the different growing seasons. The analysis of the tree vegetative growth (height, canopy size, and stem diameter), main phytochemical classes (total phenolics, flavonoids, and tannins) and the antioxidant activity of the leaves indicated strong significant negative correlations between the infestation level and the biochemical traits. Multidimensional reduction of the measured traits revealed that the extreme classes of susceptibility to mites are mainly separated according to the accumulation of phytochemicals in leaves. This work, for the first time, allowed the identification of pomegranate germplasm with low susceptibility to T. punicae , with positive and useful implications for the establishment of new orchards, plant breeding, and the identification of allelochemicals of the leaves directly affecting mites.