HEART ROT OF POMEGRANATE, WHEN AND HOW DOES THE PATHOGEN CAUSE THE DISEASE?

Pomegranate (Punica granatum L., Punicaceae) is an ancient plant and fruit, native to central Asia. Since the pomegranate tree is highly adaptive to a wide range of climates and soil conditions, it is grown in many different geographical regions including the Mediterranean basin. Fruit rot also known as “heart rot” or “black heart”, is a major pomegranate disease impacting production worldwide. Although black heart is mostly recognized as a postharvest quality problem, the infection begins and may be identified in the orchard. In most cases Alternaria spp. or Aspergillus spp. are reported as the causal of black heart disease of pomegranate. Black heart caused by A. alternate is characterized by black rot of the fruit core beginning at the calyx area while the hard rind retains its healthy appearance. It is assumed that the fungus causing the disease is penetrating the flower causing the disease later in fruit development. The aim of the present study was to identify the causal agent of heart rot in pomegranate in the Israeli orchard and determining the chain of events leading to development of symptoms in the fruit. Fruits of tree cultivars were collected during 2009 to 2011. Collection was performed at different times and stages of development of the fruit. Fungal isolation was performed from fruit parts (pistil, tunnel and loculus). Koch postulates identified A. alternate as the disease causal agent in Israel. Our results suggest the infection of the stigma of an open flower, a growth of the fungus into the loculus were it stays latently until fruit ripe then the development of rot in some fruits.