Heart Rot of Pomegranate: Disease Etiology and the Events Leading to Development of Symptoms

Abstract

Pomegranate fruit rot disease, known as “heart rot” or “black heart,” is a major pomegranate disease that impacts production worldwide. Heart rot is characterized by black rot of the fruit core that spreads from the calyx area, whereas the outer peel and the hard rind retain their healthy appearance. Aims of the present study were to identify the pathogen that causes pomegranate heart rot in Israel and to study the dynamics of fruit-organ colonization by fungi during fruit development, as the first steps toward the development of management strategies. Several fungi were isolated from pomegranate fruits, among which were species of Penicillium, Aspergillus, Botrytis, and Rhizopus, but the causative pathogen of the disease was identified as Alternaria alternata. This fungus was isolated from the pistils of more than 85% of open flowers and ∼20% of the loculi of asymptomatic fruits and from all tissues of the symptomatic fruits. The dynamics of fruit-organ colonization by fungi during fruit development was recorded in six commercial orchards in 2010 and 2011. It was found that A. alternata spores germinate on the stigmata of open flowers and develop into the style. In some fruits, the mycelium grows into the tunnel and reaches the lower loculus, where the fungus becomes latent for about 3 to 4 months pending initiation of fruit ripening. Then, in a small number of fruits, the fungus starts growing and invades the arils, causing black rot of the arils in the lower loculus. At the beginning of disease development, the fungus causes brown soft rot of the arils, which becomes black and dry as the fungus grows. Eventually, the fungus grows from the lower loculus into the upper loculi, causing rot of the entire fruit.

Identification and mycotoxigenic capacity of fungi associated with pre- and postharvest fruit rots of pomegranates in Greece and Cyprus

“…Penicillium fruit rots recorded in our study were low and similar to preharvest incidence reported in Israel (Ezra et al, 2015), ranging between 3 and 5%, while others report that conventionally cold stored pomegranates at 5°C for 12 weeks developed Penicillium rot at 12.3% (Artes et al, 2000). Experimentation suggests that fruit wounding renders pomegranates more prone to Penicillium rots, compared to pistil inoculation (Ezra et al, 2015;Palou et al, 2013). Thus, different decay incidence due to Penicillium spp.…”

“…Fruit rots, caused mainly by species in the genera Alternaria, Aspergillus and Penicillium, are of major concern for the pomegranate industry worldwide and impact the produce, both quantitatively and qualitatively (Ezra et al, 2015;Michailides et al, 2008;Zhang and McCarthy, 2012). Our data show that among the symptomatic fruit sampled, heart rot caused by species in the genera Aspergillus and Alternaria is the predominant preharvest disease of pomegranates.…”

“…A. niger was the predominant species, with A. tubingensis much less common in both countries. Although Ezra et al (2015) reported that A. alternata is the predominant pathogen causing pomegranate heart rot in Israel, until our study, Alternaria heart rot of pomegranate fruit was referred to in the literature as either undefined at the species level (Palou et al, 2013;Zhang and McCarthy, 2012) or attributed to A. alternata and other Alternaria spp. (Michailides et al, 2008;).…”

“…A plethora of Penicillium species, including Penicillium adametzioides, Penicillium expansum, Penicillium glabrum, Penicillium implicatum and Penicillium purpurogenum (Bardas et al, 2009b;Ezra et al, 2015;Palou et al, 2013) have been previously reported on pomegranate. Penicillium fruit rots recorded in our study were low and similar to preharvest incidence reported in Israel (Ezra et al, 2015), ranging between 3 and 5%, while others report that conventionally cold stored pomegranates at 5°C for 12 weeks developed Penicillium rot at 12.3% (Artes et al, 2000).…”

“…Country Mycotoxins AOH AME TEN In a two year study in Israel, Ezra et al (2015) reported that rot incidence of pomegranate fruit at advanced developmental stages, caused mainly by Alternaria spp. and Penicillium spp., ranged between 5% and 8.1%.…”