Pomegranate Heart Rot Caused by Alternaria alternata, an Emerging Disease in Algeria.

Pomegranate heart rot (black heart) was observed in several pomegranate-growing areas of Algeria. From 2022 to 2025, surveys were conducted across 15 provinces (20 localities), and a total of 85 fruits (symptomatic and asymptomatic) were collected. Fruits were cut transversely to assess internal symptoms, ranging from early aril browning to dry black rot. Thirty Alternaria isolates were obtained and grouped into four morphotypes based on colony and conidial morphological traits. A subset of 18 isolates was analysed by multilocus phylogeny (ITS, EF-1α, GAPDH and OPA10-2); all analysed isolates clustered within the Alternaria alternata species complex, in the clade including the ex-type strain CBS 916.96. Fruit pathogenicity tests with Algerian isolate GA reproduced typical internal heart rot symptoms, and the pathogen was consistently re-isolated from symptomatic tissues. In fruit inoculations with isolate GA, cultivars differed in susceptibility, with mean disease severities of 94%, 62% and 9.5% in 'Taferrante', 'Ikhessène' and 'Kares', respectively, expressed as the percentage of the fruit section presenting rot symptoms. Detached leaf assays indicated isolate-dependent differences in aggressiveness, and 'Kares' showed the lowest susceptibility. Overall, the results confirm that A. alternata is the causal agent of pomegranate heart rot in Algeria and provide baseline information for disease diagnosis and management.