Neofusicoccum parvum Associated With Dieback and Fruit Rot of Pomegranate in Tunisia

Abstract

Tunisia is one of the main pomegranate (Punica granatum L.) producing countries. During surveys conducted in 2018–2020 in pomegranate orchards along Tunisia's East Coast (Sousse governorate), disease symptoms were observed on cvs. Gabsi and Kalai. Disease incidence was estimated at approximately 10%–20% and disease severity varied from dieback of one shoot or branch to almost complete tree decline. The current study aimed to characterise the etiological agent(s) associated with these symptoms. Fungal isolates associated with the symptoms were identified as Neofusicoccum parvum based on morphological and molecular phylogenetic analyses, using combined sequences of ITS, tef1 and β-tubulin (tub2) loci. Pathogenicity tests performed on 1-year-old detached shoots and on fruits demonstrated that N. parvum was pathogenic to pomegranate cv. Gabsi. The response toward N. parvum of pomegranate cultivars commonly grown throughout Tunisia, namely cvs. Gabsi, Garroussi, Zehri, Khedhri and Kalai, was evaluated using artificial inoculation. Results revealed that all cultivars tested were susceptible to fruit infection and rotted completely within 12–15 days post-inoculation. In the detached shoot tests, the eight tested cultivars responded differently to N. parvum isolates. To our knowledge, this is the first report on pomegranate dieback and fruit rot caused by N. parvum in Tunisia and in Africa. In a host range study on eight fruit tree species, all species (fig, olive, apricot, pear, loquat, lemon, cherimoya and guava) displayed symptoms on artificially inoculated shoots, with significant host species–N. parvum isolate interactions observed.