Response of Tunisian Pomegranate (Punica granatum L.) Cultivars and Several Plant Hosts to Coniella granati (Saccardo)

Abstract

Pomegranate (Punica granatum L.) disease incited by Coniella granati (Saccardo) has been recently reported in Tunisia causing branch dieback, shoot blight and fruit rot. The present study was undertaken in order to evaluate the response of nine known and widely grown pomegranate cultivars throughout Tunisia toward this emergent pathogen, to study the host range of C. granati and to identify its extracellular cell wall degrading enzymes. Plant response was determined based on fruit lesion diameter and length of external, internal and pycnidia-bearing lesions recorded on wounded and detached branches. All cultivars tested were susceptible to C. granati fruit rot where the lowest lesion diameters (87-88 mm), recorded 9 days post-inoculation (DPI), were noted on cultivars Gabsi and Zaghouani. At 30 DPI, intact detached branches were shown to be moderately susceptible to C. granati infection with only cv. Chetwi being moderately tolerant. On altered detached branches (branches devoid of bark layers) Jbali, Zehri and Zaghouani were the most susceptible to C. granati giving rise at 12 DPI to longer lesions bearing pycnidia than the other cultivars. C. granati isolates tested were able to cause dry rot on nine out of ten different fruits, with apple, tomato and fakous (Cucurbita melo var. flexuosus) fruits being the most susceptible ones while they were nonpathogenic on zucchini. On detached and intact branches, C. granati was weakly pathogenic on orange and pear compared to apple and loquat and was non pathogenic to olive, fig, peach, prune, and apricot branches. Using specific media, C. granati isolates were shown able to produce laccase, protease, pectinase, pectate transeliminase, and cellulase but no amylolytic and lipolytic activities were detected. Thus, as C. granati represents a threat to all Tunisian pomegranate cultivars as well as for other tree fruit species, the search for effective management methods towards this disease is of urgent need.