Virulence spectra and geographical distribution of Mal Secco disease of citrus caused by Phoma tracheiphila in the Mediterranean countries: Tunisia and Italy

Abstract

This work aimed to find out patterns of virulence\ud variability of a Phoma tracheiphila population of\ud 51 isolates, to determine geographic distribution of Mal\ud Secco disease in citrus orchards of six Mediterranean\ud countries and also to establish correlation between geographic\ud distribution and pathotypic distance of P. tr\ud population structure over our sampling spatial scale.\ud Based on unweighted pair-group method with arithmetic\ud averaging clustering and mean disease rating scores,\ud three distinct virulence groups were identified. The 51\ud isolates were classified into 20 pathotypes. Extensive\ud virulence variability was detected in 51 isolates of P. tr\ud causing MSD of citrus in the Mediterranean basin.\ud Regression plot between pairwise virulence and geographical\ud distance showed that virulence is independent\ud of the geographical origin and that isolates collected\ud from the same country have different degrees of virulence.\ud The lack of significant correlation between virulence\ud and geographic structure confirmed the absence of\ud isolation-by-distance pattern, suggesting non-regular and non-gradual dispersal of the pathogen over this\ud spatial scale

An Overview on Citrus Mal Secco Disease: Approaches and Strategies to Select Tolerant Genotypes in C. limon

“…The disease firstly appeared on the Greece islands of Chios and Poros at the end of the nineteenth century then, rapidly spread over the coasts of the Mediterranean basin. Currently, the geographical distribution of MSD comprises the east coast of the Black Sea (Georgia) and mainly all citrus-growing countries of the Mediterranean Basin, except for Morocco, Portugal and Spain [29] with variable incidence and severity of plant damages [27].…”

“…This movement is supported by phialoconidia, which move in the xylem by utilizing the transpiration flow of plants [55]. Since extensive virulence variability in P. tracheiphila causing MSD on citrus was detected [29], the pathogen may kill a lemon plant within a few months or years, depending on type/pathogenicity of isolate and, also, the age of tree. The disease course is strictly related to the rate of colonization of the vascular system by the fungus.…”

Scientific Opinion on the pest categorisation ofPlenodomus tracheiphilus(Petri) Gruyter, Aveskamp & Verkley [syn.Phoma tracheiphila(Petri) L.A. Kantschaveli & Gikashvili]

“…Evaluations of the susceptibility level of citrus to infection by the pathogen are sometimes contradictory, especially for rootstocks. For instance, in Tunisia, the citrus industry is based on the use of the lemon cultivars Eureka and Lunari grafted onto sour orange (C. aurantium), which is the oldest rootstock used in citriculture for its resistance to several diseases (Ziadi et al, 2014). On the other hand, sour orange is considered to be highly susceptible to the infection by P. tracheiphilus in Italy, while it is moderately susceptible in Israel (Palm, 1996).…”

“…In a recent study from Turkey, it was reported that effective control of the disease would double production in lemon-producing countries (Gulsen et al, 2007). In addition, Ziadi et al (2012Ziadi et al ( , 2014 recently reported that the disease causes serious damage in Tunisia having affected up to 100 % of trees of susceptible lemon cultivars. Nigro et al, 2011).…”

Phenotypic Evaluation of a Lemon Hybrid Population to Identify Sources of Resistance to Plenodomus tracheiphilus

“…However, Solel and Spiegel-Roy (1978) revealed discrepant behaviors between specific lemon cultivars subjected to natural infections in field conditions and artificial inoculations in controlled conditions. Moreover, these protocols have been applied mostly to test the susceptibility of lemon cultivars or sour orange seedlings, or to characterize P. tracheiphilus strains (Ziadi et al 2014). Tuzcu et al (1992) reported preliminary results of screening young lemon nucellar seedlings and intraspecific hybrids by artificial inoculation.…”