First report ofPhyllosticta citricarpaand description of two new species,P. paracapitalensisandP. paracitricarpa, from citrus in Europe

Abstract

The genus Phyllosticta occurs worldwide, and contains numerous plant pathogenic, endophytic and saprobic species. Phyllosticta citricarpa is the causal agent of Citrus Black Spot disease (CBS), affecting fruits and leaves of several citrus hosts (Rutaceae), and can also be isolated from asymptomatic citrus tissues. Citrus Black Spot occurs in citrus-growing regions with warm summer rainfall climates, but is absent in countries of the European Union (EU). Phyllosticta capitalensis is morphologically similar to P. citricarpa, but is a non-pathogenic endophyte, commonly isolated from citrus leaves and fruits and a wide range of other hosts, and is known to occur in Europe. To determine which Phyllosticta spp. occur within citrus growing regions of EU countries, several surveys were conducted (2015–2017) in the major citrus production areas of Greece, Italy, Malta, Portugal and Spain to collect both living plant material and leaf litter in commercial nurseries, orchards, gardens, backyards and plant collections. A total of 64 Phyllosticta isolates were obtained from citrus in Europe, of which 52 were included in a multi-locus (ITS, actA, tef1, gapdh, LSU and rpb2 genes) DNA dataset. Two isolates from Florida (USA), three isolates from China, and several reference strains from Australia, South Africa and South America were included in the overall 99 isolate dataset. Based on the data obtained, two known species were identified, namely P. capitalensis (from asymptomatic living leaves of Citrus spp.) in Greece, Italy, Malta, Portugal and Spain, and P. citricarpa (from leaf litter of C. sinensis and C. limon) in Italy, Malta and Portugal. Moreover, two new species were described, namely P. paracapitalensis (from asymptomatic living leaves of Citrus spp.) in Italy and Spain, and P. paracitricarpa (from leaf litter of C. limon) in Greece. On a genotypic level, isolates of P. citricarpa populations from Italy and Malta (MAT1-2-1) represented a single clone, and those from Portugal (MAT1-1-1) another. Isolates of P. citricarpa and P. paracitricarpa were able to induce atypical lesions (necrosis) in artificially inoculated mature sweet orange fruit, while P. capitalensis and P. paracapitalensis induced no lesions. The Phyllosticta species recovered were not found to be widespread, and were not associated with disease symptoms, indicating that the fungi persisted over time, but did not cause disease.

Phyllosticta citricarpa and sister species of global importance to Citrus

“…Similarly, Wang et al . () described P. citrichinaensis and distinguished two subclades within P. citricarpa , which were differentiated as two species in a later study (Guarnaccia et al ., ) and are described in greater detail below. In Brazil, Glienke et al .…”

“…citribraziliensis , combining four partial regions of DNA (ITS, tef1 , actA, gapdh ). The most recent study focusing on Phyllosticta taxonomy (Guarnaccia et al ., ) revealed two new species, namely P . paracapitalensis , from asymptomatic leaves of citrus species in Italy and Spain, and P .…”

“…citribraziliensis and P . paracapitalensis were reported as endophytes on different citrus hosts (Glienke et al ., ; Guarnaccia et al ., ).…”

“…citrichinaensis on different citrus species in Asia and P. paracitricarpa on Citrus sinensis fruit in China (Wang et al ., ). The last species was also detected from citrus leaf litter in Europe (Guarnaccia et al ., ). Nevertheless, P .…”

“…Phyllosticta species have been associated with Citrus spp. worldwide (Baayen et al ., ; Baldassari et al ., ; Brentu et al ., ; Carstens et al ., ; Er et al ., ; Everett and Rees‐George ; Glienke et al ., ; Glienke‐Blanco et al ., ; Guarnaccia et al ., ; Wikee et al ., ; Wulandari et al ., ). Citrus black spot (CBS) is an economically important foliar and fruit disease caused by P. citricarpa (Baldassari et al ., ; Kotzé, ).…”