Neofusicoccum parvum and Diaporthe foeniculina associated with twig and shoot blight and branch canker of citrus in Greece

Abstract

In a survey performed in Chania and Aetoloacarnania, Greece in years 2013–2014, fungal isolates causing twig and shoot blight and branch canker of citrus trees were morphologically characterized and identified by multiple gene sequence analysis. By sequencing the ITS‐5.8S rRNA, the elongation factor 1‐α (EF1‐α), the β‐tubulin and the RNA polymerase II subunit (Rpb2) genes, the isolates examined were associated with Diaporthe foeniculina (six isolates) and Neofusicoccum parvum (one isolate). All six D. foeniculina isolates showed slow colony growth rates (7.4 ± 3.2 mm/day), while the N. parvum isolate exhibited fast growth (41.6 mm/day). Koch's criteria were met after re‐isolation of D. foeniculina isolates from all inoculated Citrus spp. and N. parvum from inoculated C. reticulata “Ortanique” and after having developed symptoms similar to those detected on shoots and branches collected from citrus fields. Based on lesion length on detached C. medica “Lia Kritis” shoots, N. parvum caused long necrotic lesions (58 mm in length) in comparison with a length of 12–21 mm lesions caused by D. foeniculina isolates. Pathogenicity trials on nine Citrus spp., which had been inoculated with D. foeniculina and N. parvum, revealed different levels of susceptibility, indicating a host‐dependent infection effect, with Poncirus trifoliate × C. paradisi (“Citrumelo Swingle”) being the most resistant citrus genotype. Lack of host specificity suggests that their pathogen–host association could be attributed to ecological rather to co‐evolutionary factors. This work represents the first report, accompanied with pathogenicity tests, on botryosphaeriaceous and diaporthaceous pathogens associated with twig and shoot blight and branch canker of citrus in Greece.

Bot Gummosis of Lemon (Citrus × limon) Caused by Neofusicoccum parvum

“…Consistently with symptoms observed on naturally infected trees in the field, pathogenicity tests revealed that N. parvum was very aggressive on ‘Femminello 2kr’ and ‘Monachello’, which reacted to the infection with the abundant production of gum exudate, while it was weakly virulent on ‘Carrizo’ citrange, commonly used as a citrus rootstock. These marked differences in susceptibility to bot gummosis among different citrus genotypes are in agreement with results of other Authors [ 10 ]. In pathogenicity trials carried out in Greece the citrumelo ‘Swingle’ ( Poncirus trifoliata × C. paradisi ), commonly used as a rootstock, was proved to be the least susceptible to N. parvum and D. foeniculina infections among nine different citrus species [ 10 ].…”

“…hyalinum , formerly Hendersonula toruloidea ) [ 3 , 8 , 9 ]. Neofusicoccum parvum and Diaporthe foeniculina were reported to be responsible for shoot blight and branch cankers of citrus in Greece, but in pathogenicity tests N. parvum was significantly more virulent than D. foeniculina [ 10 ]. Dothiorella viticola was identified as the causal agent of bot gummosis of citrus in Tunisia [ 11 ].…”

Genetic Diversity and Pathogenicity of Botryosphaeriaceae Species Associated with Symptomatic Citrus Plants in Europe

“…causing disease on citrus are known in European countries, where N. parvum and Ne. dimidiatum were reported on C. reticulata in Greece and on C. sinensis in Italy, respectively [ 32 , 37 ].…”

Occurrence of Diaporthe species in Eucalyptus globulus, Pinus pinaster and Quercus suber in Portugal

“…Host‐pathogen interactions with other common forest‐related fungi (e.g. Alternaria , Biscogniauxia , Botryosphaeria , Cytospora , Diplodia , Dothiorella , Gnomoniopsis , Neofusicoccum , among others) combined with environmental stresses might boost tree decline, posing a threat to forests (Caldeira, 2018; Hossain et al, 2019; Oliva et al, 2014; Vakalounakis et al, 2019). Therefore, defining levels of aggressiveness exclusively on length of wood discoloration might not correlate directly with strain aggressiveness.…”

“…Among the symptoms observed are as follows: dieback, stem canker, leaf spots, blight, root and fruit rots, and seed decay (Gomes et al, 2013; Guarnaccia et al, 2018; Santos et al, 2011). Although species of Diaporthe are common on fruit crops such as grapevines (Guarnaccia et al, 2018), citrus (Guarnaccia & Crous, 2017; Vakalounakis et al, 2019), walnuts (López‐Moral et al, 2020; Luna et al, 2020), apples and pears (Guo et al, 2020; KC & Rasmussen, 2019; Santos et al, 2017), it has been shown that some species of this genus are also responsible for diseases on forest trees. For instance in Europe, Diaporthe species have been reported on a wide diversity of forest hosts, such as Acer spp., Alnus spp., Betula spp., Fraxinus spp., Ilex aquifolium , Picea abies , Pinus spp., Pseudotsuga menziesii and Quercus spp.…”