Pome fruit trees as alternative hosts of grapevine trunk disease pathogens

[摘要] ENGLISH ABSTRACT: A survey was undertaken on apple and pear trees in the Western Cape Province to determinethe aetiology of trunk diseases with reference to trunk diseases occurring on grapevine.Grapevine trunk diseases cause the gradual decline and dieback of vines resulting in adecrease in the vine's capability to carry and ripen fruit. In recent years, viticulture has beenexpanding into several of the well established pome fruit growing areas. The presence oftrunk pathogens in pome fruit orchards may affect the health of the pome fruit trees as well ascause a threat to young vineyards planted in close proximity to these potential sources ofviable inoculum.Several genera containing species known to be involved in trunk disease on pomefruit and grapevine were found, including Diplodia, Neofusicoccum, Eutypa,Phaeoacremonium and Phomopsis. Diplodia seriata and D. pyricolum, were isolated alongwith N. australe and N. vitifusiforme. Four Phaeoacremonium species, P. aleophilum, P.iranianum, P. mortoniae and P. viticola, two Phomopsis species linked to clades identified informer studies as Phomopsis sp. 1 and Phomopsis sp. 7, and Eutypa lata were found. Inaddition, Paraconiothyrium brasiliense and Pa. variabile, and an unidentified Pyrenochaetalikespecies were found. Of these the Phaeoacremonium species have not been found on pearwood and it is a first report of P. aleophilum occurring on apple. This is also a first report ofthe Phomopsis species and Eutypa lata found occurring on pome trees in South AfricaTwo new coelomycetous fungi were also found including a Diplodia species,Diplodia pyricolum sp. nov., and a new genus, Pyrenochaetoides gen. nov. with the typespecies, Pyrenochaetoides mali sp. nov., were described from necrotic pear and apple wood.The combined ITS and EF1-α phylogeny supported the new Diplodia species, which isclosely related to D. mutila and D. africana. The new species is characterised by conidia thatbecome pigmented and 1-septate within the pycnidium, and that are intermediate in sizebetween the latter two Diplodia species. Phylogenetic inference of the SSU of the unknowncoelomycete provided bootstrap support (100%) for a monophyletic clade unrelated to knowngenera, and basal to Phoma and its relatives. Morphologically the new genus is characterisedby pycnidial with elongated necks that lack setae, cylindrical conidiophores that are seldomlybranched at the base, and Phoma-like conidia. The phylogenetic results combined with itsdissimilarity from genera allied to Phoma, lead to the conclusion that this species represents anew genus. A pathogenicity trial was undertaken to examine the role of these species on apple,pear and grapevine shoots. N. australe caused the longest lesions on grapevine shoots, whilePyrenochaetoides mali, Pa. variabile, D. seriata and P. mortoniae caused lesions that weresignificantly longer than the control inoculations. On pears, D. pyricolum and N. australecaused the longest lesions, followed by D. seriata and E. lata. On apples, the longest lesionswere caused by N. australe and P. iranianum. D. seriata, D. pyricolum, E. lata, N.vitifusiforme, Pa. brasiliense, P. aleophilum and P. mortoniae also caused lesions on applethat were significantly longer than the control.The study demonstrated that close cultivation of grapevine to apple and pear orchardsmay have inherent risks in terms of the free availability of viable inoculum of trunk diseasepathogens.

[发布机构] Stellenbosch University