Multigene phylogeny, morphology, and pathogenicity trials reveal novel Cytospora species involved in perennial canker disease of apple trees in Iran.

In recent years, canker and die-back diseases have become a growing threat for the productivity and longevity of apple orchards in Iran. In this study, 131 Cytospora isolates were recovered from symptomatic tissues of apple trees in apple orchards of Iran. Multigene phylogenetic inference based on combined sequence data of ITS, act, rpb2, and tef1-α loci, supplemented with morphological characteristics and pathogenicity assay revealed four novel Cytospora species which were described as C. avicennae, C. azerbaijanica, C. ershadii, and C. iranica, and four known species, namely C. chrysosperma, C. parasitica, C. paratranslucens, and C. sorbicola. Also, C. sorbicola is newly reported on apple trees worldwide. Koch's postulates were fulfilled to confirm that all eight species in this study were pathogenic on apple trees in Iran, among which C. sorbicola was the most intensive species. The results of this study further highlight rich diversity among Cytospora species occurring on apple trees, revealing several novel Cytospora species on this host. The host range, geographical distribution, and economic significance of novel species on apple industry remains to be studied.

Phoma crystallifera with phytotoxic effects and pathogenic potential against field bindweed (Convolvulus arvensis L.) in Iran.

AIMS: To identify a potential pathogenic isolate of fungus on Convolvulus arvensis and to determine its phytotoxic activity, which revealed the presence of toxic metabolites responsible for the toxicity against the target weed. METHODS AND RESULTS: A high virulent isolate of the fungus, Phoma crystallifera was isolated from symptomatic field bindweed in the west of Iran and was screened for the production of phytotoxins, which promoted necrosis on the detached leaves and seedlings of field bindweed in the bioassays. The isolate was distinct from other isolates of the fungi on the basis of morphological characteristics and the combined sequence database of the ITS region, partial LSU rDNA and ß-tubulin gene. Isolate P. crystalifera P6 produced the highest amount of phytotoxins after 21 days in a shacked culture of Richard's broth. The active metabolites were isolated from a cell-free culture filtrate by ethyl-acetate and purified by thin layer chromatography. The result indicated that six out of nine spots had phytotoxic activity in the bioassays, with Rf values of 0·16, 0·30, 0·36, 0·43, 0·57 and 0·81. CONCLUSIONS: Phoma crystallifera P6 and its active metabolites showed significant phytotoxic effects on the detached leaves of C. arvensis. SIGNIFICANCE AND IMPACT OF THE STUDY: To date, there are no reports of possible biocontrol agent(s) on C. arvensis in Iran. Thus, P. crystallifera P6 is introduced here as a severe pathogenic fungus and which can be used as a biocontrol agent against C. arvensis.