Pleiocarpon gen. nov. and a new species of Ilyonectria causing basal rot of Strelitzia reginae in Italy

Abstract

During 2015, a new basal rot disease was observed on potted plants of Strelitzia reginae in an ornamental nursery located in eastern Sicily. Isolations from symptomatic parts of these diseased plants consistently yielded cylindrocarpon-like isolates. Multigene analyses of the partial gene regions of 28S large subunit nrDNA, β-tubulin, histone H3, translation elongation factor 1-alpha, internal transcribed spacer region and intervening 5.8S nrRNA gene, and RNA polymerase II second largest subunit genes, supported by morphological characters supported the recognition of a new genus, Pleiocarpon based on P. strelitziae sp. nov., and a new Ilyonectria species, described here as I. strelitziae sp. nov. The pathogenicity of both I. strelitziae and P. strelitziae were confirmed on young plants cultivated under controlled conditions in a growth chamber. Both cylindrocarpon-like fungi were pathogenic to S. reginae and reproduced symptoms similar to those observed in the nursery. Of the two species, P. strelitziae was more aggressive than I. strelitziae, resulting in the death of all inoculated plants.

Keywords: Nectriaceae; multigene phylogeny; pathogenicity; taxonomy.

Fig. 1.

Dry basal rot symptoms of Strelitzia reginae observed in the nursery. A–C. Wilting and dying S. reginae plants. D. Dry basal stem rot. E. Rot of internal leaf.

Fig. 2.

The ML consensus tree inferred from the combined ITS, LSU, tef1 and tub2 sequence alignments. Thickened branches indicate branches present in the ML, MP and Bayesian consensus trees. Branches with ML-BS & MP-BS = 100 % and PP = 1.0 are in blue. Branches with ML-BS & MP-BS ≥ 75 % and PP ≥ 0.95 are in red. The scale bar indicates 0.1 expected changes per site. The tree is rooted to Xenogliocladiopsis cypellocarpa (CBS 133814). Epi- and ex-type strains are indicated in bold.

Fig. 3.

Symptoms induced during the pathogenicity test on Strelitzia reginae. A–D. Basal rot and wilting of plant caused by Pleiocarpon strelitziae. E–F. Basal stem rot and rot of external leaf caused by Ilyonectria strelitziae.

Fig. 4.

Ilyonectria strelitziae (ex-type culture CBS 142253). A. Perithecia on PDA surface. B. Perithecium with simple conidiophores arising from the ascomatal wall. C. Perithecium exuding asci and ascospores. D–E. Simple conidiophores arising from the ascomatal wall. F. Ascomatal wall colour reaction in KOH. G–H. Asci. I. Ascospores. J–K. Simple conidiophores on aerial mycelium. L. Aggregation of simple conidiophores on carnation leaf. M. Aggregation of simple conidiophores. N. Microconidia. O. 1- and 2-septate macroconidia. P. 3-septate macroconidia. Bars A–B = 500 μm; C = 100 μm; D–E = 50 μm; F–K and M–P = 10 μm.

Fig. 5.

Pleiocarpon strelitziae (ex-type CBS 142251). A–B. Simple conidiophores. C-D. Sporodochia. E. Microconidia. F. Macroconidia. Bars = 10 μm