Over the last five years, rust infections have been found on commercially grown leek (Allium ampeloprasum) in the Auckland and Christchurch regions of New Zealand. Bright yellow to orange amphigenous pustules were mostly observed on outer leaves, often coalescing as the infection progressed.

From March to May 2019, samples were collected from symptomatic leek and spring onion (Allium fistulosum) for diagnostics to determine the identity of the pathogen (Fig. 1). Initial examination found numerous elongated erumpent uredinia of variable sizes and a few black telia. Urediniospores were globose to subglobose, echinulate, yellow to pale brown, measuring 25–32 × 20–26 µm with a 1.5–2.5 µm thick wall (Fig. 2). Teliospores were mostly two-celled, reddish-brown, with smooth walls and thickened apex of 4–7 µm, measuring 38–63 × 18–25 µm. The rarely found one-celled teliospores measured 27–43 × 17–23 µm with an apex of 4–6 µm (Fig. 3). These morphological characters aligned most closely with the description of Puccinia porri by McTaggart et al. (2016).

Fig. 1
figure 1

Rust symptoms on Allium ampeloprasum (A) and Allium fistulosum (B) leaf, showing erumpent orange uredinia. Formation of dark-coloured telia can be seen on A. fistulosum leaf (indicated with black arrowheads)

Full size image
Fig. 2
figure 2

Morphological characters of Puccinia porri. A, B – globose and subglobose urediniospores; note the even echinulation of the spore surface (B). C, D – Reddish-brown teliospores with a thickened apex; note the rare one-celled teliospore (D). Scale bar = 10 µm

Full size image
Fig. 3
figure 3

Phylogram generated from RaxML analysis based on ITS2-LSU region sequences of Puccinia porri and closely related taxa (sequences obtained from GenBank). Vouchers from this study are highlighted in bold. Rapid bootstrap values (> 70) from 10,000 replicates are given at branch nodes. Puccinia malvacearum was used as an outgroup

Full size image

For molecular identification, DNA was isolated from infected leaf material using the InviMag Plant DNA Mini Kit (Invitek, Hayward, CA) and the KingFisher extraction system (Thermo Scientific, Waltham, MA). The ITS and LSU regions were amplified using the primers RustITS1F/RustITS2R (Toome and Aime 2014) and Rust2INV/LR6 (Vilgalys and Hester 1990; Aime 2006), respectively. Amplified products were sequenced by EcoGene Limited (New Zealand) and analysed using Geneious Prime (New Zealand). The examined specimens were deposited to New Zealand Fungarium as PDD 116784, 116785, 116789 and 116842, and obtained sequences were submitted to Genbank under accession numbers ON495338-ON495341 and ON555768.

BLASTn analysis of the 422 bp ITS and the 1,400 bp ITS2-LSU region sequences via NCBI GenBank determined 99.8–100% identity to numerous verified P. porri vouchers, e.g. BRIP61590 and BRIP61592 (Genbank accession Nos. KU296900 and KU296907, respectively) confirming that the fungus represented P. porri. The ITS2-LSU region sequences generated in this study were aligned with a selection of verified sequences of P. porri and other closely related Puccinia taxa using Geneious aligner in Geneious Prime. The phylogenetic analysis was completed in Geneious Prime using RaxML version 8.2.11 with 10,000 rapid bootstrap inferences. Our isolate clearly clustered with the other P. porri sequences, forming a monophyletic well supported clade (Fig. 3).

McTaggart et al. (2016) studied rust fungi on Allium and found that P. porri is present in Albania, England, Germany, Greece and Montenegro, infecting A. ampeloprasum, A. fistulosum, A. porrum and A. sativum. There is also a record of P. porri on A. porrum from South Africa (McTaggart et al. 2017). Before our finding, only P. allii had been reported from Allium species in New Zealand and no rust fungi were known from leek (Manaaki Whenua – Landcare Research 2022). To the best of our knowledge, this is the first report of P. porri in New Zealand as well as the first record from the Australasian region. While the origin of the introduction of P. porri to New Zealand remains unknown, its distribution both on North and South Islands and later finds from home gardens demonstrate that the rust fungus is widely distributed.