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Melampsora laricis-populina Kleb. (as 'larici-populina')

Description
Uredinia on leaves, scattered or in small groups often covering the entire lower leaf surface, causing yellowish angular spots up to 2 mm wide on the upper leaf surface, subepidermal, erumpent, round, up to 200 µm, yellow to yellowish brown; paraphyses intrasoral, clavate or capitate, hyaline, 25‒70 × 8‒18 µm; wall up to 10 µm thick, thickened at apex.

Urediniospores cylindrical, broadly ellipsoidal or obovoid, yellow, 26‒40 × 12‒21 µm; wall 2‒3 µm thick, echinulate with apex often smooth.

Telia on leaves in groups, slightly raised, often confluent and covering much of the upper leaf surface, subepidermal, reddish brown.

Teliospores in adherent crusts 1 cell deep, cylindrical with flattened ends, reddish brown, 35‒60 × 8‒12 µm; wall 1‒2 µm thick, smooth.

Hosts
Host family: Salicaceae
Host species: Populus balsamifera
Populus nigra
Populus nigra var. italica
Populus serotina

Distribution
NSW, NT, QLD, TAS, VIC

Comments
This rust is heteroecious with spermogonia and aecia reported from Larix, although these stages have not been found in Australia (Walker 1975). This rust was introduced to Australia in 1972 and subsequently spread to New Zealand a year later, causing severe damage to species of Populus in both countries (Walker, Hartigan and Bertus, 1974).

Highslide JS
Melampsora laricis-populina on Populus nigra - BRIP 54286.
Highslide JS
Melampsora laricis-populina on Populus nigra - BRIP 54286.
Scale bar = 1 cm.
Highslide JS
Uredinium of Melampsora laricis-populina on Populus nigra - BRIP 54286.
Scale bar = 100 µm.
Highslide JS
Paraphyses of Melampsora laricis-populina on Populus nigra - BRIP 54286.
Scale bar = 10 µm.
Highslide JS
Urediniospores of Melampsora laricis-populina on Populus nigra - BRIP 54286.
Scale bar = 10 µm.
Highslide JS
Telium of Melampsora laricis-populina on Populus nigra - BRIP 3942.
Scale bar = 10 µm.