Life cycle ofPuccinia acroptilion Rhaponticum (=Acroptilon)repens

Abstract

Russian knapweed (Rhaponticum repens) is a rangeland weed pest in the western United States. One candidate fungus for biological control of R. repens is Puccinia acroptili, which causes a rust disease. Understanding the life cycle of candidate rust fungi for weed biological control is an essential component in risk assessments and evaluations, and for P. acroptili such was unknown. For this reason greenhouse studies were undertaken to clarify the life cycle of P. acroptili under artificial conditions. Spermogonia with spermatia developed on R. repens following plant inoculation with teliospores. Artificial transfer of spermatia between spermogonia resulted in the development of aecia with uredinioid aeciospores. Inoculation with aeciospores or urediniospores resulted in uredinia containing urediniospores and occasional amphispores. Telia with teliospores and occasional mesospores developed later. Teliospores produced typical basidia with four basidiospores. These results suggest that the life cycle of P. acroptili is macrocyclic and autoecious. Inoculation with teliospores also frequently resulted in production of sori that were morphologically similar to aecia but which were not associated with spermogonia or the classical transfer of spermatia. The ontology of these sori is unknown. This is the first description of spermogonia and the first report and description of basidiospores, aecia, aeciospores, amphispores and mesospores of P. acroptili.

Comparison of Puccinia acroptili from Eurasia and the USA

“…Successful mating occurred for every combination of isolates tested (Table 4), including selfs and reciprocal crosses Note: Details about each isolate can be found in Bruckart et al 2010.…”

“…These fungi are autoecious, in that they complete their life cycle (all five stages) on a single host (Bruckart et al 2010), and they are distin- guished by aecia that are morphologically similar to the uredinia (Kirk et al 2001). Although P. acroptili is morphologically very similar to rust fungi from species of Carduus, Carthamus, Centaurea, and Cirsium (Savile 1970a(Savile , 1970b, evidence has been published that it is distinct from these other rust fungi on the basis of morphology (Savile 1970b), host range (Mortensen et al 1991), and polypeptides (Kim and Mortensen 1986).…”

“…Protocol for inoculation with teliospores has been described (Bruckart et al 2010). Both spermagonia and aecium-like pustules (ALP) developed following foliar inoculations by teliospores (Bruckart et al 2010). Locations of spermagonia that developed were recorded on hand-drawn maps of leaves.…”

“…Thirteen isolates of Eurasian and USA origin were included in this study (Table 1; Bruckart et al 2010). Inoculum was received from the various locations as viable urediniospores on dried leaf material, except for two, nonviable New Mexican herbarium specimens that were used solely for DNA analysis.…”

“…For crosses, spermatia from a single spermagonium were suspended in sterile distilled water, and a 1 µL drop of suspension was applied to as many available spermatia as possible (Bruckart et al 2010). The isolate that was the donor source of spermatia in each cross was classified as the male component.…”