Pine

Insects can act as vectors for all spore stages. Pissodes pini, Dioryctria splendidella, Laspeyresia coniferana, Lagria hirta, and Dioryctria abietella are reported as possible vectors for the rust on the basis of their occurrence and because they all feed on C. flaccidum aecia.

Spermogonia with spermatial fluid occur on the infected bark; aecia appear on the bark in the early summer; uredinia and hair-like telia appear on the lower leaf surface of the alternate hosts in mid-to-late summer.

Causes blister rust in pines, resulting in chlorosis and necrosis of the infected sites, yellowing and premature defoliation of leaves, branch death, bark discoloration, cankers, and deformed growth.

The infected part of the shoot (lesion) is often swollen; resinosis in the lesion; green shoots below the lesion; light greenish to yellowish needles above the lesion.

A Climate suitability map is now available. This survey should only be considered in the states with appropriate climate conditions and suitable hosts for this pathogen.

The map was produced by the SAFARIS Team. SAFARIS is a modeling framework that enables PPQ to quickly respond to emergencies, efficiently survey for pests, and assess potential pest impacts by collecting critical geospatial data and developing predictive models. SAFARIS is developed and maintained by the NC State University, Center for Integrated Pest Management (CIPM) with support from PPQ PERAL.

The SAFARIS team used a climate suitability model for Scots pine blister rust occurrence in the continental United States, that was developed by PPQ PERAL and NCSU CIPM, to support CAPS survey planning. The model predicts the suitability of an area for Scots pine blister rust occurrence based on the likelihood of favorable climate conditions for the disease occurring using tools and data within SAFARIS. The detailed method used in this assessment is described here.

Morphological: Characteristics of pycnia, aecia, aecispores, uredinia, urediniospores, telia, and teliospores can be used to distinguish from other rust fungi (Mordue and Gibson, 1978).

C. flaccidum can be cultured (axenically) by seeding aeciospores on modified Schenk and Hildebrandt"s and Harvey and Grasham"s media and incubating at 23-25°C (73-77°F) in the dark (Morrica and Ragazzi, 1994).

Further study is possible in vitro on Pinus spp. callus tissue (Ragazzi et al., 1995).

Many Cronartium species occur in North America and their symptoms are very similar to those of C. flaccidum.

Symptoms can be confused with those of C. ribicola, the causal agent of white pine blister rust. C. ribicola does not infect Pinus sylvestris, whereas C. flaccidum does not infect five-needle pines or Ribes spp. This macrocyclic fungus is genetically identical to the autoecious Endocronartium pini (=Peridermium pini), but requires both primary and alternate hosts to complete its life cycle.

The recovery plan for Scots pine blister rust suggests a morphological identification to genus and DNA sequencing to determine species (Geils et al., 2009).

Biochemical: Cheng et al. (1995) were able to differentiate three Cronartium spp. (C. ribicola, C. flaccidum and C. quercum) using isozyme analyses on the aeclospores.

Molecular: Kaitera and Hantula (1998) provide a protocol to compare restriction fragment length polymorphisms in ITS-region DNA based on digestion of PCR products with the restriction enzyme Alu I.

Melampyrum sylvaticum (small cow-wheat) and Vinetoxicum hirundinaria (Louise"s swallow wort) are considered the primary alternate (telial) hosts, though several alternate hosts have been reported including: Asclepias spp., Impatiens spp., Loasa spp., Melampyrum spp., Nemesia spp., Paeonia spp., Pedicularis spp., Ruellia spp., Schizanthus spp., Tropaeolum spp., Verbena spp., and Vincetoxicum spp. spp.