This datasheet represents an Approved Method for:
2015, 2016, 2017, 2018, 2019, 2020
Major Hosts identified in the CAPS Host Matrix*:
*This list includes important economic or environmental hosts but does not represent all major hosts of the pest. Check CAPS pest datasheet for complete list of hosts.
Pest is vectored by:
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.
NAPIS Survey Method
Collect symptomatic plant material.
3031 - General Visual Observation
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.
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.
In Progress / Literature-based Diagnostics:
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.