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Record Year for Rust Resistant Sugar Pine Cone Collection

Ryan McKillop – 2014 cone collection of SW#798, our only identified blister rust resistant sugar pine tree in our eastside ownership. This year, we are testing an additional 11 trees from this seed zone (zone 523) for rust resistance.

October 2014, Ryan McKillop, Inventory Forester –

This year’s sugar pine cone collection season was one for the books. In August, we collected 335 bushels of cone from 31 of our 46 blister rust resistant sugar pines, with the help of the crew from Acton Arboriculture out of Grass Valley. Statewide, just over 1,500 bushels were collected from various private landowners, including 2 very impressive trees on SPI ground which yielded 97 bushels and 101 bushels.

This record setting collection is no doubt a stress crop related to our ongoing statewide drought, likely the only good thing to come from it. Our 335 bushel collection this year represents 27% of all the blister rust resistant cone we have collected over the last 25 years!

Bushels of BRRSP Collected in Last 25 Years.

White pine blister rust (Cronartium ribicola) is a non-native disease which made it’s way into Canada from Asia in the early 1900’s. By 1941, it had spread into the northern Sierra Nevada mountains, and by 1998, it reached the far southern extent of white pines in southern California.

Today it is found affecting various white pine species in 38 states. Sugar pine (Pinus lambertiana), by far the largest of the white pines, is particularly susceptible to the disease, primarily because the moderate climate where they exist also allows the disease to flourish.

Current Blister Rust Distribution in the West

Bister rust is an interesting disease in that it must have an alternate host (gooseberry and or indian paintbrush) in order to complete it’s lifecycle and infect the white pines. Without the alternate host, there would be no disease. Infection of the pines from the alternate host occurs in the fall. Once inside the pine needle the fungus grows down to the twig and into the branch and ultimately to the main stem of the tree.

The damage caused by the rust is the death of the cambium layer, which girdles the branch or stem, preventing water and nutrients from passing through the infected area. If the canker forms on the main stem, it causes significant top-kill, eventually causing the tree to die, or allow bark beetles to finish it off. Young sugar pines are highly susceptible and typically die almost immediately after infection.

A small percentage of sugar pines, as well as the other white pines, have what we call major gene resistance (MGR) to the disease, which is the presence of a dominant gene (R) which is known as Cr1. All of the resistant sugar pines have this trait, either in the form of (Rr) – one dominant Cr1 gene in the pair, or (RR) – both dominant Cr1’s in the gene pair. If one is present (heterozygous), 50% of the trees progeny will inherit the resistance.

If both are present (homozygous), then 100% of the progeny will inherit the resistance. Naturally, however, it is not that simple. There is another gene (Avcr1), found in the disease itself, which can influence whether or not a resistant tree fights the infection. If this gene is active, resistance occurs. If it is inactive, the resistant tree can become infected.

This has recently happened at two separate sites in California, where an inactive virulent strain of blister rust has infected sugar pine trees which were previously proven resistant.

The resistance reaction to blister rust.

I think it’s safe to say that the future existence of sugar pine is questionable in light of the nature of this disease, but there’s no doubt that we are doing our very best to help preserve it. A huge amount of time, effort and expense has gone into our resistance testing program and collection efforts over the years. And without that effort, we probably would not have any sugar pine in our plantations at all.

The resistance reaction to the blister rust (upper needle) is characterized by a hypersensitive response resulting in small necrotic flecks; this contrasts with bright yellow areas found in a susceptible tree’s reaction (lower).


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