Showing 1 - 2 of 2 Items

Date: 2005-01-01

Creator: Vladimir Douhovnikoff, Joe R. McBride, Richard S. Dodd

Access: Open access

Willows are important riparian colonizers. However, the predominant models of early riparian colonization, which emphasize seedling recruitment, are inadequate to explain the success of these species in light of the extremely low rates of seedling survival observed. We used molecular fingerprinting markers (AFLPs) to identify and characterize Salix exigua clones on six sites, ranging in size from 850 to 1150 m2, located on two rivers. Clones as large as 325 m2 were detected, and an average of six clones per site occupied 75% of the vegetated area. Building on Mahoney and Rood's recruitment box model, we propose a model whereby prolific clonal growth allows for long-term colonization of riparian zones, and the balance between the relative importance of seedling regeneration and clonal growth varies based upon disturbance regime. A reduction in disturbance regime resulted in greater clonal growth and reduced genotypic variation. It is probable that, with an extended reduction in disturbance, the Salix exigua component would be represented by fewer, larger clones and would eventually decline significantly when these clones are replaced by taller and more shade tolerant species. © 2005 by the Ecological Society of America.

Date: 2005-01-01

Creator: Richard S. Dodd, Daniel Hüberli, Vlad Douhovnikoff, Tamar Y. Harnik, Zara, Afzal-Rafii, Matteo Garbelotto

Access: Open access

California coastal woodlands are suffering severe disease and mortality as a result of infection from Phytophthora ramorum. Quercus agrifolia is one of the major woodland species at risk. This study investigated within- and among-population variation in host susceptibility to inoculation with P. ramorum and compared this with population genetic structure using molecular markers. Susceptibility was assessed using a branch-cutting inoculation test. Trees were selected from seven natural populations in California. Amplified fragment length polymorphism molecular markers were analysed for all trees used in the trials. Lesion sizes varied quantitatively among individuals within populations, with up to an eightfold difference. There was little support for population differences in susceptibility. Molecular structure also showed a strong within-population, and weaker among-population, pattern of variation. Our data suggest that susceptibility of Q. agrifolia to P. ramorum is variable and is under the control of several gene loci. This variation exists within populations, so that less susceptible local genotypes may provide the gene pool for regeneration of woodlands where mortality is high. © New Phytologist (2004).