Stability of Slash Pine Families with Major Gene and Partial Resistance to Single-Gall and Mixed-Gall Inocula of Cronartium quercuum fusiforme in Greenhouse Studies

Abstract

Single-gall and mixed-gall inocula from fusiform rust (Cronartium quercuum fusiforme) galls in field studies were used in greenhouse tests to investigate their pathogenic variability and the temporal and spatial stability of fusiform rust incidence of resistant slash pine (Pinus elliottii var. elliottii) seedlings. Analyses of variance showed significant main effects for families and inocula and for the interactions of families and inocula indicating abundant pathogenic variation and differential family resistance. Averaged over all families and inocula, there were no significant differences between sequential inocula, i.e., inocula from successive generations of the pathogen. However, when analyzed separately Family R1 with segregated major gene resistance showed increased rust incidence with successive generations of the pathogen. Also Family R1 accounted for a major portion of the temporal (51.4%) and spatial (49.6%) interaction sum of squares. In contrast the other resistant families each accounted for a minor portion of this statistic. These results indicate pathogen virulence toward major gene resistance, possible selection for virulence and the relative instability of Family R1 compared with other resistance families.

Genetic Resistance to Fusiform Rust in Southern Pines and White Pine Blister Rust in White Pines—A Contrasting Tale of Two Rust Pathosystems—Current Status and Future Prospects

“…For loblolly or slash pine, there is currently limited information on durability in the field of R genes, but data from slash pine indicate that these genes may be overcome relatively quickly and durability of loblolly R genes (Fr1 etc.) is greater [60]. Future molecular dissection of resistance and virulence should help determine what types of resistances are likely to be durable.…”

“…Partial resistance can display numerous phenotypes, including partial or reduced size galls and non-sporulating galls and these phenotypes are considered quantitative (under control of multiple genes) and non-race-specific. Although resistant slash pine families have been identified [60] most research on resistance to FR has been carried out in loblolly pine and has focused on complete resistance rather than partial resistance [15]. There are several reasons for this.…”

“…These trials generally show good gain in resistance from breeding, with a financial benefit:cost ratios of 2.2 to 20.4 [76] and gains are especially noted for loblolly pine [77][78][79]. Significant family × location interactions have been observed for resistant slash pine families (Figure 8), which may be due to increased virulence of local rust populations to this resistance or phenological phenomena in this host [60,79]. In general, resistance has greatly reduced incidence of FR, especially on high-hazard sites [77].…”

Narrative History of the Resistance Screening Center: It’s Origins, Leadership and Partial List of Public Benefits and Scientific Contributions

“…Fortunately, RSC staff had the flexibility necessary to fulfill the requirements of these specialized objectives. Most "Research" tests at the RSC were conducted for one or more of the following four kinds of client-defined scientific purposes: (a) To identify possible histological, physiological, or biochemical mechanisms of resistance to fusiform rust [32]; (b) To determine the number and types of genes that control resistance and susceptibility to fusiform rust in loblolly and pine seedlings [33,34]; (c) To determine the number and types of genes that control virulence and avirulence in the fusiform rust pathogen [35]; and (d) To determine if the gene-for-gene theory of evolution discovered in cereal rust pathosystems also exists in the fusiform rust pathosystem [33] and explore the possibility that additive effects of minor genes may also be involved [36,37]. (4) Other developmental tests performed included more complicated procedural issues such as optimizing the basidiospore inoculum density to maximize discrimination between slash and/or loblolly pine seed lots that should be classified as "susceptible", "moderately resistant" or "highly resistant" to a given geographic source of inoculum, or, alternatively, to a mixed basidiospore inoculum derived from aeciospores collected from several different geographic regions [29][30][31].…”