Inoculum Source and Density Influence Assessment of Fusiform Rust Resistance in Slash Pine

Abstract

to a much lesser extent than for 8-7. The Griggs, M. M., Dinus, R. J., and Snow, G. A. 1984. Inoculum source and density influence third parent (18-62) was highly and assessment of fusiform rust resistance in slash pine. Plant Disease 68: 770-774. uniformly susceptible throughout the research cited above. Open-pollinated seedlings from resistant, moderately resistant, and susceptible slash pines (Pinus One inoculum source (LM) was elliottii var. elliottii Engelm.) were inoculated with basidiospores of Cronartium quercuum f. sp. derived from five single-gall aeciospore fusiforme from two geographic sources at three densities. Variation among pine families, inoculum densities, and sources was assessed in terms of presence or absence of initial symptoms (purple spots collections made near Laurel, MS. The on stems and needles), seedlings galled 6 and 9 mo after inoculation, gall lengths, and seedling second (MG) was produced from five recovery. Recovery was indicated either by lack of gall formation or small galls that ceased to grow. single-gall collections made near Macon, More seedlings of the resistant and moderately resistant parents than of the susceptible parent GA. Aeciospores from individual galls developed initial symptoms without subsequently forming galls (early recoveries). Frequency of were processed and stored separately early recovery varied with inoculum density. Fewer seedlings from the resistant parent were galled 9 (20). In an effort to apply more uniform mo after inoculation, but the distinction between families diminished with increasing density. Most numbers of basidiospores per gall than seedlings with small galls (<2.5 cm long) were free of external symptoms and active rust mycelium would have resulted from simply mixing 33 mo after inoculation (late recoveries). Family effects on seedlings with small galls were aeciospores, two water oak (Quercus significant. Family differences were increased when late recoveries were deducted from those galled at 9 mo. Results confirm that uniform, appropriate inoculum densities are prerequisite to accurate nigra L.) seedlings were inoculated with resistance tests and indicate that tests with varied sources and densities will help discern resistance each aeciospore collection. Three leaves types, degrees, and stabilities, bearing uniform numbers of telia were removed from the two oak seedlings representing each LM gall and distributed at random in the leaf chamber of the