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

Karina Gramacho,Thomas Miller,Robert Schmidt

doi:10.3390/f4020488

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.

Highlights

Fusiform rust caused by Cronartium quercuum (Berk.) Miyabe ex Shirai F. sp. fusiforme (Cqf) was of rare occurrence at the beginning of the 20th century, but reached epidemic proportions during the second half of the century [1]
Four decades of research and development have resulted in the successful deployment of rust-resistant pine families to significantly reduce losses to fusiform rust [4,5]
Stability is of special concern in this perennial crop species, since pathogenic variability appears great [6,7,8,9], and major genes in the host are associated with resistant loblolly pine [10] and slash pine [11,12] including Family R1 in this paper [13]

Summary

Introduction

Fusiform rust caused by Cronartium quercuum (Berk.) Miyabe ex Shirai F. sp. fusiforme (Cqf) was of rare occurrence at the beginning of the 20th century, but reached epidemic proportions during the second half of the century [1]. Stability is of special concern in this perennial crop species, since pathogenic variability appears great [6,7,8,9], and major genes in the host are associated with resistant loblolly pine [10] and slash pine [11,12] including Family R1 in this paper [13] The objective of these four artificial inoculation tests was to assess the pathogenicity of temporally and spatially diverse single- and mixed-gall inocula on a small number of representative rust-resistant slash pine families with major gene resistance and partial resistance

Methods

Results

Discussion

Conclusion