Abstract
BackgroundThe relationship between allopolyploidy and plant virus resistance is poorly understood. To determine the relationship of plant evolutionary history and basal virus resistance, a panel of Nicotiana species from diverse geographic regions and ploidy levels was assessed for resistance to non-coevolved viruses from the genus Nepovirus, family Secoviridae. The heritability of resistance was tested in a panel of synthetic allopolyploids. Leaves of different positions on each inoculated plant were tested for virus presence and a subset of plants was re-inoculated and assessed for systemic recovery.ResultsDepending on the host-virus combination, plants displayed immunity, susceptibility or intermediate levels of resistance. Synthetic allopolyploids showed an incompletely dominant resistance phenotype and manifested systemic recovery. Plant ploidy was weakly negatively correlated with virus resistance in Nicotiana species, but this trend did not hold when synthetic allopolyploids were taken into account. Furthermore, a relationship between resistance and geographical origin was observed.ConclusionThe gradients of resistance and virulence corresponded to a modified matching allele model of resistance. Intermediate resistance responses of allopolyploids corresponded with a model of multi-allelic additive resistance. The variable virus resistance of extant allopolyploids suggested that selection-based mechanisms surpass ploidy with respect to evolution of basal resistance to viruses.
Highlights
The relationship between allopolyploidy and plant virus resistance is poorly understood
Test for virus presence Twenty-four Nicotiana species and synthetic allopolyploids of distinct geographic origins were evaluated for their reaction to infection with Grapevine fanleaf virus (GFLV) strains GHu and F13, and Tomato ringspot virus (ToRSV) strain AP (Table 1)
Since GFLV-GHu displays levels of virulence intermediate to that of GFLV-F13 and ToRSV-AP in most Nicotiana species, plants were primarily assessed for resistance to GFLVGHu
Summary
The relationship between allopolyploidy and plant virus resistance is poorly understood. To determine the relationship of plant evolutionary history and basal virus resistance, a panel of Nicotiana species from diverse geographic regions and ploidy levels was assessed for resistance to non-coevolved viruses from the genus Nepovirus, family Secoviridae. Allopolyploidy could provide an opportunity for host species to outpace Red Queen coevolution and achieve epochal gains in resistance such as when two moderately-resistant diploids give rise to an allotetraploid with a full complement of resistance genes. This allopolyploid resistance hypothesis incorporates resistance into models explaining heterosis [2,3], and has been tested experimentally in multiple plant and animal systems [4,5]. N. tabacum and N. rustica likely originated in South America, N. clevelandii and N. quadrivalvis are endemic to the Western US, and all but one species of section Suaveolentes are endemic to Australia [10]
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