Intraspecific variation in mycorrhizal response is much larger than ecological literature suggests.

Mycorrhizal response is the most common metric for characterizing how much benefit a plant derives from mycorrhizal symbiosis. Traditionally, ecologists have used these metrics to generalize benefit from mycorrhizal symbiosis in plant species, ignoring the potential for plant intraspecific trait variation to alter the outcome of the mutualism. In order for mean trait values to be useful as a functional trait to describe a species, as has been attempted for mycorrhizal response traits, interspecific variation must be much larger than intraspecific variation. While the variation among species has been extensively studied with respect to mycorrhizal response traits, variation within species has rarely been examined. We conducted a systematic review and analyzed how much variation for mycorrhizal growth and nutrient response typically exists within a plant species. We assessed 28 publications that included 60 individual studies testing mycorrhizal response in at least five genotypes of a plant species, and we found that intraspecific trait variation for mycorrhizal response was generally very large and highly variable depending on study design. The difference between the highest and lowest growth response in a study ranged from 10% to 350% across studies, and 36 of the studies included species for which both positive and negative growth responses to mycorrhizae were observed across different genotypes. The intraspecific variation for mycorrhizal growth response in some of these studies was larger than the variation documented among species across the plant kingdom. Phosphorus concentration and content was measured in 17 studies and variation in phosphorus response was similar to variation in growth responses. We also found that plant genotype was just as important for predicting mycorrhizal response as the effects of fungal inoculant identity. Our analysis highlights not only the potential importance of intraspecific trait variation for mycorrhizal response, but also the lack of research that has been done on the scale of this variation in plant species. Including intraspecific variation into research on the interactions between plants and their symbionts can increase our understanding of plant coexistence and ecological stability.

Genome-wide Inference of Somatic Translocation Events During Potato Dihaploid Production.

Potato ( L.) breeders often use dihaploids, which are 2× progeny derived from 4× autotetraploid parents. Dihaploids can be used in diploid crosses to introduce new genetic material into breeding germplasm that can be integrated into tetraploid breeding through the use of unreduced gametes in 4× by 2× crosses. Dihaploid potatoes are usually produced via pollination by haploid inducer lines known as in vitro pollinators (IVP). In vitro pollinator chromosomes are selectively degraded from initially full hybrid embryos, resulting in 2× seed. During this process, somatic translocation of IVP DNA may occur. In this study, a genome-wide approach was used to identify such events and other chromosome-scale abnormalities in a population of 95 dihaploids derived from a cross between potato cultivar Superior and the haploid inducing line IVP101. Most Superior dihaploids showed translocation rates of <1% at 16,947,718 assayable sites, yet two dihaploids showed translocation rates of 1.86 and 1.60%. Allelic ratios at translocation sites suggested that most translocations occurred in individual cell lineages and were thus not present in all cells of the adult plants. Translocations were enriched in sites associated with high gene expression and H3K4 dimethylation and H4K5 acetylation, suggesting that they tend to occur in regions of open chromatin. The translocations likely result as a consequence of double-stranded break repair in the dihaploid genomes via homologous recombination during which IVP chromosomes are used as templates. Additionally, primary trisomy was observed in eight individuals. As the trisomic chromosomes were derived from Superior, meiotic nondisjunction may be common in potato.