Plant Genebanks: Present Situation and Proposals for Their Improvement. the Case of the Spanish Network.

Genebanks were created by the middle of the twentieth century to preserve cultivated biodiversity when landraces began to be substituted by modern varieties. This move was generally accepted as a necessary step to safeguard the future. After about 75 years of collecting and maintaining genetic resources, the increasing ability of biotechnology to create new variability brings the roles of genebanks in the present and near future into question. As a continuation of several workshops that started in 2014, staff of some representative genebanks have met to discuss how the Spanish Plant Genetic Resources Network can be improved, identifying the following major shortcomings: lack of efficient coordination in the distribution of species among genebanks; too many genebanks; existence of detected and undetected duplicates; insufficient rate of regeneration; insufficient phenotyping, genotyping, and epiphenotyping; unsatisfactory rate of use by end users; and, insufficient funding. As a considerable increase in public funding is unlikely, we propose some strategies to increase the efficiency of the system. The most urgent tasks are to strengthen the rationalization of the network by establishing a clear hierarchy and functions, to improve the information in the base collection by deep characterization including not only phenotypes but also uses and utilities, to progressively replace the active collections with focused core collections constructed to meet users' needs, to optimize regeneration protocols, to limit new collecting expeditions of Spanish crop wild relatives to those growing in threatened habitats, and to develop user-friendly platforms to access germplasm documentation, including a unified system of descriptors and classification categories. Current advances in biotechnology, and especially those in gene editing will have without doubt an impact on the role of genebanks. However, the high number of genes and gene combinations created by evolution they hold cannot be produced by these techniques at present. So, these reservoirs of variability will continue to be indispensable for the near-medium future while the function of all the genes is unveiled. In turn, biotechnologies and gene editing will allow us to take advantage of the information held in genebanks in a more efficient and fast way, contributing to a better rationalization and functioning.

Rapid genetic diversification and high fitness penalties associated with pathogenicity evolution in a plant virus.

Under the gene-for-gene model of host-pathogen coevolution, recognition of pathogen avirulence factors by host resistance factors triggers host defenses and limits infection. Theory predicts that the evolution of higher levels of pathogenicity will be associated with fitness penalties and that the cost of higher pathogenicity must be much smaller than that of not infecting the host. The analysis of pathogenicity costs is of academic and applied relevance, as these are determinants for the success of resistance genes bred into crops for disease control. However, most previous attempts of addressing this issue in plant pathogens yielded conflicting and inconclusive results. We have analyzed the costs of pathogenicity in pepper-infecting tobamoviruses defined by their ability to infect pepper plants with different alleles at the resistance locus L. We provide conclusive evidence of pathogenicity-associated costs by comparison of pathotype frequency with the fraction of the crop carrying the various resistance alleles, by timescaled phylogenies, and by temporal analyses of population dynamics and selection pressures using nucleotide sequences. In addition, experimental estimates of relative fitness under controlled conditions also provided evidence of high pathogenicity costs. These high pathogenicity costs may reflect intrinsic properties of plant virus genomes and should be considered in future models of host-parasite coevolution.

Quantitative genetic analysis of flowering time in tomato.

Artificial selection of cultivated tomato (Solanum lycopersicum L.) has resulted in the generation of early-flowering, day-length-insensitive cultivars, despite its close relationship to other Solanum species that need more time and specific photoperiods to flower. To investigate the genetic mechanisms controlling flowering time in tomato and related species, we performed a quantitative trait locus (QTL) analysis for flowering time in an F2 mapping population derived from S. lycopersicum and its late-flowering wild relative S. chmielewskii. Flowering time was scored as the number of days from sowing to the opening of the first flower (days to flowering), and as the number of leaves under the first inflorescence (leaf number). QTL analyses detected 2 QTLs affecting days to flowering, which explained 55.3% of the total phenotypic variance, and 6 QTLs for leaf number, accounting for 66.7% of the corresponding phenotypic variance. Four of the leaf number QTLs had not previously been detected for this trait in tomato. Colocation of some QTLs with flowering-time genes included in the genetic map suggests PHYB2, FALSIFLORA, and a tomato FLC-like sequence as candidate genes that might have been targets of selection during the domestication of tomato.