Sweet potato (Ipomoea batatas (L.) Lam., Convolvulaceae) counts among the most widely cultivated staple crops worldwide, yet the origins of its domestication remain unclear. This hexaploid species could have had either an autopolyploid origin, from the diploid I. trifida, or an allopolyploid origin, involving genomes of I. trifida and I. triloba. We generated molecular genetic data for a broad sample of cultivated sweet potatoes and its diploid and polyploid wild relatives, for noncoding chloroplast and nuclear ITS sequences, and nuclear SSRs. Our data did not support an allopolyploid origin for I. batatas, nor any contribution of I. triloba in the genome of domesticated sweet potato. I. trifida and I. batatas are closely related although they do not share haplotypes. Our data support an autopolyploid origin of sweet potato from the ancestor it shares with I. trifida, which might be similar to currently observed tetraploid wild Ipomoea accessions. Two I. batatas chloroplast lineages were identified. They show more divergence with each other than either does with I. trifida. We thus propose that cultivated I. batatas have multiple origins, and evolved from at least two distinct autopolyploidization events in polymorphic wild populations of a single progenitor species. Secondary contact between sweet potatoes domesticated in Central America and in South America, from differentiated wild I. batatas populations, would have led to the introgression of chloroplast haplotypes of each lineage into nuclear backgrounds of the other, and to a reduced divergence between nuclear gene pools as compared with chloroplast haplotypes.

We analysed a representative collection of New World sweet potato landraces (329 accessions from Mexico to Peru) with both chloroplast and nuclear microsatellite markers. Both kinds of markers supported the existence of two geographically restricted genepools, corresponding to accessions from the north-western part of South America and accessions from the Caribbean and Central America region. Our conservative cpSSRs markers revealed that the divergence between the two haplotype groups is associated with numerous mutation events concerning various markers, supporting the idea that this divergence may be ancient, predating domestication. For both kinds of markers, we found no significant difference in diversity between the two genepools and detected region-specific alleles in both groups. Previous studies have favoured the hypothesis of a single domestication of this crop. Our analysis suggests at least two independent domestications, in Central/Caribbean America and in the north-western part of South America. Sweet potato was then dispersed from these centres throughout tropical America. Comparison of nuclear and chloroplast data suggests that exchanges of clones and sexual reproduction were both important processes in landrace diversification in this clonally propagated crop. Our analysis provides useful tools for rationalizing the conservation and use of sweet potato germplasm collections.

Seed germinability and storability are important aspects of seed quality determined by the genotype and environment of seed development. Lettuce (Lactuca sativa L.) is produced commercially in most temperate and subtropical areas of the world. The objective of this study was to determine how photoperiod and light quality of the mother plant environment affects lettuce seed quality. Seeds of cv. Tango were produced in growth chambers under one of two treatments: a) short day (SD), consisting of 8 hours of fluorescent light (≈310 μmol·m−2·s−1) plus 16 hours of darkness daily, and b) long day (LD), consisting of 4 hours of incandescent light (≈21 μmol·m−2·s−1), 8 hours of fluorescent light, 4 hours of incandescent light, and 8 hours of darkness daily. The red to far-red ratio was ≈6.8 and 1.0 for the fluorescent and incandescent light, respectively. In both treatments, the temperature was 23 °C. The LD treatment produced significantly heavier seeds; however, germination at optimal conditions (20 °C-light) was similar for both treatments. Germinability (percentage and rates) at suboptimal conditions (30 °C, 20 °C with different external ABA concentrations, negative osmotic potentials, or dark) was higher for seeds produced under the LD treatment. On the other hand, seeds produced under the LD treatment presented better storability (evaluated by the accelerated aging test and standard germination after storage at 30 °C and 74% RH). The critical period for light environment effects was also studied. Seed weight patterns were determined early in seed development, during the first 6 days after flowering. Conversely, light environment effects on seed germinability and storability were determined at the end of seed development, after physiological maturity, which occurred by 11 days after flowering. These results show that lettuce seed germinability and storability may be modified by management of light conditions during seed production and provide useful information for seed producers, seed companies, and seed conservation institutions.

Andean potatoes are gaining popularity not only for their appealing colors and culinary uses but also for their potential higher content of polyphenolic compounds. The objective of this study was to identify potato varieties with increased phenolic content. This was achieved through characterization and quantitation of the phenolic composition in 20 varieties of native Andean potatoes from 4 different Solanum species with different colors. Major quantitative and qualitative differences among evaluated samples were more dependent on the coloration of the extracted sample rather than on the species. The most predominant anthocyanidins were petunidin-3-coumaroylrutinoside-5-glucoside and pelargonidin-3-coumaroylrutinoside-5-glucoside in purple and red potato extracts, respectively, while chlorogenic acid and its isomers were the main phenolic compund (43% of the total phenolic content). Our study suggested that the appropriate selection of native potatoes could provide new sources of polyphenolics with health promoting properties and natural pigments with increased stability for food applications.

Thermoinhibition and photosensitivity are two characteristics of lettuce seed that frequently affect its stand. The main objective of this study was to evaluate the hypothesis that lettuce seed germinability and longevity are affected by the red to far-red light ratio (R:FR) under which seeds maturate. ‘Tango’ lettuce seeds were produced in growth chambers under one of two treatments: 1) red-rich light (R treatment) and 2) far-red-rich light (FR treatment). For both treatments, the percentage of normal seedlings germinated at 20 °C–light was ≈100%. When germinated under the light, seeds from the R treatment exhibited a higher germination percentage and a faster germination (under a broader range of temperatures) than seeds from the FR treatment. When germinated in the dark, seeds from the R treatment germinated 100% between 12 and 23 °C and over 50% at 30 °C, whereas seeds from the FR treatment germinated less than 35% between 12 and 23 °C and less than 5% at 30 °C. Seeds from the R treatment had lower abscisic acid (ABA) content and were better able to germinate when exposed to external ABA concentrations than seeds from the FR treatment. Seed longevity as assessed by the accelerated aging test was higher in seeds from the FR treatment, indicating that red-rich light was detrimental to longevity. In another experiment, lettuce seeds that developed under similar conditions were harvested at approximately the moment of maximum dry weight accumulation and desiccated in dark, far-red, red, or fluorescent + incandescent light. Seeds desiccated under red light exhibited higher dark germination than the other treatments; however, no differences were observed in thermoinhibition or longevity. These results suggest that lettuce seed produced in an environment with a high R:FR light ratio will exhibit reduced thermoinhibition and photosensitivity as compared with production in a lower R:FR light environment.

The effect of cold and sucrose pretreatment for increasing tolerance to cryopreservation was evaluated with eight diverse genotypes, six cultivars belonging to the cultivated species, Solanum tuberosum spp., S. tuberosum subsp. andigena, S. x juzepczukii and S. x ajanhuiri, and two genotypes from the wild species, S. commersonii. In vitro plantlets were cultured at either 6 or 22°C in media supplemented with either 0.07 or 0.3 M sucrose prior to droplet PVS2 cryopreservation. The sucrose pretreatment appeared to have no positive effect on post-cryo survival. The cold-hardening pretreatment increased significantly post-cryo recovery in drought and frost tolerant cultivars. When 755 accessions, representing 10 taxa, were cryopreserved after cold-hardening, 96 % responded with at least one shoot recovering and 63 % showed a high recovery rate (40-100 %). Therefore this method is recommended for the long term conservation of diverse accessions of potato germplasm.

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