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      Morphological phenotypes, pollen viability and pollen-pistil relations in three natural populations of the wild potato Solanum chacoense bitter Translated title: Fenotipos morfológicos, viabilidad del polen y relaciones polen-pistilo en tres poblaciones naturales de la papa silvestre Solanum chacoense bitter

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      BAG. Journal of basic and applied genetics
      Sociedad Argentina de Genética

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          Abstract

          Argentina is center of diversity of approximately 35 wild taxonomic potato species that have wide geographical distribution. These species, which form polyploid series with 2n=2x=24 up to 2n=6x=72 (x=12), can reproduce both sexually and asexually. Most of them are diploid obligate outcrossers because they possess a one-locus gametophytic self-incompatibility system. In nature, wild potatoes can present both external and internal reproductive isolation barriers, within and between populations, which can be incomplete. Most accessions in germplasm banks have been assigned specific categories based on morphological phenotypes (taxonomic species concept), without taking into account the natural reproductive behavior of the sampled populations. One of these species, Solanum chacoense Bitter (2n=2x=24, 2 EBN 1), spontaneously grows from the NW provinces to SE Buenos Aires province, in very diverse habitats and overlapping with other taxonomic potato species, with which it can spontaneously hybridize. As preliminary activities of an in situ study, individual plants from three populations classified as S. chacoense (APEC-1, APEC-2 and APEC-3) that spontaneously grow in Balcarce, Buenos Aires province, were characterized for morphological phenotypes of leaves, flowers and fruits, pollen viability and pollen-pistil relations. The percentage of pollen viability (determined by staining) varied from 34.5 to 98.8% (=81.3%) in APEC-1 (n=23), 0 to 98.8% (=62.8%) in APEC-2 (n=26) and 63.3 to 95.4% (=85%) in APEC-3 (n=21). Variability was also observed for pollen size (<n, 2n, > 2n and 4n, in addition to normal n) and pollen size frequency. Abnormalities were observed at the tetrad stage of meiosis in eight plants of APEC-2 with heterogeneous-size pollen. According to the site of pollen tube arrest, pollen-pistil relationships within APEC-1 and APEC-2 revealed events of cross-incompatibility and/or self-incompatibility, whereas only cross-incompatibility was detected within APEC-3. No relations were found between morphological phenotypes and pollen-pistil reactions, and between corolla shape and pollen viability. The results are indicative of a likely hybrid origin of the studied populations and the need for revising the current taxonomic approaches in wild potatoes. 1 EBN: Endosperm Balance Number (Johnston et al., 1980

          Translated abstract

          Argentina es centro de diversidad de aproximadamente 35 especies silvestres de papa, que tienen amplia distribución geográfica. Estas especies, que forman series poliploides con 2n=2x=24 hasta 2n=6x=72 (x=12), pueden reproducirse tanto sexual como asexualmente. La mayoría de ellas son diploides, y alógamas obligadas debido a que poseen un sistema de auto-incompatibilidad gametofítica. En la naturaleza, las papas silvestres presentan barreras de aislamiento reproductivo externas e internas, dentro y entre poblaciones, que pueden ser incompletas. A la mayoría de las colecciones de bancos de germoplasma se les ha asignado categoría específica en base a fenotipos morfológicos (concepto de especie taxonómica), sin considerar el comportamiento reproductivo natural de las poblaciones muestreadas. Una de estas especies, Solanum chacoense Bitter (2n=2x=24, 2NBE2), crece espontáneamente desde las provincias del noroeste hasta el sudeste de la provincia de Buenos Aires, en hábitats diversos y superponiéndose en su distribución con otras especies taxonómicas de papa con las que puede hibridarse espontáneamente. Como actividades preliminares de un estudio in situ, se caracterizaron por fenotipos morfológicos de hojas, flores y frutos, viabilidad de polen y relaciones polen-pistilo, tres poblaciones naturales de Balcarce, provincia de Buenos Aires, clasificadas como S. chacoense (APEC-1, APEC-2 y APEC-3). El porcentaje de viabilidad del polen (determinado por tinción) varió de 34,5 a 98,8% (=81.3%) en APEC-1 (n=23), 0 a 98,8% (=62.8%) en APEC-2 (n=26) y 63,3 a 95,4% (=85%) en APEC-3 (n=21). Además, se observó variabilidad para tamaño de polen (<n, 2n, >2n y 4n, en adición al polen n normal) y para frecuencia según tamaño. Se observaron anormalidades en el estadio de tétrada en ocho plantas de APEC-2 con polen de tamaño heterogéneo. De acuerdo al sitio de detención del tubo polínico, las relaciones polen-pistilo dentro de APEC-1 y APEC-2 revelaron eventos de incompatibilidad cruzada y/o autoincompatibilidad mientras que en APEC-3 sólo se detectó incompatibilidad cruzada. No se encontraron relaciones entre fenotipos morfológicos y reacciones polen-pistilo, ni entre forma de corola y viabilidad de polen. Los resultados obtenidos son indicativos de un posible origen híbrido de las poblaciones estudiadas y de la necesidad de revisar el enfoque taxonómico en las papas silvestres. 2 NBE: Número de Balance del Endosperma (Johnston et al., 1980)

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          THREE MECHANISMS OF 2n POLLEN FORMATION IN DIPLOID POTATOES

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            Substitutes for genome differentiation in tuber-bearing Solanum: interspecific pollen-pistil incompatibility, nuclear-cytoplasmic male sterility, and endosperm.

            The cultivated potato, Solanum tuberosum L. (2n=4x=48), has a very large number of related wild and cultivated tuber-bearing species widely distributed in the Americas. These species, grouped in 16 taxonomic series, range from the diploid to the hexaploid level. Polyploid species are either disomic or polysomic, and sexual polyploidization via genetically controlled 2 n gametes has played a major role in their evolution. Species are separated in nature by geographical and ecological barriers. However, there are several examples of sympatric species that share the same niches but do not readily cross (i.e., the diploids S. commersonii and S. chacoense in certain areas of Argentina). External barriers alone are, therefore, not sufficient to explain species integrity. In addition, there is no strong evidence indicating that genome differentiation is important in the group. In this review we present evidence supporting the assertion that interspecific pollen-pistil incompatibility, nuclear-cytoplasmic male sterility, and the endosperm are major forces that strengthen the external hybridization barriers allowing, at the same time and under specific circumstances, a certain amount of gene exchange without jeopardizing the integrity of the species.
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              2n gametes in potato species and their function in sexual polyploidization

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                Author and article information

                Journal
                bag
                BAG. Journal of basic and applied genetics
                BAG, J. basic appl. genet.
                Sociedad Argentina de Genética (Ciudad Autónoma de Buenos Aires, , Argentina )
                1852-6233
                December 2014
                : 25
                : 2
                : 16-31
                Article
                S1852-62332014000300002 S1852-6233(14)02500200002
                85e7006d-2b8e-4baa-b2c6-a10b0ed4b150

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

                History
                : 25 July 2014
                : 01 March 2014
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 33, Pages: 16
                Product

                SciELO Argentina


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