Paul Grun

The evolution of cultivated potatoes

In the first stages of potato evolution in the northern Andes, diploid cultivated species of theSolanum stenotomum complex were selected, in all probability, from wild progenitors in theS. brevicaule complex. TetraploidSolanum tuberosum ssp.andigena arose by fusion of unreduced gametes of a parent in theS. stenotomum complex with those of an unidentified wild species having actinomorphic calyces. Unreduced male gametes of several diploid species fertilized eggs of ssp. andigena leading to extensive introgression.Solanum tuberosum ssp.tuberosum probably originated from a cross between ssp.andigena as staminate parent and an unidentified wild species which contributed cytoplasmic sterility factors encoded in mitochondria and/or plastids having a distinctive type of DNA. Derivatives of this hybridization, which may have occurred in northwestern Argentina, evolved to ssp. tuberosum in southern Chile and southern Argentina. In the 1570’s ssp.andigena was imported to Europe and spread from there to become a major crop with worldwide distribution. In the 1840s it was essentially eliminated by late blight,Phytophthora infestans.Solanum tuberosum ssp.tuberosum was introduced from Chile into North America and Europe in the late 1800s, and in turn achieved a worldwide distribution, filling the vacated agricultural niche of ssp.andigena. The differences between ssp.andigena and ssp.tuberosum in South America are sufficient that the two could reasonably be considered to be separate species. Since the 1960’s the two taxa have been hybridized often in breeding programs. Neotuberosum, a northern-adapted strain of ssp. andigena, has been selected to mimic ssp.tuberosum. Substitution back-cross products have been produced that have the chromosomal genes of ssp.tuberosum combined with cytoplasmic factors of Andean species. These breeding activities are blurring the distinctions between the two subspecies throughout much of the world, though they remain distinct in their native areas in South America.ResumenEn las primeras etapas de la evolutión de la papa cultivada en el norte de los Andes, las especies diploides del complejo Solanum stenotomum se originaron, probablemente, de progenitores silvestres pertenecientes al complejoS. brevicaule. Solanum tuberosum ssp.andigena se originó por fusión de gametos no reducidos de un padre proveniente del complejoS. Stenotomum con otros gametos de especies silvestres no identificadas, las cuales tienen calices actinomorfos. La introgresión de muchas especies diploides en tetraploide ssp.andigena ocurrió a traves de fertilización por el polen no reducido de especies diploides. El comienzo de la evolutión deSolanum tuberosum ssp.tuberosum surgió, probablemente del cruce entre ssp.andigena como pariente macho y otra especie silvestre no identificada la cual contribuyó con los ovulos y por lo tanto con los factores cytoplasmáticos esteriles encodados en las mitocondrias o en los plastidios con distintos tipos de ADN. Los productos de esta hibridación evolucionaron a ssp.tuberosum en el noroeste de Argentina hasta el sur de Argentina y Chile. Hacia los años 1570, la ssp.andigena fue introducida a Europa y de allí se expandió quedando plantada en todo el mundo. En los 1840 fue practicamente eliminada excepto en America del Sur por el tizón tardio(Phytophthora infestans). Solanum tuberosum ssp.tuberosum fue introducida desde Chile hacia Norte America y Europa a finales del 1800 y desde entonces se distribuyó a traves del mundo, llenando el vacío ecológico creado por la desaparición de ssp.andigena. Las diferencias entre ssp.andigena y ssp.tuberosum son tales que las dos pueden con mucha razon ser consideradas como dos especies separadas. Desde 1950 los dos taxa han sido frecuentemente hibridizados enprogramas de fitomejoramiento. Neotuberosum, una cepa de ssp.andigena adaptada a las condiciones del norte, ha sido seleccionada y hoy algunas de ellas son muy semejante a ssp.tuberosum. Tambien en el norte se han producido plantas que tienen los genes cromosómicos de ssp. tuberosum combinados con factores cytoplasmáticos de especies andinas. Estas actividades de fitomejoramiento han oscurecido en cierta forma las diferencias entre las dos subespecies en muchas partes del mundo, sin embargo las dos permanecen bien distintas en sus areas nativas de America del Sur.

The inheritance and expression of unilateral incompatibility in Solanum 1

A SUBSTANTIAL body of evidence exists showing that the cross of selfincompatible pistillate parent by self-compatible staminate parent of a number of genera fails while the reciprocal succeeds. The phenomenon, termed unilateral incompatibility, has been demonstrated in crosses between species of ]Vicotiana (Anderson and DeWinton, 1931), Petunia (Mather, 1943), Lycopersicon (McGuire and Rick, 1954; Martin, 1961a, ig6ib, 1963), Antirrhinum (Harrison and Darby, 1955), and Solanum (Garde, 1959; Grun and Radlow, 1961; Pandey, 1962). One mechanism that leads to unilateral incompatibility operates through an inhibition of growth of self-compatible pollen tubes down selfincompatible styler tissue. It has been demonstrated (Lewis and Crowe, 1958) that this mechanism can operate even in crosses between members of separate genera and families. Since, therefore, unilateral incompatibility has been long established in a diverse spectrum of genera, the details of its genetic basis and mechanism of action are of interest in interpreting its role in plant evolution. The phenomenon plays a major role as an internal isolating mechanism in the genus Solanum. Self-compatible S. verrucosum pollen growth is inhibited on some self-incompatible clones of S. chacoense, kurtianum, tarijense, tube rosum Groups Phureja and Stenotomum, soukupii, simpli4folium, neohaw/cesii, sparsipilum, vernei, cardiophyllum, ehrenbergii, jamesii, pinnatisectum and megistacrolobatum (Garde, 1959; Grim and Radlow, 1961; Pandey, 1962) while the pollen tube growth of the reciprocal crosses is not inhibited. Growth of self-compatible S. brevidens pollen tubes is inhibited on styles of eight self-incompatible species while the reciprocal pollen tubes grow normally (Pandey, 1962). It was shown in earlier studies that self-incompatible biotypes of S. chacoense, S. soukupii (Grun and Radlow, 1961) and S. vernei (Pandey, 1962) included clones that did not show unilateral incompatibility when crossed with self-compatible S. verrucosum. The present report analyses two questions concerning this material: (i) What is the genic basis for the difference between self-incompatible clones that show

Cloning and sequencing of cDNAs encoding two self-incompatibility associated proteins in Solanum chacoense

SummaryWe have isolated and sequenced cDNAs for S2- and S3-alleles of the self-incompatibility locus (S-locus) in Solanum chacoense Bitt., a wild potato species displaying gametophytic self-incompatibility. The S2-and S3-alleles encode pistil-specific proteins of 30 kDa and 31 kDa, respectively, which were previously identified based on cosegregation with their respective alleles in genetic crosses. The amino acid sequence homology between the S2- and S3-proteins is 41.5%. This high degree of sequence variability between alleles is a distinctive feature of the S-gene system. Of the 31 amino acid residues which were previously found to be conserved among three Nicotiana alata S-proteins (S2, S3, and S6) and two fungal ribonucleases (R Nase T2 and R Nase Rh), 27 are also conserved in the S2- and S3-proteins of S. chacoense. These residues include two histidines implicated in the active site of the R Nase T2, six cysteines, four of which form disulfide bonds in R Nase T2, and hydrophobic residues which might form the core structure of the protein. The finding that these residues are conserved among S-proteins with very divergent sequences suggests a functional role for the ribonuclease activity of the S-protein in gametophytic self-incompatibility.

Identification of pistil-specific proteins associated with three self-incompatibility alleles in Solanum chacoense.

SummaryPistil proteins associated with three different S-alleles of the self-incompatibility locus (S locus) in Solanum chacoense have been identified which cosegregated with their respective S alleles in a series of genetic crosses involving six S. chacoense plants, their F1 progeny, and backcrosses. The molecular weights of these three S-allele-associated proteins, designated S1 S2, and S3, were 29 kDa, 30 kDa, and 31 kDa, respectively. They were all basic proteins with a similar pI of approximately 8.6. They have been found only in the stigma and style of the pistil where their maximum synthesis was reached at one day before anthesis. Their rate of synthesis in both self- and cross-pollinated pistils was the same as that in the unpollinated pistil until 2 days after pollination.

Ultrastructure of plant plasma and vacuolar membranes

Roop tip cells of diploid Solanum species of the section Tuberarium were fixed in buffered osmium, embedded in Vestopal W, and sections were stained in uranyl and lead acetate. The plasma membranes of such cells were 3-layered, symmetrical, and approximately 75 A wide. Invaginations at the cell surface were frequently seen. Such invaginations appeared to contain small projecting strands of cytoplasm running perpendicular to the plane of the section. Vacuolar membranes were also 3-layered and varied in degree of asymmetry. Symmetrical vacuolar membranes measured approximately 75 A in width while the asymmetrical ones had a cytoplasm-side opaque layer of approximately 25 A, a middle light layer of approximately 25 A, and a vacuole-side opaque layer that varied from 25 A to approximately 250 A in width.

Relationship between radiation dose rate and lethality of diploid clones of Solanum

Abstract A preliminary study was carried out to establish the relationship between dose rate and the lethal effect of 60Co radiation. Clonal rooted cuttings of Solanum were exposed to 9 kR, a predicted lethal dose, during twelve different periods of time corresponding to dose rates of 2250 R/min through a geometric progression to 1·09 R/min. The 9 kR dose was lethal when the dose rate was 70·3 R/min or greater. The dose was progressively less effective when delivered at lower rates, presumably as a result of operation of repair mechanisms, and at the lowest rates used the irradiations had a negligible effect.

Cytoplasmic substitution inSolanum. II. Tuber characteristics of reciprocal backcross progeny

SummaryRecurrent backcrosses (BC) were used to introduce nuclear factors ofS. tuberosum L. ssp.tuberosum into the cytoplasm of Andean potatoesS. tuberosum ssp.andigena (Juz. and Buk.) Hawkes andS. phureja Juz. and Buk. Each generation BC was produced in reciprocal directions to test the effect of cytoplasmic substitution on yield. This report analyses tuber number, tuber weight, and tuber length of BC2 and BC3 substitution into ssp.andigena cytoplasm and BC2 and BC2 substitutions intoS. phureja cytoplasm. Direction of cross had no consistent significant effect on yield components of ssp.andigena substitution lines. InS. phureja reciprocal progenies direction of cross was responsible for significant differences of some reciprocal sets. When there were significant differences the higher yield usually occurred when ssp.tuberosum was the pistillate parent, but in some progenies when ssp.tuberosum was the pistillate parent the yield was significantly lower than in the reciprocals. It is suggested that differences between reciprocals resulted from chromosomally encoded gene action, resulting from maternal and/or paternal effects, rather than cytoplasmic factors.

Cytoplasmic substitution inSolanum. I. Seed production, germination, and sterilities of reciprocal backcross generations

SummaryGenes ofSolanum tuberosum L. ssp.tuberosum were introduced into cytoplasm ofS. tuberosum ssp.andigena (Juz. & Buk.) Hawkes andS. phureja Juz. & Buk. to reduce cytoplasmic sterilities. Alleles that influenced berry set and seed content produced differences between reciprocal progenies. Their expressions were interpreted in terms of genes of the maternal and/or paternal parents. When the ssp.andigena genotype was introduced from the maternal parent if favoured high berry set and low seed number. Maternal ssp.tuberosum favoured lower berry set and higher seed number. The source ofS. phureja cytoplasm, aS. phureja×S. chacoense F1, used as maternal parent favoured lower berry and seed set. During successive backcrosses progeny expressions approached those of the recurrent ssp.tuberosum pollen parents. A low level of pollen sterility occurred in BC2 plants, unrelated to direction of cross or cytoplasmic factors. By BC4, seed set and fertility were as good as ssp.tuberosum, and recurrent backcrossing could be terminated without loss of seed production or fertility.

EFFECTS OF GAMMA IRRADIATION ON RADIATION SENSITIVITY IN THE DIPLOID POTATO SPECIES SOLANUM CHACOENSE.

Abstract The effect of ancestral exposure to radiation on the radiation sensitivity of progeny was tested the diploid potato species Solanum chacoense f. gibberulosum (Juz. and Buk.) Corr. Approximately 83 per cent of seedlings of a parental population that received 0 and 3 kR of gamma radiation survived and grew normally while only 26 per cent of those receiving 6 and 9 kR survived and appeared to grow normally. The survival and vigor of seedlings derived from plants that had survived these doses were compared following exposure to the same doses. The results indicated that radiation damage measured in terms of survival and vigor was increased following irradiation among most of those plants whose ancestors had received doses of 6 and 9 kR of radiation. This increase was attributed to the hereditary transmission of radiation-induced genetic damage in the form of recessive lethals and detrimentals. Certain lots failed to show increased radiation sensitivity as measured by decreased survival. This result was interpreted as resulting either from chance failure of mutation in the parental plants involved, or to somatic elimination of radiation damage induced in young seedlings.

Parental effects on growth in Solanum conditioned at multiple levels

SummaryReciprocal crosses were made between plants that had nuclear genes of S.tuberosum L. ssp tuberosum combinated, by recurrent backrossing, with cytoplasmic factors of S. phureja Juz. & Buk. and, separately, of S. tuberosum ssp. andigena (Juz. & Buk.) Hawkes. Significant differences in growth between 19 of 23 intra-cytoplasmic reciprocal progenies occurred in vigor at one or more growth stages during the season and/or in yield as measured by tuber number and weight. If no transmission of cytoplasmic factors occurred through the pollen, the cytoplasmic factors of the parents were the same, and these reciprocal differences were caused by parental chromosomal gene mechanisms such as maternal effect, pollen-tube selection, and/or imprinting. Early seedling vigor was, in some cases, associated with greater seed weight, but this did not account for all of the reciprocal contrasts. The data do not show whether these parental effects are a result of maternal and/or paternal effects. Analysis to determine whether parental effect was a single gene character or alleles expressed at two levels, or multi-genic and so expressed at multiple levels, was based on a study of progeny of ten parents that were used in more than one reciprocal pair combination. The data showed that the parents could be classified at eight successive levels of relative effectiveness as staminate or pistillate parents. Of 23 crosses, 19 showed significant differences between reciprocal progenies that were consistent with this eight-level array. The data support the interpretation that parental effect is a multi-genic character.