Heterotic effects for yield and tuber solids and type of gene action for five traits in 4x potato families derived from interploid (4x-2x) crosses

The degree of heterosis for total tuber yield (TTY) and total solids (TS) in 4x‐2x crosses was estimated by comparing the performance of 12 families with their respective parents in two locations in Wisconsin (USA). The parental 2x clones were Phureja‐haploid Tuberosum hybrids with 2n‐pollen production by first‐division restitution. The general combining ability (GCA) and specific combining ability (SCA) were estimated for TTY, TS, vine maturity (VM), length of tuber sprout dormancy (LD), and tuber eye depth (ED). Family performance for TTY ranged from 74 to 146% at Hancock (E#1) and from 77 to 287 at Rhinelander (E#2) when compared with that of the 4x parent group. For VM, the families were late maturing, but a few precocious ones were identified. For TS, the families had heterosis of 5.1% over the 4x parent group. The families had slightly higher ED values than the 4x parents, but families with values within the commercial range were identified. The family average for LD (54 days) was closer to the 2x group (51 days) than to the 4x group (88 days). The direction and magnitude of the parent‐family relationships were variable. The 4x parent TTY was correlated with progeny in E#1 but not E#2. The 2x parent VM had correlation with the offspring at E#2 but not at E#1. The type of gene action had a trait‐specific expression. Significant SCA and GCA variances were observed, suggesting that additive as well as non‐additive genetic effects were operating. The 4x‐2x crosses were able to generate heterotic families for TTY and TS in combination with other useful traits. However, no promising results were found for LD because of the apparent dominance of the short‐dormancy phenotype. This result indicates the need of additional selection and breeding efforts for some specific traits when using S. phureja‐derived germplasm.     

Comparison of haploid Tuberosum-Solanum chacoense versus Solanum phureja-haploid Tuberosum hybrids as staminate parents of 4x–2x progenies evaluated under distinct crop management systems

The relative value of haploid Tuberosum-Solanum chacoense (TCH) vs. Solanum phureja-haploid Tuberosum (PTH) hybrids as male parents in 4x–2x crosses was estimated under two distinct crop management systems. The first experiment (E#1) was carried out with supplementary irrigation (three times a week) at Hancock-Wisconsin (WI) with 27 families derived from a sub-set of crosses involving 11 tetraploid (4x) cultivars and 10 diploid (2x) clones (3 TCH; 6 PTH; and one TCH-PTH hybrid clone). A second experiment (E#2) was conducted at Rhinelander-WI with the same group of families but it was only rainfed with no supplementary irrigation being provided during the entire course of the assay. For comparison, a complete set of 4x and 2x clones (used as parents) was also planted in each location. Three traits were evaluated in both locations: total tuber yield (TTY), haulm maturity (HM), and plant vigor (PV). Altogether, 18 out of 27 and 10 out of 27 families outyielded the corresponding 4x parents at E#1 and E#2, respectively. Significant differences among all 4x–2x families and among families of the TCH group were observed for TTY at both locations. No difference was found for TTY among families of PTH and [TCH–PTH] groups at each location. A total of 75% and 50% of the TCH families outyielded their 4x parents at E#1 and E#2, respectively. The percentage of families from the PTH group that outyielded their 4x parents at E#1 and E#2 was 83.3% and 25%, respectively. The TCH group had on average lower HM scores than PTH (at both locations) indicating some segregation for earliness. However, the HM values of the 4x–2x families were, in general, higher than those observed for the 4x parents. For PV, the PTH group mean was significantly higher than TCH group only in E#1. The PV values of the 4x–2x families were higher than the 4x-parent group at both locations. Our results indicated that TCH hybrids might be as good parents as PTH to increase the TTY of 4x–2x progenies. In addition, the TCH families displayed a slight higher level of performance under more stressful growing conditions than PTH hybrids as indicated by the assay at Rhinelander. Therefore, selection of genetic materials with potential broad range of adaptation seems to be feasible with both hybrids via the 4x–2x breeding scheme. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding behavior for tuber protein in Solanum tuberosum and Tuberosum-phureja hybrids

Summary True protein content among tubers within a plant of Solanum tuberosum cv. Oneida was found to be negatively correlated with tuber size. A similar study of S. phureja genotype 148-17 revealed no correlation. Tuber protein was determined for 250 genotypes in each of four hybrid potato populations in a factorial mating design with four potato cultivars as stylar parents mated to four groups of pollen parents (4x cultivars, 4x high protein selections, 2x S. phureja, 2x high protein S. phureja). The hybrid population derived from the 4x high protein selections was significantly higher in protein content than the other populations. High estimates of general combining ability for tuber protein content were found for both stylar and pollen parents. Poor photoperiodic adaptation to growing conditions in northern latitudes was a possible explanation for the variable protein phenotypes typical of S. phureja and the lack of transmission of the high protein character in phureja to 4x-2x hybrids. Although protein content was negatively correlated with total yield, high protein segregates with good yield potential were identified in all four populations.Scientific Journal Series Article 11, 616 of the Minnesota Agricultural Experiment Station.     

The transfer of the synaptic gene (sy-2) from 1EBN Solanum commersonii Dun. to 2EBN germplasm

Summary Crosses of a synaptic mutant (sy-2) of 2x(1EBN) S. commersonii Dun. with 2x(2EBN) S. chacoense Bitt. resulted in the production of 3x(2EBN) hybrids. Low levels of 2n egg production in these hybrids allowed subsequent crosses to be made with 4x(4EBN) cultivars, resulting in 5x(4EBN) S. commersonii-S. chacoense-Group Tuberosum hybrids. Seed set in these crosses averaged 0.22 seeds per fruit. Fifty-four unspotted seeds were produced in 1225 crosses of the 5x(4EBN) hybrids with 2x(2EBN) Group Phureja haploid extraction clones carrying dominant seed spot markers. These seeds yielded a total of 15 confirmed haploids having a diploid (2n=2x=24) or near diploid chromosome number. One haploid clone recovered displayed a synaptically abnormal phenotype similar to the original S. commersonii synaptic mutant. Preliminary test crosses of these haploids indicated that all haploids produced were 2EBN.This method for the transfer of alleles across EBN levels holds promise for the recovery of both qualitative and quantitative traits from 1EBN species. In these recovered, cross-compatible forms, clones with desired characteristics may be selected and easily incorporated into breeding programs.     

Usefulness of Andigena (Solanum Tuberosum SSP. Andigena) Genotypes as Parents in Breeding Early Bulking Potato Cultivars

Summary Seven Solanum tuberosum ssp. tuberosum and three Solanum tuberosum ssp. andigena accessions were crossed to produce 12 Tuberosum × Tuberosum (T × T) and 9 Tuberosum × Andigena (T × A) progenies. These families were evaluated for five important traits for two successive clonal generations under short day sub-tropical plains. The differences in yield, average tuber weight and tuber number between {T × T }and T × A families in an early (75 days) crop were not significant. Compared to conventional intra-Tuberosum families, T × A families had significantly higher % tuber dry matter and specific gravity. In contrast to intra-Tuberosum crosses, T × A crosses exhibited a positive heterosis for tuber yield. Compared to T × T families, T × A families showed significantly higher heterosis for yield and tuber number. Comparison of T × T and T × A families and parents using canonical analysis led to the identification of superior hybrid families and superior parents. Some T × A progenies were close to breeding goal and thus can be used for selecting high-yielding cultivars. This revealed the usefulness of Andigena genotypes as parents in developing early bulking potato cultivars with broad genetic base for short day sub-tropical plains.     

A biosystematic study of the origin of the cultivated diploid potato,Solanum x Ajanhuiri Juz. et Buk.

Summary The origin and nature of the diploid cultivated potato species S. ajanhuiri Juz. et Buk. was studied. Several lines of evidence indicate that S. ajanhuiri might be derived from natural crosses between primitive cultivars of the diploid species S. stenotomum and the wild species S. megistacrolobum. Morphological comparisons were made between S. stenotomum x S. megistacrolobum F₁ hybrids and naturally occurring S. ajanhuiri to investigate this hypothesis. Comparisons were also made between S. ajanhuiri x S. stenotomum crosses and the F₂ generation of the first-mentioned cross.Crosses between the two major groups of S. ajanhuiri cultivars, Ajawiri and Yari, showed not only genetic breakdown but also a wide range of phenotypic variation similar to those of artificial F₂ families of S. stenotomum x S. megistacrolobum. Furthermore, there was strong evidence showing that the Yari group of S. ajanhuiri could almost certainly be an F₁ S. stenotomum x S. megistacrolobum hybrid, whereas the Ajawiri group could be a backcross of an F₁ hybrid to S. stenotomum. These results added further support to the hypothesis of a hybrid origin of S. ajanhuiri, as well as indicating its putative parents. It is suggested that this hybridogenic taxon be retained at the species level under the name Solanum x ajanhuiri.     

The Use of Potato Haploids to Put 2x Wild Species Germplasm into a Usable Form

An effective method of incorporating germplasm of wild 2x Solanum species into the cultivated potato is through hybridization with haploids of 4x S. tuberosum Group Tuberosum. This procedure provides for the introduction of desirable traits and genetic diversity from wild species into potato. Haploid and wild species genotypes can be evaluated for parental value based on the presence of good tuberization, desirable traits, fertility, and 2n gametes in their hybrid progeny. Haploid-wild species hybrids may be intercrossed and evaluated at the 2x level to take advantage of diploid genetic ratios. Selected 2x genotypes may then be brought to the 4x level through sexual polyploidization with 2n gametes.     

Enhancement of diploid Solanum chacoense Bitt. using adapted clones of Solanum phureja Juz. & Buk.

Summary F₁ hybrids between Solanum phureja and S. chacoense were studied in a new approach to enhance wild diploid potato species using adapted S. phureja clones as the female parent. S. chacoense parents had few tubers, whereas S. phureja parents had been previously selected for tuberization under long days. Twenty hybrid families were evaluated for haulm vigor, vine maturity, stolon development, frequency of tuberization, tuber set, tuber yield and average tuber weight under naturally occurring increasing or decreasing photoperiods in spring and fall growing seasons in Morocco. The hybrid plants were more vigorous, later maturing with thicker stolons in the spring season. Frequency of tuberization and tuber set did not vary with season. Tuber yield and average tuber weight were higher in fall; the maximum yield was 2.4 and 4.6 kg per hill under spring and fall conditions, respectively. Remarkable variation was found both between and within hybrid families for all traits in this first cycle of enhancement. The selection of vigorous, fertile clones incorporating the S. chacoense genome is possible by using S. phureja as an adapted germplasm source.     

Comparison of diploid and tetraploid potato families derived from Solanum phureja x dihaploid S. tuberosum hybrids and their vegetatively doubled counterparts

Summary To determine whether in potatoes the tetraploid level is preferable to the diploid level, especially regarding tuber yield, four diploid (2n=2×=24) Solanum phureja x dihaploid S. tuberosum hybrid parents and their vegetatively doubled, tetraploid (2n=4×=48) counterparts were intermated, which resulted in two F₁ hybrid families at both levels of ploidy. The parents and clones of the F₁ families and their offspring were used in crosses in such a way that in addition Sib₁, Sib₂, F₁×Sib₁, BC₁ and Sib₁×Sib₁ families were produced. Of the first clonal generation of the 12 2 x families and their 12 counterpart 4 x families two tubers per clone were planted in three replications in a field experiment at Sturgeon Bay in 1969; of the parents six tubers were planted in each replication. Data were recorded on 16 characters, including plant height at four different times.The ANOVA's showed significant clone effects within each family for all characters. Computed from all family means as well as from the family means per ploidy level, differences due to family were also significant for all characters except one.As at the 2 x level and at the 4 x level of ploidy the mean phenotypic correlations between characters were of similar magnitude, it is concluded that they are independent of ploidy level.With the exception of eye depth, the mean coefficient of variation was greater at the 2 x than at the 4 x level of ploidy, indicating the greatest response to selection for those characters at the 2 x level. From the differences in family means between the 4 x and the 2 x level of ploidy it was apparent that the 4 x families generally had significantly taller plants, later maturity, fewer tubers, higher mean tuber weight, more tuber yield and more dry matter yield than their counterpart 2 x families. In contrast, the 4 x parents had on the average shorter plants, lower mean tuber weight, much lower tuber yield and lower dry matter yield than their 2 x counterparts.The phenotypic correlation and Spearman's rank correlation between the family means of the 2 x and the 4 x level of ploidy were positive for almost all characters and significant for nearly half of them.From the results it is concluded that 1. in potatoes the 4 x level of ploidy is preferable to the 2 x level, and 2. the performance of 4 x families is predictable from the performance of their counterpart 2 x families.Based on results mentioned in the literature and on the present results, a continued use of S. tuberosum dihaploids in potato breeding needs to be dissuaded.     

Crossability and cytological studies in Solanum macrocarpon and Solanum linnaeanum (Solanaceae).

Summary Crossing experiments involving the various groups of Solanum macrocarpon L. complex, including wild (dasyphyllum), semi-wild and cultivars produced fully fertile F1 and F2 hybrids. This confirmed earlier findings that these groups belong to the same biological species. S. macrocarpon complex and S. linnaeanum Hepper ex Jaeger are isolated by reproductive barriers. F1 and F2 hybrids between various groups of S. macrocarpon showed heterosis. F2 superior hybrids were isolated as candidates for the future breeding programmes. Most wild-type traits like prickliness, hairiness were dominant to those possessed by cultivars. Relatively resistant hybrids to pest attack were noted. S. macrocarpon complex and S. linnaeanum are diploids (2n=24). The overall nature of the karyotype suggests that the two are related. The F1 hybrids between the cultivars of S. macrocarpon and the wild group (S. dasyphyllum) showed normal meiosis. A lack of isolating barriers confirmed that S. macrocarpon complex constitute a single biological species.     

Assessment under short-day conditions of genetic materials derived from three potato breeding strategies: 4x-4x (intra-Tuberosum), 4x-2x (FDR 2n-pollen), and 4x-4x (diplandrous tetraploid)

Families and cultivars derived from three breeding strategies [the conventional 4x-4x (intra-Tuberosum), the interploid 4x (Tub)-2x (Phureja-haploid Tub), and 4x (Tub)-4x (diplandrous tetraploid-DTO)] were evaluated under short-day conditions in Brazil. Two 4x-4x (intra-Tub) cultivars (`Bintje' and `Delta') were used as standards. The 4x-2x (FDR) and 4x-4x (DTO) strategies were equivalent for all traits but they presented superior performance when compared to the 4x-4x (intra Tub) scheme(as a group) for total tuber yield (TTY), commercial yield (CY), and plant vigor (PV). No differences among breeding schemes were observed for three other traits: eye depth (ED), plant uniformity (PU), and haulm maturity (HM). As a group, the 4x-2x (FDR) and 4x-4x (DTO) strategies were similar to the two standard cultivar for all traits but HM. However, eight families [six 4x-2x (FDR) and two 4x-4x (DTO)] had significantly superior performance for TTY when compared with the standard cultivars. For CY, the best 4x-4x (DTO) and the best 4x-2x (FDR) families outyielded `Bintje' by161% and 128%, respectively. No major differences were observed between breeding schemes for TTY and CY when comparing families derived from one single cultivar (`Chiquita') as 4x female parent. However, superior families, based upon multi trait selection criteria, could be obtained only with the 2n-pollen-based strategies. It was possible to select high yielding 4x-2x (FDR) and 4x-4x (DTO) families with favorable trait combinations (e.g., high yielding with ED scores similar to the standards). Individual DTO clones selected within these families may represent outstanding parental materials for crosses with tropical-adapted commercial cultivars. This initial comparison of progenies and cultivars derived from these breeding strategies suggests that 4x-2x (FDR) and 4x-4x (DTO) schemes could be viable alternatives to the conventional 4x-4 × crosses also in tropical/subtropical areas of the world. This revised version was published online in August 2006 with corrections to the Cover Date.     

Alteration of the genomic composition of Solanum nigrum (+) potato backcross derivatives by somatic hybridization: selection of fusion hybrids by DNA measurements and GISH

Fusion experiments were performed with a first (BC₁‐6738) and a second (BC₂‐9017) generation backcross hybrid of 6x Solarium nigrum (+) 2x potato somatic hybrids with potato cultivars. Because no progeny was obtained from the BC₂ genotypes, alternative approaches were sought to overcome the sexual crossing barrier. Five potato genotypes, one of which contains the hygromycin resistance gene, were used in the fusion experiments. All vigorous regenerants were used for the estimation of nuclear DNA content using flow cytometry. Plants with a DNA content higher than that of the BC₁‐6738 or BC₂ genotypes were considered potential somatic hybrids. Forty‐nine potential somatic hybrids resulted from fusion experiments with BC₁‐6738, from which 20 grew vigorously in the greenhouse and flowered. After pollination with several 4x potato cultivars, eight genotypes produced seeded berries and five genotypes gave seedless berries. In addition, 11 of these 13 somatic hybrids were selected for genomic in situ hybridization (GISH) analysis to determine their genomic composition. Nine had exactly or approximately the expected number of 36 S. nigrum and 60 potato chromosomes. In one genotype, only 22 instead of 36 S. nigrum chromosomes were found and one potato chromosome was possibly missing. Only five potential somatic hybrids were detected among the 79 regenerants from BC₂‐9017 (+) 2x potato fusion experiments that were analysed by flow cytometry. Two of these hybrids were rather vigorous and did flower, but pollinations with potato have not yet set any berries.     

Interspecific hybrids between three eggplant (Solanum melongena L.) cultivars and two wild species (Solanum torvum Sw. and Solanum sisymbriifolium Lam.)

Three Greek eggplant cultivars, ‘Langada’, ‘Tsakoniki’ and ‘Emi’ (2n= 24), were crossed with two wild species (Solanum torvum Sw., 2n= 24 and Solanum sisymbriifolium Lam., 2n= 24). Ovules isolated 15-27 days after pollination were cultured in a modified MS medium at 24°C and a 16h photoperiod. Fifty days later, the ovules were dissected and the interspecific embryos were cultured in the same medium. Interspecific hybrids were achieved only from crosses between the eggplant cultivars and S. torvum. The hybridity of the putative interspecific F¹ hybrid (Solanum melongena×S. torvum) was confirmed by using morphological and biochemical (isozyme isocitrate dehydrogenase A, phosphoglucomutase A, phosphoglucose isomerase B, 6-phosphogluconate dehydrogenase A, 6-phosphogluconate dehydrogenase B) markers. The F¹ plants (‘Langada’×S. torvum) were selfpollinated and backcrossed to both parents. Fruits, however, were produced only when the F¹ hybrid was backcrossed as female with the eggplant cultivar ‘Langada’.     

Variation for agronomic and processing traits in Solanum tuberosum haploids × wild species hybrids

Summary The broad range of wild and cultivated species relatives of the commerical potato (Solanum tuberosum L.), guarantees the existence of a gene reservoir to be screened for traits that are absent or present only in low frequencies in the cultivated germplasm. Haploids (2n=2x=24) extracted from the cultivated tetraploid (2n=4x=48) germplasm cross easily with diploid (2n=2x=24) potato species and produce fertile progeny. As most haploid × species hybrids tuberize under long day conditions they can be maintained clonally and evaluated for the traits of interest. Three populations involving Tuberosum haploids × Solanum bukasovii (tub x buk), Tuberosum haploids × Solanum sparsipilum, (tub × spl) and Tuberosum haploids × Solanum berthaultii (tub x ber) clones, were planted at two locations in Wisconsin. The haploids were derived from W231, a selected clone from the University of Wisconsin Potato Breeding Program. The objectives were: to evaluate the H-S populations for agronomic and processing traits, and to determine the phenotypic associations between them. Data were recorded on haulm maturity (HM), tuber weight (TW) and tuber number (NT) per plant, specific gravity (SG), chip color after harvest (CH), and chip color after storage at 4° C and one week of reconditioning at room temperature (CH1). Results for SG and CH indicated good potential of the germplasm evaluated to introgress these traits into the commercial potatoes. For instance, the SG mean for tub x buk, tub x spl and tub x ber were 1.079, 1.086 and 1.082, respectively, and their means for CH were 4.8, 3.9 and 3.5. Chip color after storage and reconditioning was found in low frequency in the populations. Four clones in the tub x spl population, and three clones in the tub x ber population had CH1 4.0, the commercially acceptable score for this trait. Significant (p 0.01) phenotypic correlations (r) were found between HM and SG (r=–0.46 in tub x buk, r=–0.61 in tub x spl, and r=–0.34 in tub x ber), NT and TW (r=0.79 in tub x buk, r=0.88 in tub x spl, and r=0.71 in tub x ber), and TW and SG (r=0.40 in tub x buk, and r=0.36 in tub x spl). The correlation coefficients between processing traits were not significant, which may indicate the presence of separate genetic mechanisms governing the inheritance of these traits.     

Molecular characterization of the progeny of <Emphasis Type="Italic">Solanum etuberosum</Emphasis> identifies a genomic region associated with resistance to potato leafroll virus

Potato leafroll virus (PLRV; Genus Polerovirus; Family Luteoviridae) is one of the most important virus pathogens of potato worldwide and breeders are looking for new sources of resistance. Solanum etuberosum Lindl., a wild potato species native to Chile, was identified as having resistances to PLRV, potato virus Y, potato virus X, and green peach aphid. Barriers to sexual hybridization between S. etuberosum and cultivated potato were overcome through somatic hybridization. Resistance to PLRV has been identified in the BC₁, BC₂ and BC₃ progeny of the somatic hybrids of S. etuberosum (+) S. tuberosum haploid × S. berthaultii Hawkes. In this study, RFLP markers previously mapped in potato, tomato or populations derived from S. palustre (syn S. brevidens) × S. etuberosum and simple sequence repeat (SSR) markers developed from tomato and potato EST sequences were used to characterize S. etuberosum genomic regions associated with resistance to PLRV. The RFLP marker TG443 from tomato linkage group 4 was found to segregate with PLRV resistance. This chromosome region has not previously been associated with PLRV resistance and therefore suggests a unique source of resistance. Synteny groups of molecular markers were constructed using information from published genetic linkage maps of potato, tomato and S. palustre (syn. S. brevidens) × S. etuberosum. Analysis of synteny group transmission over generations confirmed the sequential loss of S. etuberosum chromosomes with each backcross to potato. Marker analyses provided evidence of recombination between the potato and S. etuberosum genomes and/or fragmentation of the S. etuberosum chromosomes.     

Genetic analyses for bioactive potential in tetraploid potato (Solanum tuberosum L.)

A total of four traits related to bioactive potential of the tetraploid potato were studied in a North Carolina II cross‐experiment. The objectives of this study were to estimate genetic parameters for target bioactive compounds in a tetraploid potato population, to determine phenotypic and genotypic correlations and to calculate combining ability effects of cultivars and breeding lines included in the crossing scheme. Total monomeric anthocyanins, phenolics, carotenoids and hydrophilic antioxidant capacity were measured by spectrophotometric methods. The sources of variation female (GCA_f), male (GCA_m) and their interaction (SCA) were significant for bioactive compounds and antioxidant capacity. Narrow‐sense heritability estimates (h²) were moderate for all the traits (0.413–0.657). Both phenotypic and genotypic correlations were highly significant for phenolic compounds and antioxidant capacity. As regards combining ability, positive and negative GCA and also SCA effects have been identified for bioactive compounds and antioxidant capacity. These results indicate that hybrid breeding lines can be obtained by choosing parents with significant GCA, whose bioactive potential can also be further enhanced if the crosses have a significant SCA.     

Double-bridge hybrids of Solanum bulbocastanum and cultivars of Solanum tuberosum

Summary Solanum bulbocastanum (2n=2x=24) has valuable characters for potato breeding, but cannot be hybridized directly with S. tuberosum cultivars. Both S. acaule (2n=4x) and S. phureja (2n=2x) were used as bridging species. Triploid S. acaule × S. bulbocastanum were doubled with colchicine and the resulting fertile hexaploid F₁'s crossed with S. phureja. The triple hybrids obtained were tetraploid or nearly so. The two genomes of S. acaule in these triple hybrids probably pair preferentially, which may provoke pairing and possibly crossing over between the chromosomes of S. bulbocastanum and S. phureja.More than 20000 pollinations of the triple hybrids with four potato cultivars had to be made to produce 40 quadruple hybrids. These highly vigorous hybrids varied greatly in many morphological characters, resistance to Phytophthora infestans, fertility and crossability. The chromosome numbers are 48 (24 hybrids), 49 and 46, but some higher ploidy levels (65, 66, 72 chromosomes) were found as well. Their origin is to be sought in the fusion of an unreduced egg cell from triple hybrids (either euploid or hypoploid) and a reduced male gamete from the cultivars. This view is corroborated by their extreme resistance to Phytophthora. Also some 48-chromosome hybrids are highly resistant, which may indicate introgression from S. bulbocastanum.Most quadruple hybrids are readily inter-crossable and crossable as females with cultivars; several also as males. Two could be hybridized with S. bulbocastanum, but the few seeds dit not germinate.Studies of pachytene stage of meiosis revealed the presence of a S. bulbocastanum chromosome in at least one tetraploid hybrid, which is highly resistant to Phytophthora. At metaphase I of meiosis chromosome associations higher than quadrivalents were not found. Except in one hybrid, the frequency of quadrivalents did not exceed one per cell and the average proportion of chromosomes associated as bivalents amounted to 90%.The quadruple hybrids (double-bridge hybrids) appear good starting material for breeding programmes aimed at introducing genes from S. bulbocastanum into S. tuberosum cultivars.     

Inheritance in Solanum aethiopicum,the scarlet eggplant

Summary Analyses of F₁ and F₂ hybrid progenies from crosses between the ancestral species Solanum anguivi and cultivars of its domesticated derivative S. aethiopicum, have proved the mode of inheritance of prickles, stellate hairs and some other morphological characters and suggested the mode for several more. Most wild-type traits were dominant: many recessive domesticated traits involved imperfect morphogenesis suggesting loss of genetic control. F₁ hybrids between cultivars show marked heterosis and are recommended for crop production.     

Reciprocal differences between hybrids of Solanum tuberosum Groups Tuberosum (haploid) and Phureja

Summary Yield components including total tuber yield, total tuber number, vine maturity, vine vigor and average tuber weight as well as seed germination and pollen stainability were studied in 28 exact reciprocal hybrid families, between 12 Solanum tuberosum Group Tuberosum (haploid) (TH) and 12 S. tuberosum Group Phureja (PH) clones in a NC Mating Design II in 4 sets of 3 by 3 reciprocal hybrids at three locations, one in Minnesota (USA) and two in Morocco. TH parents were insensitive to daylength whereas most PH clones required critical photoperiods equal to or less than 14 hours for tuberization. Mean reciprocal differences were significant for most traits at all 3 locations. Hybrids with TH cytoplasm were superior to those with PH cytoplasm by 18% for tuber yield, 21% for tuber number, and 9% for vine maturity, but inferior to hybrids with PH cytoplasm by 11% for vine vigor and 19% for time to reach 80% seed germination. Reciprocal differences were not detected for average tuber weight. Six reciprocal crosses revealed significant differences for pollen stainability but the overall mean difference (one location) was not significant. Possible reasons for the observed reciprocal differences included gamete selection, pseudo-self-compatibility and/or interaction of cytoplasm with both nuclear genes and environment. Differences for critical photoperiod of TH and PH parents were also demonstrated as a probable source of reciprocal differences.Scientific Journal Series Article 14896 of the Minnesota Agricultural Experiment Station supported in part by the U.S. Agency for International Development, contract no. 608-0160, IAV Morocco Project.     

Breeding behavior of yield components and hollow heart in tetraploid-diploid vs. conventionally derived potato hybrids

Summary A factorial mating design with six 4x cultivars as stylar parents mated to three groups of pollen parents (4x cultivars, 4x high protein selections, and 2x S. phureja) was used to study breeding behavior of yield, tuber set, marketable yield and hollow heart in potatoes. Mean yield for the 4x-2x hybrids was equivalent to that of their cultivar parents although yield components, tuber set and average tuber size, were greater and less, respectively, than the cultivar parents. High estimates of general combining ability were found in both pollen and stylar parents for yield, tuber set, marketable yield, number of marketable tubers and hollow heart in all three hybrid populations. Specific combining ability estimates were significant only for yield and hollow heart. Frequency of white-fleshed 4x-2x progeny of five heterozygous yellow-fleshed 2x phureja genotypes was used to confirm cytological identification of a first division restitution mechanism operative in the 2x parents. Although three of these phureja genotypes generated high-yielding progeny, two others produced 4x-2x progeny with mean yield similar to that of hybrids among 4x cultivars.Scientific journal series article 11,601 of the Minnesota Agricultural Experiment Station.