Breeding for quantitative resistance to potato cyst nematode (Globodera pallida) in tetraploid potatoes using dihaploids and unreduced gametes

Summary Dihaploids were produced from tetraploids resistant to potato cyst nematode (Globodera pallida (Stone)). High levels of resistance were found in the dihaploids and three were used to produce tetraploid progenies by crossing them with susceptible tetraploid cultivars. One dihaploid, PDH505, produced more highly resistant offspring than the other two, PDHs 417 and 418. The latter gave progenies whose levels of resistance were similar to those obtained from susceptible dihaploids crossed with resistant tetraploids.The differences between the progenies of the resistant dihaploids were probably due to different modes of unreduced gamete formation (PDH505 producing gametes by first division restitution (FDR) and PDHs 417 and 418 by second division restitution (SDR)) although cytological studies would be necessary to confirm this. The methods by which dihaploids could be utilised in a tetraploid potato breeding programme are discussed in relation to the mode of unreduced gamete formation.     

The use of dihaploids in increasing the homozygosity of tetraploid potatoes

Summary Electrophoresis banding patterns of the tuber proteins of 12 dihaploids of the cultivar Pentland Crown showed that four had types of patatin unlike that of the parent. The patatin types of somatically chromosome-doubled clones derived from three of the dihaploids were identical to those of the dihaploid progenitors. Fourteen dihaploids produced from the chromosome-doubled derivative (PDH40X2) of one dihaploid, which had a variant patatin, had the patatin type of the parent dihaploid.The experiment showed that dihaploids and somatic chromosome doubling could be used to fix variation found in heterozygous tetraploid potatoes. Used together, haploidisation and chromosome doubling can generate highly homozygous tetraploids for use by plant breeders.     

Intraspecific somatic and sexual hybridisation between dihaploid lines of Solanum tuberosum L.: evaluation of morphological traits and resistance to late blight Phytophthora infestans (Mont.) de Bary in the foliage

Intraspecific tetraploid somatic and sexual hybrid plants have been resynthesised following protoplast fusion and by sexual crosses between two dihaploid potato (Solanum tuberosum) lines each possessing complementary agronomic traits. The dihaploid PDH 40 possesses good tuber shape and yield but has foliage susceptibility to late blight (Phytophthora infestans). On the other hand, the dihaploid PDH 727 possesses resistance to blight in the foliage but has a low yield of small and irregular shaped tubers. Since it was only possible to use a partial selection strategy based on culture media to facilitate recovery of somatic hybrid plants-further morphological and esterase isozyme based characterisations were performed to identify somatic hybrid plants from amongst the non-hybrid plant material. When the blight resistance of both the intraspecific somatic and sexual hybrid plants was assessed there was no significant difference in the mean resistance value and it was intermediate between those of their parents. However, the range of resistance was much wider among the sexual hybrids than among the plants derived from somatic fusion. An assessment of tuber yield between tetraploid sexual and somatic hybrids showed no significant difference and it was higher than that of either parent value. The implication of these results in the context of potato genetics and breeding is discussed.     

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.     

Solanum phureja genes are expressed in the leaves and tubers of aneusomatic potato dihaploids

Summary The expression of leaf isozymes and tuber patatin in dihaploids derived from the Solanum tuberosum cv. Pentland Crown was investigated. Seven of the dihaploids were aneusomatic containing additional chromosomes from the S. phureja dihaploid inducer. Of these, four genotypes expressed leaf isozymes characteristic of the S. phureja dihaploid inducer, and the tubers of three aneusomatic dihaploids contained a S. phureja form of patatin. Aneusomatic dihaploids in which the proportion of cells containing additional S. phureja chromosomes was relatively small (i.e. 1–15%) did not express leaf isozyme markers or patatin bands characteristic of the dihaploid inducer or showed only faint expression of one or two markers. However, those with a high proportion of cells containing additional chromosomes (50–55%) had a range of strongly expressed leaf isozymes that were characteristic of the dihaploid inducer and also expressed the S. phureja tuber patatin.One dihaploid genotype was exclusively euploid (2n<24), yet is expressed a S. phureja leaf isozyme marker and S. phureja tuber patatin, suggesting recombination or chromosome substitution between the genome of the S. phureja dihaploid inducer and the cultivar Pentland Crown.     

Ploidy reduction in blackberry

Polyploidy in blackberries and ploidy differences between Rubus species are obstacles to the efficient introduction of valuable germplasm, both intra- and interspecific, into blackberry breeding programs. Expansion of the germplasm base would be facilitated by reducing the ploidy level of blackberry cultivars to the diploid level. In this report selection of twin seed, interspecific hybridization, and pollen irradiation were compared as methods in the recovery of dihaploids from tetraploid blackberry cultivars. One dihaploid was obtained through selection of twin seed and several were obtained following interspecific hybridization. The infrequency of twinning and difficulty in detecting twin seed in Rubus reduced the efficiency of this method. The efficiency with which dihaploids could be obtained following interspecific hybridization varied with the pollen parent. Reduced seed set and seed quality following pollinations with respectively R. parvifolius and R. hirsutus could be used to advantage in the recovery of dihaploids from blackberries. Ploidy reduction in several tetraploid blackberry cultivars was obtained following pollinations with 100 and 150 kR gamma irradiated pollen. Most of the seedlings obtained at the 50 kR dosage were aneuploid. Pollen irradiation at 150 kR was the most efficient method of obtaining dihaploids from tetraploid blackberries. Twenty percent of the seedlings obtained following this treatment were dihaploid.     

Widespread introgression of Solatium phureja DNA in potato (S. tuberosum) dihaploids

Dihaploids were assumed to be of parthenogenic origin but cv. ‘Pentland Crown’ dihaploids produced at the Scottish Crop Research Institute (SCRI), Dundee, Scotland, are known to contain DNA from the S. phureja dihaploid inducer. This study investigates whether inducer DNA occurs in dihaploids of cultivars ‘Aminca’, ‘Brio’, ‘Lizen’ and ‘Sirtema’, produced at INRA, Ploudaniel, France. Two microsatellite markers and five simple sequence repeat 5′-anchored polymerase chain reaction (PCR) primers were used to generate markers. Markers originating from the dihaploid inducer were detected in 13 of the 19 INRA dihaploids and in some dihaploids from each cultivar. Greater introgression occurred in ‘Lizen’ dihaploids than in ‘Brio’ dihaploids, suggesting that the female (S. tuberosum) parent influences introgression. The percentage of INRA dihaploids containing inducer DNA was similar to that for ‘Pentland Crown’ dihaploids (c. 65%). The micro-satellite markers provided the first evidence of the transfer of specific, potentially useful, genes from the inducer to the dihaploid offspring. Interspecific introgression during dihaploid induction is more widespread than previously thought and researchers should be aware that it may influence the results of research using dihaploids.     

Analysis of dihaploid induction and production ability and seed parent x pollinator interaction in potato

Summary The production of dihaploids is the first step in a potato breeding program at the diploid level. Dihaploid induction ability, dihaploid production ability and seed parent x pollinator interaction were analyzed for 28 × 3, seed parent x pollinator combinations. This is the first report on significant interaction between seed parents and pollinators. Despite this interaction, IVP 101 had a significantly higher dihaploid induction ability than the widely used pollinators IVP 35 and IVP 48. Previous findings on significant differences in dihaploid production ability between seed parents were clearly confirmed.     

应用双单倍体克服籼粳交的不亲和性初探

通过对籼粳交Ｆ１体细胞愈伤组织的秋水仙素处理和四倍体花药培养，建成了水稻四倍体诱导及双单倍体分解系统。应用这一系统获得了４４个籼粳交组合的双单倍体及其自交４后代。对这些双单倍体及其后代的遗传分析表明，籼粳交育性可能受寡基因控制，双单倍体途径通过改变正常的世代交替过程，能部分克服籼粳交的不育性及倾籼或倾粳的偏态分离，并具有比Ｆ２更丰富的遗传多样性。在双单倍体一代群体中，育性正常的植株约占４０％，这是     

The association of sexuality with plant traits and tuber yield in white yam

Summary One 3-to 5-year clonal and two recent seedling-derived populations of white yam cultivars were grown and studied for the association of sex, flowering intensity, number of fruits and seed yield with vegetative characters and tuber yield. Yield was lowest in non-flowering plants and increased in the following order: male, monoecious and female plants; with females yielding almost twice as much as the non-flowering plants. The plants produced from small tuber setts, with higher leaf virus infection, low plant leafiness either had low flowering intensity, fewer fruits and seeds or even failed to flower. The sequence and timing of vegetative and reproductive processes in relation to the difference in yield between male and female plants is discussed. There is a strong indication that the intensity of flowering and fruiting is lower in plants from previous vegetative propagation compared to recent seedling-serived clones.     

The production of 2n pollen in rose

Based on the size differences found between haploid and diploid pollen produced by diploid and tetraploid rose cultivars, respectively, 2n pollen producers were identified in a population of 53 diploid hybrids from a cross between a dihaploid rose, derived from the haploidization of a tetraploid modern cultivar and the diploid species R. wichuraiana. Frequency of 2n pollen producers was estimated in 2002, 2003 and 2004. Highly variable frequencies were found i) within population; ii) during years of observation (between years and between different months in the same year). The variation of 2n pollen production could be related to environmental fluctuations. A cytological analysis of male meiosis was carried out in 10 hybrids randomly chosen. Among meiotic abnormalities leading to 2n pollen formation, triads (containing a 2n microspore at one pole and two n microspores at the other) resulting from abnormal spindle geometry were frequently observed. The mode of 2n pollen formation is genetically equivalent to a First Division Restitution (FDR) mechanism. FDR 2n pollen transmits a high percentage of the heterozygosity from the diploid parent – 2n pollen producer-to the tetraploid offspring.     

The effect of seed tuber weight on characters in the first and the second clonal generation of potato populations

Summary Fifty-five populations from crosses of three Solanum tuberosum ssp. tuberosum cultivars and seven selected S. tuberosum ssp. andigena clones adapted to the northern temperate zone have been studied in the seedling and the first and second clonal generation. This paper only deals with the effect of seed tuber weight on various important agronomic characters which are selected for in early clonal generations, independently of the type of crosses.The results showed that a distinction has to be made between the effects of differences in seed tuber weight within and between seedlings, i.e. genotypes. The effects on the first clonal generation of differences in weight of the tubers within seedlings and those of the first heaviest tubers between seedlings were similar and comparable to seed tuber weight effects within cultivars. In contrast to the within seedlings effects the between seedlings effects proved to be heritable. This is concluded from the fact that, on average, independent of seed tuber weight seedlings with larger first heaviest tubers performed better in the second clonal generation than those with smaller ones. Notably plant height, general impression, date of maturity and particularly tuber yield and mean tuber weight in the second clonal generation were related to the weight of the first heaviest tubers of the seedlings. The potentialities of these findings for an early generation selection are discussed.     

Assessment of genetic and phenotypic variation among intraspecific somatic hybrids of potato, Solanum tuberosum L.

Intraspecific somatic hybrids have been produced by protoplast fusion in eight combinations involving 10 dihaploids (2n= 2x= 24) in an attempt to provide new material for potato breeding. Cytological analysis revealed extensive variation in chromosome number, such as aneuploid, aneusomatic and mixoploid hybrids. Most of the hybrids represented the expected chromosome number of 48; however, the frequency of aneuploids reached 50% in some combinations. Some hybrids carried structurally rearranged chromosomes and exhibited a high frequency of aberrant anaphases. Isozyme and random amplified polymorphic DNA (RAPD) patterns of the hybrids from the same fusion combination were uniform. In the field, somatic hybrids showed wide phenotypic variation in 20 morphological characters. There was a significant correlation between certain leaf characters and the ploidy level, which may be used to distinguish the tetraploid hybrids from hexaploids and octoploids. Tuber yield and flowering intensity were highest in tetraploid hybrids (2n= 4x= 48). Eighteen of the 73 hybrids reached higher yields than the standard variety ‘Adretta’. Floral development and fertility were restored in hybrids derived from fusions between non-flowering or sterile dihaploids.     

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.     

Correlations within and between characters between and within generations as a measure for the early generation selection in potato breeding

Summary The main objective was to determine the reliability of selection in early generations of a potato breeding programme. To that end data were recorded in the seedling generation, an early and a late harvested experiment of the first clonal generation and the late harvested second clonal generation on up to 30 genotypes of 55 populations from crosses of three Solanum tuberosum ssp. tuberosum cultivars and seven selected S. tuberosum ssp. andigena clones, adapted to the northern temperate zone. Phenotypic correlations were computed per population in almost all possible combinations within and between characters between and within generations. The mean across 55 comparable correlation coefficients was considered to be the best estimate of the relationship concerned.In all four experiments data were collected on number of tubers, tuber yield and mean tuber weight; in the three experiments of the two clonal generations in addition on date of emergence, number of stems, plant height, haulm type, and general impression of the underground plant parts and in the two late harvested clonal generations on date of maturity and under water weight.The results confirmed that general impression which is largely decisive for the selection in early generations, is a little reliable measure. However, from the magnitude of the mean correlations between experiments within characters it must be concluded that selection for most of these separate characters is hardly more reliable. An exception was date of maturity for which a mean correlation was determined of r=0.78 between the two clonal generations. The second strongest mean correlations, perhaps surprisingly, were for tuber yield, viz. r=0.52 between the seedling generation and the late harvested first as well as the second clonal generation and r=0.63 between the late harvested clonal generations. From the correlations between characters it appeared that for a high tuber yield, besides its components, in particular an early emergence, a large plant height, an attractive haulm type and a late maturity are of importance.The main conclusion is that, as long as not enough seed tubers are available for the layout of statistically sound experiments, a negative instead of a positive selection should be applied to avoid the rejection of most of the valuable genotypes in an early stage. On the basis of the results directives for the application of such a negative selection are given.     

Exploitation of the incompatibility mechanism for the production of F1 hybrid forage grasses

Summary The utility of the two locus (SZ) incompatibility system for the production of F₁ hybrids in forage grasses is examined in relation to its mode of action at the tetraploid level and in dihaploids. Schemes are proposed for producing tetraploid populations with a high level of within population incompatibility or of single or double cross hybrids from the dihaploids.     

Early generation selection for potato tuber quality in progenies of late blight resistant parents

Developing disease resistant cultivars is one of the major objectives for a potato (Solanum tuberosum L.) breeding program, but many resistant clones have not achieved commercial acceptance because of late maturity and non-marketable tuber characteristics. Selection for tuber quality should have greater emphasis inbreeding disease resistant cultivars. The objectives of this study were 1) to evaluate the ability of late blight (Phytophthora infestans (Mont.) de Bary) resistant parents to transmit chip-processing (tuber appearance, specificgravity, and chip-color) or tablestock (tuber appearance) quality to the offspring and 2) to compare selecting for tuber quality in single-hill versus eight-hill generations. We made crosses among eight unadapted potato cultivars (B0718-3,Bertita, Bzura, Greta, Libertas, Stobrawa, Tollocan, and Zarevo) with reported late blight resistance with adapted susceptible cultivars/breeding clones to generate 95populations (4,750 seedlings). Approximately 10% of the progeny from each cross were selected from single-hill plots based on tuber appearance, number, shape, and internal defects. These selected clones (408) were evaluated for tuber appearance, specific gravity, and chip-color. The same evaluations in the following year were made on tuber samples from eight-hill plots. Libertas and Tollocan were the best parents for transmitting chip-color; B0718-3, Zarevo, and Tollocan for transmitting tuber appearance; and Bzura, Libertas, and Zarevo for transmitting high specific gravity to the highest percentage of the offspring. Overall, 50% and 56% of the clones based on single- and eight-hill generation, respectively, were considered to possess chip-processing quality; over 90% of the clones had acceptable tablestock quality. A total of 71% of the clones possessing acceptable chip-processing and 95% of the clones possessing acceptable tablestock quality selected in both generations were identified in single-hill plots. The evaluation of tuber quality characteristics in single-hill generation not only permitted the identification of clones with acceptable chip-processing and tablestock, but also increased the amount of clonal information for the following generation of selection. In crosses between late blight resistant and susceptible clones, selection for tuber quality traits can be initiated in single-hill generation using a moderate selection intensity and precede late blight testing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Field resistance to late blight and potato root eelworm in group tuberosum dihaploids

Summary An examination of the feasibility of obtaining dihaploids with high levels of field resistance to important potato pathogens, showed that dihaploids may be produced which are more resistant to late blight or to potato root eelworm pathotype E than are their tetraploid parents. The significance of this is discussed in relation to the possible types of gene action involved in conferring field resistance.     

Analysis of an incomplete diallel cross among three ssp. tuberosum varieties and seven long-day adapted ssp. andigena clones of the potato (Solanum tuberosum L.)

Summary The main aim of the experiment was to study the behaviour of seven long-day adapted clones of Solanum tuberosum ssp. andigena (A) and three varieties of S. tuberosum ssp. tuberosum (T) in an incomplete diallel cross. The four groups of crosses, TxT, TxA, AxT and AxA, held 2, 12, 20 and 21 populations, respectively. Eleven of the intersubspecific crosses were exact reciprocals. Thirty random clones per population were grown as second clonal generation in an incomplete block design with four replications in plots of two plants per clone in 1980, the parents included in many plots. Data were recorded on ten characters.The results showed that group TxA gave the highest tuber yield and AxT the second highest. The F-values indicated highly significant genotypic effects for all characters in all populations. The mean genotypic coefficients of variation (GCV), were the highest for group AxA for all characters. The ANOVA, based on population means showed significant mean squares for general combining abilities (GCA) and for differences of reciprocalls for all characters; the specific combining ability (SCA) mean squares were significant only for date of emergence, plant height and haulm type. Almost all GCA effects of the parents were significant positive or negative. Several populations showed also significant SCA effects. The correlations between the GCA effects and the parental values were of about the same magnitude as the heritabilities; those between the population means and the midparental values were slightly lower.Compared to the midparental values, most populations showed significant positive heterosis for date of emergence, haulm type, number of tubers and under water weight; all populations had significant negative heterosis for mean tuber weight and nearly all for plant height and general impression. All populations from groups TxT and AxA had significant negative heterosis for tuber yield and so had 13 out of the 20 populations from group AxT, while seven of the 12 from group TxA showed significant positive and four significant negative heterosis. The average heterosis for tuber yield of group TxT was –11%, of TxA 3.4%, of AxT–9% and of AxA–18%. The highest mean tuber yields were obtained from crosses with a very high yielding A-parent as female, while the heterosis was negative. Though significant differences between the 11 reciprocals occurred for all characters, consistent differences occurred only for tuber yield. Averaged over the 11 crosses the TxA populations outyielded their exact reciprocals by 10.7%. For the highest tuber yields in A-T crosses, therefore, the tuberosum cytoplasm seems to be preferable. By contrast for a high male fertility the andigena cytoplasm is preferable.     

Identification of somatic hybrids of dihaploid Solanum tuberosum lines and S. brevidens by species specific RAPD patterns and assessment of disease resistance of the hybrids

Summary Symmetric somatic hybrids were produced by electrofusion of protoplasts of two dihaploid tuber-bearing potato (Solanum tuberosum L.) lines and Solanum brevidens Phil., a diploid non-tuber-bearing wild potato species. A total of 985 plants was obtained. Verification of nuclear hybridity of putative hybrids was based on additive RAPD patterns, general morphological characteristics and chromosome counts. 53 (90%) calli regenerated into plants which were identified as somatic hybrids. Most of the hybrids were aneuploids at the tetraploid (4×) or hexaploid (6×) level. The 20 hybrids tested expressed a high level of resistance to potato virus Y (PVY ^N ) characteristic of the S. brevidens parent. Resistance to late blight (Phytophthora infestans (Mont.) de Bary) varied between hybrids, but was on average better than that of the fusion parents. Resistance of hybrids to bacterial stem rot (Erwinia carotovora subsp. atroseptica (van Hall) Dye) was not superior to that of commercial potato cultivars.