The breeding of the cultivated potato species solanum x juzepczukii and S. x curtilobum II. The resynthesis of S. x juzepczukii and S. x curtilobum

Summary The possibility of combining anew the genomes of wild and cultivated progenitors of triploid S. x juzepczukii and pentaploid S. x curtilobum by following the known evolutionary pathway of these species was investigated.The resynthesis of S. x juzepczukii was easy, and a wide range of synthetic forms was bred. Among these were forms with higher frost resistance (-5°C) than has been found in natural S. x juzepczukii. The total tuber glycoalkaloid content of several synthetic hybrids was lower than or as low as that of natural clones. Most synthetic hybrids were more vigorous than natural S. x juzepczukii and produced about the same types of tubers as are found in the natural range of variation. The best diploid parents were found in the species S. goniocalyx.The attempt to resynthesize pentaploid S. x curtilobum has not been successful but tetraploid plants were obtained in the process. An explanation for the occurrence of tetraploids resulting from triploid x tetraploid and/or diploid crosses is offered.The newly bred tetraploids contain at least one genome from S. acaule (possibly two) and hybridize easily with ssp. andigena. They thus provide a means for the transfer of S. acaule germ plasm into the tetraploid cultivated gene pool which would profit from the frost resistance of S. acaule.     

Inheritance of early blight resistance in diploid potatoes

Early blight (Alternatia solani) is a fungal disease in hot and humid environments, which causes leaf, stem and tuber lesions. Early blight resistance should be incorporated into potato cultivars because the fungicide spraying is an expensive solution for developing countries. The diploid cultivated species Solanum tuberosum group Phureja and group Stenotomum are sources of resistance alleles. The elucidation of the inheritance for early blight resistance must help to decide what could be the best breeding procedure to improve this diploid germplasm and transfer the resistance to the tetraploid level. Three experiments were carried out under controlled and field conditions to determine the heritability of this trait using nested and diallel mating designs with haploid, species and haploid-species hybrids. The narrow-sense heritability estimates were relatively high (0.64–0.78). This means that additivity was the most important type of gene action for determining resistance to early blight at the diploid level. The results suggested that diploid parents showing highest levels of resistance, throughout the cycle of disease development, can be used in 4x×2x crosses to obtain resistant tetraploid progenies to this fungal disease.     

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.     

Fingerprinting of alfalfa meiotic mutants using RAPD markers

Summary A calendar of female sporogenesis and gametogenesis was made for both apomictic tetraploid (2n=4x=36) Brachiaria brizantha and Brachiaria decumbens and their apomictic F₁ hybrids with sexual tetraploid (2n=4x=36) Brachiaria ruziziensis. Microgametogenesis was used as a reference. Apospory was facultative in both species and hybrids. Environmental conditions had variable effects on the level of apomixis according to each genotype. Ratios of segregation into sexuals and apomicts in the interspecific hybrids suggest an oligogenic determinism with dominant apomixis in the genus Brachiaria. Highly apomictic and partially male fertile hybrids were identified and will be used in an improvement program to transfer genes for apomixis into the sexual species B. ruziziensis.     

Isolation and characterisation of somatic hybrids of diploid Solanum tuberosum and Solanum brevidens and the use of amylose-free starch mutation for detection of introgression

Summary Somatic hybrids of diploid amylose-free (amf) Solanum tuberosum and diploid S. brevidens were made by Poly-Ethylene-Glycol (PEG) or electrofusion methods. For the isolation of interspecific hybrids the use of selection markers (kanamycin and hygromycin resistance) was useful but not essential. In this 2x+2x interspecific combination 4x and 6x somatic hybrids were obtained. Seed set was the best in 4x×4x (S. tuberosum) backcrosses, but seed germination was the best in 6x×4x combinations, using in vitro germination of unripe seeds harvested 25 days after pollination. A high degree of pollen stainability (30–40%) was observed in 7 tetraploid hybrids and very low in all hexaploids. After iodine staining, the recessive amf marker was expressed by a red colour instead of blue, visible in starch-containing cells like columella cells of root tips, (micro)tubers or microspores. As expected, complementation was observed in starch-containing cells of the fusion hybrids. Segregation of the amf marker was clearly observed in microspores of 4x and 6x hybrids. Segregation ratios in the 4x hybrids showed variable recombination frequencies. In the backcross progeny of hexaploid F12-5 with a tetraploid amf mutant one amylose-free recombinant among 67 plants was found, indicating the occurrence of meiotic recombination in the megaspore mother cells.     

Evaluation of resistance to verticillium wilt in diploid,wild potato interspecific hybrids

Summary Verticillium wilt (V. albo-atrum Reinke & Berthold or V. dahliae Kleb) threatens potato (Solanum tuberosum L.) production in most growing areas of the world. Genetic resistance offers the most cost-effective and environmentally-sound control measure. However, there is a dearth of genetic and breeding information on resistance to verticillium wilt in potato, because of obscure parentage of some standard cultivars and the complex segregation at the tetraploid level. The wide range of genetic variability in wild relatives of potatoes can be potentially useful as a source of disease resistance, such as verticillium wilt resistance. Six diploid, wild, interspecific Solanum hybrids involving resistant x resistant and susceptible x resistant crosses, were assayed for verticillium wilt resistance under greenhouse conditions to evaluate their potential as sources of verticillium wilt resistance. The cross between S. gourlayi Oka. and S. chacoense Bitt. and its reciprocal had the most resistant progenies based on mean colony counts. No simple mode of inheritance can be proposed based on the observed segregation ratios. However, the continuous distributions observed on verticillium wilt disease response among hybrid families indicate that inheritance of resistance may be polygenic and complex. In addition, skewness of colony count distributions toward the resistance parents were characteristic of all resistant x susceptible crosses suggesting that resistance may be dominant. By contrast, the susceptible x susceptible cross showed a more normal distribution. Overall, the cross between S. gourlayi and S. chacoense showed the most potential as a source of verticillium wilt resistance.     

Variation in resistance level of potato genotypes and virulence level of potato cyst nematode populations

Summary In two experiments, using different testing methods, the number of newly formed cysts was determined on nine potato genotypes with resistance from various sources. Ten potato cyst nematode (PCN) populations were used in these experiments. Rank correlation between numbers of cysts over potato genotype-PCN population combinations for both experiments was high (r_s = 0.90). Dendrograms for PCN populations and potato genotypes were constructed, based on a simultaneous hierarchical clustering procedure for potato genotype-PCN population interaction terms. Several virulence groups could be identified within Globodera rostochiensis as well as within G. pallida. Host genotypes, derived from the same sources of resistance, were clustered in different resistance groups.     

Chromosomal location of resistance to Septoria tritici in seedlings of a synthetic hexaploid wheat, Triticum spelta and two cultivars of Triticum aestivum

Chromosomal location of resistance to two virulent Argentinean isolatesof Septoria tritici was studied in two wheat (Triticum aestivumL.) cultivars (Cappelle-Desprez & Cheyenne), a synthetic hexaploid(Synthetic 6x) and Triticum spelta in seedlings. Substitution lines of these(resistant or moderately resistant) genotypes into (susceptible) ChineseSpring were selected from a previous screening. For Synthetic 6x,resistance was clearly located in chromosome 7D. Chinese Spring with the7D chromosome substituted by Synthetic 6x showed almost completeresistance, similar to the level of Synthetic 6x. For the substitutions withCappelle-Desprez, Cheyenne, and T.spelta there were no lines with abehaviour similar to the resistant parent. However, some substitutions weremore resistant than the susceptible parent suggesting that severalchromosomes could be involved in the resistance of these genotypes toSeptoria leaf blotch.     

Genetic analysis of resistance to barley scald (Rhynchosporium secalis) in the Ethiopian line `Abyssinian' (CI668)

A doubled haploid barley (Hordeum vulgare L.) population from a cross between the cultivar `Ingrid' and the Ethiopian landrace `Abyssinian' was mapped by AFLP, RFLP, SSR and STS markers and tested for resistance to isolates`4004', `2', `16-6', `17', `22' and `WRS 1872' of Rhynchosporium secalis (Oudem.) J.J. Davis, the causal agent of leaf scald. Resistance tests were conducted on parents, DH-lines, a near-isogenic line of `Abyssinian' (NIL) into `Ingrid', and an F₂ population descended from the same F₁ plants as the DHs. The DH population segregated for at least two major R. secalis resistance QTL. All isolates tested identified a major QTL on chromosome 3 (3H) associated with R. secalis resistance, in a 4 cM support interval between the co-segregating markers Bmac0209/Falc666 and MWG680. The QTL was linked with the markers Falc666 (2.3 cM), YLM/ylp (0.3 cM), MWG680 (1.7 cM), cttaca2 (2.5 cM) and agtc17 (9.8 cM). The second QTL was located on chromosome 1 (7H).However, this QTL was only detected by one isolate and was located in an interval of 16 cM in the distal part of the chromosome. At this QTL the allele for improved scald resistance originated from the parent `Ingrid'. There were a number of minor QTL on chromosomes 2 (2H), 4 (4H) and 6 (6H) that were not repeatable either across replications or analysis methods. The importance of checking QTL-models by cross-validation is stressed. This revised version was published online in August 2006 with corrections to the Cover Date.     

A study on disease variation in the populations of an interspecific cross of Brassica juncea L. x B. napus L.

Summary F₁ behaviour and F₂ variation in disease reaction were studied in the interspecific cross Brassica juncea x B. napus. Gene(s) for adult resistance to blackleg (Leptosphaeria maculans) were found to be present in the A genome of B. juncea and could be transferred to B. napus. Gene(s) for complete (seedling plus adult) resistance in B. juncea appeared to be located in the B genome. The chance of their transfer to the oilseed rapes (B. napus or B. campestris) would therefore seem to be remote.     

Gene transfer from non-tuberous to tuberous Solanum species: Evidence from meiosis in hybrids

Summary The distant hybrids between non-tuberous Solanum species and tuberous S. pinnatisectum display little or no pairing in F1 and predominantly bivalent formation (preferential pairing) after chromosome doubling. In such a situation the question about the potential and extent of gene transfer from the non-tuberous parent to the tuberous one is relevant to potato breeding. This question was investigated by studying meiosis in triploid and hexaploid hybrids from crosses between diploid TV⁵ x tetraploid (S. etuberosum x S. pinnatisectum). TV⁵ is similar to S. verrucosum with cytoplasm of S. tuberosum. The following evidence was found for the desirable transfer of S. etuberosum genes to the tuberous species.The triploid F1 hybrids did not display the configurations 12 II+12 I expected if no gene exchange would take place between S. etuberosum and the tuberous species; however, a considerable number of multivalents per cell was observed in all plants studied.In the hexaploid F1 hybrids, obtained from the triploids through somatic doubling in vitro, 36 bivalents could reasonably be expected. Although bivalents were predominant (an overall average of 24.2 per cell) quite a few chromosomes were associated as multivalents in all plants investigated.It is concluded that in the hybrids studied a considerable amount of pairing and chiasma formation occurs between chromosomes of non-tuberous and those of tuberous Solanum species. This pairing affinity is larger than that found in 2x and 4x hybrids from S. etuberosum x S. pinnatisectum. Some hypotheses are put forward to explain this increased pairing affinity.     

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.     

Transmission of bacterial wilt resistance by First Division Restitution (FDR) 2n pollen via 4x×2x crosses in potatoes

Summary Resistance to bacterial wilt (Pseudomonas solanacearum) found in tuber-bearing Solanum species was transferred into a diploid potato breeding population. Simultaneous selections were made for agronomic characters, production of first division restitution (FDR) 2n pollen, and resistance. Diploid resistant genotypes were identified via inoculation with a virulent isolate (CIP-204) of race 3 of Pseudomonas solanacearum. These resistant diploid genotypes were crossed to susceptible tetraploid potatoes. An investigation was made to assess whether resistant diploid genotypes transmit resistance to bacterial wilt, which is a quantitatively inherited trait, to tetraploid potatoes via FDR 2n pollen. Tetraploid seedlings from 4x×2x crosses were inoculated with the same isolate CIP-204, and the percentage of surviving seedlings was scored. Some 4x×2x families from resistant diploid genotypes demonstrated a high level of survival rate. The transmission of bacterial wilt resistance was achieved by the use of FDR 2n pollen. It was speculated that a female x male interaction effect on the survival rate of the evaluated progeny may exist. Selecting proper 4x and 2x parents would be important for obtaining a higher frequency of transmission of resistance to bacterial wilt in the progeny.     

Isoenzyme aided selection in the transfer of mildew (Podosphaera leucotricha) resistance fromMalus hupehensis to the cultivated apple

Summary The isoenzymic geneGOT-1 was used as an indicator of ploidy levels and hybridity in the progeny of a 4x × 2x (A878/5,GOT-1 abdn × ‘Gloster 69’,GOT-lcc) cross, derived from the apomictic species (Malus hupehensis), which segregated for mildew resistance. The distinction between resistant and susceptible plants was sharp. After 3 months in a greenhouse, resistant plants showed no signs of sporulation. Of the hybrid seedlings (diploid and triploid) 78% were mildew resistant. This analysis was facilitated through the use of theGOT-lc allele, as a marker of hybridity. It appears that the prospects of transferring high mildew resistance fromM. hupehensis to the cultivated apple are promising; of the 65 hybrid resistant seedlings 18 were diploid. A similar approach in earlier generations might have facilitated the earlier transfer of this resistance to the cultivated apple.     

Identification of QTLs for powdery mildew and scald resistance in barley

A population of 103 recombinant inbred lines (RILs, F₉-derived lines) developed from the two-row spring barley cross L94 × ‘Vada’ was evaluated under field conditions for resistance against powdery mildew (Blumeria graminis f.sp. hordei) and scald (Rhynchosporium secalis). Apart from the major resistance gene mlo on chromosome 4 (4H), three QTLs (Rbgq1, Rbgq2 and Rbgq3) for resistance against powdery mildew were detected on chromosomes 2 (2H), 3 (3H), and 7 (5H), respectively. Rbgq1 and Rbgq2 have not been reported before, and did not map to a chromosome region where a major gene for powdery mildew had been reported. Four QTLs (Rrsq1, Rrsq2, Rrsq3 and Rrsq4) for resistance against scald were detected on chromosomes 3 (3H), 4 (4H) and 6 (6H). All four mapped to places where QTLs for scald resistance had been reported before in different populations.     

Introgression of the low browning trait from the wild Mexican species Solanum hjertingii into cultivated potato (S. tuberosum L.)

Internal discoloration of tubers resulting from impact damage (blackspot bruise) is a serious quality problem in potato production and utilization, reducing profits to growers and increasing costs for processors. Resistance to blackspot bruise has been identified in the wild species Solanum hjertingii and is therefore a potential germplasm resource for genetic resistance to this problem. A bridging cross between S. hjertingii and a cultivated diploid clone was used to produce a triploid hybrid population that exhibited very low tuber browning potential, indicating a dominant pattern of inheritance for this trait. The triploid progeny were subjected to in vitrochromosome doubling and the resulting hexaploid clones were screened for browning potential. A hexaploid clone selected for low browning was reciprocally crossed with cultivated S. tuberosum cultivars exhibiting high susceptibility to blackspot bruise. Tubers obtained from the seed progeny of these 4x-6x crosses (hereafter referred to as the BC₁ populations) were evaluated for browning potential and polyphenol oxidase (PPO) activity. Tubers from the BC₁ populations displayed a very low potential for melanin production, while PPO activity was quite variable. The low Pearson correlation coefficient (r² = 0.45), between browning potential and PPO activity suggests that the mechanism of blackspot bruise resistance derived from S. hjertingii cannot be explained simply as a reduction in the initial PPO activity. The expression of substantial resistance to browning and dominant expression pattern in these BC₁ progeny indicate that utilizing genetic elements derived from S. hjertingii provides a robust approach for developing blackspot bruise resistant potato varieties. This revised version was published online in August 2006 with corrections to the Cover Date.     

Utilizing Arachis cardenasii as a source of Cercospora leafspot resistance for peanut improvement

Summary Advanced generation 40-chromosome hybrids between A. hypogaea (2n=4x=40) and a wild diploid species. A. cardenasii were evaluated for early leafspot, Cercospora arachidicola resistance and agronomic potential. The objective of this investigation was to determine if early leafspot resistance derived from a wild species could be incorporated into the A. hypogaea genome. Interspecific hybrid selections were made and then compared in the field and greenhouse to susceptible cultivars and to A. hypogaea lines which are reported to be resistant to early leafspot. Significantly higher levels of resistance were found in five hybrid selections than in cultivated lines based on numbers of lesions per leaf. In a greenhouse study, several hybrid selections also had greatly reduced sporulation from lesions as compared to A. hypogaea. Several mechanisms of resistance are believed to be present. Although hybrid selections had small seeds and low yields as compared to A. hypogaea, a new and valuable source of early leafspot resistance derived from the species A. cardenasii is present.Paper no. 8814 of the journal series of the North Carolina Agricultural Research Service, Raleigh, NC 27695. This research was partially funded by AID-Peanut CRSP grant DAN-4048-G-SS-2065-00.     

Integration of transgenes into sexual polyploidization schemes for potato (Solanum tuberosum L.)

Most potato transgenic research has focused on development of resistance to pathogens and modification of potato physiology. Many transgenes, particularly those conferring pathogen resistance, could substantially lower potato production costs in developing countries. However, transgenes have not been reported in sexually propagated 4x-2x potato hybrids commonly grown in developing countries. Two transgenes,the Bacillus thuringiensis cry3Aa endotoxin protein gene and the PVY°coat protein gene, were engineered intodiploid and tetraploid potato using Agrobacterium tumefaciens-mediated transformation. Cry3Aa was produced at high levels in several lines while the PVY° coat protein was not expressed. Diplandroid and tetraploid genotypes were crossed to produce transgenic 4x-2x hybrids. Genetic transformation had no discernable effect on fertility ofthe primary transformants, germination of4x-2x seed derived from the transformants and agronomic performance(tuber set, average tuber weight and total tuber yield) of the 4x-2xhybrids. The transgenic 4x-2xhybrids produced non-viable pollen and could only be crossed as female parents. Results suggest that transgenes, such ascry3Aa, could be expressed in 4x-2x hybrids to lower costs of production with no significant effect on plant phenotype. This revised version was published online in July 2006 with corrections to the Cover Date.     

Crosses between Beta vulgaris L. and Beta lomatogona F. et M.

Summary A population of 2x^ms sugar beets was crossed with 4x Beta lomatogona F. et M. The 3x F₁-plants were male sterile and were backcrossed with 2x and 4x sugar beets and multiplied without pollination as well. After the 1st backcross mainly 3x apomict types arose again and, among others, a small number of successful 4x backcrosses. After pollination by 4x sugar beets this 4x F₁ B₁ produced. besides predominatly apomictically multiplied 4x plants, also about 7% haploid 2x hybrids. The latter probably possess 1 genome from B. vulgaris and 1 genome from B. lomatogona. In the meiosis of the PMC's a certain amount of homeology between a number of chromosomes of both species could be established. The amphihaploid hybrids can be used as breeding parents for the creation of types in which introgession can occur. During hybridization in addition to 2x and 4x B. vulgaris types a number of 2x-, 3x-, 5x- and 6x-hybrids arose. This is presumably caused by the presence of gametes with the somatic number of chromosomes and the occurrence sometimes of haploid apomictic multiplication.The presence of large numbers of bolters in the F₁ and F₁ B₁ suggests that the bolting tendency of both species is based on different genes.