Breeding research in sweet potato,Ipomoea batatas poir

In the sweet potato fruit formation following artificial selfing, artifical cross pollination and natural pollination was investigated. Artificial self-pollination in one case gave a fruit formation of 21.2%; in five other cases no or hardly any fruit formation took place. Artificial cross-pollination produced a fruit formation varying from 0 to 52.9%. Natural fertilization did not occur in cases when the nearest flowering sweet potato clone stood at a distance of 80 m. When other flowering clones were in the direct vicinity the percentage of fruit formation through natural pollination differed from 0 to 25.2%.Pre-treatment of sweet potato seed with concentrated sulphuric acid applied during 10 or 20 minutes had a favourable effect on the speed of germination and the germination percentage, also when the seed after treatment was kept in store in or outside an exsiccator for one or two months. The method of scarifying the seed showed a reasonably good influence in this respect. Two different warm water treatments were not or practically not satisfactory.     

Screening sweet potato for source potentials

Summary Screening sweet potato, Ipomoea batatas, L., for source potentials is more difficult than for sink capacities. Twenty clones were grafted to four tester varieties to screen them for source potentials in relation to sink capacities which are interdependent. Source potential of a clone was measured by its average scion effect when grafted on the four tester varieties. There were significant differences in source potentials among the twenty clones. Seven clones were selected for having high source potentials. Clone TIS 2498 was the best. Degrees of response of source to sink were estimated using the regression method for twenty clones showed significant differences and ranged from b–0.45 to b=2.06. Source potential showed significant relationship (r=0.62^**) with response of source to sink. Implication of this approach to sweet potato breeding is discussed.     

Studies on maturity,yield, under water weight and some other characters of potato progenies

Summary In 1965 the relation between maturity, tuber yield and under water weight was studied in 756 unselected fourth-year potato clones of twelve crosses. Other characters studied were seed potato weight, date of emergence, plant height, general impression of the tubers at lifting, tuber weight and payment weight, as the above relation could be influenced by or depend on these characters.The experiments were carried out on a clay soil at Wageningen. The experimental design was a partially balanced lattice with four replications and five plants per plot.The clone means, corrected according to F-values for blocks, were used for determinating normal correlation coefficients between all possible combinations of characters per population as well as for composition of frequency distributions and of population means with coefficients of variability. To estimate heritabilities within the populations the separate data of the four replications per clone were used.In 1966 the investigations were continued with 136 selected clones on both clay and sandy soil. In addition to the statistical operations used in 1965, normal correlation coefficients were calculated between the years and between the soil types using corrected clone means. The results are given and discussed.     

A comparison between single plant plots and five plant plots for the initial selection stage of a potato breeding programme

Summary The efficiency of single plant selection in the initial selection stage of a potato breeding programme was examined. A random sample of potato clones was grown in single plant plots and also in tworeplicates of five plant plots. After harvest, each plot was visually assessed by three potato breeders; total tuber weight and number of tubers per plant were also recorded, from which mean tuber weight was calculated. The error variances of the single plant plots were found to be significantly greater than from the five plant plots for total tuber weight, mean tuber weight and number of tubers per plant, but not significantly different for breeders' preference. Coefficients of correlation between single and five plants plots were significantly greater than zero for all traits examined, but they were lower than the corresponding correlations between the two replicates of five plant plots. Although a random sample of clones was examined, each clone had been assessed for breeders' preference the previous year. When the clones were grouped according to the previous years preference scores, it was found that the correlation coefficients between single and five plant plots for breeders' preference were inversely related, in magnitude, to the mean preference score of each group. It was concluded that single plant selection was generally ineffective, particularly when only the better clones, from the previous years assessment, are examined.     

Interactions between plant and aphid genotypes in resistance of lettuce to Myzus persicae and Macrosiphum euphorbiae

Summary Six lettuce lines, representing two types of resistance to the green peach aphid, Myzus persicae, and a control line with high susceptibility to M. persicae were tested for resistance to six different clones of Myzus persicae and two clones of the potato aphid, Macrosiphum euphorbiae.The clones of M. persicae showed very different levels of aggressiveness on lettuce: two had a high level of reproduction, two had an intermediate level and two were poorly adapted to lettuce as a host. Differences between lettuce lines in aphid reproduction increased with increasing aggressiveness of the aphid clone, which means that aggressive clones are most effective for selection purposes. No evidence was found for clone-specific plant genotype reactions, meaning that lines resistant to one clone will also be resistant to other clones of M. persicae, allthough not neccessarily at the same level. The lettuce lines selected for partial resistance to the aggressive clone WMp1 were completely or almost completely resistant to less aggresive clones.No differences in level of reproduction were found between the two clones of M. euphorbiae and no relation was observed between resistance to M. persicae and M. euphorbiae, indicating the species-specific character of resistance to leaf aphids in lettuce.     

Late blight resistance in a diploid full-sib potato family

Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most destructive disease of potato worldwide. As this pathogen can rapidly overcome major race‐specific resistance genes, identifying the basis for enhanced quantitative resistance has become a crucial element for implementing advanced breeding strategies. A population of 230 full‐sib progeny derived from a cross between two diploid hybrid Solanum phureja × S. stenotomum clones was evaluated for foliage resistance against late blight in replicated trials at multiple locations in Pennsylvania between 1999 and 2002. In field experiments, plants were evaluated visually for per cent defoliation, and area under the disease progress curve (AUDPC) was determined. The two parents and three control cultivars (‘Atlantic’, ‘Kennebec’ and ‘Katahdin’) were included in all trials. In all three experiments, the presence of a significant number of clones exhibiting transgressive segregation were observed. There were significant differences among environments as well as among clones, and the clone × environment interaction was also significant. Stability analysis revealed that 37 clones made a significant contribution to the overall environment × clone interaction. Broad‐sense heritability for resistance, measured as AUDPC, was estimated as 0.67. The overall results indicate the presence in this potato family of a high level of field resistance against late blight. This segregating diploid family appears to be a good candidate for quantitative trait loci mapping to identify and characterize the genetic components of partial late blight resistance.     

Identification of RAPD markers linked to the Ns locus in potato

Using the RAPD method and bulked segregant analysis we identified four RAPD markers linked to a dominant gene Ns, responsible for a hypersensitive reaction of potato (Solanum tuberosum L.) to potato virus S (PVS) infection. The markers OPE15⁵⁵⁰, OPJ13⁵⁰⁰, OPG17⁴⁵⁰ and OPH19⁹⁰⁰ were found to be closely linked to the Ns gene in diploid potato clones. They are situated at 2.6, 3.3, 4.6 and 6.6 cM from Ns, respectively. As a source of the gene, clone G-LKS 678147/60, which is known to carry Ns transferred from S. tuberosum ssp. andigena was used. These RAPD markers were not amplified in resistant tetraploid clones containing Ns derived from the clone MPl65 118/3, also having an andigenum origin. This suggests that there may be two separate loci of Ns in the sources identified, or different alleles with the same specificity at a single locus, or that the genetic background of tetraploids tested results in different RAPD amphlification patterns.     

Drought tolerance screening for potato improvement

Six potato genotypes including ‘Desiree’ and five breeding clones (2/14, 95C, 125B, 3589, 4056) were grown in the field under well-watered and stress conditions. The stress response of leaf tissue was assessed 8 and 12 weeks after plant emergence (WAE) by measuring canopy temperature and chlorophyll α fluorescence induction kinetics in detached leaves. Under drought-stress conditions, chlorophyll α fluorescence dropped in clones 2/14 and 4056, remained constant in 95C and 125B and increased in clone 3589. The canopy temperature exhibited little difference between drought and irrigated treatments in clones 95C and 125B, and significant effects in the other genotypes. This performance was interpreted in terms of tolerance to drought stress, and the potential use of canopy temperature and chlorophyll fluorescence as tools for drought screening of potato germplasm and segregant generations is discussed. The physiological properties of 95C and 125B highlighted by this study need further investigation and, if confirmed, they could be recombined with other useful agronomic characters by crossing in a breeding programme.     

Heritability of resistance to foliar late blight in a diploid hybrid potato population of Solanum phureja×Solanum stenotomum

The emergence of new races of Phytophthora infestans has necessitated the search for additional sources of potato germplasm with resistance to late blight. This study examined 281 clones, derived from 72 families of a diploid random-mated hybrid population of Solanum phureja×Solanum stenotomum. The clones were evaluated in a replicated field trial for 2 years with the control cultivar ‘Atlantic’ in Pennsylvania, USA. The P. infestans US-8 A2 mating type culture was used to inoculate spreader rows of susceptible S. tuberosum cv.‘Russet Burbank’. Percent defoliation caused by the late blight fungus was estimated visually in each plot three times near the end of the growing season. Area under the disease progress curve (AUDPC) was estimated and showed that late blight was more severe in 1997 than in 1996. Genetic differences among clones and significant, but small, clone–environment interaction were detected for AUDPC. Broad-sense and narrow-sense heritability estimates, over years, were 0.79 ± 0.05 (P = 0.05) and 0.78 ± 0.29, respectively. Seventy-five percent of the diploid clones had a significantly lower mean AUDPC than Atlantic. These results support the idea that this diploid population is worthy of use in breeding for late blight resistance in tetraploid potato cultivars.     

Flowering stimulation in sweet potato

Flower formation of most sweet potato clones in the collection at Manokwari was poor and when seed for breeding purposes was desired flowering had to be stimulated accordingly.Of various methods applied to stimulate the flowering some proved to be satisfactory. Good results were obtained in training tendrils to racks and grafting on different species of the genus Ipomoea.     

Effects of Root Zone Temperature on Root Activity of Two Potato (Solanum tuberosum L.) Clones with Different Adaptation to High Temperature

Under controlled environmental conditions, the effect of optimal (20 °C) and supraoptimal (30 °C) root-zone temperature on root activity (respiration, soluble sugar content, ethylene release, nitrogen uptake and translocation) was studied in water culture with two potato clones differing in the heat tolerance of their root systems. Root respiration was little affected by raising temperature from 20 °C to 30 °C. However, in both clones assimilate allocation to the roots was strongly depressed. In the heat sensitive clone LT-1 exposed to 30 °C root-zone temperature, concentrations of soluble sugars in the apical root zone (0–10 mm) increased with time, presumably as a result of the cessation of root growth. The rate of nitrate absorption was not significantly affected by root-zone temperature. However, the export of nitrogen (xylem exudate) was depressed in the heat tolerant clone whereas in the heat sensitive clone the export of total nitrogen and the proportion of nitrate increased. No effect of root-zone temperature on ethylene release was observed in our experiments.     

Clonal variation and stability assay of chimeric Pinot Meunier (Vitis vinifera L.) and descending sports

This project studied the genetic variation of the periclinal grape chimera Pinot Meunier, its natural occurring mutations (loss of trichomes on leaf surfaces) and the German Pinot noir clone Samtrot. Eleven Pinot Meunier clones of French, Italian and foremost German origin, Pinot Meunier mutations of differing ages and with various dispersions of hairless sectors as bud-, shoot- and complete vine mutations and six Samtrot clones were investigated with amplified fragment length polymorphisms (AFLPs) and microsatellites (SSRs). SSR-analysis proved chimerism of all Pinot Meunier clones tested and confirmed identical genotype for all hairless mutations and Samtrot clones at the analyzed loci. Clonal variation was shown by AFLP-analysis yielding a total of 670 bands out of 18 primer combinations of which 161 were polymorphic. Pinot Meunier, Samtrot and the naturally occurring hairless Pinot Meunier mutations could be significantly differentiated. Most of interclonal varying AFLP fragments (mean 1.5% per sample) originated within the groups of Samtrot or Pinot Meunier mutations, whereas intraclonal identity was highest within the Pinot Meunier clones. According to the analysis of molecular variance (AMOVA), variation among wild type and mutated Pinot Meunier leaf halves is significantly smaller than between phenotypically identical Samtrot and Pinot Meunier mutants. Average gene diversity calculated on variability of loci reduced from Samtrot (0.040 ± 0.023) towards Pinot Meunier (0.025 ± 0.013) clones.     

Low temperature tolerance of biomass and pollen germination in potato clones of Andean and European origin

Summary The temperature-related performances of six tetraploid potato clones, two Andean, three European, and one hybrid, were compared by cultivating them in growth chambers under one of two temperature regimes: 10°C day/4°C night or 20°C day/10°C night. Preformance was measured in terms of biomass production and pollen germinability.For dry matter yield at second harvest, the temperature-related performance ratios (performance at 10°C/4°C divided by performance at 20°/10°C) were highest for the Andean clones, intermediate for the Andean/European hybrid clone 201₅×S₁₂, and lowest for the European cultivars. The ability of the European cultivars to maintain their normal rates (i.e. rates at 20/10°C) of biomass production when cultivated at low temperatures varied greatly, with clone S₃ performing most poorly at 10/4°C.For pollen germinability in vitro, performance ratios were highest for the hybrid clone 201₅×S₁₂ and lowest for the European clones.The high tuber yield of hybrid 201₅×S₁₂ at 10/4°C can be attributed to its low-temperature tolerance and it being daylength neutral.     

Somaclonal variation in explant-derived potato clones over three tuber generations

Summary Tuber characteristics of potato clones (Solanum tuberosum L.) regenerated from cultured leaf, rachis or stem pieces of cv. Desiree were assessed in field trails over three years. In the first two seasons, when the crop was grown for seed potato production, tuber numbers and the tuber yields were normally distributed and the population means of the clones were about the same as those of the controls. When 78 of the clones were grown as a ware crop in a replicated field trial there were statistically significant differences between most clones and the controls in total yield (generally lower) and ware yield (generally higher), brought about by alterations of the size distributions of tubers. In all years the population of clones had fewer scab (Streptomyces scabies) lesions than the controls. Clones with consistent differences in flesh colour and eye depth were also observed. Two out of 78 clones, in 1984, had significantly higher dry matter content. No stable decrease in susceptibility to the cyst nematode Globodera pallida was observed amongst 167 clones tested. These potato plants regenerated from explants clearly show that somaclonal variation can include agronomically relevant changes.     

The Use of Multivariate Analyses to Eliminate Redundant Variables when Evaluating Potatoes for Chip Quality

Selection for good chipping clones in potato breeding often takes place during the middle and late selection stages. This is due to the considerable resources needed for the assessment of several characteristics. Objective multivariate methods for the elimination of redundant variables were applied to eight standardized chipping quality traits recorded on advanced clones over 15 years at two locations in New Brunswick, Canada. The clones were evaluated of specific gravity and the following chipping scores: direct from the field in August; after 10 days storage at 13 °C; from 4 °C storage in February; from 4 °C storage in February with 1 week, 2 weeks, 3 weeks and 4 weeks reconditioning at 16 °C. Five elimination methods produced a similar deletion order. In every subset obtained, specific gravity and direct chipping from the field were always retained. Reconditioning treatments from one to four weeks after cold storage were shown to be the most redundant. The reduction in the number of traits from eight to four by every technique could recover more than 80 % of the original variation, showing that redundant variables were effectively discarded.     

Characterisation of genetic variation between Vitis vinifera cultivars from central Chile using RAPD and Inter Simple Sequence Repeat markers

The origins and authenticity of many grape cultivars (Vitis vinifera) used for wine production around the world is unclear and the subject of some controversy. In this study, DNA fingerprints generated by Randomly Amplified Polymorphic DNA (RAPD) and Inter Simple Sequence Repeat Polymerase Chain Reaction (ISSR-PCR) analyses were used to compare the four most widely planted V. vinifera cultivars in Chile (viz. Cabernet Sauvignon, Cabernet Franc, Merlot and Carmenere). Material obtained from France was used as an external reference. Both techniques were able to distinguish between the cultivars studied although the resolving power of ISSR profiles was higher than that of RAPDs, suggesting that the latter would be more suited for use on a wider range of cultivars. Surprisingly, however, variability was observed between clones of Merlot, the original Chilean clone and the representative clone from France. Furthermore, the high degree of divergence between the two sources (64% similarity) suggests that the French Merlot is not even a close relative of the stock in Chile. Interestingly, the latter was derived directly from the original French founder clones of the Merlot cultivar. No variation was found within the Chilean Merlot clone using either ISSR or RAPD analyses. These results indicate that French and Chilean vines grown for Merlot production represent different genotypes. The history of Merlot cultivation and the implications of these findings are explored. This revised version was published online in August 2006 with corrections to the Cover Date.     

Behaviour of genetically modified amylose free potato clones as progenitors in a breeding program

Three amylose-free genetically modified potato clones were used both as male and female parents in a breeding program with non-GMO potato clones. Segregation data on the expression of the inserted antisense gene construct in tubers of progeny plants were in agreement with previous molecular analysis of the transgenic clones. The inheritance of the inserted genes was according to Mendelian segregation. Therefore, these clones can be very useful in a breeding program for large scale introduction of amylose free potato cultivars into agriculture. Because of varying number and expression levels of inserts in the GMO-clones, but also because of the varying strength of the endogenous GBSS-alleles of the non-GMO-clones, a segregation into a range of amylose contents occurred. The segregation of the starch colour after iodine staining of pollen of transgenic clones did not follow the obtained segregation in the progeny and was, therefore, not useful in predicting the breeding result. This revised version was published online in July 2006 with corrections to the Cover Date.     

甘薯实生系与其无性系性状相关关系及早期选择利用研究

甘暮实生系是分离世代,其性状的变异与资源品种表现同一趋势,与其无性系在诸多性状上呈强弱不同的正相关关系,这是对实生系进行早期选择利用的基础.根据结薯性可将实生系分为成薯、膨大和直根3个类型,成薯系%因组合而异,受环境影响不明显.5年的研究结果证明:无性系类型间的产量性状有明显差异,从成薯类型选育高产新品系的入选率高.在此问题上和美国Granberry.M.等的认识不同.建议把我国甘薯育种的初选期提早到实生系时期,以缩短育种周期,提高育种效率.笔者认为把甘薯杂交种子培育的株系,定名为实生系,比较确切.     

Morphology and vigour of monohaploid potato clones,their corresponding homozygous diploids and tetraploids and their heterozygous diploid parent

Summary To study the joint effects of homozygotization and polyploidization in potato, the performance has been examined of five potato genotypes at three (x, 2x, 4x) and two genotypes at two (x, 2x) ploidy levels. Six out of the seven genotypes studied were compared with their heterozygous diploid parental clone. In this way comparisons could be made between i) the heterozygous diploid and its monohaploid derivatives, ii) three or two ploidy levels per genotye and iii) homozygous di- and tetreploids and their heterozygous diploid source.Large variation could be detected between monohaploids obtained from one diploid source. A striking increase in vigour was observed with somatic chromosome doubling from x to 2x, but less clearly from 2x to 4x. The relatively vigorous diploids showed a weaker response to tetraploidization than the less vigorous ones. The heterozygous diploid exceeded all homozygous di- and tetraploid derivatives in performance. The results of this study suggest positive gene dosage effects for tuber production more than for leaf area and plant height. The observations on plant vigour in homo- and heterozygotes suggest that dominance effects are stronger than additive gene effects. Owing to sterility problems, homozygous potato clones will presumably be of little importance for practical breeding.