A comparison of progeny from diallel crosses of diploid potato with regard to the frequencies of 2n-pollen grains

Summary Selection of diploid potato genotypes that produce high frequencies of 2n-pollen grains in different environments is an important requirement for analytic breeding as well as for true potato seed production. In this context, quantitative estimates of 2n-pollen formation were made in two type of diploid potato populations. One population set consisted of the progeny from diallel crosses of five well-known diploid potato clones (A=US-W 5293.3, B=US-W 5295.7, C=US-W 5337.3, D=US-W 7589.2 and E=772102-37). Another population set was obtained by pollinating three genotypes of Solanum phureja, IvP35, IvP48 and IvP101 with clones A, C and E. It was observed that the behaviour of the parental clones with respect to 2n-pollen grains formation in different environments, such as in Europe and China, was stable. The correlation coefficient between means of 2n-pollen grains frequency of combinations and percentage of genotypes with more than 5% 2n-pollen grains in a given combination were estimated and that between mean and maximum frequency of 2n-pollen grains formation in each combination. The results showed that the former coefficients were significant wheareas the latter were not. The combining ability analysis revealed variation in 2n-pollen grains formation between families. Specific combining ability (SCA) effects contributed much more than general combining ability (GCA) to the variation in 2n-pollen grains formation. The broad-sense heritability of 2n-pollen grains formation was estimated to vary between 0.45 and 0.53 and the narrow-sense heritability was calculated to be 0.15 and 0.20 in the two types of populations. This means that additive variance was relatively low. Two to four genes were estimated to control the inheritance of 2n-pollen grains formation.     

Genotype × environment interaction for resistance to the white potato cyst nematode (Globodera pallida,pathotype E) in Solanum vernei x S. Tuberosum hybrids

Summary The standard root-ball test for assessing quantitative resistance of Globodera pallida in host material derived from Solanum vernei has produced variable results. This study of two sets of clones shows that genotype x environment interactions are responsible and that linear regressions (b) of phenotypic means on environments may enable good predictions to be made of the effects of the interactions. A relationship between the regression value (b) and phenotypic mean is shown for this material. The implication of this for a screening procedure in a potato breeding programme aimed at increasing potato cyst nematode resistance in adapted cultivars of S. tuberosum is discussed.     

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.     

Identification of molecular markers associated with sweet potato resistance to sweet potato virus disease in Kenya

Sweet potato virus disease (SPVD), a result of the co-infection of whitefly transmitted Sweet potato chlorotic stunt virus (genus Crinivirus, family Closteroviridae) and the aphid transmitted Sweet potato feathery mottle virus (genus Potyvirus, family Potyviridae), is the most destructive disease of sweet potato in East Africa. A study was conducted to establish if genotypes identified as resistant or susceptible to SPVD in Kenya could be distinguished using molecular markers. A total of 47 unrelated sweet potato genotypes were selected from germplasm collections and classified into two phenotypic groups as resistant or susceptible to SPVD. Genotype selection was based on disease severity or days to symptom development in plants following graft inoculation. Amplified fragment length polymorphism (AFLP) marker profiles were generated for each individual and used in association studies to identify markers suitable for classifying the two pre-defined phenotypic groups. Analysis of molecular variance showed significant (P < 0.002) variation between the two groups using 206 polymorphic AFLP markers. Discriminant analysis and logistic regression statistical methods were used to select informative markers, and to develop models that would classify the two phenotypic groups. A training set of 30 genotypes consisting of 15 resistant and 15 susceptible were used to develop classification models. The remaining 17 genotypes were used as a test set. Four markers, which gave 100% correct classification of the training set and 94% correct classification of the test set, were selected by both statistical methods.     

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.     

Variation of sweet potatoes with respect to source potentials and sink capacities

Summary By using four tester clones either as scions or stocks, source potentials and sink capacities of two groups of 13 and 20 sweet potato clones were measured in 1986 and 1987, respectively. Results obtained in the 1986 trial were generally consistent with those in the 1987 trial, though different clones were used in both trials. There were significant differences in source potentials and in sink capacities among tested clones. Responses of source to sink and of sink to source were also estimated using a regression method. No significant correlation was observed between source potential and response of source to sink. However, sink capacity showed significant relationship with response of sink to source.     

甘薯苗期耐盐性鉴定及其指标筛选

以18个甘薯品种(系)为试验材料, 设置对照和200 mmol L ^-1 NaCl浓度处理, 通过苗期盐土栽培胁迫方式, 对各处理下各品种(系)的茎叶鲜重、根系鲜重、茎叶干重、根系干重、叶片相对电导率、F_v/F_m、SPAD值、SOD酶活性、MDA含量、脯氨酸含量、根系活力、根系Na ⁺和K ⁺含量、Na ⁺/K ⁺比值等14个生理指标进行测定, 通过对各单项指标的耐盐系数进行相关分析、主成分分析、聚类分析和逐步回归等方法对品种(系)耐盐性进行综合评价。通过主成分分析, 将盐胁迫处理下甘薯苗期的14个单项指标转换成5个彼此独立的综合指标; 通过隶属函数分析, 得到不同品种(系)苗期耐盐性综合评价值(D值), 并通过聚类分析, 将18个甘薯品种(系)划分为4种耐盐类型, 其中盐敏感型4个、弱耐盐型3个、中度耐盐型7个和高度耐盐型4个。在此基础上, 利用逐步回归方法建立了可用于甘薯苗期耐盐性评价的回归方程, 同时筛选出茎叶鲜重、根系鲜重、茎叶干重、叶片SPAD值、SOD酶活性、MDA含量、脯氨酸含量、根系Na ⁺/K ⁺比值等8个可用于甘薯苗期耐盐性评价的生理指标。本研究可为甘薯耐盐新品种选育提供种质并为甘薯苗期耐盐性评价及耐盐机制研究提供理论依据。     

Ethylene production as a possible indicator of wound healing in roots of several sweet potato cultivars

Summary Fleshy roots of 18 sweet potato cultivars were wounded and cured for 12 days. Significant differences were found between cultivars for ethylene production, cell lignification, and wound periderm formation. Average ethylene production, the number of days ethylene was produced, or the day of peak ethylene production showed nonsignificant and low (r²=0.40) correlations with cell lignification or wound periderm formation; however, multiple regression analysis indicated statistically significant and moderate correlations between selected daily ethylene production and cell lignification (r²=0.74) and wound periderm formation (r²=0.73). These observations suggest that measurement of ethylene produced by wounded sweet potato roots may be useful in helping screen large numbers of sweet potato breeding lines and their progeny for the ability to produce lignified and wound periderm cell layers. Wound healing, however, is only one aspect of good storage capability in sweet potato cultivars.     

甘薯与低倍体种间杂种杂交低结实性的克服

通过观察花粉萌发、 花粉管生长、 受精、 胚发育等过程, 发现甘薯与低倍体(3 x, 5 x)种间杂种杂交低结实性的原因： 一是花粉附着量少、 花粉萌发量少、 花粉管生长缓慢导致子房受精不足, 使子房出现第一次大量脱落; 二是胚发育异常导致子房出现第二次大量脱落。 这种胚发育异常对甘薯×5 x杂种来说是受精卵发育缓慢; 对     

Increasing productivity in sweet almond using selected clones of bitter almond

Summary Eight controlled crosses were made between seven different sweet-kerneled almond cultivars (Prunus dulcis [Mill.] D. A. Webb), and five crosses were made between sweet x highly floriferous bitter almond clones. Sweet x bitter progenies out-yielded the sweet x sweet matings by more than three to one in the first year of production. This was attributable to greater cropping efficiency rather than to tree size or precocity. There was no pleiotropic association or association due to linkage between bitterness and yield. The selected Alnem (bitter) clones appear to be potentially useful progenitors for increasing almond yield capacity by conventional breeding methodology.     

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.     

Heritility of field resistance to potato leafroU virus in cultivated potato

Potato progenies in a line x tester mating design and the clonal parents were screened for field resistance to potato leafroll virus (PLRV) to determine the heritability of this trait. Twelve advanced potato clones or varieties were crossed as pistillate parents to two pollen testers. The seedling progenies and clonal parents were exposed to aphid-transmitted potato leafroll virus for two growing seasons. Cumulative infection by potato leafroll virus was determined by post-season sero-logical indexing of foliage grown from sprouted tubers after 2 years of exposure. Narrow-sense heritability was estimated from regression of mid-parent on progeny as h = 0.72. This estimate indicates a high level of useabie genetic variance for PLRV resistance in advanced breeding materials. Although variation in resistance to PLRV appears to be a quantitative trait in susceptible and moderately resistant clones, per-formance of the most resistant parents suggests that genes with major effects may be present. These results are similar to the conclusions of other researchers who found one or two genes controlling the pheno-types of extreme resistance, resistance to infection, or suppression of virus titre.     

Adaptation and stability analysis of sweet potato varieties for low-input systems in Uganda

Sixteen sweet potato varieties were evaluated for fresh storage root yield in 20 trials during 2000–2001 for three seasons in four locations in Uganda. Of the 16 varieties, 11 were developed by farmers and five by a central breeding programme. The behaviour of the varieties was quantified in terms of wide adaptation (genotypic mean across trials), specific adaptation (genotypic predictions for specific locations) and stability (Shukla stability variance). With respect to all three aspects of yield behaviour, farmer varieties performed on average better than the official varieties. The results illustrate the potential that farmer varieties can have in the improvement of sweet potato in Uganda and other regions where high diversity of sweet potato landraces exists.     

利用简化基因组技术分析甘薯种间单核苷酸多态性

选用Xushu18 (6x)和Nancy Hall (6x)、2个二倍体I. trifida (2x)品系(4597-10和4597-21)、四倍体I. trifida (4x)、六倍体I. trifida (6x)、二倍体I. temussima (2x)和I. littorallis (2x)以简化基因组测序技术SLAF-seq测序,获得724 589个SLAF标签,其中多态性SLAF标签35 310个。通过序列分析,获得40 765个有效单核苷酸多态(SNP),并用这些SNP分析了8个种质的群体结构和系统发生树。结果表明,利用简化基因组测序技术SLAF-seq能高效、低成本地开发出大量可用于群体遗传分析的SNP标记;通过构建进化树发现甘薯栽培种和野生种I. trifida的亲缘关系比较近。这些分析结果为进一步研究甘薯栽培种的起源提供了基础数据。     

Analysis of parental effects on mean vine maturity and chip colour of 4x.2x potato progenies

Summary The parental effects on progenies from potato 4x.2x(FDR) crosses were analyzed to determine anether and to what extent selection criteria used for selecting tetraploid breeding lines have to be adjusted when selecting diploid breeding lines. For vine maturity and chip colour multiple regression analysis of progeny means on means of diploid and tetraploid parents revealed high coefficients of determination (R²) for both characters, indicating good predicting power of the performance of both diploid and tetraploid parents on the performance of their 4x.2x progenies. For vine maturity the multiple regression slope for the tetraploid perents was significantly larger than for the diploid parents, and progeny means were towards the tetraploid parents. This indicates that selection criteria for vine maturity may be less stringent at the diploid level. However, diploids may be earlier maturing than tetraploids and therefore selection criteria can better be similar at both ploidy levels. For chip colour, multiple regression slopes for diploid and tetraploid parents were similar and progeny means were towards the darkest coloured parent irrespective of its ploidy level. This indicates that selection of breeding lines for chip colour can be conducted similarly at both ploidy levels.     

黑色地膜对甘薯光合作用及叶绿素荧光特性的影响

为了揭示黑色地膜影响甘薯产量的光合机理,试验以‘烟薯25’为材料,进行了覆盖黑色地膜和不覆膜(CK)的处理,研究黑色地膜对甘薯光合作用和叶绿素荧光特性的影响。结果表明,覆盖黑色地膜使甘薯的Pn和Cond值显著提高(P＜0.05),二者呈直线正相关性;Ic、Isat和Pmax值也显著提高。随着光强的不断增加甘薯的ETR、PCR和qP值逐渐变大,PhiPS2、Fv′/Fm′和NPQ值逐渐变小;当光强大于1500μmol/(m²·s)时,黑色地膜使甘薯的荧光参数值(ETR、PCR、PhiPS2、Fv′/Fm′和qP)显著提高,NPQ值则降低;黑色地膜甘薯的鲜重和干重分别提高40%和31%以上。因此,覆盖黑色地膜可显著提高甘薯在强光下吸收光子效率及其供给效率,进一步加强了甘薯能量转化速率和对强光环境的适应能力,最终提高甘薯光合生产能力。     

Investigation of yield and persistence of white clover using cluster analyses

Summary A visual growth score method was used to monitor the growth performance of 24 populations of white clover (Trifolium repens) over a three year period. The mean growth scores for each year were used as population x year data for cluster analyses. Cluster analysis methods based on a regression model where genotypes were grouped for similarity of both intercepts and slopes (Method 1) or slopes only (Method 2), were able to differentiate the persistent populations from those that showed a yield decline over time. The deviations from regression mean square was used as an indication of stability. Method 1 was able to cluster the high yielding persistent populations into a separate cluster, thus facilitating the selection of desirable populations. Deviations from regression identified the stable populations from the cluster. In combination with the simple growth score system, this analytical method is a powerful tool for evaluating a large number of breeding families of perennial pasture clovers and grasses for yield and persistence.     

甘薯主要数量性状对单株产量的通径分析

用秦薯1号自交后代实生苗为试验材料,试验对甘薯的分枝数(x1)、最长蔓长(x2)、分枝总长(x3)、节间长(x4)、蔓粗(x5) 、叶面积(x6)、单株绿叶重(x7)、藤叶重(x8)、单株薯数(x9)、单薯重(x10)、根冠比(x11)和单株产量(y)12个数量性状进行了测定。通过相关分析、逐步回归和通径分析表明单株绿叶重对单株产量的影响最大;单株薯数和单薯重对单株产量的直接作用较大。高产育种以单株产量为选择目标时,应以单株绿叶重、单株薯数和单薯重的选择为主,结合根冠比、分枝数、叶面积和蔓粗,对这7个性状进行综合考虑和选择。     

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.