Resistance to soft rot (Erwinia carotovora subsp.atroseptica) in tetraploid potato families obtained from 4x-2x crosses

Diploid potato clones, interspecific hybrids ofSolanum species, having in their originS. tuberosum,S. chacoense, S. yungasense, S. phureja, S. gourlayi, andS. demissum, with resistance to soft rot, were crossed to tetraploid potato clones in 4x-2x crosses. The 24 tetraploid families obtained in a North Carolina II design were examined for tuber resistance to soft rot in a laboratory test and for basic agronomic traits in field trials conducted for two consecutive years. In addition, one family originating from a 4x-2x cross of two susceptible parents was tested. Statistical analysis of the data revealed significant general (GCA) and specific combining ability (SCA) effects, year, GCA (female) × year, GCA (male) × year, and SCA × year upon the inheritance of resistance to soft rot. About 35% of the progeny was selected as resistant to tuber soft rot, and of these 11% showed high resistance combined with good tuber yield, tuber weight, and tuber appearance. The relationships between resistance to soft rot and chosen agronomic traits were not noted or were weakly significant and sporadic. The resistance to tuber soft rot found in diploid potato hybrids can be transferred to the cultivated tetraploid pool through 4x-2x crosses, and a high frequency of offspring posses resistance.     

Inheritance and stability of resistance to fusarium tuber rot in tetraploid potatoes

Fusarium tuber rot of potato (Solanum tuberosum L.) is one of the most economically important diseases of stored potatoes. Dry rot is caused by several species of Fusaria, particularlyFusarium sambucinum in North America. The objective of this study was to determine the inheritance of resistance to Fusarium tuber rot. A highly resistant (B0172-22) and a highly susceptible (B0178-34) potato clone were crossed as female parents with two male parents. Tubers from varying numbers of progeny (28–37) from these four crosses were inoculated withFusarium sambucinum in the laboratory. Three tubers from each progeny were inoculated at approximately monthly intervals six times in each of 2 years. The depth and diameter of the lesion were measured 40 days after inoculation. Estimates of broadsense heritability (H) for lesion depth and a 95% confidence interval about these estimates were similar in 2000 and 2001: 0.84 (0.84, 0.91) and 0.77 (0.77, 0.87), respectively, as were the estimates for lesion diameter: 0.83 (0.83, 0.90) and 0.80 (0.80, 0.89), respectively. The differences in lesion depth for the female parents were significant the second year, but not the first year. The differences in lesion diameter for the female and male parents were significant both years. The female x male interactions were not significant for either lesion depth or lesion diameter. There were significant differences between clones in each of these four families for both traits both years. In 2000 and 2001, 24% and 38%, respectively, of the clones were unstable for resistance. In only one of the four families did instability increase as susceptibility increased, suggesting that there sometimes may be a genetic component to instability per se. These results indicate that resistance to Fusarium dry rot has a large genetic component. They also indicate that lesion diameter is more informative than lesion depth for evaluating resistance.     

Ear rot,aflatoxin accumulation,and fungal biomass in maize after inoculation with Aspergillus flavus

Aflatoxin, a toxin produced by the fungus Aspergillus flavus Link: Fries, occurs naturally in maize (Zea mays L.). Aflatoxin is a potent human carcinogen and is also toxic to livestock, pets, and wildlife. When contaminated with aflatoxin, the value of maize grain is markedly reduced. This investigation was conducted to compare ear rot, aflatoxin accumulation, and fungal biomass in maize single crosses with varying degrees of resistance to aflatoxin accumulation and to determine the relative importance of general combining ability (GCA) and specific combining ability (SCA) in the inheritance of resistance to ear rot, aflatoxin accumulation, and fungal biomass. Eight germplasm lines with different levels of resistance to aflatoxin accumulation were used as parents of a diallel cross. The cross was evaluated for visible ear rot, aflatoxin accumulation, and A. flavus infection in the grain. A. flavus infection was determined by quantitative real-time polymerase chain reaction (qRT-PCR) assays. Both GCA and SCA were significant sources of variation in the inheritance of the three traits although GCA accounted for a greater portion of the variation among single crosses. The interactions of GCA and SCA with years were highly significant for aflatoxin accumulation, but not significant for A. flavus infection. Estimates of GCA effects were highly significant for both reduced A. flavus infection and reduced aflatoxin accumulation for Mp313E, Mp715, and Mp717. Conversely, GCA effects associated with GA209 were significant for reduced levels of A. flavus infection and ear rot, but high levels of aflatoxin accumulation. Mp313E, Mp715, and Mp717 should be useful in breeding programs targeting both reduced levels of fungal infection and aflatoxin accumulation.     

Introgression and stabilization oferwinia tuber soft rot resistance into potato after somatic hybridization ofsolanum tuberosum ands. brevidens

Resistance to potato tuber soft rot caused byErwinia carotovora was transferred fromSolanum brevidens to the cultivated potato over the course of four backcross generations originating from a somatic hybrid. Soft rot reactions were determined via a tuber plug inoculation method developed during the course of these experiments. Soft rot resistance was highest in the somatic hybrid (only ca. 20% of tubers and plugs showed evidence of severe rotting) and lowest among progeny of control potato x potato crosses (ca. 80% of tuber plugs showed severe rot). Backcross generations involving somatic hybrids were intermediate in their reaction, and resistance stabilized to about 60% of tuber plugs showing severe rot in the BC₂ through the BC₄. Reciprocal crosses showed no difference in the inheritance of soft rot resistance, indicating that neitherS. brevidens norS. tuberosum donor cytoplasm had a significant effect on the expression of resistance. Crosses between BC₃ siblings where noS. brevidens genetic markers were detected but resistance was segregating demonstrated a dosage effect for soft rot resistance. We conclude that introgression of soft rot resistance has occurred and that at least one locus responsible for resistance inS. brevidens now resides in theS. tuberosum genome.     

Inheritance of tuber greening under light exposure in diploid potatoes

Low tendency to tuber greening under light exposure is a desirable trait for marketing and processing potatoes. Knowledge of the genetic basis of this trait is limited. During two consecutive years tuber greening after 2-week light exposure was evaluated on 17 unselected diploid potato families obtained between parents with varying tuber-greening tendencies. Parents of these families and standard cultivars were evaluated at the same time. External and depth of tuber greening were examined after tubers were exposed to 2 weeks of light in the greenhouse followed by storage at 10 C, 4 C, and after reconditioning at 18 C. Families, storage conditions, and years significantly influenced tuber greening. Distribution of greening indicated it would be possible to select individuals with very low tuber-greening tendency. Generally, external tuber greening was more intense than depth of greening. External tuber greening increased during storage while depth of tuber greening decreased. A significant maternal effect on external tuber greening was found in one of the three sets of reciprocal crosses after storage at 4 C. Both general and specific combining abilities were important in the inheritance of tuber greening. The correlations between external and depth of tuber greening in most families were significant and relatively high. The results indicated that genotypes with low tendency to tuber greening can be selected in diploid families.     

Erwinia resistance in backcross progenies ofSolanum tuberosum x S. tarijense andS. tuberosum (+) S. commersonii hybrids

Summary The resistance to tuber soft rot caused byErwinia carotovora ofSolanum tuberosum x S. tarijense andS. tuberosum (+) S. commersonii hybrids and their backcrosses is reported. A number of resistant diploid sexual hybrids and tetraploid/hexaploid somatic hybrids were selected. Backcross progenies were obtained through 2x×4x crosses involving a resistant diploid hybrid and tetraploidS. tuberosum, and through 4x×4x crosses between a resistant somatic hybrid andS. tuberosum. The hybrids showed high variability interms of resistance to tuber soft rot. The resistance of progeny from 2x×4x backcrosses was similar to that of the parental sexual hybrid. By contrast, the resistance of genotypes deriving from 4x×4x backcrosses was reduced compared with the resistant somatic hybrid. In general, tuber characteristics of the backcross hybrids improved considerably as compared with their parents, and tuber yield per plant was good.     

The Effect of Long Term Storage on Bacterial Soft Rot Resistance in Potato

Bacterial soft rot is a serious disease in potato (Solanum tuberosum L.), causing rapid tuber tissue maceration and, consequently, marketable yield loss. Soft rot bacteria, including Pectobacterium carotovorum subsp. carotovorum (Pbc), are favored by moist conditions, which are prevalent in large potato storage facilities. However, although most potatoes in North America are stored before use, there are no published surveys of soft rot resistance in cultivars exposed to long-term storage conditions. Thus, we tested 65 cultivars and 13 breeding lines for soft rot resistance after 6 months of storage. There was a significant effect of cultivar and production environment on soft rot resistance score. During 6 months of storage, tuber soft rot resistance in resistant clones did not change, while it changed in susceptible clones. The three most resistant cultivars to soft rot were Freedom Russet, Anett, and Alaska Red Eye.     

Evaluation for chipping and tuber soft rot (Erwinia carotovora) resistance in potato clones from unilateral sexual polyploidization (2x × 4x)

The aim of this work is the evaluation of tetraploid potato clones with germplasm fromS. chacoense andS. phureja for chipping and resistance to tuber soft rot (Erwinia carotovora subsp.carotovora). Tetraploid potato clones were obtained via 2n eggs through 2x–4x crosses. Cytological mechanisms were investigated in the diploid hybrid 2n-egg producer used as parent in the unilateral sexual polyploidization scheme; the omission of the second meiotic division and cytokinesis failure at the end of meiosis were identified with a genetic consequence equivalent to second division restitution (SDR). Tuber marketable yield, specific gravity and chip-processing ability evaluated at harvest and after cold storage with and without reconditioning were higher in some clones as compared to theS. tuberosum tetraploid parent. Tuber soft rot resistance, contributed byS. chacoense, was successfully transferred to the4x level. After inoculation withErwinia carotovora subsp.carotovora and estimation of the rotted area, one tetraploid clone proved to be resistant and three partially resistant. The genetic value of exotic germplasm and sexual polyploidization strategy are discussed in relation to potato improvement.     

Screening tuber-bearingSolanum spp. for resistance to soft rot caused byErwinia carotovora ssp.atroseptica (van Hall) Dye

Summary Soft rot caused by Erwinia carotovora ssp. atroseptica is a major disease of stored potatoes. Since varietal resistance can contribute to control, the work reported was designed to find new sources of resistance among related tuber-bearing Solanum spp. True seeds were imported from two international collections and families were screened for resistance to tuber soft rot. Forty-eight resistant clones were found in 21 out of 100 accessions. These clones will be used in breeding programmes at the diploid or tetraploid level.     

利用体细胞杂交获取马铃薯软腐病的抗性

对马铃薯四倍体栽培种和二倍体野生种Solanumbrevidens的体细胞杂种通过叶片离体培养获得的四倍体植株,以及用四倍体栽培种进行回交获得的五倍体植株的块茎对软腐病的抗性进行了测定。结果表明,由体细胞杂种通过叶片组织离体培养再生植株中,有一个株系SC107对软腐病菌Erwiniacarotovora具有较强的抗性。在用不抗软腐病的马铃薯栽培种对体细胞杂种进行回交获得的杂种后代中,大部分株系对软腐病菌具有高水平的抗性,从而说明Solanumbrevidens对软腐病的抗性基因已转移到马铃薯栽培种。     

Inheritance of resistance to late blight in foliage and tubers of progenies from parents differing in resistance

Summary TenSolanum tuberosum genotypes differing in resistance to late blight (Phytophthora infestans (Mont.) de Bary) in foliage and tubers were intercrossed to determine the inheritance of disease resistance in their progenies. Plots of 10–15 clones per progeny were established in each of 2 years and resistance assessed by field or laboratory tests. The parental genotypes were similarly tested each year. The parents differed in general combining ability (GCA) for both foliage blight (FB) and tuber blight (TB). The parental and GCA scores were significantly correlated for both aspects of the disease, but the correlations between foliage and tuber scores for parents and for GCAs were not significant. Three parental genotypes were highly resistant in both foliage and tubers, and the genotype with the highest GCA for resistance to both FB and TB (cv. stirling) is recommended as the best parent. There was no evidence of strong genetic correlation between both aspects of resistance, and it is suggested that both be selected for in a breeding programme.     

Soft rot and blackleg reactions in diploid potato hybrids inoculated withErwinia spp.

From 1993 to 1996 three groups of potato genotypes were evaluated for resistance toErwinia spp.: (1) 31 interspecific diploid hybrids (28 resistant and three susceptible), (2) five hexaploid or pentaploid somatic hybrids ofSolanum tuberosum (tbr) ×S. brevidens (brd), and (3) eight cultivars. Two evaluation methods were applied: tuber point inoculation with eitherErwinia carotovora ssp.atroseptica (Eca) orE. chrysanthemi (Ech) to test tuber soft rot resistance and stem base inoculation with Eca to test blackleg resistance. Some resistant diploid hybrids and somatic hybrids oftbr × brd were superior to cultivars for both tuber and stem resistance. Tuber and stem resistance toErwinia spp. in the most resistant diploid hybrids were equal to the highly resistant somatic hybrids oftbr xbrd. Tuber resistance to Eca was highly correlated to tuber resistance to Ech (r=0.815***). In two years of evaluation for stem resistance, three diploid hybrids and a derivative of one of the somatic hybrids (USA M 264) failed to develop symptoms of blackleg following inoculation with Eca, Analyses of variance for tuber and stem resistance indicated significant effects of genotype, year and genotype × year interaction. A positive relationship between tuber and stem resistance toErwinia spp. has been found, however the genetic control of resistance in tuber and stem is partially independent. In the case of Eca the correlation coefficient was r = 0.725***. Therefore it should be possible to obtain resistant genotypes to both blackleg and tuber soft rot. Several resistant diploid hybrids were selected from among those tested, which also have several other characters desirable for potato breeders.     

Resistance to blackleg and tuber soft rot in sexual and somatic interspecific hybrids with different genetic background

Diploid interspecific hybrids from crosses betweenSolanum tuberosum haploids andS. canasense, S. multidissectum, andS. tarijense, along with tetraploid and hexaploid somatic hybrids S.tuberosum (+)S. commersonii, were screened for resistance to blackleg and tuber soft rot byErwinia carotovora subsp.atroseptica andE. carotovora subsp.carotovora. Among the diploid hybrids, those involving clone mlt la of S.multidissectum and tar 2b ofS. tarijense yielded the highest number of genotypes resistant to both blackleg and tuber soft rot. By contrast, all the hybrids involving clone tar 1lb ofS. tarijense were susceptible to both bacterial diseases. As far as resistance of somatic hybrids is concerned, the most interesting genotype was the tetraploid one which showed resistance to both blackleg and tuber soft rot Significant correlations were found betweenE. carotovora subsp.atroseptica andE. carotovora subsp.carotovora both in resistance to blackleg and in resistance to tuber soft rot, suggesting that resistance to the two subspecies is controlled by the same gene/s or that the relevant genes are linked. On the other hand, correlations between blackleg and tuber soft rot were never significant, indicating that different mechanisms may control resistance in tuber and stems. Alternatively, the resistance could be controlled by the same gene/s under a different spatial/temporal expression pattern. Twelve diploid sexual hybrids and one tetraploid somatic hybrid were selected for resistance to blackleg and/or tuber soft rot and for tuber characteristics.     

Combining ability and parental effects in 4x–2x crosses for potato breeding

Summary Nine 2x clones with different genetic backgrounds and 2n pollen production by first division restitution (FDR) were each mated with five 4x females in a linextester design. Estimates of both general combining ability (GCA) and specific combining ability (SCA) were significant for tuber yield, among female and male parents. Four FDR clones with similar genetic background (half-sibs) showed significantly different GCA for total yield, illustrating the importance of progeny testing for FDR clones before their utilization as progenitors. A stronger influence of the 2x parents, compared to that of the 4x parents, on the performance of the hybrids was observed for characters studied. The significance of male and female interactions for characters other than tuber yield reinforced the importance of careful choice of the male and female parents for improving horticultural traits of 4x–2x progenies.     

Factorial cross analysis of pre-harvest sprouting resistance in white wheat

The lack of understanding of the genetics of sprouting resistance as well as the lack of white wheat germplasm with sprouting resistance is impeding the development and production of white wheat cultivars. Two sets of factorial crosses were made with 15 white wheat genotypes possessing different origins and different levels of sprouting resistance. These crosses were statistically analyzed to characterize the inheritance of sprouting resistance by assessing sprouting percentage in ears. In experiment I (5 × 10), it was shown that the general combining ability (GCA) effects of resistant (male) and susceptible (female) parents, and specific combining ability (SCA) effects were highly significant based on both single-year analysis and 2-year combined analysis. There was a significant genotype-year interaction, and the performance of F₁ hybrids was more vulnerable to environments than that of the parents. Hybrids have a greater risk of suffering from the sprouting damage than the pure lines. In experiment II (4 × 4), both GCA and SCA effects were significant for F₂s. Cultivars FLXXM, WXBMZ, SNTTM, ZTNEM and Fengchan 3 had higher sprouting resistance and are thus good donors in white wheat breeding programs for sprouting resistance.     

Combining ability among apomictic and sexual parents of Urochloa humidicola

The diallel cross constitutes an informative genetic design for choosing genitors and crosses in breeding programmes since it provides estimates of general (GCA) and specific (SCA) combining abilities. Because the breeding programme for Urochloa humidicola ([Rendle] Morrone & Zuloaga; syn. Brachiaria humidicola [Rendle] Schweick) at Embrapa Beef Cattle is recent, these estimates are still unknown. Thus, the aim of this study was to obtain the estimates of GCA and SCA from the partial diallel cross design between sexual and apomictic parents. The crosses involved nine sexual and ten apomictic parents. Seventy‐one full‐sib progenies were obtained and evaluated in an incomplete block design, using all parents and the cv. BRS Tupi as a check. The agronomic and forage quality traits were evaluated using seven harvests. Statistical analysis was performed using the mixed model approach. Significant variations were associated with GCA among sexual parents for biomass yield and forage quality traits. However, this cannot be observed for apomictic parents for GCA. The SCA effect was not significant for the assessed traits. These results showed the predominance of additive effects. Sexual parents SEX3 and SEX4 presented the highest potential for contributing favourable alleles in hybrid combinations. The absence of GCA among apomictic parents and SCA suggests the need to increase genetic variability for the generation of breeding populations of U. humidicola.     

马铃薯二倍体栽培种S.phureja与普通栽培种的四倍体杂种品质性状育种价值的研究

试验选用 3份含有二倍体栽培种富利亚薯 (Solanum phureja)血缘的 4x 2x四倍体杂种材料和 1份四倍体普通栽培种 (Solanumtuberosum )优良无性系为亲本 ,按照Griffing方法Ⅲ配制成双列杂交组合 12个 (包括正交 6个 ,反交 6个 ) ,分析了杂种实生苗当代薯形、品质等 6个性状的群体遗传参数和配合力效应。遗传分析结果表明 ,芽眼深度、比重、Vc含量、还原糖含量等 6个被测性状的遗传变异均以加性效应为主。配合力效应估算结果表明 ,同一性状的一般配合力效应值在不同亲本间差异亦较大 ,并且同一性状的特殊配合力效应值在不同组合间差异亦较大。本试验结果还表明 ,比重上存在极显著的反交效应     

General combining ability of Neo-Tuberosum for potato production from true seed

Neo-Tuberosum clones from the Cornell breeding population were evaluated as female parents in combination with Tuberosum for production from true seed. Field trials of hybrid seedling families were carried out in 1982 and 1983. Families were also grown in a hot greenhouse to measure combining abilities for tolerance to heat stress. General combining ability was highly significant for yield, vine and tuber characteristics, and heat tolerance. Several clones were identified which produced outstanding seedling families for yield, uniformity, and tuber appearance. Some individual crosses were equal to cultivars in yields, uniformity, and tuber appearance. Hybrids of Neo-Tuberosum and Tuberosum appear to be an excellent choice for potato production from true seed.     

马铃薯杂种群体的性状相关及其配合力分析

本试验以7个优良马铃薯品种(系)按不完全双列杂交设计配制组合,分析了群体主要性状与生产力的遗传相关及其配合力效应.结果表明,群体平均单株结薯数、平均块茎重、商品薯数量和产量及小薯数量和产量与群体产量的遗传相关达显著或极显著.平均块茎重、商品薯数量和产量是筛选商品价值较高的优良群体的重要相关性状.亲本的一般配合力效应在平均单株结薯数、平均决茎重、商品薯产量、小薯产量和数量几个性状上对模型Ⅰ差异显著,组合间的特殊配合力效应均达到显著差异.特殊配合力方差为总方差的61.47%～147.52%,表明该群体的生产力主要由非加性基因控制.相对配合力总效应值与产量的相关达极显著水平(r_(3.4)=0.99).综合评定亲本801-5,Katahdin和Baraka在马铃薯群体和品种选育中具有较高的利用价值.     

马铃薯品种块茎性状的遗传分析

对Mira等 10个马铃薯品种的 2 2个杂交组合无性一代的块茎产量等 8个块茎性状的群体遗传参数和配合力效应进行了试验研究 ,结果表明 :淀粉含量的遗传受母本加性效应和亲本间非加性效应控制 ;单个块茎重的遗传受父本加性效应的控制 ;皮色、结薯数和块茎产量的遗传受非加性效应控制 ;薯形、肉色和块茎外观的加性和非加性效应同等重要。两个亲本 (至少有一个 )的一般配合力高的杂交组合后代的群体表现优于双亲具有一般配合力平均值的杂交组合 ;而双亲具有一般配合力平均值的杂交组合的群体表现优于双亲一般配合力都很低的杂交组合。根据一般配合力选择亲本配制大量杂交组合 ,并从中筛选优良单株和优良TPS组合的方法非常适合于马铃薯育种