An evaluation for genetic variation within maize inbred lines maintained by sib-mating and self-pollination

Summary Maintaining maize (Zea mays L.) inbred lines without genetic change is an important concern of maize breeders and seed producers. Long-time inbred lines, however, have been shown to be genetically unstable, and with selection pressure acting on the resulting genetic variation, these lines have evolved into different strains. The objective of this study was to compare maintenance of line integrity under reproduction by sib-mating and self-pollination in ear-to-row progenies. Ten lines, varying from 5 to 35 generations of previous ear-to-row selfing, were maintained for 11 successive generations under each method of reproduction. Alternate generations were compared by using a randomized complete-block design with each family of lines as a separate experiment. Data were collected for 10 plant and yield traits: pollen shed and silk emergence dates, plant and ear heights, tassel branch number, kernel row number, ear length and diameter, grain yield, and 300-kernel weight. Summarizing for F-tests over all traits and experiments, 30% were significant among sib-mated generations and 56% among selfed generations. Also, overall generation means of the two methods were different for 51% of the comparisons, and the selfed lines were less vigorous for 79% of the significant comparisons. It was concluded that sib-mating lessens the effect of genetic instability and that a reproduction system of sib-mating with intermittent generations of selfing may be more beneficial than continuous ear-to-row selfing for certain lines.Joint contribution: USDA-ARS, and Journal Paper No. J-11880 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project No. 2194.     

Influence of timing of cross-versus self-pollination on self-incompatibility in Brussels sprout inbreds

Summary The impact of cross pollination 30 h, 4 h, and immediately prior to self-pollination, and self-pollination 2, 4, 8, 12, 24 and 30 h prior to cross-pollination was assessed for pollen tube number per style, seed number per siliqua, and proportion of self-seed (sibs) per siliqua, in two inbred lines of brussels sprout. Pollination procedure had a marked effect on the amount of sib-and hybrid seed produced. Cross pollination 30 h prior to self-pollination produced significantly greater numbers of sib progeny, as did self-pollination 8–12 h before cross pollination. Prior application of self pollen reduces the number of pollen tubes in the style. The results of this experiment suggest that self-incompatibility in brussels sprout could better be assessed by self-pollination with a subsequent cross pollination 8 h later, and the determination of amounts of sib and F₁ hybrid seed per siliqua.     

Optimal pollination conditions for seed set after a self-pollination,an intraspecific cross and an interspecific cross of marrow-stem kale (Brassica oleracea var. acephala)

Summary The effects of different pollination techniques, with and without emasculation and delayed pollination, were investigated to find the conditions for maximum seed set after self-pollination and intraspecific and interspecific crosses of Brassica oleracea var. acephala. The results indicated that the pollination conditions achieving maximum seed set vary with the type of pollination. After controlled self-pollination, the best seed set occurs in bud 3 to bud 10. For the intraspecific cross, the youngest flower and the oldest bud produced the largest number of developed ovules but bud pollination was productive to bud 8. The yields from these two pollination types were best when the female parent was not emasculated. In the interspecific cross with B. campestris cv. Marco the best results came from the youngest flowers and the oldest buds subjected to the standard practice of pollinating directly after emasculation. Possible reasons for these effects are discussed.     

Sunflower seed yield as influenced by some agronomic and seed characters

Summary An investigation was made to the interrelationships of agronomic and seed characters and their effect upon seed yield. Twenty genotypes of sunflower (Helianthus annuus L.) from diverse origin were studied in spring and autumn season, 1989.Most of the studied characters exhibited different relationships in spring and autumn seasons. The correlations between plant height and oil content, 100-achene weight and number of achenes per head and plant height and head diameter were, however, consistent in both seasons and across the seasons. Stepwise multiple regression analysis identified six relevant characters on which path analysis was done.Path analysis indicated that yield components like head diameter, number of achenes per head and 100-achene weight had comparatively smaller direct effects on seed yield (0.22, 0.15 and 0.23, respectively). Days to physiological maturity, plant height and oil content had relatively stronger direct effects on seed yield (0.33, 0.38 and 0.29, respectively). Days to physiological maturity, plant height and head diameter had considerable indirect effects. Head diameter, 100-achene weight and number of achenes per head were indentified as selection criteria for yield improvement.     

Genetic variability and interrelationship of traits in the industrial oil crop Vernonia galamensis

Vernonia galamensis is a wild plant from the family Asteraceae which is endemic to East Africa and has the potential to become a new oil crop for industrial uses. Its seed oil is rich in vernolic acid, a fatty acid of high interest for oleochemical applications. However, a breeding program for Vernonia galamensis cultivars with high seed and oil yields requires knowledge about the genetic variability of traits that influence seed and oil production. This study was undertaken to examine phenotypic and genotypic variability, broad-sense heritability, genetic advance under selection and interrelationships of agronomic and seed quality traits. A total of 122 Vernonia accessions, 115 collected from different regions of Ethiopia and seven introduced, were grown at two locations in Ethiopia (Alemaya and Babile), in 2001/2002 and were analyzed for 20 traits including phenology, yield, yield components, and seed quality with special emphasis on fatty acid composition. The collections exhibited significant variation for all traits except for days to emergence. Genotypes and locations interacted significantly (P 0.01) for all traits. Broad-sense heritability estimates ranged from 11% (for days to emergence) up to 79% (for days to maturity). Expected genetic advance was between 1.3% (for days to emergence) and 44.8% (for seed oil yield). Genetic correlation analysis revealed that seed yield per plant is highly and positively correlated with seed weight and head number; highly significant and negative correlations (r = –0.59, –0.82, –0.85, and –0.89) were found between vernolic acid and palmitic, stearic, oleic, and linoleic acid, respectively. Highly significant positive correlations (r = 0.55, 0.44, and 0.36) were observed between vernolic acid and oil content, meal protein content and seed oil yield, respectively. Path-coefficient analysis indicated seed weight and secondary head number to be the most important components of seed yield per plant. Vernolic acid, oleic acid and linoleic acid had positive direct effects and stearic acid had a negative direct effect on oil content. The direct positive effect of oleic acid on oil content was, however, compensated by the negative indirect effects of stearic and vernolic acid resulting in a negative correlation (r = –0.60) between oleic acid and oil content. These observations will support the selection of accessions with high seed and oil yield, high meal protein contents, and high vernolic acid content.     

Effect of floral morphology on pollination in Brassica rapa L

Summary Flower structure, especially the anther–stigma separation (ASS), is well known to affect pollination efficiency, and thus to potentially increase or decrease seed production in crops. Therefore, investigating the relationship between flower characteristics and pollination ability is crucial to a full understanding of mechanisms to improve F₁ seed production in Brassica rapa. We used image analysis to measure three flower characteristics: short stamen height (SSH); long stamen height (LSH); and pistil height (PH) in seven cultivars. We calculated the ratio of PH to LSH as an index of anther–stigma separation (ASS). We investigated the number of pollen grains (NPG) deposited on the stigma and the seed-set percentage (SSP) under open-pollination and self-pollination conditions (with and without insects, respectively). Nested ANOVA indicated significant differences between the seven cultivars in the floral characteristics except for PH. Moreover, much larger variation was observed in NPG and SSP than in floral characteristics. Although stepwise multiple regression analysis indicated that plants with relatively high PHs produced more seed under self-pollination, the number of seeds that resulted from self-pollination did not affect seed production because of incompatibility. Therefore, the effect of the spatial position of pistils on the F₁ seed production was low. Possibly other factors such as the total pollen production and visiting times of pollinators were important factors in the low yields observed in some cultivars     

Path-coefficient analysis of some yield components of sunflower (Helianthus annuus L.), I

Summary Interactions of seven bio-morphological characteristics of sunflower (head diameter, number of flowers per head, number of seeds per head, 1,000-seed weight, volume weight, kernel content in seed, oil content) and their correlations with seed yield per plant were examined. The path-coefficient analysis provided information about direct and indirect effects of the examined characteristics on seed yield per plant. The correlation coefficients were positive and highly significant. The highest direct positive effect on seed yield per plant was exhibited by the weight of 1,000 seeds. Head diameter, volume weight and kernel content had a direct negative effect on seed yield per plant.     

Effect of Phaeosphaeria nodorum-induced seed shrivelling on subsequent wheat emergence and plant growth

Summary The bread wheat cultivars Pasqua and Katepwa, and durum wheat cultivars Kyle and D8257 were used to test the effects of sowing Phaeosphaeria nodorum-shrivelled seed. In a controlled environment, emergence, tillering, and dry weight of seedlings were compared at two sowing depths. Emergence, tillering and plant dry weights were also determined in field plots in 1992 and 1993, as were yield and thousand kernel weight (TKW) in plants inoculated with P. nodorum. Under controlled conditions the level of shrivelling did not affect emergence at depths of 25 mm and, except for Katepwa, 50 mm. Deeper seeding reduced emergence regardless of the level of shrivelling. Seeding depth did not affect dry weight of roots and shoots and the effect on tillering was inconsistent in the two years. Dry root weight was positively correlated with original seed size and decreased with level of shrivelling. In the field, seedling emergence of severely shrivelled seed was significantly lower in Katepwa and Pasqua. Tillers per plant appeared to increase with increased level of shrivelling, but was significant only for D8257 in one year. Dry tiller weight was inversely related to tillering and decreased consistently with level of shrivelling. Excepting Pasqua, in one year, yield and TKW did not differ between plots originating from plump or shrivelled seed. Inoculation with P. nodorum caused a significant reduction in TKW and yield in all cultivars but Kyle. Seed shrivelled due to P. nodorum was in general found to be as suitable as plump seed for growing a wheat crop.     

Variation in traits affecting nodulation of common bean under intercropping with maize and sole cropping

Common bean (Phaseolus vulgaris L.), an important food crop in Europe, America, Africa and Asia, is thought to fix only small amounts of atmospheric nitrogen. It contributes significantly to the sustainability of traditional cropping systems because of the predominance of small-scale farmers who cultivate beans in those areas. The objectives of this work were to evaluate bush bean varieties under common agronomic cropping systems and to evaluate breeding lines under low N-fertility sole cropping and intercropping systems. The purpose of the study was to characterize the genotype and cropping system's variability in symbiotic and plant characters and to identify the most suitable genotypes to establish an effective symbiosis with indigenous strains of Rhizobium. No significant differences among the bush bean varieties evaluated under typical fertilization practices were observed for N₂-fixation and plant traits except for seed nitrogen. Significant differences among the bean lines studied under low N-fertilization conditions were detected for plant growth,plant component and N₂-fixation traits. A significant interaction of bean genotype x cropping system was found for number of nodules per plant and nodule moisture on the bush bean varieties studied, and for days to emergence, days to flowering, end of flowering, shoot length, root dry weight and shoot nitrogen on the bean lines evaluated. Nodulation parameters were correlated positively with the yield components, shoot and root parts and duration of flowering, and correlated negatively with seed crude protein, pod and seed dimensions and seed dry weight. These observations indicate that it may be possible to increase both the symbiotic N₂-fixation and seed yield through plant breeding. This revised version was published online in August 2006 with corrections to the Cover Date.     

Independence of self-compatibility and potentiality for self-pollination in peach x almond hybrids

Summary The almond of commerce (Prunus dulcis (Mill.) D.A. Webb) is self-incompatible (SI) and requires honey-bees to effect the transfer of pollen among cultivars that flower simultaneously. Four year old trees from the F₂ generation of several peach x almond hybrids were studied to determine whether self-compatibility (SC) and the potentiality for natural, i.e., abiotic, self pollination (NSP) are genetically related or are inherited independently. Both SC and the high potentiality for NSP are characteristic of peach (Prunus persica (L.) Batsch) but not almond. Forty percent of SC genotypes exhibited adequate NSP (SC, +NSP) for good fertility i.e., without insect-mediated pollination. The remaining 60% of SC genotypes (SC,-NSP) exhibited an average 61% reduction in fruit set on limbs bagged to exclude honeybees during anthesis relative to fruit set on open pollinated limbs. Our data are consistent with the concept that fertility is dependent upon the load of compatible pollen deposited on the stigma. Fruit set reduction on bagged limbs, compared with bagged and self-pollinated limbs, was presumably due to a) lack of/insufficient pollination for fertilization and/or b) post-zygotic abortion of genetically inferior recombinants. Selection following manual self-pollination may result in SC genotypes with or without the capacity for NSP. In contrast, significant fruit set on limbs enclosed during pistil receptivity necessitates that the genotype selected express both SC and the potentiality for NSP.     

Pollen germination and pollen tube growth following self-pollination and intra- and interspecific pollination of Medicago species

Summary Pollen germination and pollen tube growth after self- and intra- and interspecific pollinations of annual [M. scutellata (L.) Mill., M. disciformis DC., and M. rigidula (L.) All.] and perennial (M. sativa L.) Medicago species were studied using a Carl Zeiss microscope with a fluorescence filter attachment.Self-pollination of self-fertile annual and intraspecific pollination of cross-fertile perennials were characterized by high pollen germination and rapid normal pollen tube growth. In contrast pollen germination percentages were very low and many pollen tube growth abnormalities occurred following interspecific pollination and self-pollination of self-sterile plants. The time period from pollination to fertilization for interspecific crosses was about double that following self-pollination of the annual species. However, fertilization occurred frequently following interspecific pollinations. Much of the sterility was due to factor(s) operating after fertilization.Cooperative investigations of the Kansas Agricultural Experiment Station, Dept. of Agronomy and the U.S. Department of Agriculture, Agricultural Research Service. Contribution No. 82-582-J- Mention of a trademark name or proprietary product does not constitute a guarantee or warranty by the U.S. Department of Agriculture, and does not imply its approval over other products that also may be suitable.     

Inheritance of ‘domestication’ traits in bambara groundnut (Vigna subterranea (L.) Verdc.)

Controlled crosses in bambara groundnut were attempted between a range of thirty-six bambara groundnut landraces (thirty domesticated (V. subterranea var. subterranea) and six wild (V. subterranea var. spontanea)). Ten F₁ seed were produced. Of these, eight germinated producing F₂ populations. On seed set, four populations could be unambiguously confirmed as true crosses by F₃ seed coat colour. A single F₂ population, derived from a domesticated landrace from Botswana (DipC; female parent) crossed with a wild accession collected in Cameroon (VSSP11; male parent) was used to study a range of agronomic and domestication traits. These included; days to emergence, days to flowering, internode (fourth) length at harvest, number of stems per plant, leaf area, Specific Leaf Area (SLA), Carbon Isotope Discrimination (CID), 100 seed weight, testa colour and eye pattern around the hilum. On the basis of variation for internode length and stems per plant, 14 small F₃ families were selected and grown under field conditions to further investigate the genetic basis of the ‘spreading’ versus ‘bunched’ plant character, a major difference between wild and cultivated bambara groundnut. Results presented suggest that traits including leaf area, SLA, CID and 100 seed weight are controlled by several genes. In contrast, the variation for traits such as internode length, stems per plant, days to emergence and seed eye pattern around the hilum are likely to be under largely monogenic control. The results of this work are discussed in relation to the domestication of bambara groundnut.     

Emergence response of the pepper at low soil temperature

Summary One-hundred and five cultivars representing s species of Capsicum were screened at constant 13, 16, 18°C and greenhouse temperatures. Daily observation on emergence were made for 60 days following seeding in flats.Using a calculated emergence index as the criterion for emergence at low temperatures, the various cultivars were classified by species. Within the C. annum group significant differences were found between cultivars for the lowest and highest index suggesting heritability of this trait. The fowest indexes for all temperatures was a cultivar from the C. baccatum v. pendulum group.Michigan Agricultural Experiment Station Journal No. 8132.Present address: 2306 1/2 Murray Avenue, Pittsburgh, PA 15217, USA.     

Inter-accession variation in floral morphology in radish (Raphanus sativus L.)

We investigated variation in floral morphology among 36 accessions of radish (Raphanus sativus L.). We found wide, continuous inter-accession variation in 15 traits related to the size of the floral organs and the stigma position relative to the anthers of long stamens. A principal-component analysis of the 15 floral traits also showed wide variation among accessions. A large proportion of this variation was accounted for by lengths of stamens and the petal tube. In addition, the phenotypic stabilities with respect to the macro-environment (as affected by different sowing dates) and the micro-environment (among the flowers within a plant) differed between traits. Correlation analyses using all traits suggest the existence of genetic linkages or pleiotropies among floral organs. Our results indicate that floral morphologies varied greatly among radish accessions and they could be affected by the macro- and micro-environment. To explore the relationship between floral morphology and pollination efficiency, we compared the number of pollen grains deposited on the stigmas in the presence and absence of insect pollinators using three accessions with very different floral morphology. Because an accession with a higher stigma position than anthers might avoid self-pollination and an accession with a large stigma size received more pollen grains, floral morphology may affect pollination efficiency. Because the effect of pollination efficiency on seed production is well known, our results suggest that radish floral morphology affects seed production through its effect on pollination efficiency.     

Evaluation of the germ plasm collection of safflower,Carthamus tinctorius L. VII. Variability of capitulum width and outer involucral bracts' dimensions

Summary A germ plasm collection of safflower, Carthamus tinctorius L., with about 900 lines from over twenty countries was evaluated in Utah, USA for head width and outer involucral bracts (OIB) dimensions, traits affected by both human and natural selection. The regional germ plasm pools contained considerable variability for these traits. Plants bearing short or long as well as narrow or wide OIB were well adapted. Geographical clines were detected for the means of OIB dimensions, indicating possible gene flow. The correlations of the OIB dimensions with yield, yield components, oil content and growing period were not instructive and at times very inconsistent. Primary head diameter varied considerably within the regional gene pools. Its correlations with yield/plant, number of heads/plant, seed weight and oil content were inconsistent. Capitulum width was positively and significantly correlated with the number of seeds per head. Head diameter, however, can vary considerably without affecting seed yield per unit area.     

Selection for resistance to Septoria nodorum in wheat

Summary A population of 572 F₂ derived F₃ lines from six crosses were used to estimate parameters relevant to selection for resistance to Septoria nodorum of wheat. Lines were grown in disease free (fungicide sprayed) and inoculated microplots in 2 replications of a split-plot design in a single environment in 1977. Average yield reduction due to disease was approximately 50%; this was associated with an average septoria score of 50% on the flag leaf, an average septoria score of 42% on the head, and a reduction of 37% in seed weight. Low S. nodorum scores were correlated with late heading date, tall plant height, high grain yield, and high seed weight in diseased plots, and high seed weight % (seed weight in diseased plots expressed as a percentage of seed weight in fungicide sprayed plots).Restricted selection indexes were used to study the relative contributions of disease escape, true resistance, and tolerance to variability in grain yield in diseased plots, seed weight in diseased plots, and seed weight %. True resistance appeared to be the most important factor causing variation in grain yield in diseased plots and seed weight %. Tolerance and escape seemed to be more important for seed weight in diseased plots.Heritabilities of S. nodorum scores on the flag leaf and head were 63% and 52%, respectively. Leaf and head scores could be used most effectively as selection criteria to upgrade resistance in a population before harvest.Selection for high seed weight % slightly reduced yields in disease free plots, although yield in diseased plots and seed weight in diseased plots were increased. However, selection for increased yield or increased seed weight in diseased plots improved yield in disease free plots. It is suggested that direct selection for yield or seed weight in diseased plots is likely to achieve more desirable goals than selection for seed weight %.     

Effectiveness of selection for plant characters of barley in simulated segregating rows

Summary Single plants of 12 barley (Hordeum vulgare L. and H. distichum L.) cultivars were randomized to form simulated segregating (mixed) rows. There were 16 mixed rows 15 cm apart, each row containing 24 plants 5 cm apart. In addition, every third row was a control row of one of the cultivars, Bonanza. Each plant was harvested separately.The cultivars differed significantly for all seven characters measured. These seven characters fell into 3 performance groups. Group I characters, seeds/head, 1000 kernel weight, days to ripe and height, showed a higher variance in the mixed rows than in the control rows, had high average heritabilities, and were consistent in performance from one row to another when measured by correlation amongst the cultivars. In Group II, yield/plant and seeds/plant, variance, heritabilities and performance consistency were all low or non-significant. Group III, heads/plant, fell between Groups I and II. These results suggested that single plants with the desired genotype could be successfully selected for characters in Group I only.The frequency with which the most desirable genotype would actually have been chosen with 12.5% selection intensity generally confirmed the above conclusions but indicated that the degree of differences among genotypes was also important in selecting the most desirable genotypes.Contribution No. NRG 77–9 from the Beaverlodge Research Station.     

自花授粉诱导的甘蓝功能基因BoSPI的克隆与表达分析

自交不亲和性是甘蓝在长期进化过程中形成的防止自交衰败、促进杂交优势的一种复杂而完善的遗传机制。克隆自交不亲和性相关基因对甘蓝自交不亲和性的深入研究和利用有重要意义。本研究通过挖掘0~60 min自花和异花授粉的甘蓝柱头转录组数据, 筛选到一个受自花授粉诱导上调表达的基因, 命名为BoSPI。BoSPI开放阅读框534 bp, 编码177个氨基酸, 理论等电点为4.21, 不包含信号肽和跨膜区, 含有4个保守的EF-hand结构域。BoSPI基因起始密码子上游2000 bp的核苷酸序列中含有真菌诱导响应、代谢调节以及器官形成等应答元件。BoSPI基因在大肠杆菌中可诱导表达为17 kD的蛋白。BoSPI在柱头中表达量最高, 在花瓣、萼片、叶片、雄蕊表达量较低。BoSPI蛋白被定位在细胞膜和细胞质。自花授粉30 min后对BoSPI基因的诱导表达显著增强。表明BoSPI参与了柱头响应自花花粉刺激的分子过程, 可能是实现甘蓝自交不亲和性相关的某种新功能基因。     

Field evaluation of somaclonal variation in sunflower (Helianthus annuus L) and its application for crop improvement

Immature zygotic embryos from the American fertility restorer line RHA-857 were used as donor material for induction of direct organogenesis in sunflower (Helianthusannuus L.). The range of spontaneous somaclonal variation among the progenies of regenerants was studied. The genetic modifications observed in regenerants included agronomic traits such as oil content in seed, 1000 seed weight, plant height, leaf width, leaf length, petiole length, internode length, head diameter, number of branches, length of branches, number of ray florets, seed width, seed length, and seed thickness. RAPD molecular analysis carried out on sunflower materials in the R-11 generation showed the absence of a specific 358 bp band in somaclonal line 11/2/51 R. This line showed a modified architecture, full resistance to Phomopsis helianthiand higher oil content in seed in comparison to the standard RHA-857. Line31/3/53 R was with modified architecture and higher 1000 seed weight. Hybrid No. 144 produced with the participation of somaclonal line 20/5/52 R demonstrated high production capacity, shorter vegetation period and reduced height. The combination of these favourable changes is desirable in breeding work on sunflower. Somaclonal variation through director ganogenesis has facilitated the creation of genetically heritable variation in sunflower, which can be used with great success for hybrid seed production of highly productive hybrids. This revised version was published online in July 2006 with corrections to the Cover Date.