Unselected Plants Research Articles

Genomic Selection for the Traits Expressed after Pollination in Allogamous Plants

ABSTRACTMass selection, a breeding method commonly used to improve allogamous crops, is characterized by low efficiency, especially when a target trait is expressed after pollination. The trait cannot be observed before pollination. Therefore, pollen from unselected plants contributes to the next generation. Genomic selection (GS) enables prediction of the genetic potential of plants from marker genotypes and selection of good pollen parents before pollination. This study investigated the potential of GS in mass selection of a trait expressed after pollination via breeding simulations with annual allogamous plants. We compared GS and phenotypic selection (PS) in traits expressed before and after pollination. Genetic gain attained by PS breeding was much lower than the gain by GS breeding in a trait expressed after pollination. Genetic gain attained by GS breeding was almost equal between traits expressed before pollination and after, except when the breeding cycle was once per year. High efficiency of GS breeding in a trait expressed after pollination was attributable to the high selection accuracy of chromosomes derived from a pollen parent at GS immediately after selection with model update, where we did not select pollen parents because of phenotype requirements. It engendered increased population size and prevented depletion of genetic variation in a breeding population. Results show that GS is effective for improvement of a trait expressed after pollination.

Can barley (Hordeum vulgare L. s.l.) adapt to fast climate changes? A controlled selection experiment

The projected future climate will affect the global agricultural production negatively, however, to keep abreast of the expected increase in global population, the agricultural production must increase. Therefore, to safeguard the future crop yield and quality, the adaptive potential of crops to environmental change needs to be explored in order to select the most productive genotypes. Presently, it is unknown whether cereal crops like spring barley can adapt to climate stressors over relatively few generations. To evaluate if strong selection pressures could change the performance of barley to environmental stress, we conducted a selection experiment over five plant generations (G0–G4) in three scenarios, where atmospheric [CO2] and temperature were increased as single factors and in combination. The treatments represented the expected environmental characteristics in Northern Europe around year 2075 [700 ppm CO2, 22/17 °C (day/night)] as well as a control mimicking present day conditions (390 ppm CO2, 19/12 °C). Two different barley accessions, a modern cultivar and an old landrace, were evaluated in terms of yield and biomass production. In all treatments representing future environmental scenarios, the G4-generation of selected plants did not improve its reproductive output compared to the G0-generation, as G4 produced less seeds and had a lower yield than unselected plants. These results indicate that barley might not respond positively to rapid and strong selection by elevated [CO2] and temperature, contrary to previous results from oilseed rape. The two barley accessions analyzed presented almost the same response pattern in a given treatment, though the modern cultivar had the highest yield in the climate scenarios, while the landrace was superior in yield under present day climate conditions.

Evolutionary change in flowering phenology in the iteroparous herb Beta vulgaris ssp. maritima: a search for the underlying mechanisms

The potential for evolutionary change in flowering time has gained considerable attention in view of the current global climate change. To explore this potential and its underlying mechanisms in the iteroparous perennial Beta vulgaris ssp. maritima (sea beet), artificial selection for earlier and later flowering date was applied under semi-natural greenhouse conditions. Mean flowering date occurred more than 30 d earlier in 13 generations in the early selection line, but response was weaker in the late selection line. Taking advantage of the growing knowledge on the genetics and the physiology of flowering induction, particularly in Arabidopsis thaliana, the results obtained here were analysed in terms of the four different pathways of flowering induction known in this species. A first significant correlated response was stem elongation (bolting) in the vegetative stage, suggesting that plants were thus able to flower earlier as long as other requirements were satisfied. Vernalization had a clear influence on flowering date and its influence increased during the selection process, together with sensitivity to photoperiod. Vernalization and photoperiod could compensate for each other: each additional week of vernalization at 5 degrees C decreased the necessary daylength for flowering by about 15 min during the later selection stages, while in unselected plants, it was about 7 min. Devernalizing effects were observed at short days combined with higher temperatures. Special attention was given to the role of the B (bolting) gene that cancels the vernalization requirement. The results here obtained suggest that all four known pathways may simultaneously participate in evolutionary change.

Avaliação de sabiazeiro (Mimosa caesalpiniaefolia Benth.) quanto a acúleos e preferência por bovinos

This work aimed to evaluate cattle preference and level of thorns of 16 “Sabiazeiro” (Mimosa caesalpiniaefolia Benth.) progenitors previously selected for thorns absence. The study was carried out at Itambe Experimental Station, sub-humid forest zone of Pernambuco State, Brazil. The treatments included 189 progenies from 16 selected progenitors and 40 progenies from unselected progenitors (control treatment). All plants were obtained by open pollination, but the selected progenitors were isolated from other plants. Note scales were used for thorn evaluation and cattle preference. The progenies from selected plants had a higher proportion of plants in the categories without and with little thorns and higher cattle preference than the progenies from unselected plants. In general, “sabiazeiro” showed higher cattle preference in the begining of the dry season, than the remaining part of the year. The progenitors number 6, 9,12 and 19 were selected for continuity of the breeding programe. The progenies variability indicate it is possible to obtain a forage “sabiazeiro” variety without absence thorns and high preference.

In vitro Selection and Characterization of Drought Tolerant Somaclones of Tropical Maize (Zea mays L.)

Somaclonal variation for drought tolerances of two Kenyan maize genotypes, KAT and PH01, were obtained from in vitro selection. Three-month-old calli derived from immature embryos were grown on N6 medium supplemented with mannitol or polyethylene glycol (PEG-6000) to find-out the appropriate concentrations of selection pressure. Calli were sequentially transferred to 3.28 and 5.28% mannitol or 18 and 20% PEG and maintained for 9 weeks. Survival percentage and regeneration capacities of selected and unselected calli were determined. It was observed that selected calli had lower survival and regeneration capacities than unselected calli. The result showed that survival percentages of maize calli grown in mannitol and PEG were 8.4 and 4.2%, respectively. Six plantlets were regenerated from mannitol-tolerant calli, while, only two plantlets were regenerated from the PEG tolerant calli. Plantlets were regenerated from selected calli at lower frequencies than those from unselected calli. To investigate the putative genetic basis of water stress tolerance, the mannitol tolerant PH01 somaclones designated MT JM1-01, MT JM2-01, MT JM3-01 and MT JM4-01 and the PEG tolerant clone, PT JM1-01, were further evaluated using RAPD. The assay with the decamers OP-07 and OPD-08 revealed that the water stress tolerant somaclones were genetically different from the controlled, unselected plants.

Response and correlated response of yield parameters to selection for salt tolerance in rice

Lack of reliable selection criteria is one of the major reasons for the limited success in salt tolerance. This study was designed to determine the responses of yield parameters in rice plants to the selection for salt tolerance. F2 populations were developed from crosses between ‘M-202’ (salt-sensitive) and ‘Agami’ (moderately salt-tolerant) and grown in the greenhouse under salt stress (NaCl and CaCh, 5: 1 molar concentration). Selections were made among the F2 plants for the highest values of grain weight per plant, tillers per plant, and panicle weight under salt stress. The F3 populations of the selected F2 plants and unselected F2 plants, and their parental plants were evaluated for salt tolerance. Broad-sense heritability and realized heritability of grain weight per plant were determined to be 0.40-0.45 and 0.25, respectively. Higher broad-sense heritability (0.45 to 0.65) and realized heritability (0.42) of tillers per plant suggest this trait is genetically controlled. Moderately high realized heritability indicates the effectiveness of early selection for salt tolerance if tiller number is used as selection criterion. Low genetic correlation between tiller number and panicle weight was identified in F3 populations derived from the selected F2 plants. The low genetic correlation indicates the low compensatory relationship between these two yield parameters in equal spaced rice plants under salt stress.

Ion accumulation in lucerne plants regenerated from salt-adapted suspension cultures compared with recultured cells from these plants

Lucerne (Medicago media cv. Rambler) plants, regenerated from cell suspension cultures adapted to 200 mM NaCl, and cell cultures derived from the leaflets of regenerated plants showed enhanced Na+ exclusion compared with the unselected plants and cell cultures. There was a decrease in the K+ concentration in response to NaCl treatment but the selected plants and cell cultures maintained a significantly higher K+ concentration and showed much lower Na+/K+ ratios than unselected plants and cell cultures. The proline concentration increased in the shoots and cell cultures in response to NaCl stress but the selected plants and cell cultures showed a significantly higher proline concentration than unselected plants and cell cultures.

Nursery Selection for High Early Fruit Yield in Subtropical Strawberries

Development of new strawberry cultivars for winter fruit production in Florida entails growing of hybrid seedlings in a nursery in the summer of the first year for runner plant production. Two runner plants are taken from each seedling and planted in the fruiting field in the fall. An experiment was conducted to see if it is possible to predict which genotypes in the nursery will have the highest early season fruit yield. Seedlings from 24 families from a 6 × 4 factorial mating design were grown in a nursery. From each family, daughter plants of 20 seedlings with the highest vigor and 20 randomly picked seedlings were then evaluated in the fruiting field. Plants from selected (high-vigor) seedlings were more vigorous, but had fewer crowns and runners, than unselected plants. More inflorescences were counted in selected plants than in unselected plants during the second week of January. This could account for higher early yield (yield at the end of January) and total yield (yield at the end of March) in selected than in unselected plants.

Response to selection for root dimension in a Mediterranean natural population of Lolium rigidum Gaud

AbstractIn the Mediterranean environment, root systems are very important for water utilization. For this reason, the effects of selection for increased root dimensions upon root and shoot characteristics of a natural population of Lolium rigidum Gaud, were analysed. Two cycles of phenotypic recurrent selection were carried out on a population collected in Nurra (north‐western Sardinia, Italy). Plants derived after two cycles of selection, together with unselected plants, were grown hydroponically in a greenhouse. Data on root volume, longest root length, number of stems and leaves, leaf length, shoot and root dry weight were collected from the selected material and also from unselected material for use as a control. An analysis of variance was performed and correlation coefficients were calculated. The increased size of the root system did not have a negative effect on the above‐ground biomass and there was genetic variation for root traits in the ‘Nurra’ population. The improved population will be utilized for further breeding work to obtain L. rigidum varieties capable of withstanding dry periods during the vegetative phase.

Comparative NaCl tolerance of Lucerne plants regenerated from salt-selected suspension cultures

Batch suspension cultures of Lucerne ( Medicago media cv. Rambler), initiated directly from surface-sterilized leaflet explants, were used to produce cell lines tolerant to 200, 250 and 300 mol/m 3 NaCl by successive subculture into media of progressively higher salinity. Plants regenerated from these cell lines were significantly more salt tolerant than the original, unselected Rambler plants, another cultivar of M. media and 4 cultivars of M. sativa. The salt-tolerant plants showed enhanced Na + and Cl − exclusion when compared with the unselected cultivars. Comparisons of the salt-tolerant, 250 mol/m 3 NaCl-selected with original unselected Rambler plants showed the salt-tolerant plants were able to maintain lower Na + K + ratios than the unselected plants. Ca 2+ gave some amelioration of NaCl toxicity but the salt-tolerant plants did not differ from the susceptible plants in this respect. A multiple regression equation has been computed accounting for 90% of the observed variation, that relates the growth of the plants to Na + K + ratios and Cl − concentrations of roots and shoots and their interactions.

Identification of Two Mechanisms of Sulfonylurea Resistance Within One Population of Rigid Ryegrass (Lolium rigidum) Using a Selective Germination Medium

A biotype of rigid ryegrass (Lolium rigidumGaudin biotype VLR69) resistant to some ALS inhibitors was characterized to determine the mechanisms of resistance to the sulfonylurea herbicides. The biotype had a high level of resistance to chlorsulfuron (20×) and triasulfuron (25×), and an intermediate level of resistance to imazaquin (7×) and sulfometuron (7.5×) but exhibited a low level of resistance to imazapyr (2.5×). At 60 to 90 g ai ha-1sulfometuron, 4% of the population survived without apparent herbicidal effect The same response to sulfometuron was also observed when seeds of the resistant biotype VLR69 were germinated on agar containing sulfometuron. At 27 nM sulfometuron, 4% of the seeds germinated and grew normally while the growth of the bulk of the population was retarded. This differential response to sulfometuron at the seedling stage allowed selection of sulfometuron-resistant individuals from the population. Activity of ALS extracted from these sulfometuron-resistant plants was less sensitive to inhibition by chlorsulfuron than ALS extracted from plants considered sulfometuron susceptible in the same system. Unselected plants from the VLR69 population were able to detoxify chlorsulfuron more rapidly than susceptible VLR1 plants. It is apparent that there are at least two mechanisms of sulfonylurea resistance in the resistant biotype VLR69 which occur at different frequencies within the population. These data show that more than one mechanism or resistance may develop in response to herbicide selection pressure and that the resulting populations are not necessarily homogeneous.

Selection in vitro for UV‐tolerant sugar beet (Beta vulgaris) somaclones

With a reduced stratospheric ozone concentration, the generation of UV‐tolerant plants may be of particular importance. Among different crop plants there is large variation in sensitivity to UV‐B radiation. This study was undertaken to investigate the possibilities of using somaclonal variation and selection in vitro for improving UV‐B tolerance in sugar beet (Beta vulgaris L.).Sugar beet callus was exposed to UV radiation (280–320 nm, 0.863–5.28 kJ m‐2 day‐1, unweighted) and resultant shoots were selected from surviving cells. After establishment of the plants, they were grown under either visible radiation (114 μmol m‐2 s‐1 PAR) or with the addition of UV radiation (6.3 kJ m‐2 day‐1 biologically effective UV‐B). Screening of regenerants in vivo for tolerance to UV radiation was undertaken 10 months after termination of the UV selection pressure. Screening was done visually and by using a number of physiological parameters, including chlorophyll fluorescence induction, ultraweak luminescence, pigment analysis and total content of UV‐screening pigments. A clear difference between the unselected and the UV‐selected somaclones was observed when visually studying the UV damage and other leaf injury. The observations were supported by the ultraweak luminescence measurements. Unselected plants showed significantly greater damage when subjected to subsequent UV radiation as compared to the selected plants. The clones subjected to UV selection pressure displayed a significantly higher concentration of UV‐screening pigments under subsequent UV radiation. The unselected plants under subsequent UV treatment showed a lower carotenoid concentration when compared to selected plants. However, no significant difference between treatments was found for chlorophyll a/b, or F/Fmax, a measure of photosynthetic quantum yield.

Characterization of progeny of Coleus blumei following an in vitro selection for salt tolerance

An in vitro selection method was developed for Coleus blumei to enhance salt tolerance of this amenity species. Leaf disc explants were incubated on a Murashige & Skoog medium containing benzylaminopurine, 2 mg l-1, and napthalene acetic acid, 1 mg l-1, which initiated both callus and plantlets from the explants. A large number of explants were incubated on this differentiating medium containing 90 mM NaCl, which inhibited over 90% of plantlet formation. Surviving plantlets. were grown to maturity, when apical cuttings were taken and propagated. Plants were also allowed to flower and set seed. Cuttings from the selected regenerated plants showed consistently better growth in the presence of NaCl than unselected cuttings. Seed progeny of selected plants also showed more vigorous growth in the presence and absence of NaCl than progeny from unselected plants. The in vitro selection was compared with the results of an earlier in vivo selection to assess the contribution from tissue culture derived somaclonal variation. Progeny from the in vitro selection showed a higher level of tolerance than progeny from the in vivo selection.

In vivoselection for salt tolerance inColeus blumei

SummaryThe aim of the investigation was to examine by in vivo screening the potential for salt tolerance in a selected cultivar of the amenity annual, Coleus blumei. Seedlings were placed on a capillary mat soaked in salinized nutrient solution. An initial dose response over the range 0-120 mM NaCl showed that at 90 mM NaCl only 15% of seedlings survived. A large scale screen of seedlings at 90 mM produced a number of survivors of which about 2% grew normally. Cuttings from these survivors showed more tolerance than cuttings from unselected plants. Seed progeny from some of these surviving plants were vegetatively more vigorous in the presence of 90 mM NaCl than seed progeny from unselected plants. Using this simple technique it was possible to screen large numbers of seedlings for salt tolerance in this species. It is suggested that the technique could also be used to screen for a wide range of other characters.

Development of salt tolerant lines of KDML and LPT rice cultivars through tissue culture

Salt tolerant lines of indica rice (Oryza sativa L.) were selected out of KDML and LPT cultivars. The first selection was made in vitro by incorporating 1 or 2% NaCl in the culture media. Embryogenic calli from mature embryo were subjected to a salt stress for four weeks. Regeneration rates after salt stress were reduced to 0.076% or less as against regeneration rates of 8.3 to 30% normally obtained for non-stressed conditions. Seedlings of regenerants and of following generations were treated with 0.5% NaCl in water culture for four weeks. Definite salt tolerance of the progenies of selected and unselected plants appeared in both cultivars. The best survival rate of line LPT 171 in R3 was 94.3% while only 2% of the control survived. The result of the fourth generation was similar to the third.

THE POTENTIAL FOR EVOLUTION OF SALT (NaCl) TOLERANCE IN SEVEN GRASS SPECIES

SUMMARYThe seedling root growth of Agrostis stolonifera L., Agrostis capillaris L., Holcus lanatus L., Lolium perenne L., Dactylis glomerata L., Festuca rubra L. and Puccinellia distorts (L.) Parl. was examined after 14 d of immersion in dilute nutrient solutions containing 0, 150, and 250 mol m−3 NaCl. Root growth of all species was significantly reduced by increasing NaCl concentration.Samples of 10000 to 20000 seeds of each species were then screened for ability to root in solution cultures at NaCl concentrations which markedly inhibited root growth in the first experiment. Small numbers of individuals of all species rooted in these solutions and high and low selection lines were established based upon root length values.Adult plants from these high and low selected lines were compared with an unselected sample for ability to root in a range of NaCl concentrations. The high line plants had significantly longer roots than the unselected plants in all species, and than the low selected line in all species except Agrostis capillaris. Low selected plants had significantly longer roots than unselected plants in Holcus lanatus, and Dactylis glomerata.The pattern of response to selection showed no consistent relationship to the known ecology of the species examined, and suggests that variability in salt tolerance is widely present in species, but for other reasons salt tolerance does not always evolve in natural situations.

Selection of perennial and Italian ryegrass plants resistant to ryegrass mosaic virus

SUMMARY Perennial ryegrass plants collected from fields and Italian ryegrass plants grown from seed were selected for resistance to infection by ryegrass mosaic virus (RMV) by repeated manual inoculation. Two of 108 perennial ryegrass plants and one of 150 Italian ryegrass plants were symptomless after seven and nine inoculations respectively. These three plants were propagated vegetatively. Plants of the two perennial ryegrass clones showed no symptoms after further manual inoculations with the initial isolate of RMV, or with an inoculum from infected plants collected from several fields, or after inoculation by viruliferous mites. Electron microscopy and back tests indicated that the plants were virus free. Some plants of the selected Italian ryegrass clone became infected after a further inoculation with mites or sap, but fewer than similarly inoculated unselected plants.

Inherited resistance of sugar beet to aphid colonization

SUMMARYResults of glasshouse experiments have confirmed that inbred lines of sugar beet differ in each of three types of resistance to Myzus persicae Sulz. and Aphis fabae Scop., namely: resistance to settling, resistance to multiplication, and tolerance. Resistance to multiplication was not invariably associated with resistance to settling, although plants of some lines showed both forms of resistance. Plants that were resistant to settling of alatae were not always resistant to apterae of the same species, and there was not a close relationship between resistance to M. persicae and to A. fabae. The mechanisms involved in resistance to aphids in sugar beet are not understood.Progenies of plants, selected for resistance to aphids from inbred lines, were often more resistant than progenies of unselected plants. Inheritance of each type of resistance is probably polygenic. The potential value of the different kinds of resistance, in reducing direct feeding damage and controlling the spread of virus yellows in the field, is discussed. The ultimate breeding objective is to produce commercial varieties in which appropriate kinds of resistance to aphids are combined with resistance to virus yellows. The use of such varieties would reduce the need to control aphids in the field by applications of chemicals.

Variability in Components of Seed Production in Panicum coloratum L. 1

Seed shattering is a critical problem in Panicum coloratum L. Detailed studies of seed production components failed to detect any significant differences in actual seed holding ability within a limited population. However, plants with the greatest number of seed in panicles 14 days after initial anthesis also tended to have the greatest number at [atervals up to 31 days after initial anthesis. Significant and heritable differences were obtained in the important seed production components of fertile fiorets per panicle, seed per panicle, and percent fertility. Thus, differences in seed production potential were discovered though not in seed retention after individual floret maturity. An advanced generation of selected plants produced 47% more seed than unselected plants and verified the increased seed production potential of plants selected for individual seed production components.

Interrelationship of Three Laboratory Screening Procedures for Breeding Alfalfa Resistant to the Alfalfa Weevil 1

Seventy-five alfalfa varieties, synthetics, and ecotypes were evaluated in a study designed to: (1) evaluate the effectiveness of mass screening alfalfa in the cotyledon stage for isolating resistance to the adult and larval stages of the alfalfa weevil, (2) study possible relationships among plant reactions in laboratory [or adult feeding and larval development, and (3) search for sources of resistance to adult and larval feeding. Plants selected by a cotyledon feeding test were compared with unselected checks for resistance to adult leaf feeding and larval development. Plants selected by the cotyledon test had significantly less adult feeding and smaller larvae than did unselected plants of the same variety. Differences, however, were small. Some varietal differences were noted, but no entry had a high degree of resistance. Plants with some resistance were isolated in low frequency from most varieties.