Mean Flowering Time Research Articles

Genomic prediction of regional-scale performance in switchgrass (Panicum virgatum) by accounting for genotype-by-environment variation and yield surrogate traits.

Switchgrass is a potential crop for bioenergy or carbon capture schemes, but further yield improvements through selective breeding are needed to encourage commercialization. To identify promising switchgrass germplasm for future breeding efforts, we conducted multisite and multitrait genomic prediction with a diversity panel of 630 genotypes from 4 switchgrass subpopulations (Gulf, Midwest, Coastal, and Texas), which were measured for spaced plant biomass yield across 10 sites. Our study focused on the use of genomic prediction to share information among traits and environments. Specifically, we evaluated the predictive ability of cross-validation (CV) schemes using only genetic data and the training set (cross-validation 1: CV1), a subset of the sites (cross-validation 2: CV2), and/or with 2 yield surrogates (flowering time and fall plant height). We found that genotype-by-environment interactions were largely due to the north-south distribution of sites. The genetic correlations between the yield surrogates and the biomass yield were generally positive (mean height r = 0.85; mean flowering time r = 0.45) and did not vary due to subpopulation or growing region (North, Middle, or South). Genomic prediction models had CV predictive abilities of -0.02 for individuals using only genetic data (CV1), but 0.55, 0.69, 0.76, 0.81, and 0.84 for individuals with biomass performance data from 1, 2, 3, 4, and 5 sites included in the training data (CV2), respectively. To simulate a resource-limited breeding program, we determined the predictive ability of models provided with the following: 1 site observation of flowering time (0.39); 1 site observation of flowering time and fall height (0.51); 1 site observation of fall height (0.52); 1 site observation of biomass (0.55); and 5 site observations of biomass yield (0.84). The ability to share information at a regional scale is very encouraging, but further research is required to accurately translate spaced plant biomass to commercial-scale sward biomass performance.

Spring temperature drives phenotypic selection on plasticity of flowering time.

In seasonal environments, a high responsiveness of development to increasing temperatures in spring can infer benefits in terms of a longer growing season, but also costs in terms of an increased risk of facing unfavourable weather conditions. Still, we know little about how climatic conditions influence the optimal plastic response. Using 22 years of field observations for the perennial forest herb Lathyrus vernus, we assessed phenotypic selection on among-individual variation in reaction norms of flowering time to spring temperature, and examined if among-year variation in selection on plasticity was associated with spring temperature conditions. We found significant among-individual variation in mean flowering time and flowering time plasticity, and that plants that flowered earlier also had a more plastic flowering time. Selection favoured individuals with an earlier mean flowering time and a lower thermal plasticity of flowering time. Less plastic individuals were more strongly favoured in colder springs, indicating that spring temperature influenced optimal flowering time plasticity. Our results show how selection on plasticity can be linked to climatic conditions, and illustrate how we can understand and predict evolutionary responses of organisms to changing environmental conditions.

The evolution of flowering phenology: an example from the wind-pollinated African Restionaceae.

Flowering phenology is arguably the most striking angiosperm phenophase. Although the response of species to climate change and the environmental correlates of the communities have received much attention, the interspecific evolution of flowering phenology has hardly been investigated. I explored this in the wind-pollinated dioecious Restionaceae (restios) of the hyperdiverse Cape flora, to disentangle the effects of phylogeny, traits, and biotic and abiotic environments on flowering time shifts. I recorded the flowering times of 347 of the 351 species, mapped these over a 98 % complete phylogeny and inferred the evolutionary pattern and abiotic correlates of flowering time shifts. The patterns and biotic/abiotic correlates of restio community mean flowering time were explored using 934 plots. Restios flower throughout the year, with large spring and smaller autumn peaks. Species flowering time is evolutionarily labile, poorly explained by either the environment or traits of the species, with half of all sister species allochronic. Community mean flowering time is related to elevation, temperature and rainfall. Flowering time shifts may result from assortative mating and allochronic speciation, possibly leading to non-adaptive radiation. However, community mean flowering time may be environmentally selected. Diversification of flowering time may be non-adaptive, but species could be filtered through survival in suitable communities.

Selection and plasticity both account for interannual variation in life-history phenology in an annual prairie legume.

As the environment changes, so too must plant communities and populations if they are to persist. Life‐history transitions and their timing are often the traits that are most responsive to changing environmental conditions. To compare the contributions of plasticity and natural selective response to variation in germination and flowering phenology, we performed a quantitative genetic study of phenotypic selection on Chamaecrista fasciculata (Fabaceae) across two consecutive years in a restored tallgrass prairie. The earliest dates of germination and flowering were recorded for two parental cohorts and one progeny cohort in an experimental garden. Environmental differences between years were the largest contributors to phenological variation in this population. In addition, there was substantial heritability for flowering time and statistically significant selection for advancement of flowering. Comparison between a progeny cohort and its preselection parental cohort indicated a change in mean flowering time consistent with the direction of selection. Selection on germination time was weaker than that on flowering time, while environmental effects on germination time were stronger. The response to selection on flowering time was detectable when accounting for the effect of the environment on phenotypic differences, highlighting the importance of controlling for year‐to‐year environmental variation in quantitative genetic studies.

English

Roselle (Hibiscus sabdariffa var. altissima), a bast fibre crop adapted to the warm climate of Northern Ghana, offers a great economic potential not yet explored for lack of information on its distribution, collection, and genetic diversity. Little variability is reported in exotic genotypes to merit trait improvement. The objective of this study is to investigate distribution and diversity in roselle of Northern Ghana. Twenty-five accessions collected from seven districts were field evaluated in a 5×5 lattice square design in three replications at twelve qualitative and five quantitative morphological traits. Data were analysed for within- and between-population variability and multivariate analysis. Large within-population variability of SDI 0.72 to 0.87 was identified in accessions of Kassena-Nankana East district. The most variable traits, plant height and branch number, varied from 184 cm to 284 cm with six accessions HA-44, HA-47, HA-43, HA-38, HA-52, and HA-42 having the tallest plants and least basal branching of four. Mean flowering time was between 96 and 104 days. Mean Euclidean distance of 3.03 ± 0.90 ranged from 0.41 to 5.17. Based on means across pairwise distances of 2.22 and 3.94, three accessions were divergent, namely, HA-61 (3.94), HA-57 (3.66) and HA-59 (3.63). Clustering and principal components analyses delineated three distinct groups. The first three PCs explained 100% of the variance. The ample diversity in roselle awaits exploitation for genetic improvement, particularly for fibre yield. Key words: Bast fibre crop, cluster analysis, discriminant analysis, genetic diversity, morphology, PCA, roselle.

Four‐Parent Maize (FPM) Population: Development and Phenotypic Characterization

To measure the effectiveness of multiparent population design in maize (Zea mays L.), an unprecedented, four‐parent maize (FPM) population was developed, incorporating a series of different mating designs. The FPM population incorporated up to three generations of intermating to allow for comparison of traditional biparental, multiparent, and multiparent intermated populations for phenotypic diversity. A total of 1291 inbred lines were evaluated per se with at least one replication among 5551 total progeny plots across two inbred trials 2013 and three inbred trials in 2014 at College Station, TX. These trials were phenotyped for days to anthesis and silking, plant and ear height, leaf rolling, and cob and kernel color (yellow endosperm, blue aleurone). Significant genetic variation was found for all traits analyzed, as well as substantial environmental variation for days to anthesis and days to silking. Overall, single replications of population entries performed well for agronomic trait analysis as indicated by low residual variation. Although mean flowering time did not show a particular relationship to specific subpopulations, greater variance was observed for plant height in some of the FPM populations than in the biparental populations. The creation of this population and the analysis of these traits serve to showcase the advantages and disadvantages of traditional and complex mating designs and reveal the potential to research agronomic and other traits within this population resource.

Circadian Rhythms and Reproductive Phenology Covary in a Natural Plant Population.

The circadian clock is a molecular timekeeper that matches endogenous rhythms in diverse traits with 24-h cycles in the external environment. Although a lack of clock resonance to the environment is detrimental to performance, clock phenotypes in wild populations nevertheless deviate substantially from the predicted optimal cycle length of 24 h, and significant genetic variation exists for circadian parameters. Here, we describe covariation between 2 traits considered to reflect adaptation to different aspects of temporal environmental heterogeneity, circadian rhythms (adaptation to daily environmental cycles) and flowering time (adaptation to seasonal cycles), in a Rocky Mountain population of the mustard Boechera stricta, a North American relative of Arabidopsis thaliana. We found that 18 families that differ in circadian period in leaf movement by 3.5 h expressed genetic diversity in first-year growth, reproductive phenology, vegetative size at reproduction, and starch concentration following vernalization. The families exhibited a large (~90-day) range in mean flowering time, even though the spatial scale of population sampling covered only a few hundred meters. Circadian period covaried with other traits such that longer-period families flowered earlier and at a larger size, a trait combination predicted to yield a fitness benefit in the wild. Circadian clock research in model systems has previously shown that mutations in clock genes influence phenology. Our results widen the scope of this research by illustrating a link between naturally segregating clock variation and reproductive phenology among wild genotypes, suggesting that the causes of genetic diversity in the clock lie partly in adaptation to seasonal environmental heterogeneity.

On the potential strength and consequences for nonrandom gene flow caused by local adaptation in flowering time.

Gene flow is generally considered a random process, that is the loci under consideration have no effect on dispersal success. Edelaar and Bolnick (Trends Ecol Evol, 27, 2012 659) recently argued that nonrandom gene flow could exert a significant evolutionary force. It can, for instance, ameliorate the maladaptive effects of immigration into locally adapted populations. I examined the potential strength for nonrandom gene flow for flowering time genes, a trait frequently found to be locally adapted. The idea is that plants that successfully export pollen into a locally adapted resident population will be a genetically biased subset of their natal population - they will have resident-like flowering times. Reciprocally, recipients will be more migrant-like than the resident population average. I quantified the potential for biased pollen exchange among three populations along a flowering time cline in Brassica rapa from southern California. A two-generation line cross experiment demonstrated genetic variance in flowering time, both within and among populations. Calculations based on the variation in individual flowering schedules showed that resident plants with the most migrant-like flowering times could expect to have up to 10 times more of the their flowers pollinated by immigrant pollen than the least migrant-like. Further, the mean flowering time of the pollen exporters that have access to resident mates differs by up to 4weeks from the mean in the exporters' natal population. The data from these three populations suggest that the bias in gene flow for flowering time cuts the impact on the resident population by as much as half. This implies that when selection is divergent between populations, migrants with the highest mating success tend to be resident-like in their flowering times, and so, fewer maladaptive alleles will be introduced into the locally adapting gene pool.

Association of mid-reproductive stage canopy temperature depression with the molecular markers and grain yields of chickpea (Cicer arietinum L.) germplasm under terminal drought

Canopy temperature depression (CTD) has been used to estimate crop yield and drought tolerance. However, when to measure CTD for the best breeding selection efficacy has seldom been addressed. The objectives of this study were to evaluate CTD as a drought response measure, identify suitable crop stage for measurement and associated molecular markers. CTD was measured using an infrared camera on 59, 62, 69, 73, 76 and 82 days after sowing (DAS) and the grain yield, shoot biomass and harvest index (%). CTD recorded at 62 DAS was positively associated with the grain yield by 40% and shoot biomass by 27% and such association diminished gradually to minimum after 76 DAS. Moreover, CTD at 62 DAS also showed similar positive association with the grain yield recorded in two previous years (r=0.45***, 0.42***). Genome-wide and candidate gene based association analysis had revealed the presence of nine SSR, 11 DArT and three gene-based markers that varied across the six stages of observation. Two SSR markers were associated with CTD through crop phenology or grain yield while the rest were associated only with CTD for computing marker-trait associations (MTAs). The phenotypic variation explained by the markers was the highest at 62 DAS. These results confirm the importance of continued transpiration and the ability of the roots to supply stored soil water under terminal drought. The selection for grain yield through CTD is done best 15 days after the mean flowering time.

Climate Change and Flowering Phenology in Worcester County, Massachusetts

Premise of research. Flowering times are sensitive indicators of climate change. This study explores important methodological issues in the use of samples of phenological records, quantifies change in flowering times, and examines causes of variability among species.Methodology. I used Monte Carlo simulations to explore effects of sample size on estimates of phenological statistics. I documented 60 yr of change in temperature and flowering times of forbs in Worcester County, Massachusetts, a largely nonurban area, using a combination of herbarium specimens and observations, and I tested several hypotheses using these data. I also compared changes in flowering times in eastern North America from several published studies.Pivotal results. Average spring temperatures increased 1.4°C (0.24°C/decade) during the last 60 yr. Mean and median flowering dates were most robust for small sample sizes, while early and late flowering dates and ranges were least stable. Mean flowering time advanced 2.9 d (0.4°C/decade), with greatest advances in early-flowering species. The predicted advance for a spring-flowering species was 4–10 d (0.6°–1.5°C/decade) using different models, corresponding to 2.5–6.3 d/°C of springtime warming. Flowering advanced more in species with shorter blooming periods than in species with longer blooming periods. Flowering advance was unaffected by a species’ native status and by whether it was locally increasing or declining. Phenological advances reported for the same species in different studies showed no significant correlation.Conclusions. Advances in flowering times were comparable to those in other north temperate studies, as was the large change in spring-flowering species. Contrary to other studies, phenological changes were unrelated to a species’ native status and to changes in species frequency. Results of simulations and comparisons across studies suggest that sampling error may contribute substantially to reported variation among species.

A 170 year spring phenology index of plants in eastern China

AbstractExtending phenological records into the past is essential for the understanding of past ecological change and evaluating the effects of climate change on ecosystems. A growing body of historical phenological information is now available for Europe, North America, and Asia. In East Asia, long‐term phenological series are still relatively scarce. This study extracted plant phenological observations from old diaries in the period 1834–1962. A spring phenology index (SPI) for the modern period (1963–2009) was defined as the mean flowering time of three shrubs (first flowering of Amygdalus davidiana and Cercis chinensis, 50% of full flowering of Paeonia suffruticosa) according to the data availability. Applying calibrated transfer functions from the modern period to the historical data, we reconstructed a continuous SPI time series across eastern China from 1834 to 2009. In the recent 30 years, the SPI is 2.1–6.3 days earlier than during any other consecutive 30 year period before 1970. A moving linear trend analysis shows that the advancing trend of SPI over the past three decades reaches upward of 4.1 d/decade, which exceeds all previously observed trends in the past 30 year period. In addition, the SPI series correlates significantly with spring (February to April) temperatures in the study area, with an increase in spring temperature of 1°C inducing an earlier SPI by 3.1 days. These shifts of SPI provide important information regarding regional vegetation‐climate relationships, and they are helpful to assess long term of climate change impacts on biophysical systems and biodiversity.

Pollination mode predicts phenological response to climate change in terrestrial orchids: a case study from central Europe

Summary Herbarium collections contain long‐term data for a wide range of taxa and provide unique opportunities to evaluate the importance of life‐history components in driving species‐specific responses to climate change. In this paper, we analyse the relationships between change in flowering dates and life‐history traits within a phylogenetic framework. The study is based on an extensive data set of herbarium specimens of orchids collected in Hungary between 1837 and 2009, supplemented by recent field observations (1980–2011). Of the 39 taxa investigated, 31 (79%) showed apparent advancement in mean flowering time. Among these, advancement was statistically significant in nine taxa. The rest (eight taxa) showed non‐significant delays in flowering. Averaging across all taxa, flowering time advanced by 3 days (3.8% of flowering period) during the last 50 years compared with the period before 1960. In taxa showing significant advancement, flowering times advanced by 7.7 days (8.6% of the flowering period). The most extreme advancement was 13.9 days. Multivariate models were used to evaluate ways in which life history may affect phenological responses to climate change. Pollination mode (i.e. deceptive vs. rewarding vs. autogamous), life span (i.e. short‐lived vs. long‐lived), biogeographical distribution type (i.e. Mediterranean vs. non‐Mediterranean) and flowering time (i.e. mean date of blooming) emerged as important factors that influence changes in flowering through time. Phylogenetic relatedness did not predict phenological response. The strongest response was observed in orchids that flower relatively early in spring, exhibit an autogamous or deceptive pollination mechanism, have a long life span and possess a Mediterranean centre of distribution. Synthesis. Our investigation demonstrates that the majority of Hungarian orchids have shifted their yearly mean flowering to earlier dates during the past 50 years. Certain life‐history traits, but not phylogenetic relatedness, were found to be important in predicting climatic responsiveness in European terrestrial orchids.

The response of flowering time to global warming in a high-altitude plant: the impact of genetics and the environment

In high-altitude habitats, an increase in temperature and greater precipitation in the form of rain represent climate changes typically associated with global warming. We determined whether phenotypic plasticity and genetic changes in the mean phenotype could affect the adaptation of flowering time to changes in the environment resulting from global warming in a montane plant species, Aquilegia coerulea James. We collected seeds from 17 plants from each of three natural populations. For each of these 51 families, we assigned 3–4 individuals to each of four water and temperature treatments. We observed phenotypic plasticity in flowering time in response to both temperature and water availability but no genetic variance or genetic differentiation in phenotypic plasticity. These results indicate that phenotypic plasticity could provide a quick response to environmental changes but provides little evolutionary potential. In contrast to phenotypic plasticity in flowering time, the mean flowering time did vary among families and among populations, suggesting a genetic basis to flowering time and adaptation in the different populations. The most likely scenario for the adaptation of this plant species to climate change is a rapid response via phenotypic plasticity followed by selection and micro-evolutionary changes in the mean phenotype.

Structure and variation of subterranean clover populations from Sicily, Italy

A collection of subterranean clover lines singled out from populations of the species Trifolium brachycalycinum and T. subterraneum collected in Sicily, Italy, was examined at two localities for flowering time and at one locality for oestrogen content and seed yield. The structure and variation of the populations of the two species were compared. The relationship between flowering time of the populations and some environmental features of their collection sites was examined to assess whether the maturity requirements of the two species were similar and to frame selection models focused on developing varieties of appropriate maturity. Populations of T. subterraneum were, on average, more complex than those of T. brachycalycinum, being characterized by higher number of lines per population and greater intra-population variation for flowering time, oestrogen content and seed yield. Furthermore, populations of T. subterraneum were, on average, about 15 days earlier than sympatric populations of T. brachycalycinum. Both the greater variation and the relative earliness of T. subterraneum occurred irrespective of the environments of origin of the populations. Inferences are drawn on the adaptive advantages that such features confer to T. subterraneum. Mean flowering time of the populations increased on increasing annual rainfall and altitude of the collection sites. However, the changes in maturity appeared almost exclusively related to variations in rainfall in T. subterraneum, while in T. brachycalycinum the effect of altitude was greater and that of rainfall less marked than in the former species.

Evolution in sown populations of subterranean clover (Trifolium subterraneum L. ) in South Australia

The seed banks of three pastures at Kingscote, Parndana and Waterloo, S.A., were sampled to determine the frequency of divergent genotypes in subterranean clover, and the direction of natural selection. The seeds were grown in nursery rows at Adelaide, and the resulting plants classified into one of the commercial cultivars, or as divergent genotypes. The divergent genotypes from one locality, Kingscote, were described in terms of 17 variables, and compared with strains collected from southern Australia and the Mediterranean basin. At each locality there was more genetic diversity than had been sown, both in terms of additional cultivars and the presence of divergent genotypes. The percentage of divergent genotypes appeared to be proportional to the age of the pasture, and was greatest at Kingscote, where it reached 67% of the population. The Kingscote genotypes were genetically related to Mt Barker and Dwalganup, only five out of 283 genotypes having leaf markings that differed from both cultivars. The 17 variables fell between the values recorded for Mt Barker and Dwalganup, and there was evidence of directional selection. For example, formononetin content was less, and genistein more than would be expected in the absence of natural selection. Mean flowering time was about equal to that of Seaton Park, and closer to Mt Barker than to Dwalganup. Flowering time was related to elevation above the lowest point in the paddock, the latest genotypes tending to inhabit sites at the foots of slopes, and the earliest genotypes sites on the tops. Seed and burr weight were slightly larger than expected. Hybridization was the most important, but not the sole source of genetic divergence at Kingscote, whereas contamination was the main source at Waterloo. It is likely that only a minority of the divergent genotypes was generated by mutation. The Australian subterranean clovers were as diverse as those from the Mediterranean. Those from Kingscote were also diverse, but, on the whole, had longer peduncles, shorter internodes and were taller than strains from other parts of Australia and from the Mediterranean basin.

Response of a Host‐Specific Herbivore to Resource Density, Relative Abundance, and Phenology

Ovipositing females of the host—specific herbivorous moth Frumenta nundinella Zeller discriminated among horsenettle (Solanum carolinense L.) plants in the laboratory and at five field populations. In laboratory experiments, the number of larvae that developed in high—density plant groups was not significnatly greater than the number that developed in low—density groups. Consequently, individual plants in low—density groups were disproportionately affected; twice as many larvae developed on them as on individual plants in high—density groups. Moths also discriminated between groups of pure horsenettle (high relative abundance) and groups of horsenettle plus another naturally co—occurring species (low relative abundance). Individual plants in high relative abundance groups had a tenfold greater infestation than did plants in low relative abundance groups. Natural horsenettle populations varied in density, relative abundance, plant size, and fruit production. Plant size, fruit production, and population density were all positively correlated, so the populations with the greatest density had the largest plants, which produced the most fruits. Despite differences in these plant parameters among sites, the extent of infestation differed little, except for one site that lacked parasitoids that attack F. nundinella. Infestation within field sites was heterogeneous among plants. Virtually all large plants (those with @> 15 fruits), but only about half the small plants (those with < 15 fruits), became infested (one or more infested fruit per plant). However, a greater proportion of the fruit crop was infested on small plants than on large plants. Large plants remained in flower an average 2.5 wk longer than did small plants, so a smaller proportion of their flowers was available during the short period of high oviposition risk. Because of the short oviposition period, plants that flowered earlier or later than the mean flowering time of their populations appeared to have lower infestations than did plants that flowered close to the population means.

Quantitatively inherited variation in Arabidopsis thaliana induced by chemical mutagens

The effect of chemical mutagens on morphological and quantitatively inherited characters was studied, using an early flowering race of Arabidopsis thaliana, and compared with a similar study using ionizing radiations. All mutagens induced genetic variation and shifts in mean for flowering time and plant weight. Examination of the plants which were not morphologically mutant revealed substantial induced genetic variation and shifts in mean flowering time and a small amount of variation for plant weight. Selection responses were achieved for both early and late flowering. The response, however, was skewed towards lateness. There were negative phenotypic and genotypic correlations between the induced flowering time and plant weight variation in the M 2 generation. The mean plant weight of the late flowering selections was reduced to a greater extent than that of the early flowering selections. Single gene mutations for both early and late flowering occurred. No overall response to selection for increased growth rate occurred, but individual lines with increased plant weight were selected. The increased plant weight of the most extreme selection was not due to increased growth rate. Comparable amounts of genetic variation were induced by EMS, gamma rays and thermal neutrons, but larger responses to selection and realized heritabilities followed EMS treatment. The most extreme mutants for lateness were selected after EMS treatment, for earliness after thermal neutron treatment and for plant weight after EMS and gamma ray treatment. These results support the hypothesis that mutagenic treatment by either chemical mutagens or ionizing radiations results in an increase in variance for quantitatively inherited characters which can be utilized by selection. They also indicate that the mean of a character not subjected to selection will be determined by its previous selection history and any genetic correlation existing between it and the character under selection.

Acceleration of Flowering of Statice (Limonium sinuatum Mill.) by Gibberellic Acid (GA3)1

Abstract Single applications of 500 ppm GA3 on ‘Iceberg’ and ‘Midnight Blue’ statice made at 87, 101 and 115 days after seeding reduced mean flowering time 90, 72, and 45 days, respectively, compared to unsprayed plants. Applications made 129 days after seeding had no significant effect on flowering. Repeated sprays were not beneficial and, in some cases, delayed flowering as compared to single applications.

Genetic Variability in Medicago lupulina L. across a Valley in the Weka Pass, New Zealand

Summary Seed was harvested from plants of Medicago lupina L. from ten sites on a transect across a small valley in the Weka Pass, New Zealand. The transect ran from the top of the shady slope to the top of the sunny slope and included marked variation in topography and soil moisture. Approximately ten plants were taken from each site, and twenty seedlings from each plant were raised in boxes and transplanted to the field in a randomised block layout. Flowering time and mean weight per seed were recorded for each plant. There were no significant differences between sites in mean flowering time or seed weight, indicating that no genetic differentiation had taken place for these characters. This was in contrast to an earlier study of flowering time which, when re-analysed showed the between-localities component to be a major contributor to total variance, where populations were collected from widely scattered localities in the South Island of New Zealand. Total variances for flowering time were higher for si...

EFFECTS OF MUTATION FOR PHOTOPERIODIC RESPONSE ON TOBACCO PLANT DEVELOPMENT IN ISOGENIC LINES

Crosses were made between the flue-cured tobacco cultivar Delcrest and a short-day line, Mammoth Delcrest G.5, developed from a spontaneous mutation in Delcrest. Four sets of crosses were used, each set consisting of six genetic populations, viz. P1 (Delcrest), P2 (Mammoth Delcrest G.5), F1 (P1 × P2), F2 (F1 selfed), B1 (F1 × P1), and B2 (F1 × P2). The data observed on flowering time were in good agreement with the postulated monofactorial segregation of normal (day-neutral) against short-day plants, the latter being homozygous recessive. The mean flowering time of the first filial generation was very close to the Delcrest parent but the difference was still significant. The mutant gene apparently had no differential effect on the dimensions of the bottom and mid-stem leaves, but towards the top of the plant incomplete dominance was indicated for both the width and length of the leaves.