Genetic control of photoperiodic sensivity and maturity in spring wheat within narrow limits of adaptation

Summary Photoperiodic respose, as assessed by a regression technique, exhibited complete dominance averaged over the crosses of an eight parent diallel in the vernalized condition. Photoperiodic response as final leaf number for the vernalized 8-hour photoperiod diallel was closely related to photoeriodic response of the regression method. However, the diallel analyses of both sets of data showed little agreement in terms of respectieve array positions.The inheritance of photoperiodic response in diallels using regression values showed little agreement between the vernalized and unvernalized conditions. This difference was postulated to be due to interaction of vernalization and photoperiodic response in the unvernalized situation. In the unvernalized condition photoperiodic response exhibited non-allelic interaction, attributable mainly to the cultivar Pinnacle in general behaviour in its crosses. Its removal gave a situation of high average dominance for photoperiodic response with a clear indication that high photoperiodic sensitivity was dominant to comparative insensitivity.Days to ear emergence (vernalized and 18-hour photoperiod) exhibited non-allelic interaction in its expression, due mainly to the general behaviour of the cultivar Pinnacle in its crosses. Removal of its array gave a situation of a moderately strong degree of overdominance in the expression of days to ear emergence. Maturity differences amongst parents and F₁'s, vernalized and under 18-hour photoperiod, are postulated to be due to a factor other than vernalization or photoperiodic response beheved to be growth temperature in differentially in fluencing growth and/or developmental rates between genotypes.     

Effect of Temperature and Photoperiod on the Development of Lupinus albus L. in a Controlled Environment

An experiment to determine the effect of temperature and photoperiod on Lupinus albus under controlled environmental conditions was carried out, using the three Lupinus albus genotypes 'Tifwhite', 'Esta' and 'Kiev', and three temperature (10/20, 18/28 and 20 °C continuously) and two photoperiod (8 and 16 h daylength) regimes, in all combinations. Half of the seeds were vernalized for 21 days at 4 °C to alleviate the obligate vernalization requirement of Tifwhite. Although Esta and Kiev do not have obligate vernalization requirements, they were influenced by this vernalization period. Observations included the duration of the period from planting to seedling emergence, the duration of the period from planting to the beginning of flowering and the duration of flowering. The vernalization treatment accelerated plant development in all genotypes. The period from planting to emergence was shorter under the higher temperature regime. For all genotypes, the period from planting to flowering was shorter under the longer photoperiod, the same trend as would be expected for long-day plants. Duration of flowering periods were, in contrast to pre-flowering periods, shorter for all genotypes at cooler temperatures. The results of this study confirm that photoperiod does contribute to the growth period from planting to flowering in L. albus and that this species does behave as a long-day plant.     

Induction of Generative Development of Winter Rape (Brassica napus L. var. oleifera) in Relation to Vernalization Conditions and Age of Vernalized Plants

Germinating seeds and young winter rape plants were vernalized 56–63 days at 5 or 2°C under nine-hour days or in darkness. The highest percentage of generative plants and the most rapid flowering were obtained following the vernalization of young seedlings and germinating seed under conditions of nine-hour day, at 5°C. The least effective induction of generative development followed the vernalization at 2°C in continuous darkness. The vegetation period from the end of vernalization till the beginning of flowering was the shortest when four-week-old plants were vernalized under conditions of nine-hour day, yet the vegetation period from the beginning of germination to flowering was the shortest when seed germinating under conditions of nine-hour day were vernalized. The period was extending as older plants were being vernalized. Data indicating that the optimal temperature for vernalization of older plants is higher than for germinating seed and young seedlings were obtained.     

Vernalization of immature embryos of winter wheat genotypes

Summary The effect of direct vernalization of immature embryos on flowering was studied in six winter wheat genotypes. Fourteen-, 17-, and 20-day-old embryos were excised and vernalized for 0–6 weeks on synthetic medium during a conditioning period. Percent germination of embryos was high (overall 96.1%), and free from genotypic effects. Genotypes differed for flowering in response to cold treatment of excised embryos. Embryo vernalization was as effective as or more than conventional vernalization (control, seedling vernalization for 6 weeks). Seventeen-day-old embryos were the most responsive to vernalization. With a 5-week vernalization of 17-day-old embryos, the percentage of plants anthesed was higher than those from 14-and 20-day-old embryos. For 17-day-old embryos vernalized for 5 weeks, the mean number of days from culture to anthesis was less than that of 6 week vernalization, less than that of 14- and 20-day-old embryos, and less than controls.Purdue Univ., Agronomy Dept., W. Lafayette, IN 47907, USA.     

Measurement of response to vernalization in Australian wheats with winter habit

Summary Development in wheat is strongly controlled by sensitivity to vernalization and photoperiod, and to a lesser degree by non-vernalizing temperature and intrinsic earliness. A method to measure effect of vernalization in wheats with winter habit is described. Twenty seven wheats with winter habit and eight with spring/facultative habit were studied, comprising breeding lines and cultivars with maturities suited to south-central New South Wales. Effect of vernalization on the development of these wheats was quantified by integrating responses to vernalizing treatments of differing duration. Intrinsic earliness was measured as time for vernalized seedlings to grow to ear emergece in an 18h photoperiod with day/night temperature of 21/16°C, and response to photoperiod as the difference in time to ear emergence between 9 and 18h daylengths. Integrated response to vernalization is sensitive to both cumulative and thresh-hold responses and is applicable to wheats of all habit type. Integrated response to vernalization and intrinsic earliness were positively associated within wheats with winter habit. Wheats were largely of restricted origin, so that there were few allelic differences at Vrn loci to disrupt this association, which suggests intrinsic earliness may modify response to vernalization. Though integrated response to vernalization was measured with artificial treatments, it was strongly associated with ear emergence for wheats with winter habit when grown at a site in New South Wales.     

Photoperiod and vernalization response of wheat under controlled environment and field conditions

Characterization of large numbers of breeding lines for vernalization and photoperiod response in wheat is needed to enhance adaptation. A total of 20 wheat lines were evaluated for response to vernalization and photoperiod under two controlled environments and high ambient air temperatures under field conditions. Vernalized and non-vernalized seedlings were transplanted into pots and placed in three photoperiod (8, 12 and 16 h of light) cabinets, in the greenhouse or in growth chambers. Days to anthesis decreased with increasing photoperiod. Vernalized plants flowered earlier than non-vernalized. There was a significant correlation between days to anthesis in the greenhouse and the growth chamber (r = 0.88, P < 0.001). Basal vegetative period, effect of vernalization and photoperiod from the two screening techniques were positively correlated with each other. Growth habit, vernalization requirement and heading date in the field were highly correlated with the main effect of vernalization in the two controlled environments. The results indicate that selection for vernalization response in a large number of genotypes can be achieved under high ambient air temperatures in the field and the selected material can subsequently be screened for photoperiod response under greenhouse conditions.     

Effect of embryo age and culture media on plant growth and vernalization response in winter wheat

Summary Embryo age and composition of nutrient medium affected plant growth and response to vernalization in winter wheat (Triticum aestivum L.). Root and shoot development was more in older than in younger excised embryos, and more in a medium without kinetin than in one with kinetin. Kinetin (2 mg/l) in the medium did not accelerate vernalization, probably because it tended to inhibit seedling and plant growth.Embryo age and media did not completely replace vernalization. Twenty- and 16-day-old embryos responded by flowering after 4 weeks of vernalization. Among plants raised on a standard medium from 20-day-old embryos and vernalized for 4 weeks, 84.2% flowered by or before 50 days after transplanting. Time from embryo culture to heading for 20-day-old embryos with-4-week vernalization averaged 84.6 days. Immature embryos (16–20 days old) needed only 4 weeks of vernalization compared to 6 weeks for mature embryos. Excised embryos could be vernalized as efficiently as seedlings raised by embryo culture. Embryo culture at 16–20 days after anthesis coupled with 4-week cold treatment shortens generation time of winter wheat by about 40 days.Contribution No. 82-131-j, Department of Plant Pathology, Kansas Agricultural Experiment Station, Manhattan, KS 66506, USA.     

Genetic analysis of flowering and maturity time in high latitude spring wheat

Due to the short growing season in the high northern latitudes, the development of early maturing spring wheat (Triticum aestivum L.) cultivars is important to avoid frost damage which can lower production and quality. We investigated earliness of flowering and maturity, and some associated agronomic traits, using a set of randomly selected high northern latitude adapted spring wheat cultivars (differing in maturity) and their F₁ and F₂ crosses made in a one-way diallel mating design. The parents, and their F₁ and F₂ crosses were evaluated under field conditions over 2 years. Anthesis and maturity times were controlled by both vernalization response and earliness per se genes, mainly acting additively. Non-additive genetic effects were more important in controlling grain fill duration, grain yield and plant height. Additive × additive epistatic effects were detected for all traits studied except time to anthesis. Segregation analyses of the F₂ populations for time to anthesis indicated the presence of different vernalization response genes. Molecular genetic analyses revealed the presence of Vrn-A1 and Vrn-B1 genes in the parental cultivars. Narrow-sense heritability was medium to high (60–86%) for anthesis and maturity times but low to medium (13–55%) for grain fill duration, plant height and grain yield. Selection for early flowering/maturity in early segregating generations would be expected to result in genetic improvement towards earliness in high latitude spring wheats. Incorporation of the vernalization responsive gene Vrn-B1 in combination with vernalization non-responsive gene Vrn-A1 into spring wheats would aid in the development of early maturing cultivars with high grain yield potential for the high latitude wheat growing regions of the northern hemisphere.     

Pollen viability and stigma receptivity in <Emphasis Type="Italic">Lilium</Emphasis> during anthesis

Pollen viability and stigma receptivity are prerequisites for successful pollination and seed set in flowering plants. In this study, the pollen viabilities and stigma receptivities of nine Lilium genotypes (six cultivars and three species native to China) were assayed by in vitro pollen germination and the benzidine-H₂O₂ method, respectively. Embryo sac development during anthesis was observed to further ensure the timing of controlled pollination. In addition, the relationship between stigma secretion and stigma receptivity was studied to estimate the pollination time based on phenotype. Anthers cracked on the day of flowering in all genotypes, but pollen germination during anthesis was not observed in Asiatic hybrids excepted for ‘Tiny pudhye’, which exhibited low pollen viability for a short period of time (from 0 to 1 day after anthesis). In the other genotypes, pollen germination rates were highest on anthesis (five of seven genotypes), 0–1 day after anthesis (L. sulphureum), or 0–2 days after anthesis (one Longiflorum hybrid), and then gradually decreased with days after anthesis. While, stigma receptivity first increased and then decreased during anthesis. For most genotypes, stigmas began to be receptive 1 day after anthesis, and all genotypes exhibited stigma receptivity at 2 days after anthesis. The durations of stigma receptivity and strongest stigma receptivity, were genotype dependent, and were 5–8 days and 1–4 days, respectively. Moreover, on the first flowering day, 6 of 7 genotypes had mature embryo sacs, and at the time at which stigmas began to be receptive, all tested genotypes had mature embryo sacs. Some Lilium genotypes showed stigma secretion, which can be a sign of stigma receptivity. Stigmas became receptive and reached highest receptivity within 1 day of the first appearance of secretion on the surface of the stigma and at peaking, respectively. The results of this study are valuable for the implementation of successful Lilium breeding programs.     

Validation of the two-gene epistatic model for vernalization response in a winter × spring barley cross

A two gene epistatic model in which a dominant “winter growth habit” allele at Vrn-H2 encodes a repressor with a corresponding binding site in a recessive vrn-H1 allele explains the vernalization response phenotypes in an array of barley germplasm. In order to validate the model genetically, we developed an F ₂ population (and F ₂-derived F ₃ families) from the cross of Hardy (winter) × Jubilant (spring). Using gene-specific primers, we determined the Vrn-H1 and Vrn-H2 allele architecture of each F ₂ plant and we measured the growth habit phenotype of each F ₂ plant via phenotyping of its F ₃ progeny under controlled environment conditions. We used a set of treatments involving plus/minus vernalization under long photoperiod and vernalization under short photoperiod. Alleles at the two loci showed expected patterns of segregation and independent assortment. Under long day conditions, the two Vrn genes were the primary determinants of heading date, regardless of the vernalization treatment. Under short photoperiod, the effects of these loci were not significant. There was incomplete dominance at Vrn-H1: heterozygotes were significantly later to head than Vrn-H1Vrn-H1 genotypes. Vrn-H2 genotypes were also significantly later to head, even when plants were vernalized. These results validate the two-gene epistatic model for vernalization response under long-day conditions. The results under short photoperiod, and the variance in flowering with vernalization, confirm that while the two Vrn genes are the primary determinants of vernalization response, they are part of a larger interactome that determines the timing of the vegetative to reproductive transition.     

Observations of Effects of Partial Vernalization in Winter Rape Plants Grafted Onto Generative Stock

Winter rape plants vernalized under natural conditions were used as stock for grafting apical and subapical parts of rape seedlings vernalized at 5 °C in light during different periods ranging from 0 to 10 weeks. Acceleration of generative development in both kinds of grafts occurred already after 3 weeks of their vernalization, i.e. after cold treatment of insufficient length to induce flowering in plants developing independently. Effectiveness of vernalization — measured by acceleration of flowering in grafts was highest from 3rd to 5th week of cold treatment and then it declined. Processes occurring during an early stage of vernalization, though insufficient to allow independent generative development, become manifest in grafts made on vernalized stock. This allows investigations of very early stages of vernalization processes inaccessible to observation by other methods.     

油菜中内源赤霉素嫁接转移研究

在温室条件下, 将未春化的油菜接穗分别嫁接在已春化和未春化油菜砧木上, 结果已春化 油菜砧木上的接穗植株很快开花, 而未春化砧木上的接穗植株不能开花。 其主要原因是已 春化油菜砧木内源赤霉素含量高, 并传递到接穗有关。     

Comparison of Vernalization Requirements and Frost Resistance of Winter Rape Lines Derived from Double Haploids

Vernalization requirements and cold resistance of 13 lines of winter rape derived from doubled haploids obtained by androgenesis were investigated. The degree of vernalization requirements was examined in two parallel experiments. In the first experiment seedlings aged 2 weeks were vernalized during 63 and 35 days under controlled conditions, at 5 °C. In the second experiment the natural conditions of vernalization were differentiated by sowing the plants at four different dates in spring: March 15th, April 15th, May 15th, and at the latest date excluding vernalization, June 5th. The lines examined revealed differentiation of vernalization requirements that were similar in both experiments; all the lines required a period of exposure to cold before flowering. Cold resistance of lines was estimated in two successive series at −15 °C and −17 °C. Before testing the plants were kept in natural field conditions from the beginning of September until the middle of November. Testing of cold resistance was preceded by hardening under controlled conditions. Considerable differences in cold resistance was found in the forms investigated.
The results obtained do not show any relation between frost resistance and the degree of vernalization requirements, as the line characterized by the strongest winter habit of growth showed low cold resistance, whereas the lines which were closer to spring growth habit showed the highest level of cold resistance; the lines with the least vernalization requirements revealed the highest level of cold resistance. This conclusion can be confirmed by the significance of the correlation coefficients between the various indices defining the frost resistance and the indices of vernalization requirements.     

Developmental responses to vernalization in wheat deletion lines for chromosomes 5A and 5D

The aim of this investigation was to test the developmental patterns of deletion lines, generated for chromosome arms 5AL and 5DL in the variety ‘Chinese Spring’ (CS) under vernalized and non‐vernalized treatments. Plants were grown in controlled conditions under saturating daylength. Time to heading and the duration of particular phases before flowering were recorded, and leaf and spikelet production rates and numbers were analysed. The lines lacking Vrn‐A1 and Vrn‐D1 were delayed in time to heading under non‐vernalized conditions, because of the lengthening of the emergence to floral initiation phase (EM‐FI) and the terminal spikelet to heading phase (TS‐H). Differences in final leaf numbers corresponded to longer durations of the EM‐FI phase. The absence of Vrn‐A1 and Vrn‐D1 apparently decreased the number of spikelets by a lower primordium production rate, even though the duration of the FI‐TS phase was longer or equal to CS. The sensitivity to vernalization in lines where the Vrn genes were deleted was much higher.     

Vernalization response of domesticated × wild chickpea progeny is subject to strong genotype by environment interaction

Vernalization insensitivity is a key feature of domesticated chickpea, and its genetic basis is not well understood. We studied vernalization response among hybrid progeny derived from two domesticated × wild crosses. The wild parents are vernalization‐sensitive, late‐flowering genotypes while both domesticated parents are vernalization insensitive. Parental lines and hybrid progeny were tested with (28 days at 4°C) and without vernalization (control). The difference in mean days to flower (?DTF) between control and vernalization treatments was used to assess the flowering vernalization response. A wide range of ?DTF values was observed among the hybrid progeny. Strong genotype by environment interaction effect on ?DTF was observed for the parental accessions and hybrid progeny. We used the ?DTF values to select vernalization responsive and non‐responsive progeny lines. However, the genotype × environment interaction strongly interfered with our selection. Chickpea breeders interested in using the wild progenitor as a donor of exotic traits should be aware of the possibility of introducing vernalization response alleles that may alter the phenology of their breeding materials in an unpredictable manner.     

Flowering time in wheat (Triticum aestivum L.): a key factor for global adaptability

Wheat is one of the most widely cultivated crops and, being the staple diet of more than 40 countries, it plays an imperative role in food security. Wheat has remarkable genetic potential to synchronize its flowering time with favourable environmental conditions. This ability to time its flowering is a key factor for its global adaptability and enables wheat plant to produce satisfactory grain yield under very diverse temperature and soil moisture conditions. Vernalization (Vrn), photoperiod (Ppd) and earliness per se (Eps) are the three genetic systems controlling flowering time in wheat. The objective of this review is to provide comprehensive information on the physiological, molecular and biological aspects of the three genetic constituents of flowering and maturity time in wheat. Reviews written in the past have covered either one of the aspects; and generally focused on one of the three genetic constituents of the flowering time. The current review provides (a) a detailed overview of all three gene systems (vernalization, photoperiod and earliness per se) controlling flowering time, (b) details of the primer sequences, their annealing temperatures and expected amplicon sizes for all known markers of detecting vernalization and photoperiod alleles, and (c) an up to date list of QTLs affecting flowering and/or maturity time in wheat.     

Multivariate analysis of traits determining adaptation in cultivated barley

Thirty‐nine barley varieties of different origin, representing different growth types, were included in a series of experiments aimed at analysing the variability in vernalization response, photoperiod sensitivity and earliness per se and establishing the types of ecoclimatic adaptability using multivariate analysis. In the case of spring barley varieties there was no correlation between any of the three traits. For winter barleys, a negative correlation was found between photoperiod sensitivity and vernalization response and between photoperiod sensitivity and earliness per se. Vernalization response and earliness per se showed a positive correlation. Among the winter barley varieties large variations were apparent in photoperiod sensitivity, vernalization response and earliness per se, which resulted in a tremendous variation in flowering patterns and frost tolerance. Between the spring barley varieties only wider variations in photoperiod sensitivity were detected. Based on the cluster analysis, the 39 varieties could be separated into seven groups. The spring barley varieties were placed in two groups, and the winter barleys in five groups representing different adaptational types. Among these five groups two represented the two opposing extreme combinations of photoperiod sensitivity and vernalization response. The combination of large photoperiod sensitivity and no vernalization response resulted in better frost tolerance than did the combination of photoperiod insensitivity and large vernalization response.     

Intrinsic earliness and basic development rate assessed for their response to temperature in wheat

The related concepts of basic vegetative period, intrinsic earliness and basic development rate in wheat are examined. These concepts have the common assumption that, if plants are vernalised fully and then grown at long daylength in order to remove any responses to vernalisation and photoperiod, the calendar or thermal time then taken to anthesis will be a characteristic of a genotype that will be heritable. Thus, regardless of temperature, early genotypes will always be earlier than late genotypes (providing there are no vernalisation and photoperiod responses).Using four genotypes, exposed to 50 days of vernalisation, and then grown at 18 h photoperiod under six temperature regimes ranging between 10 and 25°C, it is shown that; (1) no genotype had an absolute basic period as, depending on temperature, durations to anthesis for any one genotype varied by more than 50 days; (2) no genotype had an absolute value for intrinsic earliness (to anthesis), ranging for any genotype by more than 300°Cd depending on temperature; (3) basic development rate was not a single value for a genotype but varied with stage of development; (4) some genotypes changed their ranking for earliness depending on the temperature regime; and (5) genotypes were differentially sensitive to temperature for the subphases prior to anthesis.     

Flower induction in seedlings of Aster novi-belgii and selection before and after vegetative propagation

Bolting and flowering of Aster novi-belgii seedlings as well as correlations between characteristics within seedling populations and between seedlings and their vegetatively propagated offspring were investigated in order to improve breeding efficiency. In seedlings of A. novi-belgii, flower induction was observed without vernalization. Seedlings initially formed a rosette, but bolting was a prerequisite for development of a normal flowering shoot. Bolting was promoted by long photoperiods as compared to short days. The shortest time from sowing to anthesis was recorded when plants were grown under long photoperiods until the main stem was at least 5 cm long, and then moved to short photoperiods. A large variation in time to anthesis, plant height, branching ability, and flower size and color was found among the seedlings within all crosses. Magnitude and significance of correlations between some characteristics varied among crosses. The more consistent correlations seem mainly to be due to natural courses of plant growth and development. High correlations between seedling characteristics and their vegetatively propagated offspring were only found for flower hue. Lower, but significant correlations were found for flower color intensity, plant height and branching ability. There were no significant correlations for the time-to-anthesis between the two groups of plants. This revised version was published online in July 2006 with corrections to the Cover Date.