Late-flowering Strains Research Articles

The Influence of Temperature Upon Physiological Processes in Early-Flowering and Late-Flowering Strains of Thlaspi arvense L.

This study was initiated to determine net photosynthesis, respiration, and stomatal conductance for early-flowering (EF) and late-flowering (LF) strains of Thiaspi arvense L., and to determine the relative impact of temperature on these processes in the two strains. The strains have been shown to differ by a single gene. Vernalized EF and LF plants were grown under controlled environments at day temperatures of 1 50C, 200C, and 250C (1 6-h photoperiod) each, with 1 50C nights. During the period of floral initiation for the EF strain, net photosynthesis, respiration, and stomatal conductance were determined in both strains. Plants of the LF strain had higher net photosynthesis rates and lower respiration rates. Net photosynthesis was most efficient at 200C days, while respiration rates increased with increasing temperature. Stomatal conductance was greater in the EF strain, which also had larger stomata than plants of the LF strain. Generally, EF plants grew more quickly in terms of shoot dry weight than LF plants. However, at 250C, the LF plants had significantly more shoot dry weight. We suggest that differential net photosynthesis and respiration rates of the EF and LF strains of T. arvense may influence the relative amounts of carbohydrates and nitrogen available to the shoot apices and therefore affect the time to floral transition.

Maternal Environment Effects on Plant Growth and Germination of Two Strains of Thlaspi arvense L.

The influence of maternal environment on plant development and seed germination of early- and late-flowering strains of Thlaspi arvense L. was studied. Compared to plants grown at 30^⚬/10^⚬C, those grown at 15^⚬/10^⚬C and 20^⚬/10^⚬C flowered more slowly, were shorter, and grew fewer leaves; seed production, however, was greatest at 20^⚬/10^⚬C. Plants of the late-flowering strain produced more leaves than those of the early-flowering strain, but there were no differences between strains in vegetative dry weight or height at harvest. On average, fresh seeds from plants of the late-flowering strain germinated at a faster rate than those from plants of the early-flowering strain. Seed dormancy increased with increasing temperature in which they developed, thus explaining some of the differences reported in the literature regarding germination of fresh seeds of T. arvense. The evolutionary implications of these results are discussed in relation to the single gene differences between the two strains.

Influence of Emergence Date and Strain on Phenology, Seed Production, and Germination of Thlaspi arvense L.

Plants of Thlaspi arvense L. flowered over a long period of time during summer. Plants of the early-flowering strain (EF) that emerged in the fall and overwintered flowered first, followed by overwintered plants of the late-flowering strain (LF). About 1 mo later, plants of both EF and LF strains that germinated in the spring began to flower Spring-emerging plants grew taller and had more branches but fewer lateral shoots than plants that had overwintered. In addition, the spring-emerging plants produced larger numbers of smaller seeds with no difference in total seed dry weight. LF plants grew taller than those of the EF strain. Under field conditions, seeds from these plant sources had their highest germination rates the first fall. In subsequent years, germination rates were greatest in spring with a secondary peak in the fall and little germination during the summer. Also, seeds from LF plants germinated at a faster rate than did those of the EF strain over a 3-yr period. Strain and germination period...

Studies on the Flowering of Thlaspi arvense L. IV. Genetic and Ecological Differences between Early- and Late-Flowering Strains

The genetic difference between early-flowering (EF) and late-flowering (LF) strains of Thlaspi arvense was investigated by crossing the two strains under controlled conditions. All of the F1 plants were of the LF phenotype. Self-pollination of the F1 and a backcross to the EF parent gave progenies having phenotypic LF/EF ratios of approximately 3:1 and 1:1, respectively. We concluded that the difference between the two strains was determined by a single gene, with complete dominance of the LF allele. Progeny testing of natural populations showed that both strains occurred in populations which germinated in the spring or which overwintered as vegetative rosettes after germinating in the fall. In these populations, however, the majority of the plants were of the LF genotype, whereas progeny of summer-emerging populations were all of the EF strain.

Studies on the Flowering of Thlaspi arvense L. III. The Influence of Vernalization Under Natural and Controlled Conditions

Field observations on the flowering of early-flowering (EF) and late-flowering (LF) strains of stinkweed (Thlaspi arvense L.) showed that all of the spring-germinating population had the EF phenotype. Their progeny, however, when grown under controlled conditions, were predominantly of the LF strain, indicating that expression of the LF genotype had been prevented by natural vernalization in the field. Approximately 10%-20% of the parent plants had progeny in which both strains were represented and provided a measure of the extent to which crossing between the two strains may occur. Cotyledon-stage seedlings, planted in the field in October, showed no difference in winter survival and flowered concurrently in the spring, expression of the LF genotype having been completely eliminated. Vernalization of seeds of the LF strain for 6 wk at 2 C had the greatest effect when started 48 or 96 h after the start of germination; vernalization at earlier or later stages of development was much less effective. With only 2 wk of vernalization flowering occurred first on lateral shoots, but with a 4-wk treatment most plants flowered first at the main shoot apex. The appearance of a flower first on a lateral branch was correlated with the developmental stage at vernalization and was associated with a delay in flowering at the apex of the main shoot.

Studies on the Flowering of Thlaspi arvense L. II. A Comparative Study of Early- and Late-Flowering Strains

A comparison of genetically distinct early- and late-flowering strains of stinkweed (Thlaspi arvense L.) showed that, when seedlings of each type were planted in the field at monthly intervals, differences in their rate of flowering were correlated with the planting date. Seedlings which emerged naturally in the spring all showed the early-flowering phenotype, but those emerging during the summer comprised both the early-flowering strain, which flowered within a few weeks, and the late-flowering strain, which remained vegetative until the end of the season. The two strains were readily distinguished by characteristic differences in leaf shape. Experiments conducted under controlled conditions indicated that the differences in their flowering behavior could be attributed mainly to temperature effects. These experiments showed that increasing either the day or night temperature accelerated flowering and reduced leaf number of the early-flowering genotype but delayed flowering and increased leaf number of plants of the late-flowering strain. Vernalization (2 C for 2-4 wk) also induced earlier flowering of the late-flowering strain. Germination of freshly harvested seed of both strains was 95%-100% at a 12-h 10-25-C temperature alternation and was strongly promoted by exposure to light. A constant 25-C temperature discriminated between the two genotypes, giving about 45% germination of the early-flowering plants while completely preventing germination of the late-flowering strain.

Nitrogen response of pasture grasses on duplex soils formed from granite in southern Queensland

The response to fertilizer N of native pasture containing black spear grass (Heteropogon contortus) and of buffel grass (Cenchrus ciliaris cv. Biloela) was measured on granitic soils at the Narayen Research Station, in southern Queensland. Experiments were carried out in grazed and ungrazed areas. In 1968-69, which was as dry as any year on record for this district, neither pasture responded to N; in wetter years both did, the native pasture giving a lower yield than the sown buffel grass pasture. Grazed areas that received 168 kg N ha-1 year-1 as urea did not respond to further additions. Analysis of buffel grass yields over intervals of 8 to 16 weeks during the growing season indicated that 1. there was no growth or response to N unless the rainfall exceeded about 30 mm, 2. above 30 mm the response to near-optimum rates of N increased with rainfall, 3. buffel grass grown with such rates of N produced more than four times as much DM per unit rainfall as buffel grass without added N when 100 mm of rain fell. Examination of rainfall records suggested that there is a high probability of worthwhile responses to N on these soils at Narayen.Spear grass and other native grass plants were killed by high rates of N during the first, dry season. The results of a pot trial with Biloela buffel grass and a late flowering strain of spear grass showed that N increased drought damage in both grasses but spear grass was more susceptible than buffel grass.

Studies on the Flowering of Thlaspi arvense L. I. The Influence of some Environmental and Genetic Factors

When seedlings of Thlaspi arvense were grown in the greenhouse, some flowered within 30-50 days while others grew as leafy rosettes for 90-150 days before flowering occurred. The early-flowering plants produced only early-flowering progeny, whereas the late-flowering plants had progeny of both types. Experiments under controlled conditions (16-hr days at 15 C) confirmed these results and also showed that seed from summer annuals produced only early-flowering plants while in the progeny from winter annuals both types were represented. The existence of genetically distinct early- and late-flowering strains is indicated by these results, but their phenotypic expression under field conditions and their relation to the summer and winter annual habit require further investigation. Seedlings of the early-flowering strain were grown at photoperiods of 8 and 16 hr combined factorially with nitrogen levels of 5.25 and 210 ppm. Flowering occurred under both day lengths but was significantly accelerated by the longer photoperiod. Increasing the nitrogen supply delayed flowering under long days but promoted it under short days. The number of leaves produced prior to flowering was increased to a similar extent either by increasing the nitrogen supply or by reducing the day length. This result and the additional observation that short-day effects could be simulated by reducing the light intensity suggest that for this species the C/N ratio may be significantly involved in the mechanism of flowering control.

Flower initiation in pasture legumes. IV. Flower initiation in Trifolium pratense L.

An early strain (Cowgrass) and a late-maturing strain (Montgomery) of red clover (Trifolium pratense L.) were grown at Melbourne, lat. 38°S., to study flower initiation and the relationship between initiation and flowering, because of the importance of flowering to the use of the species as a source of hay. The terminal inflorescence in red clover arises from a lateral bulge at the shoot apex, and the main shoot of the plant is strongly vegetative, only becoming reproductive in a proportion of plants under long photoperiod, particularly continuous light. In both strains, whether first-year or older plants, flower initiation and therefore flowering were confined to a short period of the year, the early strain having the longer period. Sowing the two strains at intervals through the year in the field, under natural and long photoperiods, showed the importance of both photoperiod and temperature to initiation. Both strains were hastened by a long photoperiod whatever the temperature, and initiated at a similar low leaf number, but the early strain was able to initiate at a shorter photoperiod than the late one. Seed vernalization had almost no effect; but at photoperiods of 14 to 11 hr, high temperatures strongly retarded Cowgrass and appeared to prevent initiation in Montgomery. The capacity of Cowgrass to initiate at a shorter photoperiod and at higher temperatures than Montgomery explains its longer flowering season in temperate latitudes. These genetic differences suggest that an appropriate environment can be used to differentiate early and late-flowering strains for seed certification, and that late strains would stay vegetative at low latitudes and would therefore be less useful as a source of hay than early ones.

The liability of seed crops of perennial ryegrass (Lolium perenne) to contamination by wind-borne pollen

Some aspects of intervarietal crossing in Lolium perenne have been studied.Using a number of experimental designs with non-red plants as the tester variety, results have been obtained as to the effects of isolation distance on intervarietal crossing.In all cases contamination decreases rapidly, at first with increasing distance, but there is a progressive reduction in the rate of decrease produced by repeated increases in isolation distance. The actual rate of decrease varies with the number and arrangement of plots.The effect of intravarietal pollen in reducing intervarietal crossing appears similar to that of distance in its mode of action. Within short distances from the contaminant, additional rows of intervening plants are highly effective in reducing contamination. This suggests that pollination within a population of plants occurs chiefly between neighbouring plants.The flowering periods of the different strains of Lolium perenne and L. italicum overlap to varying degrees. Several early strains flower at the same time, e.g. British commercial, New Zealand Certified Mother Seed and Station-bred S24 perennial rye-grass; others, such as Kentish indigenous perennial ryegrass and strains of L. italicum, which are intermediate in date of flowering, overlap with both the early- and late-flowering strains.Intervarietal crossing is considerably reduced when varieties which differ widely in date- of flowering are grown in close proximity to one another, but even in the case of extreme early and late strains some spatial isolation, or discarding of border rows, is necessary for maintaining varietal purity.In certain instances when seed crops of early-flowering strains are endangered by late-flowering plants growing in adjoining leys, satisfactory isolation may be achieved through cutting back the contaminant crop just before flowering. When seed crops of late-flowering strains are grown alongside leys containing early-contaminant varieties, cutting back should be delayed until a few days prior to commencement of flowering in the seed crop.The practical application of the results to grass seed production has been discussed. Existent isolation requirements appear not too great for grass seed crops intended for further seed multiplication, but for commercial seed crops the spatial isolation distance generally recommended may be reduced to 100, or even 50 yd., in the case of large fields.