Der-Ming Yeh

Growth and flowering responses of Canna × generalis to nitrogen supplied to the growing medium via top- or sub-irrigation

Summary Effects of nitrogen concentration on growth and flowering were studied in Canna generalis L. H. Bailey ‘Tropical Rose’ and ‘Tropical Red’ grown with irrigation supplied either to the top (top-irrigation) or the bottom surface (subirrigation) of the growing medium. For ‘Tropical Rose’, maximum total dry weights occurred at 4 mM N for both irrigation methods, but growth was greater with subirrigation compared to top-irrigation. For ‘Tropical Red’, maximum total dry weight occurred at 4 mM N under subirrigation, and 8 mM N under top-irrigation. Growth was reduced in all treatments when growing media EC exceeded 1.25 dS m–1. Shoot dry weight increased as leaf N content increased from 0.6% to 1.4 %. Plants under top-irrigation took longer to flower than did those under subirrigation. At 4 to 32 mM N, regardless of irrigation method, plants flowered after 9–10 leaves had been formed. Plants grown at 0 mM N did not flower after treatment for 145 d. Maximum spike length and floret number were observed at 4 mM N in both irrigation treatments.

Effects of irradiance on growth, net photosynthesis and indoor performance of the shade-adapted plant, maidenhair fern.

Summary Effects of irradiance on growth and net photosynthesis were studied in Adiantum raddianum cv. Fritz Luth grown under warm (26±3°C) greenhouse conditions. Efficiency of light conversion for frond dry weight increase was reduced from 0.0067 to 0.0016 as the mean daily light integral increased from 1.3 to 6.7 MJ m–2d–1. The maximum frond area and frond dry weight were measured in plants grown in daily light integrals of 2.6 and 3.3 MJ m–2d–1. Specific leaf area decreased exponentially from 0.046 to 0.032 m2g–1 over the daily light integral from 0.6 to 6.7 MJ m–2 d–1 . Rate of frond appearance was linearly increased with increasing mean daily light integral from 0.6 to 6.7 MJ m d and a light integral of 4.2 MJ m–2 was required for appearance of one frond. Pinnule thickness increased, and chlorophyll content decreased, as irradiance increased from 0.6 to 6.7 MJ m–2d–1. Numbers of fronds bearing sori increased linearly with increasing irradiance up to 3.3 MJ m–2d–1, beyond which the number decreased. The fronds grown under 0.6–3.3 MJ m–2d–1 conditions had a photosynthetic advantage over those under 5.9 and 6.7 MJ m–2d–1 at photosynthetic photon flux (PPF) levels less than 50 μmol m–2s–1. Light compensation points were near 15 μmol m–2 s–1 for fronds grown under 5.9 and 6.7 MJ m–2d–1, as compared with 5.μmolm–2s–1 for fronds preconditioned to lower irradiance levels from 0.6 to 3.3 MJ m–2d–1. Significantly fewer wilted fronds and better interior performance quality were recorded in plants grown under daily light integrals from 0.6 to 2.6 MJ m–2d–1.

Heat tolerance in English ivy as measured by an electrolyte leakage technique

Summary Identification of heat-tolerant English ivy (Hedera helix L.) genotypes for commercial production in hot areas is desirable. The extent to which electrolyte leakage from English ivy leaf discs, measured using a test for cell membrane thermostability (CMT), could be related to the reduction to shoot dry weight induced by heat in the greenhousegrown plants was determined. A curved relationship existed between the relative injury (RI) value occurring in leaf tissue discs of English ivy cultivars and treatment temperature. A single temperature treatment at 50°C resulted in injury values near the midpoint of the response curve and showed the greatest sensitivity in detecting genotypic differences in heat tolerance. The cultivars with a high RI value are those with the lesser CMT and more reduction in shoot dry weights by high day/night temperature at 35/30°C.

Manipulation of flowering in cineraria. III. Cardinal temperatures and thermal times for vernalization

SummaryEffects of temperatures and durations of temperature treatments on flower induction were studied in cineraria cv. Cindy Blue grown in controlled environments. The earliest flower induction, recorded as the fewest leaves below the flower, was observed as 16–17 leaves initiated in non-juvenile plants that had been chilled at 5–7°C for 3–5 weeks as compared with 30–33 in plants grown throughout at 24°C. Plants demonstrated a true quantitative vernalization response in that flowering was delayed but not prevented by higher temperatures and further leaves were initiated below the flower after chilling had ended. The rate of progress to flower induction, measured as the reciprocal of leaf number below the flower, was shown to relate linearly to temperature. This enabled the base, optimum and maximum temperatures for vernalization to be derived respectively as –0.3, 5.9 and 15.8°C, where the base temperature corresponded to the rate at which the unvernalized plants would progress to flower induction. Rate...

Differential growth and photosynthetic response of selected cultivars of English ivy to irradiance

Summary Effects of irradiance on growth and net photosynthesis were studied in four cultivars of Hedera helix L. grown in controlled environments at a mean daily temperature of 24°C. Shoot dry weights of the variegated cultivars Ingelise and Mini Adam were greatest at around 2.9 MJ m–2 d–1. For the two green cultivars, with increasing daily light integral from 1.2 to 7.2 MJ m–2 d–1, shoot dry weight increased in ‘Dark Pittsburg’, but decreased in ‘Evergreen’. Shoot or internode lengths, and leaf area decreased linearly while leaf thickness increased as light integral increased from 1.7 to 7.2 MJ m–2 d–1 in cultivars Ingelise, Dark Pittsburg and Evergreen. Leaf variegation increased in ‘Ingelise’ under 4.3 or 7.2 MJ m–2 d–1, while leaf variegation in ‘Mini Adam’ was affected little by irradiance. Plants of ‘Dark Pittsburg’ had both higher light-saturated net photosynthesis rate and light saturation point than other cultivars. The variegated cultivars Ingelise and Mini Adam had higher light compensation points than the green cultivars Dark Pittsburg and Evergreen.

Cardinal temperatures and thermal requirements for germination of cineraria seed.

Summary Effects of temperature on the rate of germination, measured as the reciprocal of the time taken for half the population to germinate, were studied in cineraria cvs Cindy Blue and Cindy Dark Red. The base, optimum and maximum temperatures for germination were derived respectively as 1.6, 24.8 and 37.8°C in cv. Cindy Blue, close to Tb = 1.9, To = 24.5 and Tm = 38.4°C in cv. Cindy Dark Red. All seeds of each cultivar had a common base temperature but needed different thermal times to germinate. Seed of cv. Cindy Dark Red began to germinate after ca. 30°Cd compared with 35°Cd required by cv. Cindy Blue. A thermal time of ca. 50°Cd was required for half the population to germinate in each cultivar and the thermal requirement for germination fraction >0.5 was similar in both cultivars. The base and maximum temperatures for germination were similar to those determined previously for leaf initiation and flower development.

LEAF INITIATION AND SHOOT APICAL DIAMETER IN RELATION TO PHASE TRANSITION IN CINERARIA

SummaryTransition from the juvenile to the competent phase of vegetative development in cineraria cvs Cindy Blue and Cindy Dark Red was coincident with a two-fold increase in leaf initiation rate and the attainment of a critical shoot apical diameter of 0.15-0.18 mm. The base (Tb), optimum (T0) and maximum (Tm) temperatures for leaf initiation in plants grown at constant temperatures in growth rooms were derived to be 3.6, 19.8 and 38.1°C respectively in cv. Cindy Blue, and Tb = 3.6, T0 = 19.7 and Tm = 37.8°C in cv. Cindy Dark Red. The thermal time required for the initiation of each leaf in the juvenile phase was 87°Cd in cv. Cindy Blue and 78°Cd in cv. Cindy Dark Red, calculated from the cardinal temperatures. Juvenile development in cv. Cindy Blue was completed after 6–7 leaves had been initiated, which occurred 565 ± 43°Cd after radicle emergence and in cv. Cindy Dark Red juvenility ended after initiation of 7–8 leaves at 585 ± 39°Cd from radicle emergence. Thermal times for leaf initiation and for th...

Manipulation of flowering in cineraria. II. Juvenility

SummaryCompetence to perceive florally inductive stimuli was examined in cineraria cvs Cindy Blue and Cindy Dark Red. Juvenility was observed in imbibed, but not germinated, seeds and persisted until the initiation of a critical number of leaves which defined transition to the senisitive, competent form at 6–7 leaves initiated in cv. Cindy Blue and 7–8 leaves initiated in cv. Cindy Dark Red. During this juvenile phase, plants were incompetent to perceive either chilling at 3°C and 6°C as a vernalization stimulus or short days as a photoperiodic stimulus. After phase transition, the level of competence was not affected by plant age or size. Chilling imbibed seeds at 4°C for four weeks reduced the leaf number below the flower in both cultivars. The competent stage for vernalization during germination appeared between radicle emergence and cotyledon unfolding. The seed vernalization effect was only apparent when plants from chilled germinated seeds were grown subsequently at a non-vernalizing temperature (ca...

Manipulation of flowering in cineraria. IV. Devernalization

SummaryEffects of post-vernalization temperatures on leaf number below the flower, and the percentage of plants flowering, were studied in cineraria cvs Cindy Blue and Cindy Dark Red. Leaf number below the flower decreased with increase in the duration of vernalization at 6°C from one to four weeks. In plants vernalized for one or two weeks, subsequent temperatures of 20 or 25°C significantly increased leaf number by ca. 4–7 below the flower when compared with 10 to 15°C. Exposure of vernalized plants to high temperatures of 27 or 30°C resulted in more leaves being initiated below the flowers in plants chilled for two weeks and completely abolished the vernalization effect in plants that had been chilled for one week. Post-vernalization temperatures had no effect on flowering in plants that had been chilled for four weeks. Ninety two to 100% of plants showed a vernalization response after treatments at 6°C for one or two weeks provided that vernalization was followed by two weeks at 10 or 15°C. A reductio...

Manipulation of flowering in cineraria. I. Effects of photoperiod

SummaryEffects of photoperiod on flowering, measured as days to macroscopic flower visibility and as leaf number below the terminal inflorescence, were studied in three cultivars of cineraria, Cindy Blue, Cindy Pink and Cindy Dark Red. Short photoperiods accelerated, and long photoperiods delayed, but did not prevent, flower initiation in plants grown under commercial temperature regimes (8–14°C) in glasshouse conditions. The critical photoperiod for flower initiation was 12 h, at and below which plants produced the fewest leaves below the flowers. In cvs Cindy Blue and Cindy Pink, the ceiling photoperiod was 16 h, at and above which plants produced their maximum final leaf number. The rates of progress to flower initiation and to flower visibility were shown to be faster in plants grown under 8–12 h photoperiods and both rates decreased approximately linearly as photoperiod increased from 12 to 16 h in cvs Cindy Blue and Cindy Pink. There was no “minimum number” of short-day cycles required for flower in...