John E. Erwin

Horticultural applications of jasmonates

Summary Plant growth and development are controlled, in part, by endogenous growth substances which are affected by biotic and abiotic signals and events. A particular class of growth regulators, collectively called ‘jasmonates’ are involved in plant responses to such events and elicit unique responses. The effects of jasmonates on plant growth are varied and include storage organ formation, induction of plant defences against biotic (e.g., herbivores and pathogens) and abiotic (e.g., drought and ozone) stresses, and growth inhibition in tissues such as roots and young shoots. In addition, jasmonates can interact with other hormone pathways, especially ethylene, to affect growth and development. Detailed knowledge of jasmonate responses in models such as Arabidopsis is being put to use in a wide variety of horticultural crops. This review summarises the impacts of jasmonates on plant growth and physiology, and how jasmonates may impact horticultural crop growth, physiology, protection from stresses, and/or handling.

Stem elongation and flowering of the long-day plant Campanula isophylla Moretti in response to day and night temperature alternations and light quality

Abstract Stem elongation and plant height at flowering in Campanula isophylla Moretti were greater when plants were exposed to far red (FR) light or light from incandescent lamps which had a low red (R)/FR ratio (0.7). The difference in final stem length between FR- and R-light-treated plants was greatest when the light treatments were given during the entire night or as a 3 h end-of-day (EOD) lighting period. Only minor differences existed between R and FR light treatments when plants were given light in the middle of the night. However, FR light suppressed lateral branching compared with R light. The reduction in plant height as a result of a lower day temperature (DT) than night temperature (NT) was nullified by day-extension lighting with incandescent lamps. With fluorescent lamps (R/FR ratio 4.2), plant heightwas significantly less at 15/21°C (negative DT-NT (DIF)) than at 21/15°C DT/NT (positive DIF). Continuous lighting (CL) during the entire night or with 3 h night interrupttion (NI) treatments with R or FR light immediately after the middle of the night was equally effective at inducing flowering, and much more effective than EOD or end-of-night (EON) lighting. DIF had a slight influence on the rate of flower development, but negative DIF grown plants had 24% more flowers and flower buds, and 26% higher dry weight, than positive DIF plants. Practical applications of light quality and negative DIF treatments for the production of high-quality pot plants of C. isophylla are discussed.

Irradiance and temperature effects on time of development and flower size in chrysanthemum

Abstract The effects of day temperature (DT), night temperature (NT) and photosynthetic photon flux (PPF), on rate of development and flower size were studied in chrysanthemum ( Dendranthema grandiflora Tzvelev. cultivar ‘Bright Golden Anne’). DT and NT ranged from 10 to 30°C and PPF from 1.8 to 21.6 mol day −1 m −2 . Flower initiation did not occur after 100 short days (SD) at low PPF levels (1.8 mol day −1 m −2 ) in combination with high DT or NT (30°C). The number of days to flower varied from 58 to 140 days among plants grown under environmental conditions allowing flower initiation within 100 SD. The time to flower from start of SD decreased nonlinearly as PPF increased. Increasing PPF by 9.9 mol day −1 m −2 at 20°C accelerated flowering 20 days when the initial PPF was 1.8 mol day −1 m −2 , but only 10 days when the initial PPF was 11.7 mol day −1 m −2 . The DT and NT for most rapid flower development were estimated from a model predicting time to flower. Independent of PPF in the range from 2 to 20 mol day −1 m −2 , the optimum DT was 17°C and the optimum NT was 18°C. Total flower area per plant varied from 14 to 310 cm 2 . The flower size increased linearly as PPF increased from 1.8 to 21.6 mol day −1 m −2 at a constant temperature of 20°C. The optimum DT NT combination for largest flower size changed from 21 14° to 20 18° C as PPF increased from 5 to 20 mol day −1 m −2 .

Micropropagation of iridaceae-a review

The Iridaceae contains many hundreds of attractive species that have been overlooked for horticultural development. The incredible variation in flower and leaf shape, size and colour suggest this little-tapped resource could offer great opportunities for developing new commercial ornamental products. Micropropagation has increasingly become a valuable tool assisting breeders to release new species and cultivars into the market more rapidly. Here we review the progress made in Iridaceae micropropagation genus by genus, and highlight the potential for future expansion in this field.

Factors Affecting Flowering in Ornamental Plants

Flowering is the cornerstone of floricultural crops, regardless of class (bedding plants, herbaceous perennials, cut flowers, flowering potted plants); the only crop exceptions are those grown for their colorful foliage. During flower breeding and crop domestication, both public and private sector flower breeding programs must conduct research to discern the various control mechanisms for flower initiation and development. Important flowering concepts covered in this chapter include autonomous regulation (phase change; species, meristem size, and environmental factor affects), external regulation (photoperiodism, vernalization, devernalization, irradiance and light quality, and their interactions), irradiance induction, stress induction (ehtylene, water), flower development requirements (photoperiodism, temperature, stress), and dormancy.

Modelling temperature, photoperiod and vernalization responses of Brunonia australis (Goodeniaceae) and Calandrinia sp (Portulacaceae) to predict flowering time

BACKGROUND AND AIMS Crop models for herbaceous ornamental species typically include functions for temperature and photoperiod responses, but very few incorporate vernalization, which is a requirement of many traditional crops. This study investigated the development of floriculture crop models, which describe temperature responses, plus photoperiod or vernalization requirements, using Australian native ephemerals Brunonia australis and Calandrinia sp. METHODS A novel approach involved the use of a field crop modelling tool, DEVEL2. This optimization program estimates the parameters of selected functions within the development rate models using an iterative process that minimizes sum of squares residual between estimated and observed days for the phenological event. Parameter profiling and jack-knifing are included in DEVEL2 to remove bias from parameter estimates and introduce rigour into the parameter selection process. KEY RESULTS Development rate of B. australis from planting to first visible floral bud (VFB) was predicted using a multiplicative approach with a curvilinear function to describe temperature responses and a broken linear function to explain photoperiod responses. A similar model was used to describe the development rate of Calandrinia sp., except the photoperiod function was replaced with an exponential vernalization function, which explained a facultative cold requirement and included a coefficient for determining the vernalization ceiling temperature. Temperature was the main environmental factor influencing development rate for VFB to anthesis of both species and was predicted using a linear model. CONCLUSIONS The phenology models for B. australis and Calandrinia sp. described development rate from planting to VFB and from VFB to anthesis in response to temperature and photoperiod or vernalization and may assist modelling efforts of other herbaceous ornamental plants. In addition to crop management, the vernalization function could be used to identify plant communities most at risk from predicted increases in temperature due to global warming.

Spider mites (Tetranychus urticae) perform poorly on and disperse from plants exposed to methyl jasmonate

Jasmonates are plant hormones involved in wound and defense responses against herbivorous arthropods. Methyl jasmonate (MeJA) is used experimentally to induce defense responses in plants. In experiments outlined here we utilized a novel preference assay with unwounded plants that allowed us to study the impact of a MeJA spray on subsequent Tetranychus urticae Koch (Acari: Tetranychidae) proliferation and preference. Spraying plants with 100 μm MeJA 1 day before infestation caused mites to disperse within 2 days from treated impatiens [Impatiens wallerana Hook f., ‘Super Elfin Pink’ (Balsaminaceae)], pansy [Viola × wittrockiana Gams, ‘Imperial Beaconsfield’ (Violaceae)], and tomato [Solanum lycopersicum L., ‘Big Boy’ (Solanaceae)] plants. In addition, MeJA application reduced mite proliferation rate on impatiens and pansy by 60% (measured 22–34 days after infestation). Proteinase inhibitor (PI) assays suggested that MeJA‐induced PIs alone were not responsible for the observed results in pansy and impatiens but may have been a factor in tomato. Implications of these results in the context of MeJA‐induced resistance responses and possible directions for future research and application are discussed.

Hormonal and cell division analyses in Watsonia lepida seedlings

The regeneration ability, cell division activity, auxin and cytokinin content of seedling regions and hypocotyl subsections of Watsonia lepida were studied. A total of 21 different cytokinins or conjugates were found in seedlings, with the highest cytokinin content in meristematic regions (root and shoot apical meristems). The greatest contribution to the cytokinin pool came from the biologically inactive cZRMP, suggesting that significant de novo synthesis was occurring. Five different auxins or conjugates were detected, being concentrated largely in the shoot apical meristem and leaves, IAA being the most abundant. Analysis of hypocotyl subsections (C1-C4) revealed that cell division was highest in subsection C2, although regeneration in vitro was significantly lower than in subsection C1. Anatomically, subsection C1 contains the apical meristem, and hence has meristematic cells that are developmentally plastic. In contrast, subsection C2 has cells that have recently exited the meristem and are differentiating. Despite high rates of cell division, cells in subsection C2 appear no longer able to respond to cues that promote proliferation in vitro. Auxin and cytokinin analyses of these subsections were conducted. Possibly, a lower overall cytokinin content, and in particular the free-base cytokinins, could account for this observed difference.

Juvenility and flowering of Brunonia australis (Goodeniaceae) and Calandrinia sp (Portulacaceae) in relation to vernalization and daylength

BACKGROUND AND AIMS The time at which plants are transferred to floral inductive conditions affects the onset of flowering and plant morphology, due to juvenility. Plants of Brunonia australis and Calandrinia sp. were used to investigate whether Australian native ephemeral species show a distinct juvenile phase that can be extended to increase vegetative growth and flowering. METHODS The juvenile phase was quantified by transferring seedlings from less inductive (short day and 30/20°C) to inductive (vernalization or long day) conditions at six different plant ages ranging from 4 to 35 d after seed germination. An increase in days to first visible floral bud and leaf number were used to signify the end of juvenility. KEY RESULTS Brunonia australis was receptive to floral inductive long day conditions about 18-22 d after seed germination, whereas plants aged 4-35 d appeared vernalization sensitive. Overall, transferring plants of B. australis from short to long day conditions reduced the time to anthesis compared with vernalization or constant short day conditions. Calandrinia sp. showed a facultative requirement for vernalization and an insensitive phase was not detected. Floral bud and branch production increased favourably as plant age at time of transfer to inductive conditions increased. Younger plants showed the shortest crop production time. CONCLUSIONS Both species can perceive the vernalization floral stimulus from a very young age, whereas the photoperiodic stimulus is perceived by B. australis after a period of vegetative growth. However, extending the juvenile phase can promote foliage development and enhance flower production of both species.

A model plant for vernalization studies

Abstract Vernalization requirements of Raphanus sativus L. ‘Early 40 Days’, ‘Chinese Radish Jumbo Scarlet’, ‘Everest’, and ‘Minowase Early Long White’ were studied to determine their potential as model plants for vernalization studies. Leaf number below the inflorescence and days to anthesis decreased as vernalization time increased from 0 to 15 days at 6.5°C for all cultivars. ‘Early 40 Days’, ‘Everest’, and ‘Minowase Early Long White’ flowered but ‘Chinese Radish Jumbo Scarlet’ did not flower under long-day-conditions (inductive) at 18°C without vernalization, i.e. ‘Chinese Radish Jumbo Scarlet’ has an obligate vernalization requirement. ‘Chinese Radish Jumbo Scarlet’ was completely vernalized in 5–10 days. Use of ‘Chinese Radish Jumbo Scarlet’ as a model plant for vernalization studies is discussed.