The vase life of waxflower (Chamelaucium Desf.) is affected by the weight ratio of flowers to stem

The effect of flower weight on changes in the vase life of flowers and leaves of waxflowers was studied by evaluating the arranged flower weight of cultivars derived from the Chamelaucium uncinatum, Chamelaucium megalopetalum and Verticordia species. Competition for water and carbohydrates between flowers and leaves influenced vase life. The removal of flowers had at least four times the effect on leaf vase life as the removal of leaves on flower vase life. Supplying exogenous sucrose to satisfy the demand for carbohydrates negated this effect, indicating that flowers depend on carbohydrates being supplied from leaves to maintain vase life. Cultivars with a greater proportion of flowers (on a weight basis) improved the vase life of flowers at the expense of the leaves. Cultivars with large flowers or many small flowers or a greater weight ratio of flowers to stem appeared to draw more carbohydrates and water from the leaves, giving them a longer vase life and decreasing the vase life of the leaves. The vase life of flowers increased with the stage of opening of flowers up to 50% opening and then decreased up to 100% opening.

Factors affecting variation in the vase life response of waxflower cultivars (Myrtaceae: Chamelaucium Desf. and Verticordia spp. Desf.) tested under various vase solutions

The effects of genotype and vase solutions on the vase lives of waxflower cultivars were studied. The vase life of 16 cultivars derived from different genetic backgrounds showed a variation. The vase life ofChamelaucium uncinatumcultivars held in deionised water was generally the shortest, with four cultivars averaging 9.5 and 8.9 days for flowers and leaves while the vase lives ofC. uncinatum×megalopetalumhybrids were on average 16.0 and 25.0 days for flowers and leaves, respectively. The hybrid ‘Southern Stars’ withC. uncinatum×Verticordia plumosaas parents had the longest flower vase life of 24.9 days, although anotherVerticordia×Chamelauciumhad a 9.5-day flower vase life and other hybrids of the cultivars ofC. uncinatumandVerticordia grandisDesf. (‘WX73’),C.sp.Gingin Marchantii(‘WX97’) andC. floriferum(‘Lady Stephanie’) as a parent had intermediate to short vase lives of 11.4 to 15.5 days. The cultivars responded most to 8-hydroxyquniline sulphate (HQS) + sucrose or HQS + sucrose + silver thiosulphate (STS), being 1.5- to 1.6-folds higher than in deionized water. The cultivars showed a varied response to a vase solution of sucrose + HQS + STS, with whichC. uncinatumvase life increased 1.9-fold compared to 1.7-fold forC. megalopetalum. Waxflowers were found to be susceptible to water stress, causing flowers to close and shortening vase life. On average for the 80 cultivar-vase solution combinations tested, flower vase life ended when the stems reached 75.5 ± 5% fresh weigh. Longer vase life cultivars had a greater ability of maintaining a water balance at or above 75% for longer.

First Report of Botrytis Blight Caused by Botrytis cinerea on Chamelaucium uncinatum in Italy

Chamelaucium uncinatum (wax flower), an evergreen shrub belonging to the Myrtaceae family, is suitable for growing in containers. In the Albenga area (northern Italy), this species is grown as a potted plant. In April 2009, symptoms of a previously unknown blight were observed in a commercial glasshouse in the Savona Province (northern Italy) on 80% of 500 potted plants of cv. Snow Flake. Glasshouse temperatures ranged between 16 and 22°C and plants were drip irrigated. Initially, leaves and calyces appeared chlorotic. Subsequently, necrotic lesions developed on flower stalks and occasionally the corollas. After 10 days, soft, gray mycelium became apparent on symptomatic tissue, especially on the foliage. Severely infected leaves and flowers eventually became completely necrotic and abscised. Tissues were excised from diseased leaves, immersed in a solution containing 1% sodium hypochlorite for 10 s, and then cultured on potato dextrose agar (PDA) medium. A fungus developed abundant mycelium when incubated under constant fluorescent light at 23 ± 1°C. Numerous, small sclerotia also developed on PDA plates incubated for 20 days at 8 ± 1°C. Sclerotia were dark, spheroid, and measured 0.5 to 1.8 × 0.5 to 1.5 (average 1.2 × 1.0) mm. Conidia were smooth, gray, unicellular, ovoid, measured 8.5 to 11.1 × 7.1 to 8.6 (average 9.7 × 7.8) μm, and similar to those described for Botrytis cinerea (2). The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and sequenced. BLAST analysis (1) of the 495-bp segment showed 100% similarity with the sequence of Botryotinia fuckeliana (perfect stage of B. cinerea). The nucleotide sequence has been assigned the GenBank Accession No. GQ149477. Pathogenicity tests were performed by spraying leaves of healthy potted C. uncinatum with a spore suspension (2 × 104 conidia/ml) obtained from PDA cultures of the pathogen. Each plant received 30 ml of the inoculum. Plants sprayed with water only served as controls. Three plants per treatment were used. Plants were covered with plastic bags for 5 days after inoculation and maintained in a growth chamber at 20 ± 1°C. The first foliar lesions developed on leaves 7 days after inoculation and were similar to those observed in the commercial glasshouse, whereas control plants remained healthy. B. cinerea was consistently reisolated from these lesions. The pathogenicity test was completed twice. To our knowledge, this is the first report of the presence of B. cinerea on C. uncinatum in Italy as well as in Europe. The disease has been reported in California (3) and more recently in South Africa (4). In Italy, the economic importance of the disease is currently still limited. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) M. B. Ellis. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, England, 1971. (3) A. M. French. California Plant Disease Host Index. Calif. Dep. Food Agric., Sacramento, 1989. (4) L. Swart and S. Coertze. Plant Dis. 86:440, 2002.

Effects of postharvest methyl jasmonate treatments against Botrytis cinerea on Geraldton waxflower (Chamelaucium uncinatum)

Cut Geraldton waxflower (Chamelaucium uncinatum Schauer) flowers are often infected with Botrytis cinerea. Release of infection from quiescence can cause ethylene production by invaded host tissues and result in flower abscission. Postharvest floral organ abscission is a major problem for the commercial waxflower industry. Methyl jasmonate (MeJA) occurs naturally in plant tissue and has a signalling role in eliciting induced systemic resistance against disease. MeJA treatments have been shown to suppress B. cinerea infecting cut rose flowers. The present experiments investigated the potential of exogenous MeJA treatments for B. cinerea management on harvested waxflower. MeJA treatments of 10 and 100 µL liquid MeJA/L of air applied to cv. Purple Pride and 1 µL MeJA/L to cv. Mullering Brook gave reductions in disease severity for uninoculated stems. However, concentrations of 100 µL MeJA/L applied to Purple Pride in addition to 1 and 10 µL MeJA/L applied to Mullering Brook increased the incidence of floral organ fall. Flower abscission upon treatment with MeJA may be due to induced systemic resistance-associated upregulation of ethylene biosynthesis. MeJA treatments had no direct effect on B. cinerea hyphal elongation in vitro. Collectively, these results show that while MeJA treatment may elicit defence in waxflower against Botrytis, the chemical also causes floral organ fall. Thus, exogenous MeJA treatments do not have potential for B. cinerea management on harvested waxflower.

Anatomy of ethylene-induced floral-organ abscission in Chamelaucium uncinatum (Myrtaceae)

Postharvest abscission of Geraldton waxflower (Chamelaucium uncinatum Schauer) flower buds and flowers is ethylene-mediated. Exposure of floral organs to exogenous ethylene (1 µL L–1) for 6 h at 20°C induced separation at a morphologically and anatomically distinct abscission zone between the pedicel and floral tube. Flower buds with opening petals and flowers with a nectiferous hypanthium were generally more responsive to exogenous ethylene than were flower buds enclosed in shiny bracteoles and aged (senescing) flowers. The anatomy of abscission-zone cells did not change at sequential stages of floral development from immature buds to aged flowers. The zone comprised a layer of small, laterally elongated-to-rounded, closely packed and highly protoplasmic parenchyma cells. Abscission occurred at a two- to four-cell-wide separation layer within the abscission zone. The process involved degradation of the middle lamella between separation layer cells. Following abscission, cells on both the proximal and distal faces of the separation layer became spherical, loosely packed and contained degenerating protoplasm. Central vascular tissues within the surrounding band of separation layer cells became torn and fractured. For flower buds, bracteoles that enclose the immature floral tube also separated at an abscission zone. However, this secondary abscission zone appeared less sensitive to ethylene than the primary (central) floral-tube abscission zone as bracteoles generally only completely abscised when exposed to 10 µL L–1 ethylene for the longer period of 24 h at 20°C. The smooth surfaces of abscised separation-layer cells suggest that hydrolase enzymes degrade the middle lamella between adjacent cell walls.