John D. Faragher

Could studies on cell responses to low oxygen levels provide improved options for fruit storage and disinfestation

Abstract Cellular responses of harvested horticultural products to reduced partial pressure of oxygen in controlled atmospheres (CA) or modified atmospheres (MA) storage include reduced energy charge, reduced energy availability for repair and maintenance, cytoplasmic acidification, and activation of glycolysis and toxic glycolytic end products. These responses are compared with those of root cells to flooding and of vertebrate and invertebrate animal cells to oxygen deficit. The capacity to sense incipient oxygen stress and, when time, temperature and stress level permit, adapt and so avoid cell damage, is emphasised. The applications of CA and MA technologies could be extended if adaptive changes in the plant products were fostered during the early stages of storage. The use of a combination of heat and oxygen deficit for disinfestation is another possibility. A need for more fundamental studies of energy metabolism in horticultural products in CA is recognised.

Water relations of cut flowering branches of Thryptomene calycina (Lindl.) Stapf. (Myrtaceae)

Abstract Cut flowering branches of Thryptomene calycina (Lindl.) Stapf. placed in water showed a decrease in water uptake, transpiration, hydraulic conductivity, fresh weight (FW), water content of flowers and water potential within 2 days of harvest. Flowers started to close approximately 3 days after harvest, and flower buds did not open throughout vase life. The longevity of the branches averaged 6–9 days and was determined by the wilting of flowers. Hydraulic conductivity, FW and longevity were increased by measures that removed or prevented the formation of occlusions in the stems, such as recutting the stems underwater or by inclusion of anti-bacterial compounds (citric acid at 250–500 mg l−1, or dichloroisocyanuric acid (DICA) at 50 mg l−1 in the vase solution. Hydraulic conductivity, FW and longevity were also significantly improved by the inclusion of the surfactant nonylphenolpolyglycol ether (Agral-600, at 160 μl l−1) in the vase solution. Agral-600 did not reduce the number of bacteria in the vase solution, and may act by bypassing bacterial occlusions. The inclusion of sucrose (10 g l−1) with an adequate anti-microbial compound, improved longevity, stimulated bud opening and further delayed flower closure. The results indicate that the longevity of T. calycina is limited by a vascular occlusion in the stem base.

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 L liquid MeJA/L of air applied to cv. Purple Pride and 1 L MeJA/L to cv. Mullering Brook gave reductions in disease severity for uninoculated stems. However, concentrations of 100 L MeJA/L applied to Purple Pride in addition to 1 and 10 L 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.

Use of 1-Methylcyclopropene to Prevent Floral Organ Abscission From Ethylene-Sensitive Proteaceae

Ethylene elicits floral organ abscission from cut inflorescences of some Australian Proteaceae [1]. A novel ethylene binding inhibitor, 1-methylcyclopropene, prevents abscission for a number of ornamentals [2, 3]. The efficacy of 1-MCP in preventing ethylene-induced floral organ abscission from Australian Proteaceae was determined.