Anastasios I. Darras

Acibenzolar-S-methyl and methyl jasmonate treatments of glasshouse-grown freesias suppress post-harvest petal specking caused by Botrytis cinerea

Summary Compounds that activate host plant defence responses potentially offer socio-environmentally sound alternative methods for disease control. In a series of glasshouse trials over 2 years, pre-harvest sprays with acibenzolar-S-methyl (ASM) and methyl jasmonate (MeJA) were tested for suppression of post-harvest infection of cut Freesia hybrida L. flowers by Botrytis cinerea. For the ASM treatments, variability in reducing the incidence of B. cinerea disease was observed between years, freesia varieties, incubation temperatures and ASM concentrations. In the first year, the greatest reductions in lesion numbers on ASM-treated var. ‘Cote d’Azur’ were recorded using 2.86 mM ASM. For three different post-harvest temperature regimes, the relative reductions in lesion numbers, compared to untreated controls, were 45% at 5°C, 40% at 12°C and 30% at 20°C, respectively. In the second year, lesion numbers were most reduced using 1.43 mM ASM to treat freesia var.‘Dukaat’ flowers. Here, the relative reductions were to 44% at 5°C, 26% at 12°C and 51% at 20°C. MeJA treatments were, in general, more consistently effective than ASM treatments in reducing lesion numbers and lesion diameters on cut freesia flowers. MeJA-treated (0.2 mM) freesia flowers (var. ‘Dukaat’) incubated at 20°C showed relative reductions of 62%, and 45% for lesion number and lesion diameter, respectively.The differing efficacy between ASM and MeJA treatments could be attributed to their differential abilities to induce the salicylic acid (SA)-mediated vs. the jasmonic acid (JA)-mediated host defence pathways, respectively.

Postharvest infection of Freesia hybrida flowers by Botrytis cinerea

Abstract‘Specking’ on harvested freesia (Freesia hybrida) flowers is a problem worldwide. The disease is caused by the fungal pathogen Botrytis cinerea. This disease symptom detracts from appearance and reduces marketability of the flowers. Unlike other important cut flower crops (e.g. gerbera), the mode of infection and epidemiology of postharvest freesia flower specking caused by B. cinerea has not been reported. Epidemiological studies were carried out under simulated conditions typical of those occurring during postharvest handling of freesia flowers. Infection of freesia flowers by B. cinerea occurred when a conidium germinated, formed a germ tube(s) and penetrated epidermal cells. Fungal hyphae then colonised adjacent cells, resulting in visible lesions. Different host reactions were observed on freesia ‘Cote d’Azur’ petals at 20°C compared to 5°C. The infection process was relatively rapid at 20°C, with visible lesions produced within 7 h of incubation. However, lesion expansion ceased after 24 h of incubation. Infection was slower at 5°C, with visible lesions produced after 48 h of incubation. However, lesion development at 5°C was continuous, with lesions expanding over 4 days. Light microscopy observations revealed increased host defence reactions during infection. These reactions involved production of phenolic compounds, probably lignin and/or callose, around infection sites. Such substances may play a role in restricting petal colonisation and lesion expansion. Disease severity and lesion numbers on freesia flowers incubated at 12°C were higher, but not significantly higher (P > 0.05), than on those incubated at 20°C. Disease severity and progression were differentially mediated by temperature and relative humidity (R.H.). Infection of freesia flowers was severe at 100% R.H. for all three incubation temperatures of 5,12 and 20°C. In contrast, no lesions were produced at 80 to 90% R.H. at either 5 or 20°C.

Efficacy of postharvest treatments with acibenzolar-S-methyl and methyl jasmonate against Botrytis cinerea infecting cut Freesia hybrida L. flowers

The known plant defence activators acibenzolar-S-methyl (ASM) and methyl jasmonate (MeJA) were applied as spray and as spray or pulse treatments, respectively, after harvest and evaluated for efficacy against freesia cv. ‘Cote d’Azur’ flower specking disease caused by the pathogen Botrytis cinerea. Lesion numbers on non-inoculated freesia flowers and lesion diameters on attached petals of inoculated flowers were reduced by 1.43, 2.86 and 5.72mM ASM at 5 and 12°C compared with untreated controls. However, ASM was ineffective in reducing lesion numbers and lesion diameters on non-inoculated and on artificially inoculated flowers incubated at 20?C. ASM showed direct antimicrobial activity in vitro, significantly reducing B. cinerea mycelial growth and conidial germ tube elongation. ASM treatments did not adversely affect the vase life of cut freesia flowers. MeJA applied as postharvest spray or pulse to freesia flowers also tended to suppress B. cinerea. MeJA treatments at 12 and 20°C were generally more effective than at 5°C. In contrast to ASM, MeJA usually did not exert direct antimicrobial activity against B. cinerea in vitro. MeJA spray treatment leads to an increase in relative fresh weight and a reduction of wilt scores of flowers during the vase life. In contrast, MeJA pulsing at 0.6mM reduced relative fresh weight and vase life of cut freesia flowers compared with untreated controls. Overall, the results suggest a potential role for postharvest ASM spray and MeJA spray or pulse treatments in suppressing B. cinerea on cut freesia flowers. However, variable efficacy needs to be overcome before such plant defence activator treatments could be used in commercial practice.

Methyl jasmonate and acibenzolar-S-methyl protect cut Freesia hybrida inflorescences against Botrytis cinerea, but do not act synergistically

Summary Methyl jasmonate (MeJA) and acibenzolar-S-methyl (ASM), two potential elicitors which activate plant defence responses, were tested on inflorescences of Freesia hybrida to suppress petal-specking caused by Botrytis cinerea. Compared to the untreated controls, MeJA applied as a vapour, pulse, or spray to freesia ‘Cote d’Azur’ inflorescences significantly reduced disease severity scores, lesion numbers, and lesion diameters on attached petals, and lesion diameters in a detached petal bioassay. ASM alone, at 143 µM, provided a degree of protection to freesia inflorescences by significantly reducing disease severity scores, lesion numbers, and lesion diameters compared to the untreated controls. However, no additive effect was observed for combined treatments with MeJA and ASM. Polyphenol oxidase (PPO) activities in 0.1 µl l–1 MeJA-treated inflorescences, at 24 h and 36 h post-treatment, were 2.7- and 2.0-fold higher, respectively, compared to the untreated controls. In contrast, phenylalanine ammonia-lyase (PAL) activity in 0.1 µl l–1 MeJA-treated inflorescences was suppressed after 36 h, 48 h, and 72 h of incubation compared to PAL activities in the untreated control flowers.

Physical and Aerodynamic Properties of Lavender in relation to Harvest Mechanisation

A laboratory study evaluated the physical and aerodynamic properties of lavender cultivars in relation to the design of an improved lavender harvester that allows removal of flowers from the stem using the stripping method. The identification of the flower head adhesion, stem breakage, and aerodynamic drag forces were conducted using an Instron 1122 instrument. Measurements on five lavender cultivars at harvest moisture content showed that the overall mean flower detachment force from the stem was 11.2 N, the mean stem tensile strength was 36.7 N, and the calculated mean ultimate tensile stress of the stem was 17.3 MPa. The aerodynamic measurements showed that the drag force is related with the flower surface area. Increasing the surface area of the flower head by 93% of the “Hidcote” cultivar produced an increase in drag force of between 24.8% and 50.6% for airflow rates of 24 and 65 m s−1, respectively. The terminal velocities of the flower heads of the cultivar ranged between 4.5 and 5.9 m s−1, which results in a mean drag coefficient of 0.44. The values of drag coefficients were compatible with well-established values for the appropriate Reynolds numbers.

Effects of storage temperature and abscisic acid treatment on the vase-life of cut 'First Red' and 'Akito' roses

Summary Abscisic acid (ABA) treatment can confer chilling tolerance upon certain plant tissues that suffer injury at low temperatures. The present study investigated the efficacy of two post-harvest ABA treatments in suppressing low temperature injury (LTI) in cut rose (Rosa hybrida L.) flowers stored at 1°C or 5°C. A shortened vase-life was recorded for roses stored at 5°C compared to untreated roses and those stored at 1°C. Storage at 1°C significantly (P ≤ 0.01) increased electrolyte leakage in ‘Akito’ roses compared to roses stored at 5°C, or to untreated roses. Storage of ‘First Red’ and ‘Akito’ roses at 1°C or 5°C significantly (P ≤ 0.01) increased the malondialdehyde (MDA) contents of petal and leaf tissues. The highest MDA contents were recorded in roses stored at 1°C. ABA at 10 µM as a spray, or at 0.1 M as a pulse treatment, did not affect the MDA contents of either leaves or petals. When averaged over the two storage temperature treatments, the ABA content was highest in roses pulse-treated with 0.1 M ABA, followed by those sprayed with 10 µM ABA, then by untreated (control) roses. However, this increase did not have any apparent effect on the longevity or senescence of the cut roses. Moreover, this trend was inconsistent across all storage treatments. Pulsing with 0.1 M ABA or spraying with 10 µM ABA before storage did not significantly (P >0.05) affect vase-life. However, pulsing ‘Akito’ roses with 0.1 M ABA before storage tended to reduce the level of electrolyte leakage from leaves.