Saprophytic microorganisms with potential for biological control of Botrytis cinerea on Geraldton waxflower flowers

Saprophytic bacteria, yeasts and filamentous fungi were isolated from Geraldton waxflower flowers and screened to identify potential antagonism towards Botrytis cinerea. Isolates from other sources (e.g. avocado) were also tested. Isolates were initially screened in vitro for inhibition of B. cinerea conidial germination, germ tube elongation and mycelial growth. The most antagonistic bacteria, yeasts and fungi were selected for further testing on detached waxflower flowers. Conidia of the pathogen were mixed with conidia or cells of the selected antagonists, co-inoculated onto waxflower flowers, and the flowers were sealed in glass jars and incubated at 20 degreesC. The number of days required for the pathogen to cause flower abscission was determined. The most antagonistic bacterial isolate, Pseudomonas sp. 677, significantly reduced conidial germination and retarded germ tube elongation of B. cinerea. None of the yeast or fungal isolates tested was found to significantly reduce conidial germination or retard germ tube elongation, but several significantly inhibited growth of B. cinerea. Fusarium sp., Epicoccum sp. and Trichoderma spp. were the most antagonistic of these isolates. Of the isolates tested on waxflower, Pseudomonas sp. 677 was highly antagonistic towards B. cinerea and delayed waxflower abscission by about 3 days. Trichoderma harzianum also significantly delayed flower abscission. However, as with most of the fungal antagonists used, inoculation of waxflower flowers with this isolate resulted in unsightly mycelial growth.

Development and senescence of Grevillea 'Sylvia' inflorescences, flowers and flower parts

To characterise the physiology of development and senescence for Grevillea 'Sylvia'. oral organs, respiration, ethylene production and ACC concentrations in harvested flowers and flower parts were measured. The respiration rate of harvested inflorescences decreased over time during senescence. In contrast, both ethylene production and ACC concentration increased. Individual flowers, either detached from cut inflorescences held in vases at 20degreesC or detached from in planta inflorescences at various stages of development, had similar patterns of change in ACC concentration and rates of respiration and ethylene production as whole inflorescences. The correlation between ACC concentration and ethylene production by individual flowers detached from cut inflorescences held in vases was poor (r(2)=0.03). The isolated complete gynoecium (inclusive of the pedicel) produced increasing amounts of ethylene during development. Further sub-division of flower parts and measurement of their ethylene production at various stages of development revealed that the distal part of the gynoecium (inclusive of the stigma) had the highest rate of ethylene production. In turn, anthers had higher rates of ethylene production and also higher ACC concentrations than the proximal part of the gynoecium (inclusive of the ovary). Rates of ethylene production and ACC concentrations for tepal abscission zone tissue and adjacent central tepal zone tissue were similar. ACC concentration in pollen was similar to that in senescing perianth tissue. Overall, respiration, ethylene and ACC content measurements suggest that senescence of G. 'Sylvia' is non-climacteric in character. Nonetheless, the phytohormone ethylene is produced and evidently mediates normal flower development and non-climacteric senescence processes.

Utility of cotyledon and detached leaf assays for assessing root reactions of lucerne to Phytophthora root rot caused by Phytophthora medicaginis

Phytophthora root rot, caused by Phytophthora medicaginis, is a major limitation to lucerne production but it can be managed through the use of resistant cultivars. Current resistance screening methods, using mature plants or post-emergence seedling assays, are costly and time consuming. The use of zoospore inoculum on detached leaves and intact cotyledons as an assay for plant resistance was assessed using genetically defined segregating populations. The detached leaf assay was a reproducible test, but this test could not be used for accurately predicting root ratings. The cotyledon tests using zoospores gave results at the population level that were indicative of the root responses of 19 cultivars and lines tested. The cotyledon reaction of individual plants also showed a strong association with root response. The cotyledon test, while not completely predictive of mature root responses, allowed the selection of Phytophthora resistant plants at a higher frequency than could be achieved by random selection.

A survey of possible associations between preharvest environment conditions and postharvest rejections of cut freesia flowers

Botrytis cinerea is the major pathogen infecting cut freesia flowers. Flecking symptoms on petals caused by this fungus result in postharvest rejections and substantial economic loss to both growers and sellers. In a limited survey for industry, numbers of freesia stems sent from a specialist grower in The Netherlands and rejected at a cut flower wholesaler in the United Kingdom were documented. Relationships between preharvest environment conditions in Holland that may predispose flowers to infection and postharvest freesia rejection levels in the United Kingdom due to B. cinerea flecking symptom expression are reported. Freesia rejections peaked during spring and, to a lesser degree, autumn periods. However, no clear correlations between preharvest growing environment conditions (e.g. 3-day means for temperature preceding harvest) and postharvest rejection frequency (%) could be discerned. Thus, sporadic freesia rejections in the United Kingdom were probably attributable either to other unresolved variables during the pre- (e.g. infection pressure) and/or postharvest (e.g. condensation events) phases or to interactions among predisposing variables.

Is the potential of Coccidoxenoides perminutus, a mealybug parasitoid, limited by climatic or nutritional factors?

The encyrtid Coccidoxenoides perminutus is a widely distributed parasitoid of citrus mealybug (Planococcus citri). Worldwide, it has been implicated in successful biocontrol in only a few widely separated localities. C perminutus contributes little to control P. citri in field situations in south-east Queensland, Australia, but invades insectary cultures and reduces mealybug populations considerably under these controlled conditions. This discrepancy between poor field performance and good performance under controlled conditions was investigated to establish whether climatic factors inhibit the field performance of this species in the biological control of P. citri. Subsequent laboratory examination of the influence of varied humidities and temperatures on the activity levels and survival of C perminutus revealed a low tolerance for high saturation deficits (i.e., low % RH at high T degreesC) with reduced reproductive output. The influence of different food sources on adult survival and reproduction was also quantified, to establish if the adverse effects of climate could be overcome by supplementing adult diet. Neither honeydew from their mealybug hosts nor nectar from Alphitonia flowers significantly enhanced parasitoid survival. A subsequent test of five nectar species revealed a significant difference in their influence on C. perminutus survival and reproduction, with only Alpinia zerumbet proving to be as suitable as honey. The floral species that proved suitable in the laboratory need to be checked for their attractiveness to C perminutus in the field and for their ability to enhance the survival and reproductive output of parasitoids. This information suggests that the prevailing dry conditions in south-east Queensland citrus-growing areas apparently impede successful biological control of P. citri by C perminutus, but possibilities are available for habitat manipulation (by providing suitable nectar sources for adult parasitoids) to conserve and enhance C perminutus activity in the field. (C) 2004 Elsevier Inc. All rights reserved.

Methyl jasmonate vapour treatment suppresses specking caused by Botrytis cinerea on cut Freesia hybrida L. flowers

Treatment of cut freesia var. Cote d'Azur flowers with methyl jasmonate (MeJA, 0.1 mu l MeJA l(-1)) vapour suppressed petal specking caused by Botrytis cinerea infection. MeJA efficacy was concentration and incubation temperature dependent. Disease severity, lesion numbers and lesion diameters decreased with increasing MeJA concentration from 0.025 to 0.1 mu l MeJA l(-1). However, there were no significant (P > 0.05) differences among MeJA concentrations examined. MeJA was more effective in reducing B. cinerea flower specking at 20 degrees C than at 12 degrees C. MeJA treatment was ineffective at 5 degrees C. At 20 degrees C, MeJA treatment at 0.1 mu l MeJA l(-1) reduced disease severity, lesion numbers and lesion diameters by 58, 50 and 48%, respectively, as compared to untreated controls. In a repeat experiment, disease severity, lesion numbers and lesion diameters on MeJA vapour treated flowers after 12 h of incubation were reduced by 68, 56 and 50%, respectively. MeJA did not exert direct antifungal activity in-vitro, suggesting that treatment in-vivo reduced B. cinerea-induced flower specking by induction of host defence responses. MeJA at 0.1 mu l MeJA l(-1) significantly (P < 0.05) increased vase life of cut freesia flowers and delayed senescence judged by lower wilt scores and higher fresh weights as compared to untreated controls. (c) 2005 Elsevier B.V. All rights reserved.

Of snakes and flowers: Does preferential detection of pictures of fear-relevant animals in visual search reflect on fear-relevance?

Previous research in visual search indicates that animal fear-relevant deviants, snakes/spiders, are found faster among non fear-relevant backgrounds, flowers/mushrooms, than vice versa. Moreover, deviant absence was indicated faster among snakes/spiders and detection time for flower/mushroom deviants, but not for snake/spider deviants, increased in larger arrays. The current research indicates that the latter 2 results do not reflect on fear-relevance, but are found only with flower/mushroom controls. These findings may reflect on factors such as background homogeneity, deviant homogeneity, or background-deviant similarity. The current research removes contradictions between previous studies that used animal and social fear-relevant stimuli and indicates that apparent search advantages for fear-relevant deviants seem likely to reflect on delayed attentional disengagement from fear-relevance on control trials.

Postharvest infection of Freesia hybrida flowers by Botrytis cinerea

'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 degrees C compared to 5 degrees C. The infection process was relatively rapid at 20 degrees C, with visible lesions produced within 7 h of incubation. However, lesion expansion ceased after 24 h of incubation. Infection was slower at 5 degrees C, with visible lesions produced after 48 h of incubation. However, lesion development at 5 degrees 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 degrees C were higher, but not significantly higher (P > 0.05), than on those incubated at 20 degrees 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 degrees C. In contrast, no lesions were produced at 80 to 90% R. H. at either 5 or 20 degrees C.