Cinerea Conidia Research Articles

The Influence of Diurnal Temperatures on the Postharvest Susceptibility of Poinsettia toBotrytis cinerea

The influence of day/night (DT/NT) temperatures of 16/16, 19/19, 22/22, 16/19, 19/22, 16/22, 19/16, 22/19, and 22/16°C during poinsettia production on postharvest bract and foliage susceptibility to Botrytis cinerea was investigated. Plants were inoculated with 2.7 x 10 5 B. cinerea conidia per ml of water following a 3- or 6-week temperature treatment and incubated at 20°C. Area under the disease progress curve (AUDPC) data indicated that the postharvest susceptibility of poinsettia bracts and foliage to B. cinerea, measured by the proportion of bracts and foliage infected and the proportion with sporulating B. cinerea, was not influenced by the difference in DT and NT but increased as DT or NT during production increased. As plants matured, as indicated by thermal time, AUDPC values increased (P = 0.001) more for the proportion of bracts infected (R 2 = 0.73) than for the proportion of bracts with sporulating B. cinerea (R 2 = 0.86) and the proportion of foliage with sporulating B. cinerea (R 2 = 0.74). Results suggested that commercial growers using higher NT than DT to limit poinsettia height are not increasing the postharvest susceptibility of their crop to B. cinerea. However, the increased susceptibility of maturing poinsettias suggests disease management strategies should be intensified during crop finishing and Dostharvest handling.

Suitability of a detergent-sensitive electrode for the determination of the absorption of cationic detergents by fungal conidial cells

The study of the process of absorption of detergents by microbial cells is important for the understanding of the mode-of-action of these chemical agents in microorganisms. With the aim to study the absorption of alkyltrimethylammonium bromides by conidia of the phytopathogenic fungus Botrytis cinerea; simple detergent-sensitive electrodes were constructed and tested for this purpose. The electrodes had a hexadecyltrimethyl-ammonium bromide and tricresyl phosphate sensor system in poly-(vinylchloride) membranes. Electrodes with an internal reference, or with the membrane applied to a support made of electrically conductive silver-epoxy resin, were prepared and evaluated in parallel for comparison. The performance of the two types of electrodes was identical. The response was linear between 10 and 100 μM and the critical micelle concentration of the detergent, with slopes of ca. 45, 48 and 56 mV/decade of activity, respectively, for dodecyl-, tetradecyl- and hexadecyl-trimethylammonium bromide. Direct comparison of potentiometry with the constructed detergent-sensitive electrodes, with a spectrophotometric procedure based on the Orange G dye, indicated that these electrodes are suitable to study the process of absorption of alkyltrimethylammonium bromides by B. cinerea conidia. The affinity of these molecules to the spores increased with the length of the hydrocarbon chain of the detergent, and was reduced in the presence of Mg 2+ or Ca 2+, or at low pH, indicating that, as reported in the literature for the binding of cationic detergents to organic molecules, the absorption of the alkytrimethylammonium bromides by B. cinerea spores was hydrophobic and ionic in nature.

Suppression of Botrytis blight in cut rose flowers with gibberellic acid: effect of concentration and mode of application

Abstract Symptoms of Botrytis blight in petals of harvested rose flowers inoculated after harvest with suspensions of Botrytis cinerea conidia become visible after five–seven days. The development of Botrytis blight was significantly suppressed in detached petals of cvs. Mercedes and Sonata treated for 24 h with a 20 mg l −1 solution of GA 3 . Botrytis was suppressed to a lesser extent in petals of cvs. Celica and Ilseta, with no effect recorded in cvs. Golden Times and Madelon. To obtain a similar level of suppression in intact flower buds to that obtained in detached petals, a postharvest spray of GA 3 , with a concentration of 346 mg l −1 (1 mM) was required. Soon after harvest, the inner petals of cv. Mercedes were more sensitive to B. cinerea than the outer petals, whereas the converse was observed when petals were removed from buds maintained for five days in a vase. Neither spore germination, germ-tube elongation nor the linear growth of the fungus mycelium were affected by gibberellin. Use of GA 3 for control of Botrytis blight in rose flowers as an alternative to environmentally-hostile fungicides is proposed.

The fungistatic and fungicidal activity of vinclozolin against Botrytis cinerea

The germination of Botrytis cinerea conidia in nutrient medium was completely inhibited by 20 μ m vinclozolin. Probits of the percentage inhibition of spore germination were linearly correlated with log vinclozolin concentration indicating that vinclozolin acted as a single compound with one mechanism of action. Treatment of resting (ungerminated) spores suspended in buffer with vinclozolin concentrations as high as 750–1000 μ m resulted in no significant release of cellular potassium and inorganic phosphate or decrease in cell viability. On the contrary, for germinated B. cinerea conidia growing in liquid medium, vinclozolin showed a slow but marked fungicidal activity. After 3 and 20 h of treatment with 2 μ m vinclozolin, 63 and 4% of the cells survived, respectively. However, if vinclozolin was added to germinated spores in non-growing conditions, no significant reduction in cell viability was observed after 20 h of treatment. The results indicated that vinclozolin has a strong fungistatic activity, but is fungicidal only in actively growing cells, and that it causes no drastic alteration in the permeability of the cytoplasmic membrane of resting conidial cells. The implications of these results for the chemical control of plant mycoses are briefly discussed.

Effects of temperature, vapour pressure deficit and radiation on infectivity of conidia ofBotrytis cinerea and on susceptibility of gerbera petals

The effect of vapour pressure deficit, temperature and radiation on the postharvest susceptibility of gerbera flowers toB. cinerea, on the water relations of gerbera flowers and on the lesion formation after conidial infection ofB. cinerea was studied. The temperature range in whichB. cinerea could germinate and growin vitro is 5–30 °C. In climate chamber experiments flowers had more lesions ofB. cinerea at temperatures of 20 and 25 °C than at 10 and 15°C. At 15, 20 and 25°C the infectivity ofB. cinerea conidia was negatively affected during a storage-period of 7 days. At a vapour pressure deficit (VPD) of 200 Pa significantly more conidia ofB. cinerea were infective than at 800 Pa. At a VPD of 800 Pa the susceptibility of gerbera flowers forB. cinerea was not significantly different than at 200 Pa. High radiation levels in glasshouses in spring and summer negatively influenced the infectivity of conidia ofB. cinerea on the flower surface, but did not affect the susceptibility of gerbera flowers forB. cinerea. In spring and early summer conidia lost their infectivity at high radiation levels, high temperatures and high levels of VPD. In summer gerbera flowers could be more susceptible toB. cinerea because of high temperatures in glasshouses, but the negative effect of radiation on the conidia ofB. cinerea seemed to overrule the temperature effect. Thus, the numbers of lesions in spring and summer can be low compared with the numbers in other seasons, although the numbers ofB. cinerea colonies on spore traps can be high. The effect of temperature on the susceptibility of gerbera flowers can probably be explained by changes of water status in the petals. At higher temperatures the number of lesions and the turgor (=water potential—osmotic potential) in the petals increased. Temperatures 95% and VPD<50 Pa) had a temporary negative effect on the number of lesions. After 3 days of incubation the numbers of lesions were about equal (≥30 lesions/cm2) from 5 to 20°C. At 30°C no lesion formation was observed even after 3 days.

Differences Between Rose Cultivars in Susceptibility to Infection byBotrytis cinerea

Differences in the susceptibility of rose flowers to blossom blight caused by Botrytis cinerea were investigated. Rose flowers, cvs. Supra and Royalty, were inoculated with various concentrations of B. cinerea conidia and incubated in humidified chambers at 21 C. Disease severity was quantified 2 days later as the number of lesions that had developed on each flower. The slope of the inoculum concentration/disease severity (IC/DS) regression line was used as a measure of susceptibility. Supra was more susceptible than Royalty, but the susceptibility of each cultivar and the difference between them varied among sampling dates. In experiments using isolated petal disks, there was no difference between cultivars in the number of B. cinerea conidia that germinated on the petal surfaces

Effects of water extracts of a composted manure-straw mixture on the plant pathogen Botrytis cinerea

Manure-straw mixtures were composted and water extracts, made by incubating compost in water for 3 to 18 days, were assessed for antagonistic activity against Botrytis cinerea, using a range of tests. Extracts of all ages inhibited conidial germination on glass slides and reduced mycelial growth on agar. Mixing extracts of all ages with droplets of suspensions of B. cinerea conidia on detached Phaseolus bean leaves suppressed lesion development, but only 3- to 8-day-old extracts had an effect when sprayed onto leaves 2 days before inoculation. Extracts contained a large and varied microbial population of actinomycetes (0.3 to 2.4×10(5) c.f.u.ml(-1)), bacteria (1.5 to 5.6×10(10) c.f.u.ml(-1)), filamentous fungi (25.0 to 45.5 c.f.u. ml(-1)) and yeasts (26.1 to 62.6 c.f.u.ml(-1)). Eight- and 18-day-old extracts lost activity completely on filter sterilization or autoclaving. Weekly sprays of 8-day-old extracts onto lettuce in the glasshouse had no effect on the incidence of grey mould, but significantly reduced its severity and increased marketable yield. The use of compost extracts in biocontrol of plant diseases and their possible mode of action is discussed.

LEAF DISK SCREENING FOR RESISTANCE TO BOTRYTIS CINEREA IN STRAWBERRY GERMPLASM

Several methods using detached leaf tissues were investigated as potential early screening techniques for identifying strawberry germplasm resistant to Botrytis cinerea, which causes gray mold fruit rot. The fungus penetrates young leaves, remaining latent and symptomless under the cuticle until the leaves die, when the pathogen resumes growth and sporulates, providing almost all the primary inoculum for fruit infections. The best leaf screening method involved spraying potted strawberry plants in a 20±5 C greenhouse with a suspension of B. cinerea conidia, enclosing the plants in a plastic tent with a humidifier to provide humidity &gt;95% for 72 hours, then resuming normal greenhouse conditions for several days before sampling young leaves. Leaf disks 1 cm in diameter were then cut, surface sterilized in 70% ethanol for 15 sec and 1% sodium hypoclorite for 2 min, dipped in paraquat herbicide (20 mg/l a.i.) to kill the tissues, rinsed twice in sterile water, and plated on water agar containing .01 % streptomyacin to inhibit bacterial growth. Plates were incubated at 21±2 C under 12 hour daylengths for seven days, and incidence and density of B. cinerea conidiophores on the disks determined. Despite much variation between disks within genotypes, clear differences in susceptibility between genotypes emerged which often correlated well with field suscpetibility to gray mold fruit rot.

Attempts to control Botrytis cinerea on roses by pre- and postharvest treatments with biological and chemical agents

The biocontrol agent Trichoderma harzianum and the fungicides polyoxine B, fenpiclonil, tebuconazole with or without dichlofluanid, and fenbuconazole were sprayed once a week in a rose greenhouse. Botrytis infection of branches was reduced by 50–70%. The importance of reduction of conidial inoculum by this treatment is discussed. Severity, but not incidence, of petal infection was found to be controlled significantly by some of the fungicides only 2 days after the application and not 5 days later. Fenpiclonil, tebuconazole, dichlofluanid alone or alternated with T. harzianum, and T. harzianum also reduced development of grey mould on flowers that were harvested soon after the treatment and incubated under Botrytis-conducive conditions. This beneficial effect was observed only with latent natural infection and not in flowers inoculated with B. cinerea conidia after harvest. The difficulty of controlling the disease by sprays in the greenhouse is discussed. Postharvest treatments by spraying cut flowers with the fungicides iprodione plus thiram, tebuconazole plus dichlofluanid and polyoxin D, but not with another 11 treatments, reduced disease incidence significantly by 50–58%.

POSTHARVEST CONTROL OF BOTRYTIS CINEREA INFECTIONS ON CUT ROSE FLOWERS WITH PYRROLNITRIN.

Pyrrolnitrin, an antibiotic isolated from Pseudomonas cepacia, was used for postharvest control of B. cinerea infections on cut `Sonia' and `Royalty' rose flowers. Pyrrolnitrin was applied as a bud dip and followed by inoculation with B. cinerea conidia. Dip treatments of 12 to 200 mg·liter-1 pyrrolnitrin significantly reduced disease severity during storage at 2C and promoted post-storage fresh weight gain (an index of cut flower quality). No phytoxicity was observed on leaves or petals at concentrations of up to 200 mg/liter. Dip treatment with 100 mg/liter pyrrolnitrin reduced disease severity to &lt;10% of that on control flowers and prevented post-storage flower rot. This level of disease control was comparable to that achieved with 1800 mg/liter vinclozolin.

Conidial germination of Botrytis cinerea in relation to aeciospores and aecia of groundsel rust ( Puccinia lagenophorae)

Interactions between conidia of Botrytis cinerea and aeciospores of Puccinia lagenophorae (rust of groundsel, Senecio vulgaris) were studied because rusted groundsel exhibits exceptionally high mortality when additionally infected by B. cinerea. The latter acts as a secondary invader via rust pustules on leaves and stems. Conidia of B. cinerea, collected dry from parent cultures, failed to germinate on agarose in Petri dishes but did so in the presence of aeciospores, germination generally increasing as aeciospore concentration increased. Germination on agarose was also stimulated by diffusates from groundsel leaves and by the removal of agarose discs to the surface of groundsel leaves. Germination on such discs was higher over sporulating lesions on rusted leaves than on healthy leaves and decreased with radial distance from the centre of individual lesions. When conidia were sown directly onto the leaf, germination over epidermis at the edge of a lesion was greater than that within a lesion, but germination in both these positions was greater than that at a distance from the lesion. The promotive effects of rust on the germination of B. cinerea conidia in vivo were quantitative rather than qualitative but they explain in part the synergy between P. lagenophorae and B. cinerea.

Substances in dead plant tissue that stimulate infection of French bean leaves by Botrytis cinerea

Spreading lesions were found in primary leaves of French bean after inoculation with pieces of dead bean tissue on which a droplet of a suspension ofBotrytis cinerea conidia was placed, and after inoculation with conidia suspended in a diffusate from dead tissue. After fractionation of aqueous extracts from dead bean leaves, the infection-stimulating activity was confined to the fractions containing sugars and phosphate esters.

Comparison of germination of Cladosporium herbarum and Botrytis cinerea conidia in vitro in relation to nutrient conditions on leaf surfaces

Conidia of Cladosporium herbarum and Botrytis cinerea differed in their ability to germinate in water. Potassium nitrate, glucose, and carbohydrate mixtures at concentrations similar to carbon and nitrogen levels on leaf surfaces were tested for their effect on germination and subsequent germ tube growth. For both fungi, all the treatments increased the rate of germination. The treatments also stimulated the total percentage germination of C. herbarum conidia. Glucose, a glucose – potassium nitrate solution, and carbohydrate mixtures stimulated both germ tube production and total germ tube lengths of conidia of C. herbarum. Botrytis cinerea conidia produced multiple germ tubes per conidium in distilled water, potassium nitrate, and carbohydrate mixtures. Glucose and glucose – potassium nitrate solutions stimulated production of a single germ tube per conidium. All treatments stimulated germ tube growth of B. cinerea conidia.

Effect on nutrient leakage, respiration and germination of Botrytis cinerea conidia caused by leaching with water

Effect on nutrient leakage, respiration and germination of Botrytis cinerea conidia caused by leaching with water

The development of Botrytis cinerea on cut flowers of carnation

SUMMARYEnclosing carnation blooms in polythene increased rotting associated with naturally occurring Botrytis infections and accelerated the rate of conidia development when flowers were artificially inoculated before being stored at 1·7 °C. Petal infections were observed 16 and 48 h after inoculation and incubation at 18·3 and 1·7 °C respectively. The products of exosmosis from petals kept at 18·3 °C for 7 days stimulated germination of B. cinerea conidia. Slight pectic enzyme activity was detected in a liquid medium, derived from carnation petals, after incubating B. cinerea cultures at 18·3 °C for 6 days. Although cultures of Botrytis evolved virtually no ethylene, the surge of ethylene produced by uncontaminated ageing flowers occurred sooner after inoculation. A spray containing 1·2% a.i. of 2‐aminobutane controlled rotting but damaged flowers.