Release of acetaldehyde from beta-cyclodextrins inhibits postharvest decay fungi in vitro.

Many naturally occurring plant volatiles are known to have antifungal properties. However, they have limited use because they diffuse rapidly in air. In this in vitro study, acetaldehyde was chosen as a prototype volatile in order to study the controlled release of antifungal volatiles from cyclodextrins (CD). The major postharvest pathogens Alternaria alternata, Botrytis cinerea, and Colletotrichum acutatum were exposed to the pure volatile for 7 days at 23 degrees C. Acetaldehyde was most effective against A. alternata, followed by C. acutatum, and B. cinerea, with 0.12, 0.56, and 1.72 microL/L in air being required to inhibit fungal growth, respectively, according to the bioassay developed. Second, the effectiveness of the new beta-CD-acetaldehyde release system was evaluated against A. alternata for 7 days at 23 degrees C. Sufficient volatile was released from 0.7 g of beta-CD-acetaldehyde to prevent fungal growth in vitro.

Effect of Temperature on Apothecial Longevity and Ascospore Discharge by Apothecia of Monilinia vaccinii-corymbosi.

Pseudosclerotia of Monilinia vaccinii-corymbosi with apothecial initials were collected from blueberry (Vaccinium corymbosi cv. Jersey) fields in Grand Junction, MI, in the spring of 2002 and 2003 and monitored during apothecial development and maturation. Apothecia with cup openings as small as 1.2 mm in diameter were able to discharge ascospores. The number of ascospores discharged increased exponentially as the diameter of the cup opening increased, before leveling off at a cup diameter of about 6 mm. Cytological studies showed that ascospore discharge correlated well with the stage of development of asci and ascospores in the apothecium. The effect of temperature on the longevity of apothecia was studied at 10, 15, 20, and 25°C. Initial ascospore discharge was greater for apothecia incubated at higher temperatures (20 and 25°C). However, total discharge was greater in apothecia incubated at lower temperatures (10 and 15°C), as they persisted longer than those incubated at 20 and 25°C. Incubating apothecia at freezing temperatures (-2, -4, -6, and -8°C) for 1 h resulted in a 50 to 98% reduction in the number of ascospores discharged compared with before freezing. However, apothecia incubated down to -6°C were able to recover their ability to discharge ascospores by 2 days after the freezing treatment. Ascospores discharged from apothecia after freezing at -2°C for 1 h remained viable. However, the germination ability of ascospores from apothecia frozen at -4, -6, and -8°C decreased with decreasing temperature such that only 10% of ascospores from apothecia frozen at -8°C germinated successfully. The information obtained in this study may be useful in the development of scouting and management strategies for the control of mummy berry disease.

Temporal synthesis and radiolabelling of the sorghum 3-deoxyanthocyanidin phytoalexins and the anthocyanin, cyanidin 3-dimalonyl glucoside.

Sorghum (Sorghum bicolor) synthesizes a complex mixture of 3-deoxyanthocyanidin phytoalexins in response to inoculation with the non-pathogenic fungus Bipolaris maydis. The anthocyanin cyanidin 3-dimalonyl glucoside, is also synthesized naturally in response to light. To determine the order and time of appearance of these compounds, etiolated sorghum mesocotyls were inoculated with B. maydis and tissue extracts were analysed by photodiode array-HPLC every 2 h for the first 24 h and at 48 h post inoculation (hpi). Uninoculated and inoculated etiolated mesocotyls were also allowed to incorporate L-[U-14 C] phenylalanine. Apigeninidin appeared at 10 hpi, followed by luteolinidin and apigeninidin 5-O-arabinoside at 14 hpi. Luteolinidin 5-methylether was not detected until 18 hpi and apigeninidin 7-methylether not until 20 hpi. The concentrations of the primary phytoalexins, apigeninidin, luteolinidin and apigeninidin 5-O-arabinoside, rose steadily between 12 and 24 hpi, and the levels of apigeninidin and luteolinidin were approximately equivalent by 24 hpi. However, between 24 and 48 hpi luteolinidin and luteolinidin 5-methylether accumulated rapidly so that by 48 hpi the amounts of luteolinidin and luteolinidin 5-methylether had increased approximately twofold. Radiolabelling also showed that 14 C was incorporated into the 3-deoxyanthocyanidins and cyanidin 3-dimalonyl glucoside. Several other unidentified phenolic compounds also accumulated radioactivity.

Screening Cherry Germ Plasm for Resistance to Leaf Spot.

A detached leaf disk assay was developed for screening sour cherry (Prunus cerasus) cultivars for resistance to cherry leaf spot (Blumeriella jaapii). This assay was used to characterize the events occurring in cv. Montmorency (susceptible) and cv. GiSelA 6 [GI 148-1] (resistant) host-pathogen interactions, and to develop a disease scoring scheme to categorize disease severity in sour cherry trees. Forty-three seedlings grown from seeds collected in Russia were screened for resistance using the scoring scheme. Cross infection studies were also carried out with leaf spot isolates from four other Prunus species. These studies were made possible by the development of a new method of culturing B. jaapii isolates, using cherry fruit agar. This method enabled large amounts of inoculum to be produced within 2 weeks rather than a couple of months as required previously. In 'Montmorency', disease symptoms were first observed 4 days postinoculation (dpi), with the appearance of small white spots on the undersides of inoculated leaves. These spots gradually grew, producing erumpent spore masses in acervuli approximately 7 dpi. In 'GI 148-1', disease symptoms were also first observed 4 dpi, with the appearance of small transparent lesions. In the majority of cases, these lesions did not increase in size; however, acervuli occasionally were formed approximately 8 dpi. These contained small cirrhi and were often surrounded by an abscission zone. Of the sour cherry seedlings tested, only 'Almaz' open pollinated (o.p.) R1(1) was rated as resistant. 'Almaz' o.p. R1(1) and 'GI 148-1' were also rated as resistant to leaf spot isolates from other Prunus species. These results and the implications for breeding resistant sour cherry cultivars are discussed.