Influence of Temperature, Inoculation Interval, and Dosage on Biofumigation with Muscodor albus to Control Postharvest Gray Mold on Grapes F. Mlikota Gabler, Institute for Adriatic Crops, Put Duilova 11, 21000 Split, Croatia; R. Fassel, PACE International, LLC, Visalia, CA 93291; J. Mercier, AgraQuest Inc., Davis, CA 95616; and J. L. Smilanick, United States Depart- ment of Agriculture–Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier, CA 93648 trol gray mold are needed that are safe, ABSTRACT effective, and economical (1,15,16,21,23). Mlikota Gabler, F., Fassel, R., Mercier, J., and Smilanick, J. L. 2006. Influence of temperature, Alternatives to sulfur dioxide for control of inoculation interval, and dosage on biofumigation with Muscodor albus to control postharvest postharvest gray mold include near-harvest gray mold on grapes. Plant Dis. 90:1019-1025. ethanol or biological control agent applica- tions (11,15) and postharvest immersion of Control of postharvest gray mold, caused by Botrytis cinerea, on Thompson Seedless grape by grapes in bicarbonates, chlorine, ethanol, biofumigation with a rye grain formulation of Muscodor albus, a fungus that produces volatiles or heated water (14,16,21,23). However, lethal to many microorganisms, was evaluated. The influences of temperature, biofumigant dos- methods requiring additional postharvest age, and interval between inoculation and treatment on disease incidence and severity on de- tached single berries were assessed. When biofumigation began within 24 h after inoculation, processing and handling increase costs and higher M. albus dosages (≥50 g of the M. albus grain formulation per kilogram of grapes at 20ºC could alter the appearance of the berries or or 100 g/kg at 5ºC) stopped infections and control persisted after M. albus removal. Biofumiga- cause detachment of berries from the clus- tion was more effective at 20 than 5ºC. Among inoculated clusters inside clamshell boxes incu- ter rachis. Altering the orientation of the bated for 7 days at 15ºC, gray mold incidence was reduced from 20.2% among untreated grape wax platelets on the surface of the berries fruit to less than 1%, when ≥5 g of the formulation per kilogram of grapes was added. Among by rubbing caused by excessive handling grape berries commercially packaged in ventilated polyethylene cluster bags incubated for 7 can destroy the bloom, which is the effect days at 15ºC, gray mold incidence was 40.5% among untreated fruit and 11.1 or 6.7% when the of light reflected and diffused by the over- formulation at 5 or 20 g/kg, respectively, had been added. In the same packaging, among grape lapping wax platelets. This gives the cuti- berries incubated for 28 days at 0.5ºC, gray mold incidence was 42.8% among untreated fruit cle a shine rather than the desirable luster and 4.8 or 4.0% when the formulation at 5 or 10 g/kg, respectively, had been added. Lower dos- effect (24). Alternatives requiring addi- ages (≤20 g/kg) suppressed disease development while M. albus was present; however, after tional processing are unlikely to be imple- their removal, B. cinerea resumed growth and gray mold incidence increased. Placement of M. mented by California table grape growers, albus inside grape packages significantly controlled gray mold and may be a feasible approach who normally pack their fruit into com- to manage postharvest decay of table grape. mercial packages in vineyards (9). The main advantage of fumigation to control postharvest decay compared with other Gray mold, caused by Botrytis cinerea ide fumigation during initial forced-air approaches is that it does not require proc- Pers., causes pre- and postharvest decay of cooling of the grape berries, followed by essing or manual handling of the grapes. table grapes. B. cinerea is especially trou- 2- to 6-h-long weekly fumigation during Most grape storage facilities in California blesome because of its rapid growth rate cold storage (17). In export packages, sul- are designed for sulfur dioxide fumigation and ability to spread among berries even at fur dioxide generator sheets are used, and use it routinely. A number of alterna- cold temperatures (–0.5ºC). Infections that which continuously emit a low concentra- tives, including fumigants (5,22,25– cause postharvest losses can originate from tion of gas within the packages (1,11). 27,32,33) and controlled atmospheres spores on the surface of the berries, micro- Sulfur dioxide fumigation effectively (7,8), have been investigated for the con- scopic latent infections that occur before controls gray mold, but bleaching injury to trol of postharvest decay of table grapes harvest during the growing season, or in- berries, particularly among those detached with some success. A novel alternative for fection of mechanical wounds (10,11). The from the cluster rachis, and injury to the controlling postharvest decay is biological fungus produces abundant aerial mycelium rachis itself occur among commercially fumigation, or biofumigation, with the which spreads from infected to healthy stored grapes (9). After fumigation with fungus Muscodor albus Worapong, berries, so that an uncontrolled infection sulfur dioxide, grape berries become more Strobel, and Hess (18,20). M. albus, which from a single berry can spread to an entire susceptible to subsequent infections by B. was isolated from a cinnamon tree in Hon- package of grape berries. Postharvest gray cinerea (30) that can occur during trans- duras, is a non-spore-producing fungus of mold usually is controlled by sulfur diox- portation and marketing. Although the the family Xylariaceae. The volatiles pro- tolerance for sulfite residues (10 µg/g) is duced by M. albus, a mixture of low mo- Corresponding author: F. Mlikota Gabler rarely exceeded in commercial practice lecular weight compounds, are biocidal or E-mail: [email protected] (4), excessive residues of sulfur dioxide biostatic to a broad variety of microorgan- can occur when it accumulates in wounded isms (29,31), including Botrytis cinerea, Current address of F. Mlikota Gabler: USDA-ARS or detached berries (28). Also, sulfur diox- Geotrichum citri-aurantii, G. candidum, San Joaquin Valley Agricultural Sciences Center, ide is not accepted for organic grapes un- Monilinia fructicola, Penicillium digi- 9611 South Riverbend Ave, Parlier, CA 93648. der current certification rules, and some tatum, and P. expansum (18,20), and con- Accepted for publication 12 March 2006. regulatory agencies do not allow the dis- trolled brown rot of peach (18), gray mold charge of sulfur dioxide to the air after and blue mold of apple (18), and green fumigation. mold and sour rot of lemon (20). Isobu- DOI: 10.1094/PD-90-1019 Because of the issues associated with tyric acid emission was closely associated This article is in the public domain and not copy- sulfite residues, sulfur dioxide emissions, with antifungal activity at both 4 and 21ºC rightable. It may be freely reprinted with custom- ary crediting of the source. The American Phyto- and sulfur dioxide’s negative impact on when Muscodor albus had been grown on pathological Society, 2006. grape quality, alternative strategies to con- a rye grain substrate (13). A preliminary Plant Disease / August 2006 1019 report (19) also indicated that M. albus sterile water to an absorbance of 0.25 at mold, gray mold incidence and severity could control postharvest gray mold of 425 nm as determined by a spectropho- were assessed. The amount and appearance table grapes at temperatures encountered tometer. This density contained 1 × 106 of M. albus mycelium present on the rye during commercial storage (–0.5 to 1ºC), conidia/ml and was diluted with sterile grain formulation at the end of incubation transportation (2 to 5ºC), and marketing deionized water to obtain the desired spore also was observed. The experiment was (15 to 20ºC) (17). In 2004, M. albus was concentrations. done twice. submitted to the United States Environ- Biofumigant. M. albus formulation The effect of temperature, M. albus mental Protection Agency for registration consisted of rye grain colonized with M. formulation dosage, and type of packag- to control postharvest diseases of food and albus strain 620 was grown according to ing on postharvest gray mold of grape nonfood crops, and to control preplant Mercier and Jiménez (18). The grain cul- clusters. Grape clusters were divided into diseases of seeds, bulbs, and tubers (2). ture was air dried at room temperature and small clusters of approximately 100 g each Sulfur dioxide and other fumigant gases stored at –8ºC prior to use. The desiccated and randomized so that a portion of each that are applied externally must penetrate M. albus rye grain culture was activated by cluster was represented in each treatment. into the grape packages to be effective. adding an equal weight of deionized water Approximately 300 ml of 105 conidia/ml Luvisi et al. (17) reported that some types 2 to 3 h prior to use (13). In all experi- was sprayed over about 50 kg of grape of table grape packaging impeded sulfur ments, M. albus was placed in an open-top clusters. Unless stated otherwise, the grape dioxide penetration more than others, al- plastic container and was never in direct clusters were inoculated about 3 h prior to though commercial packages in use today contact with grape berries. treatment. M. albus grain culture was acti- are designed to facilitate penetration of The effect of temperature, interval be- vated 2 h prior to treatment, as described sulfur dioxide and cooling air (9,17). One tween inoculation and biofumigation, previously. approach to avoid issues associated with and M. albus formulation dosage on Experiments conducted at 15°C. M. the penetration of fumigants applied exter- postharvest gray mold on detached albus formulation was placed inside a nally is to place the biofumigant M. albus grape berries. Two temperatures (20 and clamshell container with grape clusters.