of biocontrol were known; however, evidence of 

 natural biocontrol of Botrytis was found in straw- 

 berry leaves from various fields by then gradu- 

 ate student P. Gordon Braun. Another student, 

 Morven McLean, proceeded to monitor the straw- 

 berry microflora year round, including periods of 

 snow cover. She quantified mycelial fungi, yeasts , 

 and bacteria on living and dead foliage, flowers, 

 and fruits. This overview of the microflora 

 provided an important background to biocontrol 

 studies. A collection of organisms initiated by 

 Ms. McLean was expanded greatly by graduate 

 student Peng Gang, who subsequently evalu- 

 ated the isolates as biocontrol candidates against 

 Botrytis. 



The evaluation of several hundred microor- 

 ganisms as biocontrol candidates required pro- 

 cedures that were efficient but realistic. Tests in 

 field plots provide low "representational error." 

 Representational error is the error that may 

 arise from differences between conditions in the 

 tests and in growers' fields. For logistical rea- 

 sons all isolates could not be tested in field plots, 

 which must be suitably replicated and adequately 

 spaced to minimize interplot interference such 

 as that arising from the spread of biocontrol 

 organisms among plots. Conditions in labora- 

 tory tests may differ enormously from those in 

 the field but when suitably designed may allow 

 for rapid evaluation in an initial screening. 

 Tests that utilize plant materials are likely to be 

 more realistic (less representational error) than 

 those done on artificial substrates such as agar 

 media. Tests on plants in the growth room and 

 greenhouse may provide conditions intermedi- 

 ate between the laboratory and the field. 



Peng Gang conducted comparative biocontrol 

 tests on leaf discs and detached petals in the 

 laboratory, on attached leaves and flowers in the 

 growth room and greenhouse, and on plants in 

 the field. Biocontrol effectiveness of 230 isolates 

 on leaf discs ranged from to 100%. These 

 isolates were grouped into five categories repre- 

 senting different ranges of biocontrol effective- 

 ness. Representatives of each group then were 

 tested in the growth room, greenhouse, and 

 field. In most instances, relative effectiveness of 

 the isolates in various controlled conditions was 

 similar to that in the field. The controlled tests 



thus provided a strong indication of biocontrol 

 activity of organisms in the field. The more 

 effective organisms were fungi known as 

 Gliocladium roseum, Penicillium sp., 

 Trichoderma viride, Epicoccum purpurascens, 

 and Trichothecium roseum. Yeasts and bacteria 

 often did not perform well in the field. 



Field studies conducted during four crop 

 seasons at various locations in Ontario demon- 

 strated that several microfungi controlled 

 Botrytis on strawberry flowers and fruits as 

 effectively as captan, a fungicide that is recom- 

 mended widely for fruit rot control. In a majority 

 of tests, spores of the fungi were suspended in 

 water (one million spores/ml) and applied with a 

 hand-operated sprayer. The biocontrol fungi 

 were applied at five- to seven-day intervals from 

 the green flower-bud stage to the white-pink 

 fruit stage. Botrytis was applied once to improve 

 test conditions. Fruit rot was assessed after the 

 berries had been stored for seven to ten days 

 under conditions highly favorable for Botrytis. 

 The biocontrol agents generally suppressed rot 

 by about 65 to 85%. The fungi Gliocladium, 

 Trichoderma, and Penicillium each suppressed 

 Botrytis effectively, but overall, Gliocladium 

 was the best. 



Biocontrol agents or fungicides applied dur- 

 ing flowering and fruiting suppress fruit rot 

 largely by protecting the flowers against infec- 

 tion by Botrytis . In almost all instances , Botrytis 

 infects the flowers from which it grows into the 

 developing fruits, giving rise to the familiar rot 

 at the stem end of the fruit. Direct infection of 

 fruit usually occurs only when infected petals or 

 diseased berries adhere to the fruit surface. 

 Protection of the flowers is the most commonly 

 used strategy for fruit rot control; however, an 

 alternative is to destroy Botrytis at the source. 



In Ontario, and possibly in other areas of 

 northeastern North America, almost all Botrytis 

 spores produced when strawberries are flower- 

 ing are formed on dead leaves infested with 

 mycelia of the pathogen. The leaves are infected 

 chiefly when they expand, but Botrytis remains 

 dormant in the outer portion of the leaf until the 

 leaf turns yellow and dies. The fungus then 

 grows rapidly within the leaf and is able to 

 sporulate in a couple of days. The spores are 



Fruit Notes, Winter, 1992 



