Biological Control of Gray Mold with Ulocladium atrum in Annual Strawberry Crops.

The efficacy of the fungal antagonist Ulocladium atrum to control gray mold in annual strawberry crops using waiting-bed transplants under field conditions was investigated. Seven field experiments were conducted with strawberry cv. Elsanta during the summer seasons of 1996-99 in the Netherlands. Treatments included untreated controls, fungicide programs, U. atrum spray programs, and crop sanitation. Under low disease pressure, U. atrum spray programs effectively reduced gray mold at harvest in four of seven experiments. Sprays of U. atrum starting at transplanting resulted in better control of gray mold than sprays starting at the beginning of flowering in only one of five experiments. Removal of necrotic leaves did not affect the level of gray mold, which demonstrated that strawberry leaves were not a significant inoculum source for Botrytis cinerea in this annual cropping system. These results suggest that U. atrum can be effective in reducing gray mold in strawberry crops, and further studies on the use of the antagonist in annual systems should consider flowering time as the best period to apply this antagonist.

Inoculum sources of the tan spot fungus Pyrenophora tritici-repentis in The Netherlands.

Since 1994 the importance of tan spot of wheat has increased in the wheat growing areas of the Netherlands. The purpose of the present study was to determine inoculum sources of this disease caused by Pyrenophora tritici-repentis. Both in 1999 and 2000, the incidence of tan spot was assessed in 40 commercial fields of winter wheat scattered over the main wheat growing areas of the Netherlands. Adjoining fields were checked for presence of stubble or crops with straw covers and the surrounding vegetation was searched for grasses with leaf spots. Straw and affected leaves of wheat and grasses were examined for P. tritici-repentis. In greenhouse experiments the pathogenicity of isolates from alternative hosts was compared with that of isolates from wheat. The possible development of P. tritici-repentis perithecia on straw of crops other than wheat was explored for barley, oat, rye grass and rape grown in fields nearby a tan spot affected wheat field. Furthermore, dispersal of tan spot was studied in a field trial in which winter wheat was sown leeward to stubble of above-mentioned severely tan spot affected wheat crop. During the surveys three cases were found of wheat crops adjoining fields with P. tritici-repentis infested stubble or straw covers. It was only after flowering that the first symptoms of tan spot appeared in the three commercial wheat crops. Couch grass (Elymus repens) was often found as host of P. tritici-repentis. In the surroundings of more then half of the wheat crops affected by tan spot this weed was also infected. Pyrenophora tritici-repentis isolates from couch grass were found to be as pathogenic to wheat as isolates from wheat to both wheat and couch grass. The observations on straw of barley, oat, rye grass, rape and wheat revealed P. tritici-repentis perithecia only on wheat straw. In the field trial with wheat sown leeward to P. tritici-repentis infested stubble, first symptoms of tan spot appeared on wheat during April and May when the release of ascospores was at a maximum. Disease severity gradually decreased with increasing distance from the side adjoining the stubble. The results of this study indicate that straw covers and stubble from tan spot diseased wheat crops and cough grass are inoculum sources of P. tritici-repentis.

The fungal biocontrol agent Coniothyrium minitans: production by solid-state fermentation, application and marketing.

Biological control agents (BCAs) are potential alternatives for the chemical fungicides presently used in agriculture to fight plant diseases. Coniothyrium minitans is an example of a promising fungal BCA. It is a naturally occurring parasite of the fungus Sclerotinia sclerotiorum, a wide-spread pathogen which substantially reduces the yield of many crops. This review describes, exemplified by C. minitans, the studies that need to be carried out before a fungal BCA is successfully introduced into the market. The main aspects considered are the biology of C. minitans, the development of a product by mass production of spores using solid-state fermentation technology, its biocontrol activity and marketing of the final product.

Biocontrol of Botrytis cinerea by Ulocladium atrum in Different Production Systems of Cyclamen.

Ten experiments in six different commercial greenhouses were conducted to study the effect of spraying conidial suspensions of the saprophytic fungus Ulocladium atrum (1 × 106 conidia per ml) on infection of leaves and flower petioles of cyclamen by Botrytis cinerea (gray mold). The greenhouses represented the range of Dutch growing systems of cyclamen, differing considerably in the arrangement of plants, irrigation system, heating system, and material of pots. Applications of U. atrum suspensions were carried out at 4-week intervals only twice on young plants or were continued during the whole growing season until 4 weeks before plants were marketable. The antagonistic treatments were compared with untreated or water-treated controls and with fungicide applications as applied by growers. After applications of U. atrum at 4-weeks intervals, disease development was significantly reduced in experiments carried out in five different greenhouses. In no case did treatments with fungicides give better control than U. atrum treatments. Two applications of U. atrum resulted in sufficient control when plants were marketed within 60 days after the last application. In one greenhouse with an extremely high disease pressure, neither U. atrum nor fungicide applications controlled leaf rot. In additional experiments, the fate of U. atrum conidia on leaves of cyclamen grown in a system with top-irrigation three times per week was studied during a period of 70 days. The number of conidia per square centimeter of green leaves declined by 50% during the first 10 days of the experiment but remained stable during the following 60 days. The percentage of germinated conidia on green leaves increased during the experiment to approximately 50%. After additional incubation of leaf samples in moist chambers, more than 75% of the conidia had germinated, indicating that viable inoculum was present on leaves during the whole experiment. Artificial necrosis of leaves was induced by removing leaves from the plants. U. atrum colonized these leaves and competed successfully with B. cinerea on such leaves, even when they had been removed 70 days after the U. atrum application. Our results show that U. atrum has the potential to control leaf rot of cyclamen under a broad range of commercial growing conditions.

Long-Term Biosanitation by Application of Coniothyrium minitans on Sclerotinia sclerotiorum-Infected Crops.

ABSTRACT The effect of the fungal mycoparasite Coniothyrium minitans applied as a spray to crops infected with Sclerotinia sclerotiorum (causal agent of white mold) on contamination of soil with S. sclerotiorum sclerotia was studied in a 5-year field experiment. Sclerotial survival also was monitored during two subsequent years, when the field was returned to commercial agriculture. In a randomized block design, factorial combinations of four crops and three treatments were repeated 10 times. Potato (Solanum tuberosum), bean (Phaseolus vulgaris), carrot (Daucus carota), and chicory (Cichorium intybus), which are all susceptible to S. sclerotiorum, were grown in rotation. Plots were treated with C. minitans or Trichoderma spp. or were nontreated (control). Crops were rotated in each plot, but treatments were applied to the same plot every year. After 3 years during which it showed no effect on sclerotial survival, the Trichoderma spp. treatment was replaced by a single spray with C. minitans during the fourth and fifth years of the trial. The effect of treatments was monitored in subsequent seasons by counting apothecia as a measure of surviving S. sclerotiorum sclerotia and scoring disease incidence. Trichoderma spp. did not suppress S. sclerotiorum, but C. minitans infected at least 90% of S. sclerotiorum sclerotia on treated crops by the end of the each season. C. minitans lowered the number of apothecia compared with the other treatments during the second year after the bean crop. C. minitans reduced the number of apothecia by approximately 90% when compared with the control and Trichoderma spp. treatments and reduced disease incidence in the bean crop by 50% during the fifth year of the trial, resulting in a slightly higher yield. In 1993, but not 1994, a single spray with C. minitans was nearly as effective at reducing apothecia as three sprays (monitored in 1995). The final population size of sclerotia in soil at the end of the 7-year period was lower in all C. minitans plots than at the beginning of the trial, even in plots where two highly susceptible bean crops were grown during the period. The results indicate that the mycoparasite C. minitans has the potential to keep contamination of soil with sclerotia low in crop rotations with a high number of crops susceptible to S. sclerotiorum.

Biological Control of Botrytis cinerea in Cyclamen with Ulocladium atrum and Gliocladium roseum Under Commercial Growing Conditions.

ABSTRACT The effect of treatments with conidial suspensions of Ulocladium atrum and Gliocladium roseum on leaf rot of cyclamen caused by Botrytis cinerea was investigated under commercial greenhouse conditions. Spraying U. atrum (1 x 10(6) conidia per ml) or G. roseum (2 x 10(6) conidia per ml and 1 x 10(7) conidia per ml) at intervals of 2 to 3 weeks during the production period and spraying U. atrum (1 x 10(6) conidia per ml) at intervals of 4 to 6 weeks resulted in a significant reduction of natural infections of petioles by B. cinerea. U. atrum or G. roseum (1 x 10(7)conidia per ml) was as effective as the standard fungicide program. B. cinerea colonized senesced leaves within the plant canopy and infected adjacent petioles and leaves later. The antagonists colonized senesced leaves and reduced B. cinerea development on these leaves. Thus, the inoculum potential on petioles adjacent to necrotic leaf tissues was reduced. The fate of U. atrum conidia on surfaces of green cyclamen leaves during a 70-day period after application was studied. The number of conidia per square centimeter of leaf surface remained relatively constant during the entire experiment. Sixty percent of the conidia sampled during the experiments retained the ability to germinate. When green leaves were removed from the plants to induce senescence and subsequently were incubated in a moist chamber, U. atrum colonized the dead leaves. Senesced leaves also were colonized by other naturally occurring fungi including B. cinerea. On leaves treated with U. atrum from all sampling dates, sporulation of B. cinerea was significantly less as compared with the untreated control. Our results indicate that early applications of U. atrum before canopy closure may be sufficient to achieve commercially satisfactory control of Botrytis leaf rot in cyclamen.