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

Grey mould of strawberry, a devastating disease caused by the ubiquitous necrotrophic fungal pathogen Botrytis cinerea

The fungal pathogen Botrytis cinerea causes grey mould, a commercially damaging disease of strawberry. This pathogen affects fruit in the field, storage, transport and market. The presence of grey mould is the most common reason for fruit rejection by growers, shippers and consumers, leading to significant economic losses. Here, we review the biology and epidemiology of the pathogen, mechanisms of infection and the genetics of host plant resistance. The development of grey mould is affected by environmental and genetic factors; however, little is known about how B. cinerea and strawberry interact at the molecular level. Despite intensive efforts, breeding strawberry for resistance to grey mould has not been successful, and the mechanisms underlying tolerance to B. cinerea are poorly understood and under-investigated. Current control strategies against grey mould include pre- and postharvest fungicides, yet they are generally ineffective and expensive. In this review, we examine available research on horticultural management, chemical and biological control of the pathogen in the field and postharvest storage, and discuss their relevance for integrative disease management. Additionally, we identify and propose approaches for increasing resistance to B. cinerea in strawberry by tapping into natural genetic variation and manipulating host factors via genetic engineering and genome editing.

Identification and evaluation of potential bio-control fungal endophytes against Ustilagonoidea virens on rice plants

False smut disease of rice is posing an increasing concern for production, not only because of the hiking epidemic occurrence in rice production, but also because of the challenging specific pathogenesis of the disease. The aim of this work was to evaluate the potential of five fungal endophytes to reduce negative effects of rice false smut fungus (Ustilagonoidea virens) on rice plants, in both the laboratory and greenhouse. Though all the fungal isolates showed the ability to inhibit the growth of U. virens with varying degrees, isolate E337 showed significant antagonistic activity against the pathogenic fungi. The isolate E337 was identified as Antennariella placitae by molecular and morphological data analysis including 18S rDNA sequence analysis. This isolate showed a significant in vitro inhibition of mycelial growth of U. virens by dual culture method and it was subsequently tested for its in vivo biocontrol potential on false smut disease on rice plants. Greenhouse experiments confirmed that applications of conidia of A. placitae protected rice plants by improving rice yield and by decreasing the severity of false smut disease on susceptible rice plants. This is the first report where A. placitae has been identified as a biocontrol organism.

A rapid microbioassay for discovery of antagonistic bacteria for Phytophthora parasitica var. nicotianae

A simple, rapid, small-scale microbioassay for infection of tobacco seedlings by Phytophthora parasitica var. nicotianae was developed here. This assay uses tobacco seedlings cultivated in petri dishes for a standardized method for quantitation of initial zoospore inocula and high-throughput screening of antagonistic bacteria. Zoospore inocula between 10(2) to 10(5) spores per petri dish were inoculated on 14-day-old tobacco seedlings for the susceptibility test. The optimum inocula was established to be ten thousand zoospores. One hundred and fifty pure culture bacteria with different pigments, growth rates, and morphologies were isolated from rhizosphere soil of tobacco and screened for protective ability against tobacco black shank. Fifteen bacteria presented high activity against P. parasitica on tobacco seedlings. They were identified by Biolog GEN III MicroPlate and distributed as Bacillus amyloliquefaciens, B. licheniformis, Paenibacillus pabuli, B. atrophaeus, B. subtilis, B. pumilus, and B. endophyticus, respectively. Four antagonists chosen randomly from the 15 bacteria all exhibited the same 100% protective activity in planta as that in the petri dishes. This microassay proved to be a rapid, reproducible, and efficient method for screening of potential biological agents or microorganisms and may be useful for studying mechanisms of infection and control of Phytophthora spp. under hydroponic conditions.

Control of postharvest Botrytis fruit rot of strawberry by volatile organic compounds of Candida intermedia

A study was conducted to identify volatile organic compounds or volatiles produced by Candida intermedia strain C410 using gas chromatography-mass spectrometry, and to determine efficacy of the volatiles of C. intermedia in suppression of conidial germination and mycelial growth of Botrytis cinerea and control of Botrytis fruit rot of strawberry. Results showed that, among 49 volatiles (esters, alcohols, alkenes, alkanes, alkynes, organic acids, ketones, and aldehydes) identified from C. intermedia cultures on yeast extract peptone dextrose agar, two compounds, 1,3,5,7-cyclooctatetraene and 3-methyl-1-butanol, were the most abundant. Synthetic chemicals of 1,3,5,7-cyclooctatetraene; 3-methyl-1-butanol; 2-nonanone; pentanoic acid, 4-methyl-, ethyl ester; 3-methyl-1-butanol, acetate; acetic acid, pentyl ester; and hexanoic acid, ethyl ester were highly inhibitory to conidial germination and mycelial growth of B. cinerea. Inhibition of conidial germination and mycelial growth of B. cinerea by volatiles of C. intermedia was also observed. Meanwhile, results showed that incidence and severity of Botrytis fruit rot of strawberry was significantly (P < 0.01) reduced by exposure of the strawberry fruit to the volatiles from C. intermedia cultures or C. intermedia-infested strawberry fruit. These results suggest that the volatiles of C. intermedia C410 are promising biofumigants for control of Botrytis fruit rot of strawberry.

Commercialization and implementation of biocontrol

Although the number of biocontrol products is increasing, these products still represent only about 1% of agricultural chemical sales. Yet these are important contributions because biocontrol agents offer disease management alternatives with different mechanisms of action than chemical pesticides. Trends in research include the increased use of biorational screening processes to identify microorganisms with potential for biocontrol, increased testing under semicommercial and commercial production conditions, increased emphasis on combining biocontrol strains with each other and with other control methods, integrating biocontrol into an overall system.

Biological Control of Blossom Blight of Alfalfa Caused by Botrytis cinerea Under Environmentally Controlled and Field Conditions

Fungal and bacterial antagonists were tested for their inhibition of sporulation of Botrytis cinerea on detached alfalfa florets. Clonostachys rosea, Gliocladium catenulatum, and Trichoderma atroviride were evaluated for protecting young blossoms and pods of alfalfa from infection by B. cinerea in vitro. C. rosea was further tested to control pod rot and seed rot caused by B. cinerea under field conditions. The results showed that four of the tested antagonists, C. rosea, G. catenulatum, T. atroviride, and Trichothecium roseum, could inhibit sporulation by B. cinerea on detached alfalfa florets. Both C. rosea and G. catenulatum were effective in suppression of infection of alfalfa pods by B. cinerea when inoculated on fresh petals of alfalfa at the anthesis stage, and their efficacy was greater than that of Trichoderma atroviride. A significant suppression of B. cinerea by C. rosea and G. catenulatum on pods and seed of alfalfa was observed when they were inoculated on senescent petals at the pod-development stage. Results of a field trial indicated that C. rosea applied to upper parts of alfalfa plants significantly suppressed pod rot and seed rot caused by B. cinerea, and significantly increased seed production of alfalfa in each of 3 years. These studies show that C. rosea has potential as a biocontrol agent for control of alfalfa blossom blight caused by B. cinerea.