Management of white mold of soybean using winter cereal straw

ABSTRACT: The management of white mold (Sclerotinia sclerotiorum(Lib.) De Bary) has been one of the main production limitations faced by soybean (Glycine max L.) producers. Considering the complex management of this disease and resistance structure of the pathogen, the present study was conducted in the municipalities of Guarapuava and Palmas in Paraná with the objective of managing the white mold of soybean using straws of winter cereals, such as oat, rye, and triticale. Initially, the three winter cereals were cultivated simultaneously in both the study areas. Straw production, plant height, and shoot fresh and dry weight were evaluated. Subsequently, BMX Apollo soybean was cultivated on cereal straws, and the incidence and severity of white mold were evaluated. In the in vitro experiment, 20 sclerotia covered by a layer of cereal (oat, rye, and triticale) straws were added and carpogenic germination was observed only in the control treatment after 98 days. Regardless of the study site, rye presented greater height and fresh weight than the remaining two cereals. Soybean cultivation on winter cereal straw reduced the incidence and severity of white mold. Cultivation on rye straw reduced mold incidence by 77.7% and 76.6% in Palmas and Guarapuava, respectively.

Impact of preconditioning temperature and duration period on carpogenic germination of diverse Sclerotinia sclerotorium (Lib.) de Bary populations in south-western Australia

The soil-borne pathogen Sclerotinia sclerotorium is the causal agent of sclerotinia stem rot, a severe disease of broad-leaf crops including canola/rapeseed Brassica napus that can result in significant yield losses. Sclerotia, the hard melanized resting structure of the pathogen, requires preconditioning before carpogenic germination can occur. We investigated the effect of pre-conditioning temperature (4°C, 20°C, 35°C, 50°C and field conditions) and duration (0, 30, 60, 120, 179, 240, 301 days) on germination of S. sclerotorium sclerotia collected from five canola fields in the south-western Australian grain-belt. The ecological diversity of each population was characterised using mycelial compatibility groups (MCGs) typing. No response was observed for isolates conditioned at 4°C at any time period indicating chilling is not a preconditioning requirement for these isolates. Sclerotia required preconditioning for a minimum of 60 days before any significant increase in germination occurred, with no further increases in germination recorded in response to longer conditioning after 60 days. The highest germination was observed in sclerotia conditioned at 50°C. The MCG results indicated significant within and between population diversity suggesting local adaptation to different environments as well as ensuring the ability to respond to seasonal variation between years.

Carpogenic Germinability of Diverse Sclerotinia sclerotiorum Populations Within the Southwestern Australian Grain Belt

Sclerotinia stem rot, caused by the necrotrophic plant pathogen Sclerotinia sclerotiorum (Lib.) de Bary, is a major disease of canola and pulses in Australia. Current disease management relies greatly on cultural and chemical means of control. Timing of fungicide applications remains a challenge, because efficacy is dependent on accurate prediction of ascospore release and presence on the plant. The aims of this study were to determine the optimal temperature for carpogenic germination of S. sclerotiorum populations sampled from canola and lupin fields in southwestern Australia and characterize diversity using mycelial compatibility groupings (MCGs). Sclerotia were collected from four diseased canola and one diseased lupin field from across southwestern Australia. Forty sclerotia from each population were incubated at four alternating temperatures of 30/15, 20/15, 20/4, and 15/4°C (12-h/12-h light/dark cycle) and assessed every 2 to 3 days for a 180-day period. MCG groupings for populations were characterized using 12 reference isolates. Results indicated the time to initial carpogenic germination decreased as diurnal temperature fluctuations decreased, with a fluctuation of 5°C (20/15°C) having the most rapid initial germination followed by 11°C (15/4°C) followed by 16°C (20/4°C). Optimal germination temperature for all five populations was 20/15°C; however, population responses to other diurnal temperature regimes varied considerably. No germination was observed at 30/15°C. MCG results indicate extensive diversity within and between populations, with at least 40% of sclerotia within each population unable to be characterized. We suggest that this diversity has enabled S. sclerotiorum populations to adapt to varying environmental conditions within southwestern Australia.

Favorable Bioactivity of the SDHI Fungicide Benzovindiflupyr Against Sclerotinia sclerotiorum Mycelial Growth, Sclerotial Production, and Myceliogenic and Carpogenic Germination of Sclerotia

Sclerotinia sclerotiorum, which can cause Sclerotinia stem rot, is a prevalent plant pathogen. This study aims to evaluate the application potential of benzovindiflupyr, a new generation of succinate dehydrogenase inhibitor (SDHI), against S. sclerotiorum. In our study, 181 isolates collected from different crops (including eggplant [n = 34], cucumber [n = 27], tomato [n = 29], pepper [n = 35], pumpkin [n = 32], and kidney bean [n = 25]) in China were used to establish baseline sensitivity to benzovindiflupyr. The frequency distribution of the 50% effective concentration (EC50) values of benzovindiflupyr was a unimodal curve, with mean EC50 values of 0.0260 ± 0.011 μg/ml, and no significant differences in mean EC50 existed among the various crops (P > 0.99). Benzovindiflupyr can effectively inhibit mycelial growth, sclerotial production, sclerotial shape, and myceliogenic and carpogenic germination of the sclerotia of S. sclerotiorum. In addition, benzovindiflupyr showed good systemic translocation in eggplant. Using benzovindiflupyr at 100 μg/ml yielded efficacies of 71.3 and 80.5% for transverse activity and cross-layer activity, respectively, which were higher than those of acropetal and basipetal treatments (43.6 and 44.7%, respectively). Greenhouse experiments were then carried out at two experimental sites for verification. Applying benzovindiflupyr at 200 g a.i. ha−1 significantly reduced the disease incidence and severity of Sclerotinia stem rot. Overall, the results demonstrated that benzovindiflupyr is a potential alternative product to control Sclerotinia stem rot.

Efficacy of Antagonists on mycelium growth and carpogenic germination of sclerotia of Sclerotinia sclerotiorum on Indian mustard

Sclerotinia sclerotiorum (Lib.) de Bary is a soil borne pathogen capable of infecting more than 400 host plants worldwide. It is a major pathogen that plays a crucial role in reducing the yield in economically important crops. The capability of sclerotia to survive for more than 4 years becomes very difficult to manage the crop from the infection of Sclerotinia rot fungus. Stem rot of indian mustard [Brassica juncea (L.) Czern and Cross] caused by Sclerotinia sclerotiorum is potentially a serious threat in many mustard growing areas in India. Treatments of seeds and foliar spray with of fungicides applied at regular intervals are effective in reducing infection, but uses of chemicals are hazardous, harmful for beneficial micro-organisms. Biological control of plant pathogens offers an exciting opportunity to manage plant diseases. In the present study, the efficacy of four bio-agents, viz., Coniothyrium minitans, Aspergilus nidulans, Trichoderma harzianum, and Pseudomonas chlororaphis were evaluated for the control of stem rot of Indian mustard. Results on bio-efficacy of different bioagents, when evaluated under glass house condition, the Coniothyrium minitans was the most effective agent and caused highest reduction (64.7 %) in carpogenic germination of sclerotia followed by Aspergilus nidulans (52.5 %) and Trichoderma harzianum (48.8 %), over control while Pseudomonas chlororaphis (48.3 %) was at par with T. harzianum. All the bioagents showed significant reduction effective in controlling the disease. Similar results were achieved when bioagents tested on dual inoculated plates.

Overwintering Stages of Pseudosclerotia Development for Monilinia vaccinii-corymbosi, Causal Agent of Mummy Berry Disease on Highbush Blueberry in North America

Mummy berry, caused by Monilinia vaccinii-corymbosi, is an economically important disease of blueberries throughout North America. Pseudosclerotia develop apothecia and produce primary inoculum in coordination with floral bud break. Terminology for M. vaccinii-corymbosi pseudosclerotial overwintering stages is inconsistent throughout the literature, and the progression from development to sporulation has never been cohesively and sequentially outlined. A developmental classification scheme was derived from existing terminology and observations of naturally-conditioned pseudosclerotia over a two-year period in Corvallis, OR. The proposed terminology for pseudosclerotial overwintering stages include maturation, dormancy, germination, emergence, differentiation, and carpogenic germination. The standardization of these terms will allow researchers to better communicate regarding this pathogen. Accepted for publication 19 July 2016. Published 15 August 2016.