Viability of Moniliophthora roreri on Cocoa Beans Under Microfermentation and Long-Term Survival on Carrier Materials.

The viability of Moniliophthora roreri inoculum was evaluated during the microfermentation process of diseased and healthy pulp-seed masses and on a range of carrier materials: aluminum, cloth, glass, paper, plastic, raffia, and rubber tire. Fungal survival was assessed before the microfermentation (0 h) and every 24 to 96 h by the growth of colonies in potato-dextrose-agar (PDA) and sporulation in seed shells. Colonies of M. roreri and sporulation on seed shells were observed from seeds not submitted to microfermentation. No growth was recovered from diseased cocoa beans after 48 h under the microfermentation. The viability of M. roreri spores recovered from carrier materials was evaluated at 7, 15, 30, 45, and 100 days after inoculation (DAI) by collecting spores and plating them on Sabouraud dextrose yeast extract agar amended with chloramphenicol (50 mg l1). The viability was determined by counting germinated and ungerminated spores under a light microscope (40×) after incubating in a moist chamber at 26 ± 2°C for 72 h. Spores maintained long-term viability on all tested carrier materials toward the end of the experiment (overall 26%) with significant differences (<0.05) among them. Maximum spore viability occurred at 7 and 15 DAI, with cloth and plastic carrier materials considered at high risk of acting as vehicles for the fungal spread. Mathematical models of spore viability over time were fit to the data using the Bayesian information criterion. Findings confirmed the importance of the fermentation process to hamper M. roreri growth and the potential of carrier materials for fungal dispersal.

Impact of temperature, soil type and compost amendment on the survival, growth and persistence of Listeria monocytogenes of non-environmental (food-source associated) origin in soil.

Listeria monocytogenes of varied sources including food-related sources may reach the soil. Associated food safety and environmental health risks of such contamination depend significantly on the capacity of L. monocytogenes to survive in the soil. This study assessed the survival of 13 L. monocytogenes strains isolated from food and food processing environments and a cocktail of three of the strains in two types of soils (loam and sandy) under controlled temperature conditions: 5, 10, 20, 25, 30℃ and 'uncontrolled' ambient temperature conditions in a tropical region. The impact of compost amendment on the survival of L. monocytogenes in the two different types of soils was also assessed. Soil type, temperature and compost amendment significantly (P <0.001) impacted the survival of L. monocytogenes in soil. Temperature variations affected the survival of L. monocytogenes in soil, where some strains such as strain 732, a L. monocytogenes 1/2a strain survived better at lower temperature (5°C), for which counts of up to 10.47 ± 0.005 log CFU/g were recovered in compost-amended sandy soil, 60 days post-inoculation. Some other strains such as strain 441, a L. monocytogenes 1/2a survived best at intermediate temperature (25 and 30 °C), while others such as 2739 (L. monocytogenes 1/2b) thrived at higher temperature (between 30 °C - 37 °C). There were significant correlations between the influence of temperature and soil type, where lower temperature conditions (5°C - 20°C) were generally more suitable for survival in sandy soil compared to higher temperature conditions. For some of the strains that thrived better in sandy soil at lower temperature, Pearson correlation analysis found significant correlations between temperature and soil type. Steady, controlled temperature generally favored the survival of the strains compared to uncontrolled ambient temperature conditions, except for the cocktail. The cocktail persisted until the last day of post-inoculation storage (60th day) in all test soils and under all incubation temperature conditions. Loam soil was more favorable for the survival of L. monocytogenes and compost amendment improved the survival of the strains, especially in compost-amended sandy soil. Listeria monocytogenes may exhibit variable survival capacity in soil, depending on conditions such as soil type, compost amendment and temperature.

First Report of Bacterial Wilt Caused by Ralstonia solanacearum on Plectranthus amboinicus in Martinique.

Plectranthus amboinicus, commonly known as Gwo ten in the French West Indies (Martinique), is a semi-succulent perennial plant of the Lamiaceae family. This aromatic plant wich is widespread naturally throughout the tropics is of economic importance because of the therapeutic and nutritional properties attributed to its natural phytochemical compounds wich are highly valued in the pharmaceutical industry. In March 2019, wilted P. amboinicus plants intercropped with tomato plants (cv. Heatmaster) in order to reduce the insect-pest damages on tomato, were observed in a field located at the CIRAD experimental station in Lamentin, Martinique (14.663194 N, -60.999167 W). Average disease incidence of 65.74% was recorded on P. amboinicus, in 3 plots with an area of 22.04 m2. The initial symptoms observed were irregular, black, necrotic lesions on leaves. After 10 days, plants wilted and black stripes were observed on stems. Within 4 weeks, more than 50% of plants were fully wilted. Longitudinal stem sections of the wilted plants showed brown vascular discoloration. The cut stems of the wilted plants released a whitish bacterial ooze in water. In all, 108 stem sections were collected, surface disinfected with 70% ethanol and each was crushed in 2 mL of Tris-buffer, then processed for bacterial isolation by plating on modified Semi-Selective Medium from South Africa SMSA (Engelbrecht 1994). Typical Ralstonia solanacearum colonies grew on SMSA medium for 100 of the 108 samples after incubation for 48h at 28°C and were identified as Ralstonia solanacearum using diagnostic PCR with 759/760 primers (Opina et al. 1997). A phylotype-specific multiplex PCR (Fegan and Prior 2005) classified all the strains in R. solanacearum Phylotype IIA. A subset of 11 strains was selected for sequevar identification. All the strains were identified as sequevar I-39 (100% nucleotide identity with strain ANT92 - Genbank accession EF371828), by partial egl sequencing (Fegan and Prior 2005) (GenBank Accession Nos. MT314067 to MT314077). This sequevar has been reported to be widespread in the Caribbean and tropical America on vegetable crops (particularly on tomato), but not on P. amboinicus (Deberdt et al. 2014; Ramsubhag et al. 2012; Wicker et al. 2007). To fulfil Koch's postulates, a reference strain, isolated from diseased P. amboinicus (CFBP 8733, Phylotype IIA/sequevar 39), was inoculated on 30 healthy P. amboinicus plants. A common tomato cultivar grown in Martinique (cv. Heatmaster) was also inoculated on 30 plants with the same bacterial suspension. Three-weeks-old plants of both crops grown in sterilized field soil were inoculated by soil drenching with 20 ml of a calibrated suspension (108 CFU/mL). P. amboinicus and tomato plants drenched with sterile water served as a negative controls. Plants were grown in a fully controlled environment at day/night temperatures of 30-26°C ± 2°C under high relative humidity (80%). The P. amboinicus plants started wilting 9 days after inoculation, and within four weeks 60% of the P. amboinicus plants had wilted. The tomato plants started wilting 5 days after inoculation with 62% of wilted plants within four weeks. R. solanacearum was recovered from all symptomatic plants on modified SMSA medium. No symptoms were observed and no R. solanacearum strains were isolated from negative controls plants. To our knowledge, this is the first report of R. solanacearum causing bacterial wilt on Gwo ten (P. amboinicus) in Martinique. The importance of this discovery lies in the reporting of an additional host for R. solanacearum, which can be associated with other crops as tomato crop in order to reduce the abundance of insect-pests. Further studies need to be conducted to assess the precise distribution of bacterial wilt disease on P. amboinicus in Martinique and to develop a plan of action avoiding its association with R. solanacearum host crops as tomato for reducing epidemic risk.

Postharvest Incidence of Stem End Rot in 'Hayward' Kiwifruit Is Related to Preharvest Botrytis cinerea Colonization of Floral Parts and Latent Infection.

Stem end rot (SER) caused by Botrytis cinerea is the primary postharvest disease in the Chilean kiwifruit industry. Relationships between the postharvest occurrence of SER in 'Hayward' kiwifruit and the temporal dynamics of earlier B. cinerea colonization of the floral parts (petals, sepals, receptacles, styles) was studied in five orchards over two consecutive seasons in Chile. Weather conditions in the first season favored B. cinerea infection with roughly constant colonization of floral parts up to about 120 days after full bloom, but colonization then increased up until harvest. In the second season, colonization was roughly constant throughout. Latent infections of the fruit occurred in both seasons but were high in the first season and low in the second. Incidence of latent infections at harvest were the best predictors (r > 0.8) of postharvest SER. The number of preharvest infection periods calculated using temperature, leaf wetness, and relative humidity satisfactorily predicted SER incidence by an exponential model, R2 = 0.90, P < 0.001. Results indicated environmental variables play key roles in the temporal dynamics of B. cinerea colonization. Quantification of latent B. cinerea infections in asymptomatic fruit close to harvest, is a practicable way to predict later incidence of SER during storage.