Paloma Melgarejo

Bio: Paloma Melgarejo is an academic researcher from Ministry of Agriculture. The author has contributed to research in topics: Monilinia laxa & Monilinia. The author has an hindex of 32, co-authored 108 publications receiving 2679 citations.

High chlorogenic and neochlorogenic acid levels in immature peaches reduce Monilinia laxa infection by interfering with fungal melanin biosynthesis

Abstract: Chlorogenic acid (CGA) and its isomer, neochlorogenic acid (NCGA), were found to be the major phenolic compounds in the flesh and peel of three peach cultivars. Their concentrations are especially high in immature fruits (CGA, 151-548 mg/kg; NCGA, 85-380 mg/kg), whose resistance to the brown rot fungus, Monilinia laxa , is very high. The concentrations of these two phenolic compounds decline in maturing fruits (CGA, 77-181 mg/kg; NCGA, 30-82 mg/kg), and this decline is associated with a concomitant increase in susceptibility to brown rot infection. Other phenolic compounds found in the same HPLC chromatograms at 340 nm from each peach extract at varying sampling dates in each of the three peach cultivars were not correlated with the incidence of brown rot and appeared only in some cultivars. The incidence of brown rot for each cultivar at each sampling date was significantly negatively correlated with the NCGA (r > -0.85) and CGA (r > -0.90) contents. At concentrations that are similar to those in peach fruit, CGA does not inhibit spore germination or mycelial growth of M. laxa in culture but markedly inhibits the production of melanin-like pigments in the mycelia of M. laxa in culture (42% melanin reduction). Accordingly, we propose that the high concentrations of CGA and NGA in immature fruits might contribute to their reduced susceptibility or increased resistance to brown rot infection by interfering with fungal melanin production.

Induced resistance by Penicillium oxalicum against Fusarium oxysporum f.sp. lycopersici: histological studies of infected and induced tomato stems.

Abstract: Tomato (Lycopersicon esculentum) plants of ‘Lorena’ were induced with a conidial suspension (107 conidia per ml) of Penicillium oxalicum before inoculation with Fusarium oxysporum f. sp. lycopersici, the wilt pathogen. Histological changes occurred in plants under both growth chamber and glasshouse culture conditions and there was a reduction of disease severity. In noninduced plants, the pathogen produced almost a complete loss of cambium (75 to 100% reduction), an increase in the number of bundles, and a decrease in the number of xylem vessels (20% reduction), in which the diameter also was reduced by 20 to 30% in hypocotyls and epicotyls. The percentage of vessels colonized by F. oxysporum f. sp. lycopersici was positively correlated to the area under the disease progress curve (AUDPC). However, plants induced with P. oxalicum showed less disease, did not lose the cambium, had a lower number of bundles, and had less vascular colonization by F. oxysporum f. sp. lycopersici (35 to 99%). These ef...

Chemical Alternatives to Methyl Bromide in Spanish Strawberry Nurseries.

Abstract: Strawberry runners are a high-value cash crop in Spain that requires vigorous transplants free of pathogens. Preplant soil fumigation with methyl bromide, or with mixtures of methyl bromide and chloropicrin, is a standard practice for controlling soilborne diseases. Soil fumigants chloropicrin, 1,3-dichloropropene, dazomet, metam-sodium, metam potassium, and dimethyl disulfide were evaluated in combination with different plastic films as alternatives for methyl bromide soil fumigation of strawberry nurseries. The studies were conducted over a 4-year period, with fumigant applications prior to planting. Verticillium wilt (caused by Verticillium spp.) and crown rot (caused by Phytophthora cactorum) were the main diseases. Chloropicrin, 1,3-dichloropropene, and dazomet compared well with methyl bromide fumigation for control of strawberry nursery diseases. Furthermore, 1,3-dichloropropene and methyl bromide, applied at 50% rate under virtually impermeable film, provided effective disease control in strawberry nurseries. Fumigant effects on fungal soil populations are discussed.

Biocontrol of Fusarium and Verticillium Wilt of Tomato by Penicillium oxalicum under Greenhouse and Field Conditions

Abstract: Treatments with conidia of Penicillium oxalicum produced in a solid-state fermentation system were applied at similar densities (6 x 10 6 spores/g seedbed substrate) to tomato seedbeds in water suspensions (Tl: 5 days before sowing, or T2: 7 days before transplanting; 15 days after sowing), or in mixture with the production substrate (T3: 7 days before transplanting; 15 days after sowing). Treatments T2 and T3 significantly (P = 0.05) reduced fusarium wilt of tomato in both greenhouse (artificial inoculation) (33 and 28%, respectively) and field conditions (naturally infested soils) (51 and 72%, respectively), while treatment Tl was efficient only in greenhouse (52%). Verticillium wilt disease reduction was obtained with T3 in two field experiments (56 and 46%, respectively), while Tl and T2 reduced disease only in one field experiment (52% for both T1 and T2). Treatment with conidia of P. oxalicum plus fermentation substrate (T3) resulted in better establishment of a stable and effective population of P. oxalicum in seedbed soil and rhizosphere providing populations of approx. 10 7 CFU/g soil before transplanting. Results indicate that it will be necessary to apply P. oxalicum at a rate of approx. 10 6 -10 7 CFU/g in seedbed substrate and rhizosphere before transplanting for effective control of fusarium and verticillium wilt of tomato, and that formulation of P. oxalicum has a substantial influence on its efficacy.

Microbial interactions and biocontrol in the rhizosphere

Abstract: The loss of organic material from the roots provides the energy for the development of active microbial populations in the rhizosphere around the root. Generally, saproptrophs or biotrophs such as mycorrhizal fungi grow in the rhizosphere in response to this carbon loss, but plant pathogens may also develop and infect a susceptible host, resulting in disease. This review examines the microbial interactions that can take place in the rhizosphere and that are involved in biological disease control. The interactions of bacteria used as biocontrol agents of bacterial and fungal plant pathogens, and fungi used as biocontrol agents of protozoan, bacterial and fungal plant pathogens are considered. Whenever possible, modes of action involved in each type of interaction are assessed with particular emphasis on antibiosis, competition, parasitism, and induced resistance. The significance of plant growth promotion and rhizosphere competence in biocontrol is also considered. Multiple microbial interactions involving bacteria and fungi in the rhizosphere are shown to provide enhanced biocontrol in many cases in comparison with biocontrol agents used singly. The extreme complexity of interactions that can occur in the rhizosphere is highlighted and some potential areas for future research in this area are discussed briefly.

Biotechnological advantages of laboratory-scale solid-state fermentation with fungi.

Abstract: Despite the increasing number of publications dealing with solid-state (substrate) fermentation (SSF) it is very difficult to draw general conclusion from the data presented This is due to the lack of proper standardisation that would allow objective comparison with other processes Research work has so far focused on the general applicability of SSF for the production of enzymes, metabolites and spores, in that many different solid substrates (agricultural waste) have been combined with many different fungi and the productivity of each fermentation reported On a gram bench-scale SSF appears to be superior to submerged fermentation technology (SmF) in several aspects However, SSF up-scaling, necessary for use on an industrial scale, raises severe engineering problems due to the build-up of temperature, pH, O2, substrate and moisture gradients Hence, most published reviews also focus on progress towards industrial engineering The role of the physiological and genetic properties of the microorganisms used during growth on solid substrates compared with aqueous solutions has so far been all but neglected, despite the fact that it may be the microbiology that makes SSF advantageous against the SmF biotechnology This review will focus on research work allowing comparison of the specific biological particulars of enzyme, metabolite and/or spore production in SSF and in SmF In these respects, SSF appears to possess several biotechnological advantages, though at present on a laboratory scale only, such as higher fermentation productivity, higher end-concentration of products, higher product stability, lower catabolic repression, cultivation of microorganisms specialized for water-insoluble substrates or mixed cultivation of various fungi, and last but not least, lower demand on sterility due to the low water activity used in SSF