Potato crop is the fourth main food crop in the world and it will certainly feed a big part of the global population in the next years. The economical outlets for this crop are great; however, numerous diseases either soil- or air-borne can cause huge losses in the production. Worldwide, about 40 soil-borne diseases affect potato and cause severe damages especially on tubers, the economically most important part of the plant. The occurrence and development of soil-borne diseases depend on very diverse factors affecting either the pathogen or the plant. Favorable conditions for potato diseases development are frequently the same as the conditions needed for potato growth: temperature between 10°C and 25°C, high humidity, medium pH, etc. Adapted cultural practices such as a rotation longer than 4 years, appropriate fertilization and water management, an adapted delay between haulm killing and harvest, and dry and cool conditions for tuber storage are good ways to control potato diseases. In most cases, potato pathogens develop specific survival forms, dissemination ways and host penetration methods. The genetic variability of the pathogens implies the use of adapted diagnostic and control methods. Decision support systems developed to predict yield losses allow choosing good control methods such as the use of healthy seeds, adapted pesticides, cultural practices, and biological control agents for each potato disease. The complexity of the interactions between a pathogen and its host, influenced by biotic and abiotic factors of the environment, make the control of the diseases often very difficult. However, deep knowledge of pathosystems allows setting up integrated pest management systems allowing the production of healthy and good quality potatoes.

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Potato soil-borne diseases. A review

Effect of Trichoderma spp. and Purpureocillium lilacinum on Meloidogyne javanica in commercial pineapple production in Kenya

The potato cyst nematode, Globodera pallida, is one of the most important pests of potato worldwide. Owing to regulatory considerations and potential environmental impact, control options for this nematode are becoming increasingly limited. Solanum sisymbriifolium and biological control agents offer viable alternative options for controlling G. pallida. Therefore, experiments were conducted to determine the effect of the nematode trap crop S. sisymbriifolium, alone or in combination with the biocontrol agents Trichoderma harzianum or Plectosphaerella cucumerina, on population decline of G. pallida. Experiments were conducted for three different ‘cropping systems’: potato (Solanum tuberosum), S. sisymbriifolium, or soil only (fallow), each followed by a potato crop. Soil was amended with P. cucumerina, T. harzianum or left unamended, and then infested with nematodes at a rate of five eggs g−1 of soil. After 16 weeks in the greenhouse, plants were removed and the soil containing cysts was refrigerated at 4°C for 8 weeks, and then planted to potato. Cysts of G. pallida were counted after an additional 16-week period. The Pf/Pi of G. pallida was significantly reduced by 99% in potato following S. sisymbriifolium compared to both the potato-following-fallow and the potato-following-potato treatments. Amendment of soil with T. harzianum significantly reduced Pf/Pi of G. pallida by 42–47% in the potato-following-potato but not in either the potato-after-fallow nor in the potato-after-S. sisymbriifolium cycles which supports evidence that the plant species may play a role in the biocontrol activity of this fungus. Addition of the fungus P. cucumerina resulted in a 64% decrease in Pf/Pi in the potato-following-fallow in one experiment, and an 88% decrease in Pf/Pi in potato-following-potato but the decrease in Pf/Pi was not consistent over all experiments. However, both biocontrol fungi resulted in lower numbers of progeny cysts after an initial 16-week incubation with potato. To look at the effect of varied population density of the nematode on efficacy of S. sisymbriifolium to reduce G. pallida populations, potato, S. sisymbriifolium, or barley were planted into soil infested with G. pallida at rates of 5, 20 or 40 eggs g−1 soil applied as cysts (20, 80 or 160 cysts pot−1). After 16 weeks, numbers of cysts produced in each treatment were determined for each infestation rate. No new cysts were recovered from either S. sisymbriifolium or barley treatments, confirming that neither plant is a host for G. pallida. High numbers of cysts were recovered with potato. Soil from each treatment (containing original cysts and newly-formed cysts when present) were then planted with potato. After an additional 16 weeks, few cysts were found in the potato-after- S. sisymbriifolium treatments regardless of initial infestation rate. When potato followed barley, numbers of cysts were similar to those found after a single cycle of potato, indicating that the barley crop had no effect on the survival of initial inoculum. Overall, these results suggest that S. sisymbriifolium has potential to significantly reduce G. pallida populations, and also that the cropping system (i.e. the sequence of non-host and host plants) may play a significant role in the efficacy of fungal biological control agents.

Effect of the trap crop Solanum sisymbriifolium and two biocontrol fungi on reproduction of the potato cyst nematode, Globodera pallida

Incorporating beneficial microorganisms in crop production is the most promising strategy for maintaining agricultural productivity and reducing the use of inorganic fertilizers, herbicides, and pesticides. Numerous microorganisms have been described in the literature as biological control agents for pests and diseases, although some have not yet been commercialised due to their lack of viability or efficacy in different crops. Paecilomyces is a cosmopolitan fungus that is mainly known for its nematophagous capacity, but it has also been reported as an insect parasite and biological control agent of several fungi and phytopathogenic bacteria through different mechanisms of action. In addition, species of this genus have recently been described as biostimulants of plant growth and crop yield. This review includes all the information on the genus Paecilomyces as a biological control agent for pests and diseases. Its growth rate and high spore production rate in numerous substrates ensures the production of viable, affordable, and efficient commercial formulations for agricultural use.

https://www.mdpi.com/2223-7747/9/12/1746/pdf

Paecilomyces and Its Importance in the Biological Control of Agricultural Pests and Diseases

Understanding on actinomycetes-mediated stress tolerance in plants is very limited. This study demonstrated for the first time some stress tolerance mechanisms in chickpea via mediation of an actinomycetes strain Streptomyces rochei SM3. Here, we used the strain SM3 for treating chickpea seeds and plants raised from such seeds were challenged with Sclerotinia sclerotiorum and NaCl. Chickpea mortality due to Sc. sclerotiorum infection was suppressed by nearly 48%, and biomass accumulation was increased by nearly 20% in the salt-stressed condition in SM3-treated plants compared to non-treated plants. Physiological responses in chickpea under the challenging conditions showed that phenylalanine ammonia lyase activities increased in SM3-treated plants. This is followed by accumulation of higher concentrations of phenolics that led to enhanced lignifications in SM3-treated plants compared to non-SM3-treated plants challenged with the same stresses. Antioxidant activities, as assessed through catalase activities and proline accumulation, also increased in SM3-treated plants challenged with both the stresses compared to non-SM3-treated plants. Investigation at genetic level further showed that the strain SM3 triggered the ethylene (ET) responsive ERF transcription factor (CaTF2) under the challenged conditions. Thus, from this study, we conclude that actinomycetes St. rochei SM3 trigger the ET-mediated defence pathway in chickpea and activates the phenylpropanoid pathway for alleviating the stresses caused by Sc. sclerotiorum and salt in chickpea.

Streptomyces rochei SM3 Induces Stress Tolerance in Chickpea Against Sclerotinia sclerotiorum and NaCl

A major issue of potato cultivation in temperate zones is the potato cyst nematode Globodera rostochiensis. Population density of G. rostochiensis is high in Mexican potato fields. Control currently consists of the inefficient application of high doses of chemical nematicides. We evaluated the population density of G. rostochiensis in potato production plots in central Veracruz, Mexico. Plots were treated with the biocontrol agent Paecilomyces sp. and rotation with two different leguminous crop plants, Pisum sativum and Vicia faba. A random block experimental design was used with four different treatments over two crop cycles: (1) biological control with crop rotation, (2) crop rotation only, (3) biological control applied to soil left in fallow, and (4) soil left in fallow only. We measured the number and content of cysts, and the number of J2 juveniles of G. rostochiensis in the soil. We then estimated the infestation level in soil and the multiplication rate (Pf/Pi). The number of free-living nematodes was also quantified. Results show that the highest mitigation of G. rostochiensis was observed for the biological control rotation, with 89.2 % reduction, and for the biological control fallow treatments with 84.4 % reduction. In rotation plots, infestation level decreased by 30.7 %. In the biological control rotation and biological control fallow treatments, the Pf/Pi was 0.1 and 0.15, respectively. The highest Pf/Pi of 0.93 was found in the fallow plots. The biological control agent did not significantly affect the free-living nematode populations. In this study, the nematophagous fungus Paecilomyces sp. was used for the first time to efficiently reduce the population of G. rostochiensis in two crop cycles.

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89 % reduction of a potato cyst nematode population using biological control and rotation

Phytoparasitic nematodes are the important pests of sugar cane and controlled with the application of highly toxic chemicals. This study isolated fungi from the sugar cane phytoparasitic nematode Criconemoides sp. and tested the pathogenicity of one of these isolates on the nematode community of the sugar cane producing region of Veracruz, Mexico. One fungus was selected in order to monitor the in vitro infection process of Criconemoides sp. and the effect of this fungus on the density of nematodes associated with sugar cane in greenhouse was evaluated, using naturally infested soil and plants. Two treatments were established: biocontrol, applied with a spore suspension of fungus, and control treatment. A total of 42 fungal isolates were obtained, including Purpureocillium lilacinum, which was selected for use in the in vitro and greenhouse experiments. From 48 h after in vitro infection, blastospores and mycelia were observed within the body of the nematode. The most abundant phytoparasitic nematodes found in samples of the greenhouse experiment were Criconemoides sp. and Helicotylenchus sp. The initial phytoparasitic nematode populations in biocontrol and control treatments were 253+/-98 and 287+/-164 100 mL soil-1, respectively. Ten days following application of the fungus, the population of phytoparasitic nematodes was significantly (p < 0.01) lower in the biocontrol (91+/-26) than in the control (230+/-5) treatment. The fungus used in the experiment efficiently reduced the population of ectoparasitic and semiendoparasitic nematodes. We recommend field-testing of this fungus in order to determine its potential effectiveness under field crop conditions.

/pdf/isolation-of-fungi-associated-with-criconemoides-sp-and-52sim2gogp.pdf

Isolation of fungi associated with 'Criconemoides' sp. and their potential use in the biological control of ectoparasitic and semiendoparasitic nematodes in sugar cane

Fungi associated with Globodera rostochiensis cysts in Mexico.

Resumen es: Debido a la alta densidad del nematodo dorado de la papa Globodera rostochiensis en la zona montanosa del Cofre de Perote, en Veracruz, Mexico, se han bu...

EVALUACIÓN DE LA PATOGENICIDAD in vitro DE Purpureocillium lilacinum SOBRE Globodera rostochiensis

Desgarennes, D., G. Carrion, A. E. Nunez-Sanchez, and M. C. Nunez-Camargo. 2006. Distribution of stages and in vitro larval hatching in Globodera rostochiensis cysts. Nematropica 36:251-260. The classification of cysts as young (YC), mature (MC), and old (OC) on the basis of cyst wall color was shown to be a practical tool for the diagnosis of population status. Also important are differences in the stages that occur within cysts (eggs, J1, and J2), as they too are linked to differences in color. These data, from an ecological point of view, help us understand population structure. The density recorded for Los Pescados, Perote in the state of Veracruz, Mexico in one kilogram of soil was 2974 YC, 3004 MC, and 221 OC. On average, young cysts have 55-63% viable eggs, 37% of which contain a vitellus, without a developing embryo; MC have 38-54% viability, 39% of which are J1, with J2 also observed; in OC, 98% are empty eggs and have 2% viability with J1 and J2 juveniles. The greatest degree of hatching was observed in MC (19%), with juveniles hatching only four hours after being exposed to root exudates.

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Angel Enrique Nunez-Sanchez

Papers

89 % reduction of a potato cyst nematode population using biological control and rotation

Isolation of fungi associated with 'Criconemoides' sp. and their potential use in the biological control of ectoparasitic and semiendoparasitic nematodes in sugar cane

Fungi associated with Globodera rostochiensis cysts in Mexico.

EVALUACIÓN DE LA PATOGENICIDAD in vitro DE Purpureocillium lilacinum SOBRE Globodera rostochiensis

Distribution of stages and in vitro larval hatching in Globodera rostochiensis cysts.