Modeling Root-Knot Nematode Regulation by the Biocontrol Fungus Pochonia chlamydosporia.

Two models of increasing complexity were constructed to simulate the interactions between the root-knot nematode (RKN) Meloidogyne incognita and the biocontrol fungus Pochonia chlamydosporia var. catenulata in a rhizosphere microcosm. The models described discrete population dynamics at hourly rates over a 6-month period and were validated using real parasitism and nematode or fungus data. A first, general Pochonia-nematode-root model (GPNR) used five functions and 16 biological constants. The variables and constants describing the RKN life cycle included the rates of egg production, hatching, juvenile (J2), and mature female development, including root or nematode self-density-dependent factors. Other constants accounted for egg parasitism, nematode-induced root losses, growth, and mortalities. The relationship between nematodes and fungal propagules showed density dependence and cyclic variations in time, including an attractor on the propagules and J2 phases space. The simulations confirmed a P. chlamydosporia optimal initial density of 5 · 103 propagules · cc soil-1, as usually applied in assays. The constants used in GPNR showed adherence to the nematode biology, with 103 eggs per egg mass, a 10-day average lifespan of J2, with 2 days required to enter roots, and adult lifespan lasting 24 days. The fungus propagule lifespan was 25 days, with an average feeder root lifespan lasting around 52 days. A second, more complex Pochonia-nematode-root detailed model (GPNRd) was then constructed using eight functions and 23 constants. It was built as GPNR did not allow the evaluation of host prevalence. GPNRd allowed simulations of all RKN life stages and included non-parasitic and parasitic fungus population fractions. Both GPNR and GPNRd matched real J2 and fungus density data observed in a RKN biocontrol assay. Depending on the starting conditions, simulations showed stability in time, interpreted as effective host regulation. GPNRd showed a fungus cyclic relationship with the J2 numbers, with prevalence data close to those observed (38.3 vs. 39.4%, respectively). This model also showed a further density-independent nematode regulation mechanism based on the P. chlamydosporia switch from a non-parasitic to a parasitic trophic behavior. This mechanism supported the biocontrol of M. incognita, also sustained by a concomitant increase of the root density.

[Effects of pesticides and plant bio-stimulants on the germination of chlamydospores and in vitro development of the nematophagous fungus Pochonia chlamydosporia]. / Efectos de plaguicidas y bioestimulantes vegetales sobre la germinación de clamidosporas y el desarrollo in vitro del hongo nematófago Pochonia chlamydosporia.

BACKGROUND: The effects of pesticides and plant bio-stimulants used in protected vegetable production systems on the fungus Pochonia chlamydosporia are unknown. AIMS: The effectiveness of P. chlamydosporia against Meloidogyne spp. could be affected by products used in protected vegetable production systems. Two in vitro assays were carried out to evaluate any potential effect that pesticides and bio-stimulants often used in these systems could have on the fungus. METHODS: The effect on chlamydospore germination was evaluated in a first assay, and mycelia growth and sporulation in a second. With these results, the compatibility of each product with the fungus was determined. RESULTS: Chlamydospores germination was over 50% with the control, FitoMas E, Biobras-16 and Amidor. Lower results were observed with other products, with some of them even inhibiting germination completely. Fungal growth was potentiated by Biobras-16 to 106.23%, promoted up to 50-100% by the control, FitoMas E and Cuproflow, and was below 50% with the rest of the products.Cipermetrina, Benomilo, Zineb, Mitigan, Karate, FitoMas E and Amidor promoted fungal sporulation, which was below 50% with Cuproflow and completely inhibited by the other products. Fifty-four percent of the products evaluated were compatible with P. chlamydosporia, while 8% were toxic and 38%, very toxic. CONCLUSIONS: Cipermetrina, Karate, Amidor, Benomilo, Zineb, Mitigan and FitoMas E were compatible with P. chlamydosporia. If it is necessary to use any of the other products for integrated pest management in protected vegetable production systems, it is recommended to avoid direct contact with P. chlamydosporia.

Pochonia chlamydosporia: Advances and Challenges to Improve Its Performance as a Biological Control Agent of Sedentary Endo-parasitic Nematodes.

The nematophagous fungus Pochonia chlamydosporia var. chlamydosporia is one of the most studied biological control agents against plant (semi-) endo-parasitic nematodes of the genera Globodera, Heterodera, Meloidogyne, Nacobbus and, more recently, Rotylenchulus. In this paper we present highlights from more than three decades of worldwide research on this biological control agent. We cover different aspects and key components of the complex plant-fungus-nematode tri-trophic interaction, an interaction that needs to be addressed to ensure the efficient use of P. chlamydosporia as a biopesticide as part of an integrated pest management approach.

Approaches for monitoring the release of Pochonia chlamydosporia var. catenulata, a biocontrol agent of root-knot nematodes.

Pochonia chlamydosporia var. catenulata is a potential biocontrol agent against root-knot nematodes. Diagnosis of isolates has relied on morphological identification, and is both time-consuming and difficult. beta-tubulin primers have been developed for the identification of this fungus that were specific enough to distinguish between varieties of the fungus within the same species. Separate primers have been developed for the specific detection of P. chlamydosporia var. catenulata based on ITS sequences, which were able to detect the fungus in soil from various sites in Cuba where the biocontrol agent had been added. When the PCR diagnosis was combined with serial dilution of soil samples on selective medium, colonies were rapidly identified. The fungus was still present, albeit at low densities, in soils inoculated five years previously. The development of a baiting method allowed quick in situ screening of the isolates' ability to infect nematode eggs, and when combined with PCR diagnosis both varieties of the fungus could be detected in infected eggs. RFLP analysis of ITS sequences from P. chlamydosporia provided an extra level of discrimination between isolates.

Development of a new management strategy for the control of root-knot nematodes (Meloidogyne spp) in organic vegetable production.

The nematophagous fungus, Pochonia chlamydosporia (Goddard) Zare & Gams, has been investigated as a potential biological control agent for use in integrated pest management strategies for Meloidogyne incognita (Kof & White) Chitwood in vegetable crops. The release of the fungus as a biological control agent requires a diagnostic method to monitor its spread in the environment and to gain knowledge of its ecology. Only molecular methods are sufficiently discriminating to enable the detection of specific isolates of fungi in soil. A method to extract DNA from soil was developed to increase the efficacy of PCR-based diagnostic tests that use specific primers. A selected isolate of P chlamydosporia var catenulata was applied at densities similar to those that occur naturally in nematode-suppressive soils. The fungus significantly reduced nematode infestations in soil following a tomato crop, in a strategy that combined the use of the fungus with crop rotation. The survival of the fungus in soil was also examined in controlled conditions in which it remained in soil in densities significantly greater than its original application rate for at least 5 months. Hence, it seems that populations of this fungus may be built up in soil and have significant effects on the regulation of root-knot nematode populations.