Fighting Chestnut Blight: Antagonistic Microscopic Fungi
Abstract
The extent of cryphonecrosis among the chestnut populations of three Imeretian (west Georgia) villages: Darka, Eto, and Chala has been evaluated. 23 strains of Cryphonectria parasitica (Murrill) Barr (syn. Endothia parasitica (Murrill) were isolated and identified from the bark of sick trees. The collection of strains of the plant pathogen fungus has been created. The strategy of the struggle against the chestnut blight, based on the application of antagonistic to C. parasitica microscopic fungi, has been elaborated. For this purpose 50 strains of different microscopic fungi were isolated and identified (till genus) from the soil samples picked just under the stems of sick trees of above mentioned locations. The dominating genera of micromycetes in forest brown soils have been revealed. Strong biological antagonists of the plant pathogenic fungus, belonging to genera Penicillium, Trichoderma and Aspergillus have been selected on the base of the investigation of antagonistic activity of the “aboriginal” flora of studied soils. The collection of antagonistic to C. parasitica microscopic fungi, among them of new biological agents, has been created. The vegetative compatibility of the isolated strains of C. parasitica was investigated as well.
Introduction
Wood of excellent quality and high nutritional value fruits rise the chestnut plant - Castanea sativa Mill. in range of popular and economicaly significant trees in the world. (Heiniger and Rigling, 1994). Though, the plant is under the danger of extinction all over the world. The reason of it is so called “chestnut blight” disease caused by the plant pathogenic fungus from ascomycetes Cryphonectria parasitica (Murrill) Barr (syn. Endothia parasitica (Murrill)) (Anagnostakis, 1994; Rigling and Prospero, 2018).
It is more than half of a century the world scientists try efforts to fight the chestnut blight but in vain. Healing of sick trees with hypovirulent strains is regarded to be the most effective measure against C. parasitica today (Robin and Heiniger 2001; Puia et al., 2012). As it has established, hypovirulence is stipulated by the existence of Cryphonectria hypovirus (CHV) in the cytoplasm of C. parasitica. The genome of the virus is double chain RNA molecule (ds RNA). The virus lacks of capsid, which suppresses its active spreading in the environment. The virus is able “to enter” a new host organism only in case of formation of the hypae anastomoses between two stains of C. parasitica, or by means of the host’s asexual spores.
Though, wide scale integration of hypovirus under the natural conditions is not always possible because of the vegetative incompatibility of C. parasitica’s different stains (Anagnostakis, 1977). There exists another method of the biological inspection of chestnut blight: isolation of antagonistic to C. parasitica microorganisms from the natural sources and their application against the pathogen. According to literary data among the antagonistic microorganisms of C. parasitica are well known genera of microscopic fungi and bacteria (Trichoderma, Penicillium, Bacillus, Streptomyces) (Wilhelm et al., 1998; Groome et al., 2001; Akilli et al., 2011; Smith, 2013).
Combined application of antagonists and hypovirulent strains of C. parasitica appeared especially effective against the disease (Akilli et al., 2011). Those countries which are unable to control chestnut blight by hypovirulent strains, for the purpose to localize the pathogen, apply the easy way of in situ struggle against the pathogen – soil compressing or mud packing method (Anagnostakis, 1994; Groome et al., 2001).
The above mentioned botanical disaster of 20th century touched country of Geogia as well. Ten years ago 50% of Georgian chestnut forests were already dead (Prospero et al., 2013). There does not exist any effective fungicide against C. parasitica, according to the information of Georgian Ministery of Environment Protection. Cutting of sick trees is the only way of cryphonecrosis localization here. Except the joined scientific project of Swiss and Georgian investigators and attempts of the Turkish scientists of integration of hypovirulent strains in Ajara chestnut forest, practically no active measures have been performed for saving of the unique plant of Castanea sativa in Georgia, which is placed in “Georgian red list” and “Red book” (Prospero et al., 2013). Thus, elaboration and testing of the strategy of biological control against cryphonecrosis in Georgian chestnut forests is very urgent task today. Accordingly, the purpose of the presented work was to isolate the virulent strains of C. parasitica, spread in chestnut populations of one of the regions of west Georgia (Imereti), and to reveal the effective, antagonistic biological agents against them. The strategy of the fight against chestnut blight, spread in chestnut populations of west Georgian region Imereti, will be elaborated for the first time, and isolation of antagonistic to C. parasitica microscopic fungi directly from one of the hot spots of cryphonecrosis of Georgia will be performed for the first time, as well as creation of the collection of antagonists against the pathogen. All this may be regarded as the scientific novelty of the presented work.
Collection of this type may be considered as the material base for management and localization of chestnut blight epidemic in this region. We hope that creation of the antinecrotic bio-preparation and its in situ testing on the base of isolated particular antagonist microscopic fungi or their consortia will become possible in future.
Source : Microscopic fungi antagonistic to chestnut blight- Cryphonectria parasitica (Murrill) Barr.
