http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Investigations on the variability of the sorghum anthracnose fungus C̲o̲l̲l̲e̲t̲o̲t̲r̲i̲c̲h̲u̲m̲ g̲r̲a̲m̲i̲n̲i̲c̲o̲l̲a̲
Laboratory and greenhouse experiments were conducted to: 1) investigate the diversity in the sorghum anthracnose fungus Colletotrichum graminicola using biotechnological and conventional techniques; 2) study the pathogenic variability among monoconidial isolates from isolated leaf lesions and monoconidial cultures; and 3) evaluate mutation as a mechanism contributing to pathogenic variability in this organism. For the first study, monoconidial isolates of C. graminicola were established from collections made in commercial fields and experimental trials during 2 consecutive years from 4 regions of Brazil (Central, South, Southeast, and Northeast) and from the sorghum anthracnose flora of Texas and Georgia in the United States. A total of 78 monoconidial isolates were investigated for variability in virulence on 8 differential sorghum cultivars and in RAPD (Random Amplified Polymorphic DNA) banding patterns as defined by 8 primers. Average linkage cluster analysis, applied to both types of data, revealed a lack of relationship between clusters as defined by these markers. The same or related virulence phenotypes were composed by genetically distant isolates when analyzed by RAPD markers. Isolates of C. graminicola within the same or related RAPD pattern were obtained from distant regions, indicating that populations of this pathogen are not geographically defined. Pathogenicity of monoconidial cultures from a discrete lesion and from monoconidial cultures and sub-cultures from the sorghum cultivars Tx623 and SC748-5 was evaluated on 5 differentials. Monoconidial isolates from single lesions and from monoconidial cultures and sub-cultures were separated into several different virulence phenotypes, indicating the occurrence of pathogenic instability, at least in some isolates of this pathogen. Reversion from a virulent to an avirulent state was observed for some isolates. To search for the possibility of obtaining natural mutants for virulence, 2 isolates of C. graminicola, each avirulent to the sorghum cultivars Tx378 and SC326-6, were multiplied for 5 successive generations on the susceptible cultivar Tx623. In each generation, part of the spore suspension was applied to the resistant genotype. Twelve days after inoculation, leaves were examined for the presence of possible susceptible lesions of anthracnose. Mutation for increased virulence occurred spontaneously on leaves of the susceptible cultivar in relation to cultivar SC326-6.