Symptoms and Prepenetration Events Associated with the Infection of Common Bean by the Anamorph and Teleomorph ofGlomerella cingulataf.sp.phaseoli

Abstract

Glomerella cingulata f.sp. phaseoli and Colletotrichum lindemuthianum are the teleomorph and anamorph, respectively, of the pathogen causing anthracnose in common bean. The mechanisms relating to the sexual reproduction of this plant pathogen are still unclear, as are the infection structures involved and the symptoms produced. In the present study, bean plants were inoculated with ascospores and conidia, and the events taking place within the following 120 h were investigated using light microscopy and scanning electron microscopy. The symptoms exhibited by plants inoculated with the ascospores were milder than in those inoculated with conidia. Microscopy revealed that most of ascospores produced germ tubes and appressoria at an early stage (24 h after inoculation). From 48 h onwards, the formation of hyphae and the production of germ tubes and appressoria were great. In contrast, infections originating from conidia developed more slowly, and at 24 and 48 h, many non-germinated conidia were present, whereas only few conidia developed germ tubes and appressoria. Ascospore germination and appressorium formation were similar on both resistant and susceptible cultivars. Hence, the symptoms and the temporal sequence of events associated with the infection of bean plants by the two fungal forms differed, although the structures produced were similar. This is the fist report comparing symptoms and prepenetration events between anamorph and teleomorph of G. cingulata f.sp. phaseoli in common bean.

Characterization of Glomerella Strains Recovered from Anthracnose Lesions on Common Bean Plants in Brazil

“…The ability of the pathogen to rapidly overcome sources of host resistance is not well understood, but the frequent recovery of fertile Glomerella strains from anthracnose lesions suggested sexual recombination as one possibility. Previous studies have identified Glomerella strains recovered from anthracnose lesions as Glomerella lindemuthiana or Glomerella cingulata f.sp phaseoli , assuming them to be the teleomorphs of C. lindemuthianum [11], [13], [32], [34]. However, the results of the current study do not support the hypothesis that these Glomerella isolates are related to C. lindemuthianum .…”

Live-cell imaging of conidial fusion in the bean pathogen, Colletotrichum lindemuthianum

“…Roca, unpublished). On the host leaf surface, C. lindemuthianum was found to grow and undergo CAT fusion for 48-72 h before there was any evidence of penetration into the leaf (Ishikawa et al 2009). (4) Conidia from older cultures of C. lindemuthianum (optimally 16-d-old cultures grown on bean pod agar) underwent the highest amount of CAT fusion.…”

“…CAT fusion has been previously observed on the surfaces of host leaves inoculated with Colletotrichum spp. (Latunde-Dada et al 1999;Ishikawa et al 2009). In a number of other ascomycete fungi, including plant pathogens, it has been previously found that conidial germling fusion can be increased when the rich organic growth medium is diluted (Laibach, 1928;Kö hler 1930;Glass & Fleißner 2006;Read et al 2010).…”

“…In C. lindemuthianum, CAT fusion has been previously shown to occur on the host surface (Ishikawa et al 2009) and within the acervulus (asexual fruiting body) either in anthracnose lesions on the host or in culture (Roca et al 2003). Because CAT fusion only occurs within the walls of the acervulus it very difficult to analyze the whole process in situ using live-cell imaging techniques which are now widely used with filamentous fungi (Hickey et al 2005;Hickey & Read 2009).…”

Sexual recombination in Colletotrichum lindemuthianum occurs on a fine scale

“…However, absence of such symptoms in plants inoculated with G. cingulata f. sp phaseoli isolates has been reported (Camargo Jr. et al, 2007;Ishikawa et al, 2009); the symptoms in the sexual phase are milder than those presented during the asexual phase.…”