Species of Cercospora associated with grey leaf spot of maize

Abstract

Grey leaf spot is a serious yield-reducing disease of maize (Zea mays) in many parts of the world where this crop is cultivated. The causal organism associated with the disease is Cercospora zeae-maydis. Two potential sibling species have been recognized as Groups I and II. The DNA sequences for the internal transcribed spacers (ITS1 & ITS2), the 5.8S rRNA gene, elongation factor 1-α, histone H3, actin and calmodulin gene regions suggest that Groups I and II are two distinct species. Furthermore, Cercospora zeae-maydis (Group I) can be distinguished from C. zeina sp. nov. (Group II) by its faster growth rate on artificial media, the ability to produce cercosporin, longer conidiophores, and broadly fusiform conidia. A PCR-based test that distinguishes the two species was developed using species-specific primers designed from the histone H3 gene.

Molecular variability in the maize grey leaf spot pathogens in Brazil

“…Among the 91 isolates included in the U.S. study, only 12 were C. zeina isolates compared to 28 of the 69 Brazilian isolates. Nevertheless, the extent of genetic variability observed within and between Brazilian species supports the conclusions of Wang et al (1998) that the two groups they defined in the U.S. represent distinct gene pools and are likely to be different species, as suggested by Goodwin et al (2001) and recently confirmed by Crous et al (2006). This study also demonstrated a high genetic similarity among Brazilian, U.S., and African isolates.…”

“…Similarly, the East African population of C. zeina was found to lack population structure and was indistinguishable from the U.S. C. zeina (group II) population based on AFLP and RFLP analyses (Okori et al, 2003). Thus, there appears to be limited genetic variability within populations of C. zeina worldwide, which is consistent with the likelihood that this species reproduces asexually and indicates that geographically separated populations do not differ substantially from the founding population, which is proposed to be in Africa (Dunkle and Levy, 2000;Crous et al 2006). …”

“…In comparative analyses of ITS-5.8S rDNA nucleotide sequences of Cercospora species and anamorphs of Mycosphaerella, Goodwin et al (2001) concluded that groups I and II represent different species. Recently, Crous et al (2006) applied DNA phylogeny of nucleotide sequences of five nuclear-encoded genes and analysed morphological characteristics of isolates of the grey leaf spot pathogen from South Africa and compared them with isolates of the pathogen from the U.S.A. They confirmed the distinct separation of two species, provided complete descriptions, and named the African pathogen Cercospora zeina, replacing the previous designation of C. zeae-maydis group II.…”

“…Significantly, the African population of the grey leaf spot pathogen is comprised solely of C. zeina (Dunkle & Levy, 2000;Okori et al, 2003), although the possibility of a third maize pathogen more closely aligned with C. apii and C. beticola was suggested by Crous et al (2006). The considerable genetic divergence between the species, their differential geographical distribution, and slightly greater haplotype diversity of African isolates, together with historical records, led Dunkle and Levy (2000) to propose that C. zeina originated in Africa, although they did not rule out the possibility of independent origins in the U.S. and Africa.…”

Infection process in resistant and susceptible maize (Zea mays L.) genotypes to Cercospora zeae-maydis (type II)

“…African and US group type II populations were co-specific with limited variability and type II species grew much slower and did not produce any toxins in culture. Crous et al (2006) and Meisel et al (2009) reclassified group type II as distinct species now called Cercospora zeina endemic in African countries. Okori et al (2003) confirmed the widespread presence of type II biotypes in East Africa (Kenya, Uganda, and Rwanda) and indicated that gene flow was high among African populations of C. zeaemaydis.…”