244 Table 5 Molecular markers significantly (at the α00.05 level) associated with FB1 concentration estimated by regression analysis Marker symbol Estimates of regression coefficients OPC-02b OPC-15 d OPL-11c OPL-11 d OPL-11e OPL-12 d OPL-12f OPB-07b −0.223 0.173 0.226 −0.235 0.237 0.197 0.184 −0.167 P-value 0.003 0.023 0.002 0.005 0.003 0.008 0.012 0.037 24.8 13.7 26.5 22.0 24.4 19.2 16.9 11.2 J Appl Genetics (2012) 53:237–247 Percentage variation accounted Standard error of observations 0.183 0.196 0.181 0.186 0.183 0.190 0.192 0.199 morphology as well as simple PCR in some cases is insuffi- cient. The translation factor 1-α gene has high phylogenetic utility because it is very informative at the species level and non-orthologous copies of them have not been detected in the Fusarium genus (Geiser et al. 2004). Based on species-specific PCR and partial sequencing of the TEF gene, we proved undoubtedly that isolates forming FB1 belong to F. oxysporum species. The present study showed explicitly that some of the F. oxysporum isolates infecting asparagus spears have the potential to form and accumulate FB1, although, in general, they produced low amounts of fumonisin and significantly higher amounts of MON. The ability of F. oxysporum to form fumonisin has been questioned previously. Wang et al. (2010) reported that F. oxysporum strains isolated from asparagus spears in Zhejiang Province of China did not produce FB1, but only four F. oxysporum isolates were examined. Similarly, it was shown that F. oxysporum isolated from greenhouse-grown jimsonweed produced only MON at a concentration level of 3.5 μg g−1 (Abbas et al. 1992). On the other hand, Abbas et al. (1995) claimed that three of six isolates of F. oxysporum and seven isolates of F. oxysporum var. redolens from root lesions of eastern white pine seedlings produced FB1, ranging from traces (≥100) to 300.60 ng g−1. This statement was also supported by our earlier studies (Waśkiewicz et al. 2009). Fumonisin formation is positively related to the FUM genes expression (Waalwijk et al. 2004; Stępień et al. 2011a, b). The FUM genes cluster is highly collinear among F. oxysporum, F. proliferatum and F. verticillioides, regarding gene number, orientation and order (Proctor et al. 2008). The amount of FB1 produced in vitro depends on the substrate, genotype and conditions (Desjardins et al. 1992). It was shown that there is a significant impact of interacting environmental factors on the FUM transcript levels (Jurado et al. 2008). The correlation between FB1 and MON levels was not revealed, probably because of the different biosynthetic pathways of these sec- ondary metabolites (Voss et al. 2007). Naturally occurring genetic variance in the fungal population may explain why non-producing isolates were also recorded. The loss of toxi- genic ability can occur due to even a single-point mutation that shifts the open reading frame or creates a premature stop codon (Proctor et al. 2006). The detection of MAT genes in the genomes of mitosporic species is a first step into learning what causes asexuality (Kück and Pöggeler 2009). The obtained results confirm that F. oxysporum has a heterothallic origin and are in agreement with Turgeon’s hypothesis that some Fusarium species may Fig. 3 Genetic fingerprinting of F. oxysporum isolates applying RAPD-PCR with the OPC-15 primer. Lanes: MM a Gene Ruler™ 100 bp DNA Ladder Plus (Fermentas), N a negative control. *RAPD marker (OPC-15b) associated with high moniliformin level