Fumonisin producing Fusarium spp. and fumonisin contamination in commercial South African maize B. Janse van Rensburg, N. W. McLaren, B. C. Flett & A. Schoeman
European Journal of Plant Pathology Published in cooperation with the European Foundation for Plant Pathology ISSN 0929-1873 Eur J Plant Pathol DOI 10.1007/s10658-014-0558-7
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Author's personal copy Eur J Plant Pathol DOI 10.1007/s10658-014-0558-7
ORIGINAL RESEARCH
Fumonisin producing Fusarium spp. and fumonisin contamination in commercial South African maize B. Janse van Rensburg & N. W. McLaren & B. C. Flett & A. Schoeman
Accepted: 24 October 2014 # Koninklijke Nederlandse Planteziektenkundige Vereniging 2014
Abstract Fumonisins are secondary, carcinogenic metabolites produced primarily by Fusarium verticillioides and Fusarium proliferatum on maize worldwide. The natural occurrence of fumonisin-producing Fusarium spp. and fumonisin contamination of maize grain were quantified in selected maize cultivars from principal production areas of South Africa. Grain colonization by Fusarium spp. was determined using quantitative real-time PCR (qPCR) and contamination with fumonisins using HPLC analysis. Kernels from the 2007 samples were also plated onto Fusarium selective medium and subsequently, split plates containing PDA & CLA. The number of fumonisin producing Fusarium spp. were quantified and microscopically identified after 14 days. Simple linear regression analysis was used to determine the relationship between target DNA, fumonisins and the number of fumonisin producing Fusarium spp. using the plating out method. Results indicated high natural infection by fumonisinproducing Fusarium spp. and fumonisin concentrations in warmer production areas such as Northern Cape, North West and Free State Provinces. Spearman Ranking Correlations indicated that the responses of cultivars to colonization of grain by fumonisin B. Janse van Rensburg (*) : B. C. Flett : A. Schoeman Agricultural Research Council-Grain Crops Institute, Private Bag X1251, Potchefstroom 2520, South Africa e-mail:
[email protected] N. W. McLaren Department of Plant Sciences, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa
producing Fusarium spp. varied over localities/seasons (rs =0.42 to 0.64) suggesting that cultivars reacted differently to different environmental/inoculum conditions (disease potentials). Cultivars CRN3505 and DKC8012B showed a degree of resistance to fungal infection. As with fungal colonization, Spearman Rank Correlations indicated the response of cultivars to fumonisin contamination to vary over localities/ seasons (rs =0.29 to 0.70). Cultivars DKC80-12B and LS8521B showed a degree of resistance to fumonisin contamination. Regression analysis yielded a significant relationship between HPLC data and qPCR, but not with the plating out of grain data suggesting the former to be a better indicator of potential fumonisin contamination. Site-specific, daily maximum temperature and rainfall data were provided by the ARC-Institute for Soil Water and Climate’s meteorology office. No significant relationship between these weather parameters and colonization of grain by fumonisin producing Fusarium spp. was recorded, although a tendency was observed between fumonisin contamination and mean maximum temperature. Keywords Fumonisins . Fusarium spp . G X E interactions . Incidence
Introduction Maize (Zea mays L.) is an important crop in South Africa and is produced throughout the country under diverse cultural and weather conditions. The important
Author's personal copy Eur J Plant Pathol
fumonisin-producing ear rot Fusarium spp. are F. verticillioides and F. proliferatum (Rheeder et al. 1990). The distribution and predominance of these Fusarium spp. and their concomitant fumonisin production varies depending on season, geographic locality, climatic factors such as temperature and moisture, host genotype and agricultural practices (Nyaka et al. 2010). At least 28 fumonisin analogues are known, but the most abundant natural forms are fumonisin B1, B2 and B3 (Rheeder et al. 2002). Fumonisins are secondary carcinogenic metabolites, which occur naturally as contaminants of agricultural products such as maize. The consumption of maize contaminated with fumonisins causes mycotoxicoses in animals including leucoencephalomalacia in horses (Kellerman et al. 1990; Ross et al. 1990) and pulmonary edema in swine (Harrison et al. 1990). Fumonisin infected maize has been statistically associated with human esophageal cancer in South Africa (Marasas 1981, 1982, 1988; Rheeder et al. 1992), northern Italy (Franseschi et al. 1990) and Iran (Shephard et al. 2000). Chu and Li (1994) and Li et al. (2001) reported an increased incidence of primary liver cancer in humans that ingest maize contaminated with fumonisin in certain regions of The People’s Republic of China. Stack (1998), Placinta et al. (1999), Hendricks (1999) and Marasas et al. (2004) have shown a strong correlation between the consumption of fumonisincontaminated tortillas and neural-tube defects in humans. The potential carcinogenic risk of fumonisin B1 to humans was evaluated and classified by the World Health Organizations International Agency for Research on Cancer (WHO-IARC) as a “Group 2B carcinogen” which means it is possibly carcinogenic to humans (1993). The United States Food and Drug Administration (FDA) has set guidelines of 2 ppm (FB1) for degermed dry milled maize products and 4 ppm for whole or partially de-germed dry milled maize products for human consumption (FDA 2001). Currently South Africa has no legislation or monitoring system regarding allowable fumonisin concentrations and consumers may be at greater risk due to the higher consumption of maize in comparison to European countries (Marasas 2001). Marasas (2001) recorded large variations in probable daily intake (PDI) of maize ranging from 1.2 μg/kg bodyweight (bw)/day in urban South Africans consuming commercial maize, to 354.9 μg/kg bw/day in rural South Africans consuming moldy, home-grown maize.
Limited data are available regarding the incidence of Fusarium spp. and associated fumonisin levels in maize in South African production areas. Fumonisins in maize produced by subsistence farmers in northern KwaZuluNatal (Zululand) province of South Africa exceeded 2 ppm set by the United States Food and Drug Administration in 52 % and 17 % of samples collected in 2006 and 2007 respectively (Ncube et al. 2011). These authors also reported a number of samples from Mokopane (Limpopo) and Lusikisiki (Eastern Cape) containing excessive fumonisin levels. Boutigny et al. (2012) reported that F. verticillioides was the predominant fungus in maize at 14 commercial localities in the North-West, the western Free-State and Northern Cape provinces, while F. proliferatum was not detected at any of the localities. The objectives of this study were: (i) to quantify the incidence of fumonisin producing Fusarium spp. and to determine the concentrations of fumonisin in commercial maize grain samples from different production localities in South Africa, (ii) to study genotype x environment interactions associated with colonization and fumonisin contamination, (iii) to determine the relationship between fumonisin-producing Fusarium spp. with morphologically based identifications based on platingout and fumonisin concentrations, and (iv) to evaluate the relationship between maximum temperature and rainfall and the contamination of grain by fumonisinproducing Fusarium spp. and resultant fumonisin contamination.
Materials and methods Maize samples Maize kernels harvested from National Cultivar Evaluation Trials conducted by the ARC-Grain Crops Institute in Potchefstroom were collected from a range of localities (Tables 1, 2, and 3) during the 2007–2009 maize production seasons. All trials were conducted using a randomized complete block design with three replicates. Trials were conducted under dry land conditions and maintained according to “Best Practice” appropriate to the respective production areas with the exception of Vaalharts in the Northern Cape which was flood irrigated. Weather variables, including daily maximum temperature and rainfall were monitored at each locality during flowering and grain development
nd
1.95a
nd
1.11a
Wesselbron
Mean
nd
nd
2.90
nd
nd
nd
nd
nd
1.73
nd
nd
nd
nd
nd
2.43a 0.36a
nd
18.73 0.84
nd
7.25
nd
nd
nd
nd
1.56
0.06
nd
8.84
nd
nd
nd
2.00
nd
nd
nd
0.04
nd
nd
nd
nd
nd nd nd 7.31 21.30 2.11 4.36
a
a
0.67a 0.67a 0.89a 3.15a a
nd
2.96a
3.74a
nd
135.00
nd
58.10
55.60
nd
nd
nd
9.98
17.60
nd
nd
nd
nd
nd
15.90abc 18.42abc
nd
0.00a nd
nd
nd
nd
5.33
nd
0.00
a
4.46b 21.00
nd
nd
0.00a nd
nd
10.30
23.80
199.00
nd
nd
nd
nd
nd
0.00 a nd
2.39
0.00
0.00
nd
0.00a
17.72 7.83b nd
nd
nd
2.53a 1.32a
nd
9.70
nd
nd
14.88 nd
nd
nd
10.89 nd
0.12
nd
nd
2.30
nd
nd
nd
DkC Mean 80-10
0.38a
nd
1.79
nd
nd
2.40
nd
nd
nd
nd
nd
nd
nd
1.47
nd
nd
39.65de
2.08 abc
0.77a
0.58
a
0.00a
2.55 abc
1.36
1.22
1.07
1.48
0.93
0.74
6.89
nd
1.11
4.03
0.83
0.00
a
0.00a
1.36
0.28
2.63
0.56
14.44abcd 1.40
14.12abcd 1.89
0.00a
0.00a
10.35
26.70 32.25de
nd
2.19
nd
nd
nd
abcd
10.70 13.27abcd 0.93
nd
nd
nd
nd
nd
nd
10.50abc 3.10a
nd
30.00
nd
nd
26.70
nd
nd
40.60
33.00
nd
5.18
4.66
2.02
nd
15.30
29.85
31.41
30.37
28.77
30.88
30.35
31.23
25.36
30.45
29.89
29.67
30.65
31.15
28.49
28.24
30.78
28.77
30.64
29.31
28.01
29.78
29.52
29.92
24.39
29.35
29.05
28.43
29.33
29.84
27.98
27.18
28.87
Mean Mean max Mean max rainfall, temp, Feb, temp, Mar Jan, Feb, Mar Mar
Limit of detection =0.016 ppm
ND not detected
Different letters shown indicate significant differences (P
