Kui Xiang1, GuangTang Pan1, Lana M. Reid2, ZhiMing Zhang1 and XiaoYang Zhu2

A meta-analysis of QTL associated with ear rot resistance in maize

Introduction

©2011

1 Maize Research Institute, Sichuan Agricultural University, Yaan 625014, Sichuan, P.R. China 2 Eastern Cereal and Oilseed Research Centre, Agricultural & Agri-Food Canada, Ottawa, Ontario, Canada K1A 0C6

Maize ear rot (ER) is one of the most prevalent types of

maize disease worldwide. The three predominant ER

diseases, Aspergillus ear rot (AER), Fusarium ear rot

(FER) and Gibberella ear rot (GER), are responsible for

the most disease-related reductions in yield and quality.

Meta-analysis is a set of statistical procedures for

synthesizing research results from a number of different

studies. Many studies showed that QTL meta-analyses

can be used to combine results from independent

published QTL studies.

Results and discussion

Materials and methods

Fourteen studies on maize ER QTL published from 2001-

2009 were used in the current study. In these studies, the

resistance of maize was measured by kernels exhibiting

visible symptoms that were converted to percent of

infection such as rot and mycelial growth.

QTL identified in one population evaluated in a given

environment were defined as an experiment. The

identified QTL were projected onto a reference map for

meta-analysis. The original map position, logarithm of

odds score, confidence interval and R2 (% phenotypic

variance explained by the given trait) of each QTL were

used for projection. Information pertaining to all genetic

maps was collected or estimated according to the

published maps, then QTL in their original maps were

projected on IBM2 neighbors 2008 (Intermated B73×Mo17

Map) using BioMercator v 2.1 (Arcade et al. 2004). Some

controversial markers between original and reference

maps were deleted from the analysis to ensure the

accuracy of the projection (Chardon et al. 2004).

Eighty-seven initial QTL were used in the meta-analysis, which resulted in 29 consensuses ER meta-QTL (MQTL) comprising 65 initial QTL and 22 remaining individual QTL. All these MQTL occurred on all chromosomes with the exception of chromosomes 9 and 10, with two to six initial QTL on each chromosome (Table 1). Ten MQTL pooled three initial QTL, while 13 MQTL pooled two initial QTL.

References

Arcade A, Labourdette A, Falque M, Mangin B,

Chardon F, Charcosset A, Joets J (2004) Biomercator:

Integrating genetic maps and QTL towards discovery of

candidate genes. Bioinformatics 20:2324–2326

Chardon F, Virlon B, Moreau L, Falque M, Joets J,

Decousset L, Murigneux A, Charcosset A (2004)

Genetic architecture of flowering time in maize as

inferred from quantitative trait loci meta-analysis and

synteny conservation with the rice genome. Genetics

168:2169–2185

ER in maize is mainly associated with three types (AER, FER

and GER) based on the pathogen causing the ear rot. From

meta-analysis, most MQTL consisted of two or three types of ER

resistance. Eleven of 29 MQTL contributed to both FER and

GER on chromosomes 1 to 7, especially on chromosomes 2 and

3, suggesting that there were some common QTL/genes for FER

and GER resistance in these regions.

Based on 29 MQTL, a total of 21 genes were found to be co-

located within 2 cM of identified MQTL positions, located on 13

MQTL (1, 3, 4, 8, 10, 11, 14, 15, 16, 21, 22, 25 and 26).

MQTL Chrom. Number of Projected

QTL

Type of ERa MQTL Chrom. Number of projected

QTL

Type of ERa

1 1 2 FER, GER 16 5 2 FER

2 1 2 FER, GER 17 5 3 FER, GER

3 1 2 GER 18 5 3 AER, FER, GER

4 2 3 FER, GER 19 6 2 FER

5 2 3 FER, GER 20 6 2 FER

6 2 3 FER, GER 21 6 2 FER,GER

7 3 3 AER, FER 22 6 2 FER

8 3 6 FER, GER 23 6 2 AER, FER

9 3 6 AER, FER, GER 24 7 2 FER

10 3 2 AER, FER 25 7 2 FER, GER

11 3 3 AER, FER, GER 26 7 3 FER, GER

12 3 3 AER, FER, GER 27 7 3 GER

13 4 5 AER, FER 28 7 4 GER

14 4 4 AER, FER 29 8 2 FER

15 4 4 FER, GER

Table1 Characteristics of detected meta-QTL (MQTL) for ear rot (ER) resistance

Fig. 1 Projection on a reference map of chromosome 2.08 and 3.04 of MQTL for ear rot resistance in maize. The name of MQTL are on the left; names of markers and the distances in centimorgans are on the right.

Acknowledgement

The authors gratefully acknowledge Dr Yu-Ming Wei

from Sichuan Agricultural University for excellent

advice on QTL meta-analyses.

In this study, bins 3.04 and 2.08 were major QTL

containing regions of ER resistance (Fig. 1). Three MQTL

(MQTL 8, 9 and 10) were located on bin 3.04, while

another three MQTL (4, 5 and 6) were derived from bin

2.08. Further fine mapping should be worthwhile in the two

regions.

a AER = Aspergillus ear rot, FER = Fusarium ear rot, GER = Gibberella ear rot