Crop Science Journal of Natural Resources and Life Sciences Education
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published online 27 March 2006
Published in Crop Sci 46:1039-1045 (2006)
© 2006 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Zhao, M.
Right arrow Articles by Pan, G.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Zhao, M.
Right arrow Articles by Pan, G.
Agricola
Right arrow Articles by Zhao, M.
Right arrow Articles by Pan, G.
Related Collections
Right arrow Crop Genetics
Right arrow Plant Disease

CROP BREEDING & GENETICS

Quantitative Trait Loci for Resistance to Banded Leaf and Sheath Blight in Maize

Maojun Zhaoa,{dagger}, Zhiming Zhanga,{dagger}, Shihuang Zhangb, Wanchen Lia, Daniel P. Jeffersc, Tingzhao Ronga and Guangtang Pana,*

a Maize Research Institute, Key Laboratory of Crop Genetic Resources and Improvement, Ministry of Education, Sichuan Agricultural University, Xinkang 36, Ya'an, Sichuan 625014, China
b Institute of Crop Breeding and Cultivation, CAAS, Beijing 100081, China
c International Maize and Wheat Improvement Center (CIMMYT), Apdo 6-641, 06600 Mexico, D.F. Mexico

* Corresponding authors (zhangzm2{at}yahoo.com.cn; pangt{at}sicau.edu.cn)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Banded leaf and sheath blight (BLSB) caused by Rhizoctonia solani Kühn in maize (Zea mays L.) is an important disease in China as well as South and Southeast Asia. The identification of quantitative trait loci (QTL) for resistance to this disease would facilitate the development of disease resistant maize hybrids. A mapping population consisting of 229 F2 individuals derived from the cross of inbreds R15 (resistant) and 478 (susceptible) was used in this study. A genetic linkage map was constructed containing 146 single sequence repeat (SSR) markers, which covered 1666 cM of the maize genome, with an average distance of 11.4 cM. All F2:4 population individual plants were artificially inoculated by anastomosis groups AG1-IA of R. solani at two locations for disease evaluations. Composite interval mapping (CIM) identified 11 QTL for resistance to BLSB located on chromosomes 1, 2, 3, 4, 5, 6, and 10, but only four QTL located on chromosomes 2, 6, and 10, were identified across both locations. The range of phenotypic variation explained by the QTL was 3.72 to 10.35%. The information gained from mapping resistance can be used in a marker-assisted selection (MAS) program for the development of BLSB resistant germplasm.

Abbreviations: BLSB, banded leaf and sheath blight • SSR, simple sequence repeat • CIM, composite interval mapping • QTL, quantitative trait loci • MAS, marker-assisted selection • AG, anastomosis groups • GCA, general combining ability • PDA, potato dextrose agar • PH, plant height • DI, disease index • cM, centimorgan • LR, likelihood-ratio • LOD, log likelihood ratio


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
BANDED LEAF and sheath blight (BLSB) is one of the most severe maize diseases in China, South and Southeast Asia (Bertus, 1927; Sharma and Saxena, 2002). The fungus responsible for causing BLSB is Rhizoctonia solani Kühn (Zhu, 1982; Gao, 1987; Yan et al., 1984). Presently, there are 14 anastomosis groups (AG) of R. solani described in the literature, AG-1 through AG-13 plus AG-BI, representing diverse geographic origins and host range. In China, the predominant anastomosis group is AG1-IA, which is highly pathogenic and has a broad host range, affecting many crops including maize, rice (Oryza sativa L.), wheat (Triticum aestivum L.), sorghum [Sorghum bicolor (L.) Moench], bean (Phaseolus spp.) and soybean [Glycine max (L.) Merr.] (Xia and Li, 1993; Xiao et al., 2002). Epidemics of this disease are closely related to climatic conditions and farming practices. Disease losses are particularly severe under the conditions of high relative humidity and high plant population densities (Jiang et al., 1991; Liu et al., 1993). This disease initially infects maize at the first and second leaf sheath above the ground and then spreads upward to infect the ear (Song et al., 1993), leading to severe yield losses (Zhao and Liu, 1994). Recently, when the ear rot phase predominated, yield losses approached 100% in southern China (Tang et al., 2004), and the disease is spreading to new areas under intensive farming practices.

This alarming situation is further aggravated by the lack of commercial hybrids resistant to the disease. Conventional control measures, through the use of fungicides or cultural practices, have not provided adequate control of the disease or are not an economically viable option. Development of resistant hybrids through classical plant breeding has been slow because of the unavailability of disease resistant sources and because artificial inoculation is difficult (Pan and Rush, 1997; Han et al., 2002). To date, there have been limited reports on genetics of resistance to BLSB in maize (Sharma et al., 2002).

Quantitative trait loci (QTL) mapping is an effective approach for studying genetically complex forms of disease resistance, where effects of specific resistance loci can be determined and interactions between resistance genes, plant development, and the environment can be analyzed. QTL mapping also provides a framework for MAS of complex characters and the positional cloning of genes with partial resistance (Concibido et al., 1994; Wang et al., 1994). MAS is potentially an important tool for use in crop improvement.

Reliability of QTL determination depends primarily on the accuracy of measuring the corresponding traits because quantitative traits are largely influenced by environmental factors. The genesis and development of BLSB are extremely sensitive to the microclimate in the field. Therefore, proper methods of inoculation and standards for disease severity measurement were adapted to improve the accuracy of disease resistance recording. Among the many inoculation methods available (Pan et al., 1997), the method of infected wheat seed insertion was used to achieve uniform inoculation of every plant in the experiment. This method helps maximize expression of disease.

Our research objective was to identify QTL for resistance to BLSB so that the information could be used for developing a MAS program in maize.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Mapping Population Development
A cross was made between the elite inbreds R15 (resistant) and 478 (susceptible), which had been identified in earlier studies, to form the mapping population. The resistant parent R15 was bred at the Maize Research Institute of Sichuan Agriculture University and identified through many years of evaluations to have a high level of resistance to BLSB, possess good general combining ability (GCA), and have good agronomic characteristics. The susceptible parent 478 is highly susceptible to BLSB in southwestern China (Yang et al., 2003). The original cross was made at Yuanjiang farm in Yunnan Province, China, in September 2001, and one plant was selfed to produce the F2 seed during the winter. In the spring of 2002, leaf samples were collected from the individual F2 plants at the V6 and V7 stage of development for DNA extraction at the Ya'an farm of the Maize Research Institute of Sichuan Agricultural University in Sichuan Province, and the plants were selfed to generate F2:3 families. In the autumn of 2002, the mapping population was advanced to generate 229 F2:4 families at the Yuanjiang farm.

Inoculum Preparation
The R. solani AG1-IA isolate, provided by the Plant Pathology Institute of Sichuan Agricultural University, was cultured on standard potato dextrose agar (PDA) medium (potato, 200 g; dextrose, 20 g; agar, 10 g; H2O, 1000 mL) and incubated at 28°C for 3 to 5 d. Colonized grain, for use in the field inoculations, was prepared by transferring the pure culture to sterilized wheat grain and incubating for 3 d.

Field Experiment
The phenotyping was performed in field evaluations of 229 F2:4 families derived from the cross at two locations, and the F2:4 families were evaluated under artificial inoculation at the Ya'an farm and the Institute of Agricultural Science l farm in Chongqing during 2003. The two locations represented two ecological types. The climate of Chongqing is characterized by high temperature and high humidity and that of Ya'an with much rain and low sunshine. A randomized complete block design with three replications was used at both locations, with plots consisting of single rows 3 m long and spaced 0.8 m apart. The plots were overplanted and thinned to 14 plants. At each location, the experiment plot management was in accordance with local practice. At the jointing stage, two wheat seeds infected by AG1-IA were placed into the third sheath of P1, P2, and all F2:4 population individual plants in two sites. All inoculations were finished on the same day.

Data Collection and Analysis
Twenty days after inoculation, plant height (PH) and the height of the disease spot were measured on 10 plants per plot. Plant height was estimated from the third sheath line to the tip of the tassel, and the absolute disease spot height was estimated from the third sheath line to the upper disease spot. According to the relative height of the disease spot (equal to the absolute height of the disease spot divided by plant height), six disease severity classes were established: 0, 1, 3, 5, 7, and 9, for which the ratio of the relative height of the disease spot was between 0, 0.1 to 0.25, 0.25 to 0.5, 0.5 to 0.75, 0.75 to 1.0 and >1, respectively. The disease index (DI) was calculated according to the following formula (Wang and Dai, 2001, p. 261–301):

Formula

For two sites, means, standard deviations, kurtosis, and skewness of the disease index of F2:4 population were calculated. All these analyses were performed by the SPSS software (2000).

SSR Analysis and Linkage Map Construction
The total DNA samples of parents and F2 individuals were extracted via the procedure described by Saghai-Maroof et al. (1984). Four hundred fifty SSR markers were selected for screening for polymorphism between the two parents. SSR analysis followed the method described by Senior and Manfred (1993). The SSR markers that fit segregation ratio of AA:Aa:aa by Chi-square test, were used to construct linkage map via MAPMAKER version 3.0b (Lander et al., 1987). Linkage groups were created with a LOD score of 3.0 and a recombination fraction of 0.4 by the "group" command. The ripple command was used to verify the order of markers on each chromosome. Data quality was checked by "error detection" command, and unlikely double crossovers, because of possible genotyping errors, were corrected by rechecking the data. The map distance in centimorgans (cM) was derived on the basis of the Kosambi function (Kosambi, 1944).

QTL Mapping
QTL were mapped for DI via the CIM of Zeng (1993, 1994) by the QTL Cartographer version 2.0 software (Basten et al., 1997, 2001). The likelihood-ratio (LR) test statistic used was –2ln (L0/L1), where L0/L1 is the ratio of the likelihood under the null hypothesis (there is no QTL in the interval) and the alternative hypothesis (there is a QTL in the interval). We used Model 6 of the Zmapqtl module of QTL Cartographer, scanning intervals of 1 cM between markers and putative QTL with a window size of 10 cM. The number of marker cofactors for background control was set via forward–backward stepwise regression. The presence of a putative QTL was declared if the log likelihood ratio (LOD) threshold was larger than 2.5. QTL were deemed to exist only at positions where a LOD score exceeded the corresponding significance threshold. The estimation of the position, genetic effects, and percentage of phenotypic variation of the QTL were performed at the significant LOD peak in the region under consideration. The QTL were named according to the method introduced by McCouch et al. (1997). Linkage map with SSR marker and QTL was drawn by the MAPCHART Version 2.0 software (Voorips, 2001).


   RESULTS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Distribution Analysis
In this study, 229 F2:4 families from the cross of resistance parent R15 and susceptible parent 478 were artificially inoculated with the highly pathogenic anastomosis group AG1-IA in two environments. Distribution analysis (Table 1) indicated that the disease index of F2:4 population varied greatly (approximate ranges of 6.33–31.79% and 0–37.5%) in the two environments. The kurtosis and skewness were all near zero, which indicated the resistance trait fitted a normal distribution respectively at two sites. This result suggested that the disease index of the F2:4 population was continuously distributed as expected for a quantitative trait (Fig. 1 and Fig. 2 ).


View this table:
[in this window]
[in a new window]
  		Table 1. Statistical analysis of banded leaf-sheath blight caused by Rhizoctonia solani Kühn in 229 F2:4 families from a cross of inbreds R15 (resistant) and 478 (susceptible) tested at two locations in 2003.

 

Figure 1
View larger version (16K):
[in this window]
[in a new window]
  		Fig. 1. Distribution of banded leaf-sheath blight disease severity percentage in 229 F2:4 families from a cross of inbreds R15 (resistant) and 478 (susceptible) tested at Ya'an in 2003.

 

Figure 2
View larger version (16K):
[in this window]
[in a new window]
  		Fig. 2. Distribution of banded leaf-sheath blight disease severity percentage in 229 F2:4 families from a cross of inbreds R15 (resistant) and 478 (susceptible) tested at Chongqing in 2003.

 
Map Construction
A total of 450 SSR markers covering all 10 linkage groups in maize were tested for polymorphism between R15 and 478. One hundred forty-nine codominant segregation SSR markers were polymorphic between the two parents and scored in the F2:4 population. One hundred forty-six markers were found to be linked, representing 10 known linkage groups with the method of three-point command of MAPMAKER 3.0. On average, 15 markers were placed on each linkage group. The actual number of markers ranged from nine for linkage groups on chromosome 10 to 24 on chromosome 4. The total map encompassed 1666 cM with an average of 11.4 cM between loci (partly shown in Fig. 3 ).


Figure 3
View larger version (49K):
[in this window]
[in a new window]
  		Fig. 3. A QTL map of resistance to banded leaf-sheath blight disease in R15 (resistant) x 478 (susceptible) F2 population.

 
QTL Analysis
Results of the QTL analysis in both locations are displayed in Table 2 and Fig. 3. A total of 11 QTL for BLSB were identified on chromosomes 1, 2, 3, 4, 5, 6, and 10. Phenotypic variation attributed to each QTL ranged from 3.27 to 10.35%. Among these QTL, four (qBLSB-2b, qBLSB-6a, qBLSB-6b, and qBLSB-10) were identified on chromosomes 2,6, and 10 in both environments, whereas others were identified only at one site. QTL qBLSB-2b was located between bnlg1662 and bnlg1940 with LOD values 2.70 and 2.78, and the phenotypic variation explained was 4.09 and 3.72% at Ya'an and Chongqing, respectively. QTL qBLSB-6a and qBLSB-6b were located between bnlg1600 and umc1818 and bnlg1006 and umc1723. The LOD values of qBLSB-6a were 2.91 and 4.54, explaining 5.18 and 7.19% of phenotypic variation at Ya'an and Chongqing, respectively. The LOD values of qBLSB-6b were 3.01 and 3.53, corresponding to 5.12 and 5.66% of the phenotypic variation at Ya'an and Chongqing sites, respectively. QTL qBLSB-10 was identified between mmc0501 and phi054 with 2.62 and 2.51 LOD values and 4.18 and 5.62% phenotypic variation was explained at Ya'an and Chongqing, respectively. The other seven QTL were only detected at one site, with LOD values ranging from 2.54 to 4.01 (corresponding to 4.51–10.35% of the phenotypic variation). QTL qBLSB-2a, identified on chromosome 2 at Ya'an, was regarded as a major effect QTL with 4.01 LOD value and 10.35% of phenotypic variation explained. Among the 11 QTL, only one was found to have positive additive effect, and all the others had negative additive effects ranging from 1.31 to 2.40. This result indicated that most of the resistance QTL came from the resistant parent R15. The maximum genetic effects caused by a single QTL were increments of 2.40 of resistance to BLSB.


View this table:
[in this window]
[in a new window]
  		Table 2. Quantitative trait loci (QTL) and their genetic parameters estimated for resistance to banded leaf-sheath blight caused by Rhizoctonia solani Kühn in 229 F2:4 families from a cross of inbreds R15 (resistant) and 478 (susceptible) tested at two locations (Chongqing-CQ and Ya'an-YA) in 2003.

 
QTL Groups
Many investigations have been conducted to investigate the nature of QTL for correlated traits. Paterson et al. (1991) found a chromosomal region affecting both mass per fruit and soluble solids in tomato (Lycopersicon esculentum Mill.). There are many examples of phenotypic correlation between agronomic traits in maize, i.e., ear height and flowering date (Beavis et al., 1994; Veldboom and Lee, 1996). In our research, among the 11 QTL only five QTL (qBLSB-1, qBLSB-3, qBLSB-4, qBLSB-5, and qBLSB-6c) did not map close to other QTL. The remaining six QTL were detected in the same chromosomal regions, forming three groups of QTL (Fig. 3).


   DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
New Resistant Inbred Line R15
BLSB caused by R. solani is one of the most severe maize diseases. It has now become one of the major maize diseases in some areas or countries, such as China and Southeast Asia. It affects maize production both in yield loss and reduced quality. The major reason leading to the rapid spread of BLSB is the lack of resistant resources. Most of the inbred lines used in maize breeding, and the commercial cultivars used in production, are susceptible to BLSB (Yang et al., 2003). Adopting good resistant material for maize BLSB breeding will be an effective method to control the quick spreading of BLSB. For most of the QTL, the alleles contributing to an increased level of resistance all came from the resistant parent R15 (Table 2).

Marker-Assisted Selection
BLSB is an enormously destructive disease on susceptible maize. So it is desirable to exploit additional sources of resistance against BLSB to improve the disease resistance of present maize hybrids. Moreover, BLSB does not occur every year, so general resistance genes could easily be lost in the absence of selection pressure in conventional breeding programs. Marker-assisted selection (MAS) promises to be superior to conventional phenotypic selection if the trait is severely affected by environmental conditions or is difficult to evaluate (Visscher et al., 1996). Localization of genes controlling disease resistance via DNA markers could allow introgression of these genes into elite materials, even in areas where the disease is not common.

To our knowledge, this study is the first report identifying QTL associated with BLSB resistance in maize. Availability of molecular markers linked to QTL controlling BLSB in maize could facilitate MLS in breeding programs aiming to transfer the resistance from R15 to elite breeding lines. In this paper, significant QTL were located on 11 chromosomal regions (Table 2). Two major QTL (qBLSB-2a at Ya'an and qBLSB-6c at Chongqing) explaining phenotypic variation of 10.35 and 9.26% were only identified in one environment. Four other QTL (qBLSB-2c, qBLSB-6a, qBLSB-6b, and qBLSB-10) with genetic distances away from the closest linkage markers of 0.01 to 10.00 cM were found in both environments. QTL qBLSB-6b and qBLSB-10 were located to two chromosomal regions between bnlg1600 and umc1818 and mmc0501 and phi054. The QTL detected in this region each in two environments had same closest linkage markers bnlg1538 and phi054, respectively. They may be used for MAS.

Resistance QTL Clusters
The distribution of the QTL in the genome showed a high concentration of QTL in a few chromosomal regions. Such a concentration in the distribution of QTL has already been observed in previous studies (Stuber et al., 1992; Abler et al., 1991). Many resistance genes and QTL in maize have been located in 3.04 and 6.01 regions of chromosomes (Wang et al., 2003). For example, in 3.04 region, four resistance genes for rust disease (rp3, wsm2, mv1, and scm2) were located within 5 cM by RFLP markers UMC102 and UMC10 (Sanz-Alferez et al., 1995; McMullen and Simcox, 1995; Melchinger et al., 1998; Ming et al., 1997; Chaba et al., 2002). The resistance QTL for European corn borer (Ostrinia nubilalis Hübner) was located in the 3.04 region. And in the 6.01 region, resistance genes for Cochliobolus heterostrophus (Drechs.) Drechs. [= Helminthosporium maydis (Nisikado & Miyake)] rhm1 and scm1 (Ming et al., 1997; Chen et al., 1999; Zaitlin et al., 1993) were found. These results indicated that 3.04 and 6.01 regions were important for disease and insect resistance in maize. In this study, only five QTL of qBLSB-1, qBLSB-3, qBLSB-4, qBLSB-5, and qBLSB-6c were not mapped close to other QTL. The remaining 6 QTL were located in three chromosomal regions 2.06 to 2.08, 6.01 to 6.02, and 10.02 to 10.03, forming three groups of QTL. These results corroborated previous findings and supported the concept that resistance QTL to diseases and insects in maize were not randomly distributed across the genome but clustered in specific regions (Bohn et al., 2000).

This study is the first step in identifying QTL associated with resistance to BLSB in maize. Closely linked DNA markers to the QTL detected here could be used for marker-assisted selection for resistance to BLSB in maize. In future research, a linkage map with a higher marker density should be constructed.


   ACKNOWLEDGMENTS
 
We thank Drs. W.G. Yan, Nicholas Clarke, Jihong L. Clarke, M.Y. Long, and the anonymous reviewers of Crop Science who provided constructive criticism and helped improve the manuscript. This research was supported by Asian Maize Biotechnology Network, and the Program for Changjiang Scholars and Innovative Research Team in University of China (Grant No. IRT0453).


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
{dagger} Zhao, M.J. and Zhang, Z.M. contributed equally to this work. Back

Received for publication February 22, 2005.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 





This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Zhao, M.
Right arrow Articles by Pan, G.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Zhao, M.
Right arrow Articles by Pan, G.
Agricola
Right arrow Articles by Zhao, M.
Right arrow Articles by Pan, G.
Related Collections
Right arrow Crop Genetics
Right arrow Plant Disease

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Agronomy Journal Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome