1Rice Gene Discovery, National Center for Genetic Engineering and Biotechnology, Kasetsart University, Kampangsaen
Campus, Nakorn Prathom 73140, Thailand www.dna.kps.ku.ac.th Email firstname.lastname@example.org
2DNA Technology Laboratory, National Center for Genetic Engineering and Biotechnology, Kasetsart University, Kampangsaen
Campus, Nakorn Prathom 73140, Thailand www.dnatec.kps.ku.ac.th Email email@example.com
3Agronomy Department, Kasetsart University, Kampangsaen Campus, Nakorn Prathom 73140, Thailand
www.dna.kps.ku.ac.th Email firstname.lastname@example.org
4School of Land and Food Sciences, The University of Queensland, Australia Email email@example.com
In the past 20 years, the rice-breeding program in Thailand had little success in developing new cultivars to replace Kao Dawk Mali 105 (KDML105) and Kao Khor 6 (RD6). Main reason is a poor adoption of new cultivars by farmers due to poor adaptation of new cultivars to the rainfed environments, susceptibility to diseases and insect pests and unacceptable grain qualities. The conventional breeding program also takes at least 15 years for releasing new cultivars. New breeding strategy can be established to shorten period for cultivar improvement by using marker-assisted selection (MAS), rapid generations advance (RGA), early generation testing in multi-locations for grain yield and qualities. Four generation of MAS backcross breeding were conducted to transfer gene and QTL for bacterial blight resistance (BLB), submergence tolerance (SUB), brown planthopper resistance (BPH) and blast resistance (BL) into KDML105. Selected backcross lines, introgressed with target gene/QTL, were tolerant to SUB and resistant to BLB, BPH and BL. The agronomic performance and grain quality of these lines were as good as or better than KDML105.
Backcross introgressed lines of KDML105 are superior to KDML105 in biotic and abiotic stress resistance/tolerance while their grain qualities are as good as KDML105.
Rice, molecular breeding, marker-assisted selection, grain quality
Mekong region of the Southeast Asia comprises of Myanmar, Thailand, Cambodia and Laos and is known as the primary origin of domesticated rice and also for the best areas of high quality rice production. More than 60 % of total rice growing areas in the region depends on rainfall. Biotic and abiotic stresses are major constrains limiting yield and grain quality. Among them drought stress and blast disease are the most serious constrains. In the past, genetic improvement for such traits has been hampered due to lack of clear understand of genetics and incidence of genotype by environment (G x E) interactions. Biotechnology has been arisen as a powerful tool to discover genes governing these traits and understand their functions. Establishing association between such traits and genes or molecular markers would facilitate genetic manipulation via marker assisted selection (MAS). Rice-breeding program of Rice Gene Discovery Unit (RGDU) was established in 1998. One of main objectives is to enhance development of rice cultivars that adapt well to harsh environments of rainfed lowlands in North and Northeast Thailand and acceptable by farmers in the region. Marker assisted selection (MAS) in backcross breeding has been used to transfer favorable alleles of genes/QTL for biotic and abiotic stress resistance/tolerance into genetic background of KDML105 and RD6. We demonstrate here a successful implementation of MAS in the rice-breeding program to improve KDML105 for biotic and abiotic stress resistance/tolerance.
Backcross breeding was carried out in four rice populations using KDML105 as recurrent parent (Figure 1). FR13A, IR1188, Abhaya and IR68835 were used as donors for submergence tolerance, bacterial leaf blight (BLB) resistance, brown planthopper (BPH) resistance and blast (BL) resistance, respectively. Quantitative trait loci (QTL) approach identified QTL controlling these traits in donor cultivars and also cooking quality in KDML105 as shown in Table 1 and Figure 1. DNA markers flanking these QTLs were identified and developed (Table 1).
Table 1. DNA markers linked to QTL for traits of interest and were used to select the promising blackcross lines.
These markers were used for genotypic fingerprinting an individual of BC populations. BC plants containing target QTLs were selected and backcrossed to KDML105 until BC4F1 was obtained. Selected BC4F1 plants were then self-pollinated to generate BC4F2 and again DNA markers were used for genotypic fingerprinting an individual. Individuals containing target QTLs and having cooking quality of KDML105 were evaluated for target trait performance. The breeding schemes were shown in Figure 2.
Figure 1. Genomic location of QTL corresponding with submergence tolerance, bacterial leaf blight resistance, blast resistance, brown planthopper resistance, aroma, amylose content (waxy), gel consistency and gel temperature
Figure 2. Using DNA marker assisted selection (MAS) in breeding scheme
Selected backcross lines, introgressed with target QTLs, were tolerant to submergence (Table 2) and resistant to BLB, BPH and BL (Table 3). The agronomic performance and grain quality of these lines were as good as or better than KDML105.
Table 2. Submergence tolerance shown as percentage of survived individuals and agronomic performances of selected backcross lines that were introgressed with QTLSubchr9 and grain quality of KDML105. The “a” – “d” were DNA marker profile of backcross introgressed lines as described in Table 1. FR and KD stand for FR13A and KDML105 alleles, respectively.
Table 3. Selected backcross lines that were introgressed with QTLBlastchr1 and QTLBlastchr11 showing blast resistance with agronomic performance and grain quality of KDML105.
IR, H and KD stand for IR68835, heterozygous and KDML alleles, respectively.
a – aroma score (2- moderate fragrance and 3- strong fragrance)
MAS can be a powerful tool for breeders to improve the traits that lack in KDML105 and in the same time achieve the maintenance of a quality profile of KDML105. Since selected lines have the same genetic background, pyramiding all QTLs can be done using MAS approach. This work is being used as a “proof of breeding strategy’ for the Mekong Regional project which aims to use MAS for grain quality and drought tolerance. Approximately 15 populations based on crosses between donor lines selected for drought tolerance and recipient lines selected for yield and quality traits of acceptance to farmer/ markets are being developed in Thailand, Laos and Cambodia.
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