With 1 figure and 2 tables The rice varieties IR64 and Jao Hom Nin (JHN) demonstrated a broad-spectrum resistance against the rice blast pathogens in Thailand. A genomic investigation unravelled many ...resistance genes residing on four genomic regions, chromosome 2 and 12 in IR64 and 1 and 11 in JHN. A cross between these varieties was made to combine resistance genes into a single genotype. Marker-assisted selection (MAS) was employed to identify F₂ and F₃ plants carrying a combination of four resistance QTLs in a homozygous fusion. Flanking markers RM212/RM319 and RM144/RM139 to blast resistant QTLs on chromosome 1 and 11 in JHN rice and tightly-linked markers RM208 and RM179 to blast resistant QTLs on chromosome 2 and 12 in IR64 rice variety were used for MAS. The stepwise MAS screening was brought in as a strategy to provide a cost-saving and minimum number of PCR performing to select resistant genotypes. F₄ generation, lines carrying all resistant QTLs show a broader spectrum of resistance against 11 representatives of Thai blast pathogen isolates.
Two quantitative trait loci (QTL) that confer a broad-spectrum resistance to blast disease identified in the rice cultivar Jao Hom Nin (JHN) were transferred to the Thai glutinous jasmine rice ...cultivar RD6 by marker-assisted backcrossing (MAB). Four backcrosses and one selfing were conducted in which the derived introgression lines (ILs) that carried homozygous JHN alleles at the QTL recovered up to 98% of the RD6 genome. Ninety-eight BC
4F
2 introgression lines that consisted of four combinations of the two QTL were evaluated for their resistance to eight single spore isolates and natural isolates at three research locations. Introgression lines were examined for their agronomic performance by comparing them to the original RD6 in multi-location trials across five locations. All ILs that carried the QTL (either one or two QTL) showed lower disease scores than ILs without any QTL and lower scores than the recipient cultivar RD6, whereas their agronomic performances were not significantly different from the original RD6. All ILs that carried at least one QTL showed a broad-spectrum blast resistance that was similar to the donor cultivar JHN. The success in improving the blast resistance in RD6 by MAB was shown. In this study, MAB accelerated the development of broad-spectrum blast resistance in the genetic background of the Thai glutinous rice cultivar RD6 within 4 years. The improved RD6 has now been tested in cultivation for several years. Two of the ILs were released in 2008. Currently, farmers in the north and northeast regions of Thailand (areas that are particularly vulnerable to blast disease) benefit from growing these two varieties.
•Pyramiding of bacterial blight resistance genes into Myanmar mega and improved variety, aromatic Manawthukha using marker assisted backcross breeding method.•Broad-spectrum resistance that can be ...useful in different areas in Myanmar which is vulnerable to bacterial blight infection.•Development of aromatic Manawthukha lines with bacterial blight resistance while maintaining grain and cooking qualities.
Bacterial blight disease (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major threat to rice yield in rainfed and irrigated lowland ecosystems in Myanmar. Large-scale and long-term cultivation of released Myanmar rice varieties have continuously caused the outbreak of BB since 1983. In this study, a high yielding Manawthukha rice line ‘Yn 3248-2-128-76-4-3-75’ (MK-75) with fragrance and intermediate amylose content was used as a recipient parent to improve its resistance to BB. RGDU-07097-1-8M-9 (RG-9), an improved line carrying xa5, Xa21 and xa33 was used as the donor parent. Resistant alleles of xa5, Xa21 and xa33 from RG-9 were successfully transferred into MK-75 by using marker-assisted backcrossing (MAB) method while maintaining the cooking quality of MK-75. Twenty eight selected BC3F2 introgression lines (MK-75 ILs) carrying different combinations of these three loci were tested for BB resistance at seedling and maximum tillering stages against ten Thai and five Myanmar Xoo strains. The triple and double resistance gene-introgressed lines (xa5Xa21xa33 or xa5Xa21 or xa5xa33 or Xa21xa33) had higher level of resistance and wider resistance spectrum than MK-75 against both Thai and Myanmar Xoo strains. The single resistance gene-introgressed lines carrying xa5 had higher resistance against Thai Xoo strains, while lines carrying Xa21 showed higher level of resistance to Myanmar Xoo strains. These results clearly indicated that pyramiding of multiple genes is a useful approach for improving BB resistance in MK-75. All ILs had physical grain quality, fragrance and amylose content similar to MK-75. Thus the improvement of BB resistance in MK-75 may have a wide range of benefits in breeding program and should be immediately useful in areas where original Manawthukha, the progenitor or MK-75 is widely grown.
Fungicide resistance now exists in the rice blast fungus, Magnaporthe grisea, necessitating the need for new active agents. Fungi isolated from habitats in Thailand were screened with reference to ...this problem. A new, reliable in vitro screening system based on a microdilution plate format was set up using a virulent strain of M. grisea THL 16. Culture broth extracts from approximately 800 fungal strains were investigated, one of these, Aschersonia luteola BCC 8774, was found to produce an active fungicidal compound, ascherxanthone B, with an IC₉₀ value of 0·58 μg ml⁻¹ (0·95 μmol l⁻¹). An in vivo study of anti-blast efficacy of ascherxanthone B showed a positive effect in disease reduction. Previous report has shown that a species of Aschersonia produces ascherxanthone A. Research on the species, A. luteola BCC 8774, led to the discovery of related novel metabolite, ascherxanthone B with fungicidal properties. Current methods of rice blast control seem to fail leading to increase in crop losses. Our discovery of the anti-blast activity shown by ascherxanthone B is the first step in the development of a potentially novel fungicide.
► Introgression of broad-spectrum resistance through conventional breeding using mixed isolates in screening introgression lines. ► Molecular markers aid in identifying genomic regions associated ...with blast resistance. ► Allele shift allows the identification of specific resistance genes against blast disease in rice. ► Linked markers that are tightly linked to blast resistance may be useful in marker-assisted breeding programs.
Key genomic regions associated with blast resistance against a broad spectrum of isolates could be identified in backcross introgression lines developed by conventional breeding program. In this article, eighty three BC
3F
2 backcross introgression lines (BILs) derived from a cross between IR68835-98-2-B-2-1-1 (a broad spectrum blast resistance variety) and KDML105 (a susceptible variety) were developed by phenotypic selection against a mixture of six virulent blast isolates (MXL) that are widely spread out in the rainfed lowland of the North and Northeast of Thailand. The resistance spectrum of the BILs was assessed by inoculating with 12 different
Magnaporthe oryzae isolates that showed differential responses on the parental cultivars and the MXL that was used for phenotypic selection. All BILs showed highly resistant reactions (low disease score) to the MXL and to two blast isolates THL48 and THL149. Four markers, i.e., RM246, RM241, RM303 and RM164 completely favoring the IR68835 allele (shifting of allele frequencies from KDML105 to IR68835) were identified on chromosomes 1, 4 and 5, respectively. Therefore, these markers could be linked to the resistance genes functioning against the MXL, THL48 and THL149. Furthermore, significant shifting of alleles was identified at six markers located on chromosomes 2, 4, 8, 9 and 12. Seven DNA markers linked to specific resistance genes were identified, in which allele from IR68835 at 6 markers, i.e., RM6, RM205, RM211, RM252, RM273 and RM342 reduced disease score (DS), against blast isolates THL16, THL329, THL458, THL831, THL868 and THL96036 while allele from KDML105 at RM208 (
Pi-kd on chromosomes 2) reduce DS against THL84, THL191, THL557 and THL1108. In this study, the use of DNA markers enabled the identification of specific resistance genes in the backcross breeding materials developed from routine rice breeding program through the conventional phenotypic selection. In this experiment, the usefulness of breeding materials from conventional breeding program in identifying genes corresponding to the selection was illustrated. Linked markers and their genomic location provide necessary information for further use of marker-assisted selection to improve blast resistance in rice breeding program.
Blast is an economically important disease of rice. To map genes controlling blast resistance, recombinant inbred lines (RIL) were developed from Khao Dawk Mali 105, an aromatic, blast-susceptible ...cultivar and the blast resistance donor, CT 9993-5-10-M (CT). A linkage map encompassing 2112 cM was constructed from 141 RILs using 90 restriction fragment length polymorphisms (RFLPs) and 31 simple sequence repeats (SSR). Virulent isolates of blast fungus were identified by screening differential host sets against 87 single-spore isolates collected from the north and northeast of Thailand. Fifteen virulent blast isolates were selected for leaf blast screening. Neck blast was evaluated both under natural conditions and controlled inoculations. Quantitative trait loci (QTLs) for broad resistance spectrum (BRS) to leaf blast were located on chromosomes 7 and 9. In particular, the QTL(ch9) was mapped near the Pi5(t) locus. The QTL(ch7) was located close to a previously mapped partial resistance QTL. Both loci showed significant allelic interaction. Genotypes having CT alleles at both QTL(ch7) and QTL(ch9) were the most resistant. Two neck-blast QTLs were mapped on chromosomes 5 and 6. The inconsistent map locations between the leaf and neck blast QTLs indicate the complexity of fixing both leaf and neck blast resistance. The coincidence of BRS and field resistance QTLs on chromosome 7 supports the idea that BRS may reflect the broad resistance spectrum to leaf blast in rice. These findings laid the foundation for the development of a marker-assisted scheme for improving Khoa Dawk Mali 105 and the majority of aromatic Thai rice varieties that are susceptible to blast.
One hundred and seventy-four isolates of Pyricularia grisea were collected from various hosts such as barley, rice, weed and wild rice in Thailand. Seven arbitrary decamer primers from the set of ...University of British Columbia were employed and nine lineages were classified. Lineages B, C and H were predominant, contributing up to 70% of total pathogens in this study. Analysis showed that the distribution of each lineage differs from the predominant lineages across Thailand in such that other lineages were restricted in particular area. For instance, lineage A was limited only in southern Thailand, whereas wide distribution of lineages B and C reflected an influence of both biological and physical effects on pathogen variation. Principal component analysis resulted in a total of four groups of blast pathogen with small distinctions between barley-, rice-, weed- and wild rice-infected blast. Bridging relationships occurred among border isolates of weed and rice blast suggesting a chance of migrations between hosts. Higher diversity was observed in northern, north-eastern and central Thailand while eastern and southern parts were rather low. Genetic diversity indices elucidated an abundance of pathogen lineages existing in northern Thailand suggesting that it should be the centre of diversity.
Thirty isolates of Xanthomonas oryzae pv. oryzae were collected from different rice-producing area in northern Thailand. For the assessment of genetic variation of bacterial blight pathogen, 19 ...primer combinations of amplified fragment length polymorphism primer system were screened to evaluate the genetic diversity and five combinations were selected according to their producibility, number of scorable bands and differences detected among representative isolates. Six lineages of X. oryzae pv. oryzae were identified in northern Thailand base on location. Lineage A composed of members from two provinces, Phitsanulok and Chainat. Lineage B was from various provinces as Sukhothai, Phetchaboon, Phicit, Phayao and Phrae. Lineage C was from Phitsanulok and Phrae. Lineage D comprised of members from Phrae, Chiangmai and Chiangrai while the lineage E composed of isolates from Sukhothai and Phitsanulok. The final lineage, lineage F, was from Lampang. Lineages B and D were the most widely distributed while lineage E seemed to be restricted to specific planting area. Wide distribution of the pathogen might be due to seed allocation and germplasm exchanged. Analysis showed that diversity of pathogen is due to single field and cultivars-specific effects. The results of this study will facilitate the use of effective bacterial blight resistance gene in northern Thailand.
► Identification of new QTL contributed by Xa21 donor IR1188. ► Application of marker-assisted selection coupled with phenotypic selection in developing KDML105 breeding lines with broad spectrum ...resistance of bacterial blight independent of plant stage development. ► Development of KDML105 lines with bacterial blight resistance while maintaining grain quality and stabilizing yield as revealed in multi-location trials.
Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae is one of the most devastating diseases of rainfed lowland rice in Thailand. The gene Xa21 shows broad-spectrum resistance and has been widely utilized to improve BB resistance in rice worldwide. However, Xa21 is not fully expressed in the early stages of development (seedling stage). In this study, we attempted to improve the Thai jasmine rice variety KDML105 to obtain non-age-related broad-spectrum resistance to BB. The Xa21 gene and seedling resistance genes from rice variety IR1188 (a variety with non-age-related broad-spectrum resistance to BB) were introgressed into KDML105 through three rounds of marker-assisted backcrossing (MAB) and phenotypic selection. Sixty KDML105 backcross introgression lines (KBILs) carrying the Xa21 gene were successfully developed. They were used to evaluate seedling resistance against thirteen Xoo strains. Three seedling resistance (SR) loci inherited from IR1188 were identified on rice chromosomes 1 (RM302-RM212), 8 (RM210-RM149) and 11 (RM287-RM224). The agronomic characters of the KBILs were assessed by planting these lines in the paddy field at Kasetsart University in 2003. Phenotypic variation was observed in the agronomic traits of these lines. Seven KBILs carrying the Xa21 and multiple SR loci and also having a similar plant type to the original KDML105 were chosen for testing in multi-location trials at research stations in rainfed lowland environments. The trials were conducted in 10 and 11 locations in the North and Northeast of Thailand, respectively, between 2005 and 2006. The yield, agronomic traits, cooking quality and important diseases were examined and compared with those of the original KML105. All of the 7 KBILs had a cooking quality profile (aroma, amylose content, gel consistency and alkaline spreading value) and agronomic performance similar to the original KDML105. In 2007, four KBILs were planted in farmers’ fields at 5 locations. All BILs and the original KDML105 did not differ significantly in their agronomic performance. In this study, multiple loci for broad-spectrum seedling resistance were identified from the KBIL population developed by the integrated marker-assisted and phenotypic selection procedures (MAS and PS). These results facilitated the successful improvement of non-age-related broad-spectrum BB resistance in KDML105. The established non-age-related broad-spectrum BB-resistant KDML105 is currently recommended by Kasetsart University for planting in farmers’ fields where the crop is vulnerable to BB.
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