Ji Zhijuan

Advances in Mapping Loci Conferring Resistance to Rice Sheath Blight and Mining Rhizoctonia solani Resistant Resources

Sheath blight (SB) caused by Rhizoctonia solani is one of the three major diseases of rice, and now has become the most severe disease causing rice yield loss in China. Breeding and use of varieties resistant to SB is crucial in controlling the disease, but the advances achieved have been limited due to the lack of highly SB-resistant rice germplasm. Genetic analysis revealed that the SB resistance in rice was a typical quantitative trait controlled by multi-genes. Although many QTLs conferring resistance to SB have been identified in recent years, most of the QTLs only showed small effects and few of them have been evaluated for utilization potential. Many R. solani-resistant resources have been found in wild rice species, microorganisms and other plant species. It is already known that the SB-resistance could be improved in transgenic rice plants by genetic transformation. This paper reviewed the genetic mapping of loci associated with resistance to rice SB, the evaluation of the potential of resistance QTLs, and the resistant resources found in various organisms besides rice. To develop SB-resistant rice varieties, it is important to develop and explore new resistant rice germplasms, fine map and evaluate resistance QTLs, and also to pay attention to various bio-resources showing resistance to R. solani.

Identification of QTLs for Rice Cold Tolerance at Plumule and 3-Leaf-Seedling Stages by Using QTLNetwork Software

Abstract A doubled haploid (DH) population consisted of 120 lines, derived from a cross between an indica variety, TN1, and a japonica variety, Chunjiang 06, was used to identify QTLs controlling rice cold tolerance at the plumule and 3-leaf-seedling stages by using the QTLNetwork software. The percentages of normal plumules after 4°C treatments for 7 d, 9 d, 11 d, and 14 d, as well as the cold stress tolerance index (CSTI) and the withering index (WI) of rice seedling were investigated. A total of five single-effect QTLs, each for percentages of normal plumules after 4°C treatments for 9 d, 11 d and 14 d, and CSTI and WI, respectively were identified. The QTLs for the percentages of normal plumules after low temperature treatments for 9 d, 11 d and 14 d were on chromosomes 4, 2 and 11, accounting for 14.1%, 17.3% and 21.5% of the phenotypic variation, respectively. QTLs for CSTI and WI were on chromosomes 10 and 1, respectively. Two pairs of epistatic loci were identified, but none of the epistatic loci involved the single-effect QTLs. The RM528-RM340 interval on chromosome 6 interacted with the RM278-RM3919B interval on chromosome 9 for CSTI, and the epistatic interaction accounted for 17.7% of the phenotypic variation. A pair of epistatic loci was identified for WI, the RM246-RM5461 interval on chromosome 1 interacted with the ISA-RM447 interval on chromosome 8, which accounted for 22.6% of the phenotypic variation.

Construction of near isogenic lines for pericarp color and evaluation on their near isogenicity in rice.

The inheritance of purple pericarp was studied through genetic analysis using F2, BC1F1 and F3 from a cross between a purple pericarp rice variety Zixiangnuo and a white pericarp rice variety Chunjiangnuo 2. Seven pairs of near isogenic lines (NILs) for pericarp color of rice were further constructed. Genetic analysis indicated that the purple pericarp was controlled by two complementary genes (Pb and Pp). Agronomic trait analysis and polymorphism analysis using SSR markers on these seven pairs of NILs were used in the evaluation of near-isogenicity. No significant differences in agronomic traits were found except 1000-grain weight between the NILs. The polymorphic SSR markers for the parents were only detected in target segments of the five pairs of NILs different in Pb, which revealed the ideal near isogenicity of them. However, for the two pairs of NILs different in Pp, the polymorphic markers for the two parents were detected as well as in non-targeted segments of chromosomes 11 and 12, respectively.

Pyramiding blast, bacterial blight and brown planthopper resistance genes in rice restorer lines

Abstract Rice blast, bacterial blight (BB) and brown planthopper (BPH) are the three main pests of rice. This study investigated pyramiding genes resistant to blast, BB and BPH to develop restorer lines. Ten new lines with blast, BB and/or BPH resistance genes were developed using marker-assisted selection (MAS) technique and agronomic trait selection (ATS) method. Only HR13 with resistance genes to blast, BB and BPH was obtained. In addition to blast and BB resistance, four lines (HR39, HR41, HR42, HR43) demonstrated moderate resistance to BPH, but MAS for BPH resistance genes were not conducted in developing these four lines. These data suggested that there were unknown elite BPH resistance genes in the Zhongzu 14 donor parent. A more effective defense was demonstrated in the lines with Pi1 and Pi2 genes although the weather in 2012 was favorable to disease incidence. Blast resistance of the lines with a single resistance gene, Pita, was easily influenced by the weather. Overall, the information obtained through pyramiding multiple resistance genes on developing the restorer lines is helpful for rice resistance breeding.

Mapping resistant QTLs for rice sheath blight disease with a doubled haploid population

Abstract Sheath blight (SB) disease, caused by Rhizoctonia solani Kuhn, is one of the most serious diseases causing rice (Oryza sativa L.) yield loss worldwide. A doubled haploid (DH) population was constructed from a cross between a japonica variety CJ06 and an indica variety TN1, and to analyze the quantitative trait loci (QTLs) for SB resistance under three different environments (environments 1–3). Two traits were recorded to evaluate the SB resistance, namely lesion height (LH) and disease rating (DR). Based on field evaluation of SB resistance and a genetic map constructed with 214 markers, a total of eight QTLs were identified for LH and eight QTLs for DR under three environments, respectively. The QTLs for LH were anchored on chromosomes 1, 3, 4, 5, 6, and 8, and explained 4.35–17.53% of the phenotypic variation. The SB resistance allele of qHNLH4 from TN1 decreased LH by 3.08 cm, and contributed to 17.53% of the variation at environment 1. The QTL for LH (qHZaLH8) detected on chromosome 8 in environment 2 explained 16.71% of the variation, and the resistance allele from CJ06 reduced LH by 4.4 cm. Eight QTLs for DR were identified on chromosomes 1, 5, 6, 8, 9, 11, and 12 under three conditions with the explained variation from 2.0 to 11.27%. The QTL for DR (qHZaDR8), which explained variation of 11.27%, was located in the same interval as that of qHZaLH8, both QTLs were detected in environment 2. A total of six pairs of digenic epistatic loci for DR were detected in three conditions, but no epistatic locus was observed for LH. In addition, we detected 12 QTLs for plant height (PH) in three environments. None of the PH-QTLs were co-located with the SB-QTLs. The results facilitate our understanding of the genetic basis for SB resistance in rice.