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Cultivating rice varieties with robust blast resistance is the most effective and economical way to manage the rice blast disease. However, rice blast disease comprises leaf and panicle blast, which are different in terms of resistance mechanisms. While many blast resistant rice cultivars were bred using genes conferring resistance to only leaf or panicle blast, mining durable and effective quantitative trait loci (QTLs) for both panicle and leaf blast resistance is of paramount importance. In this study, we conducted a pangenome-wide association study (panGWAS) on 9 blast resistance related phenotypes using 414 international diverse rice accessions from an international rice panel. This approach led to the identification of 74 QTLs associated with rice blast resistance. One notable locus, qPBR1, validated in a F4:5 population and fine-mapped in a Heterogeneous Inbred Family (HIF), exhibited broad-spectrum, major and durable blast resistance throughout the growth period. Furthermore, we performed transcriptomic analysis of 3 resistant and 3 sensitive accessions at different time points after infection, revealing 3,311 differentially expressed genes (DEGs) potentially involved in blast resistance. Integration of the above results identified 6 candidate genes within the qPBR1 locus, with no significant negative effect on yield. The results of this study provide valuable germplasm resources, QTLs, blast response genes and candidate functional genes for developing rice varieties with enduring and broad-spectrum blast resistance. The qPBR1, in particular, holds significant potential for breeding new rice varieties with comprehensive and durable resistance throughout their growth period. [ABSTRACT FROM AUTHOR]

Background: Grain shape is a key trait in rice breeding. Although many QTLs and genes of grain shape have been identified, how different combinations of alleles of these genes affect grain shape is largely unknown. It is important to understand the effects of grain shape gene combinations for breeding by design. In the present study, we performed genetic dissection of the grain shapes in Guangdong Simiao varieties, a popular kind of rice in South China, to identify the effective alleles and their combination for breeding. Results: We selected two hundred nineteen indica accessions with diverse grain shapes and fifty-two Guangdong Simiao varieties with long and slender grain shapes for genome-wide selection analysis. The results showed that four (GS3, GS5, GW5 and GL7) of the twenty grain shape genes fall into the regions selected for in Guangdong Simiao varieties. Allele analysis and frequency distribution of these four genes showed that GS3allele3 and GW5allele2 accounted for 96.2%, and GL7allele2 and GS5allele2 accounted for 76.9% and 74.5% of the Simiao varieties, respectively. Further analysis of the allelic combinations showed that 30 allelic combinations were identified in the whole panel, with 28 allelic combinations found in the international indica accessions and 6 allelic combinations found in Guangdong Simiao varieties. There were mainly three combinations (combinations 17, 18 and 19) in the Guangdong Simiao varieties, with combination 19 (GS3allele3 + GW5allele2 + GL7allele2 + GS5allele2) having the highest percentage (51.9%). All three combinations carried GS3allele3 + GW5allele2, while combinations 17 (GL7allele1) and 19 (GL7allele2) showed significant differences in both grain length and length/width ratio due to differences in GL7 alleles. Pedigree analysis of Guang8B, the maintainer of the first released Simiao male sterile line Guang8A, showed that the parent lines and Guang8B carried GS3allele3 + GW5allele2 + GS5allele2, while the GL7 allele differed, resulting in significant differences in grain size. Conclusion: The results suggest that specific alleles of GS3, GS5, GW5 and GL7 are the key grain shape genes used in the Guangdong Simiao varieties and selected for grain shape improvement. Combination 19 is the predominant allelic combination in the Guangdong Simiao varieties. Our current study is the first to dissect the genetics of grain shape in Guangdong Simiao varieties, and the results will facilitate molecular breeding of Guangdong Simiao varieties. [ABSTRACT FROM AUTHOR]

Background: Direct seeding is an efficient cultivation technique in rice. However, poor low temperature germinability (LTG) of modern rice cultivars limits its application. Identifying the genes associated with LTG and performing molecular breeding is the fundamental way to address this issue. However, few LTG QTLs have been fine mapped and cloned so far. Results: In the present study, the LTG evaluation of 375 rice accessions selected from the Rice Diversity Panel 2 showed that there were large LTG variations within the population, and the LTG of Indica group was significantly higher than that of Japonica and Aus groups (p < 0.01). In total, eleven QTLs for LTG were identified through genome-wide association study (GWAS). Among them, qLTG_sRDP2–3/qLTG_JAP-3, qLTG_AUS-3 and qLTG_sRDP2–12 are first reported in the present study. The QTL on chromosome 10, qLTG_sRDP2–10a had the largest contribution to LTG variations in 375 rice accessions, and was further validated using single segment substitution line (SSSL). The presence of qLTG_sRDP2–10a could result in 59.8% increase in LTG under 15 °C low temperature. The expression analysis of the genes within qLTG_sRDP2–10a region indicated that LOC_Os10g22520 and LOC_Os10g22484 exhibited differential expression between the high and low LTG lines. Further sequence comparisons revealed that there were insertion and deletion sequence differences in the promoter and intron region of LOC_Os10g22520, and an about 6 kb variation at the 3′ end of LOC_Os10g22484 between the high and low LTG lines, suggesting that the sequence variations of the two genes could be the cause for their differential expression in high and low LTG lines. Conclusion: Among the 11 QTLs identified in this study, qLTG_sRDP2–10a could also be detected in other three studies using different germplasm under different cold environments. Its large effect and stable expression make qLTG_sRDP2–10a particularly valuable in rice breeding. The two genes, LOC_Os10g22484 and LOC_Os10g22520, were considered as the candidate genes underlying qLTG_sRDP2–10a. Our results suggest that integrating GWAS and SSSL can facilitate identification of QTL for complex traits in rice. The identification of qLTG_sRDP2–10a and its candidate genes provide a promising source for gene cloning of LTG and molecular breeding for LTG in rice. [ABSTRACT FROM AUTHOR]

Reverse transcription quantitative real-time PCR (RT-qPCR), a sensitive technique for quantifying gene expression, depends on the stability of the reference gene(s) used for data normalization. Only a few studies on reference genes have been done in fruit trees and none in litchi. In the present study, seven frequently used candidate reference genes, including actin ( ACTIN), glyceraldehyde-3-phosphate-dehydrogenase ( GADPH), elongation factor 1-alpha ( EF- 1α), poly ubiquitin enzyme ( UBQ), α-tubulin ( TUA), β-tubulin ( TUB) and RNA polymerase-II transcription factor ( RPII), were evaluated for their expression stability in litchi. A total of 78 samples, including different varieties, tissues, organs, developmental stages and treatments, such as NAA, shading and girdling plus defoliation, were addressed in this analysis. Our results showed that GAPDH was the most suitable reference gene among all the tested samples, different organs and NAA treatment. ACTIN was stably expressed in varieties and fruit developmental stages. RPII and UBQ exhibited better expression stability in tissues. EF- 1α was the most stable gene in shading and girdling plus defoliation treatments. Moreover, using combination of two genes as reference genes might improve the reliability of gene expression by RT-qPCR in litchi. A better combination was GAPDH + EF- 1α or GAPDH + ACTIN for all the examined samples. In addition, the validated reference genes were further relied on to quantify the expression of an interested gene, LcARF13 under different experimental conditions. These results first provide guidelines for reference genes selection under different experimental conditions and also a foundation for more accurate and widespread use of RT-qPCR in litchi. [ABSTRACT FROM AUTHOR]