Recent studies have succeeded in isolating and characterizing genes involved in rice tolerance for many important traits. Gene discovery and marker development of these agronomically important traits are the keys to solving the global rice shortage in the coming centuries. Over the years of gene discovery in the model crop species Oryza sativa, several genes controlling economically important traits have been precisely mapped and tagged with closely linked or gene-specific markers.
Alleles of different sizes at each locus were identified, combined, and used in the construction of an allelic scale per marker. Monoplex and multiplex PCR strategies were used to confirm and verify the selected alleles and to optimize the procedures for the construction of a standard allele ladder. New alleles identified in the allele alignment will be subject to verification by sequencing and for inclusion in the allele chart.
Information on the verified number of repeats present and the size of the PCR product of the alleles included in the constructed allele scale of the STR-M26 marker. New alleles (circled) identified in the alignment of allele results of rice varieties using the allele scale.
Gene Discovery and Marker Development for Agronomically Important Traits
The primary signal (LOD peak) of the QTL for RTSV and GLH resistance was located between RM16425 and RM16427, as shown in the ICIM line graph. The correlation coefficient showed a significant relationship (r = 0.322, P < 0.0001), suggesting that the two detected QTLs were controlled with two different genes located in the same chromosome region. In DR, on the other hand, the soil in the pipes was initially maintained at 22% SMC.
Drought treatments introduced by drought re-watering (fluctuating soil moisture) will end when plants mature. Upon completion of the experiment, the entire root system will be sampled for scanning and analysis. Submergence is a major stress that causes yield losses, especially in direct-seeded rice farming system, and requires the development of rice cultivars with tolerance to submergence stress.
Additional markers will be procured, polled for polymorphism, and polymorphic markers located in unfilled bins in the population will be used. Additional markers will be surveyed for polymorphism and polymorphic markers located in unfilled bins will be used in the population. Phytic acid (myo-inositol hexakisphosphate (IP6) or phytate/phytin when in salt form), is the main storage form of phosphorus in various plant tissues, especially bran and seeds.
In brown rice, phytic acid is mostly found in the aleurone layer and germ (embryo) in the form of phytic acid bodies or globoids. T7E2b/MluC1 for Pi40 will be used in the detection of blast resistance genes in the progeny of the developed cross combinations. Deployment of resistant varieties in the field is the most effective and reliable method to combat the disease.
This result suggests that there was no genome introgression from ARC11554 into the introgression lines. Among the introgression lines, ARC was selected as the donor line in the generation of the map population. In Table 12, segregation in the F2 population showed a good fit to the expected ratio of 1 AA:2 Aa:1 aa.
The calculated correlation coefficient showed a significant association (r = 0.322, P < 0.0001) suggesting that the two detected QTLs were controlled by two different genes located in the same chromosome region. ICIM plot for QTLs detected for (A) RTSV resistance and (B) GLH resistance on the short arm of chromosome 4 in the F3 population derived from the cross between NSIC Rc138 and ARC.
Marker-Assisted Line Development
The F1 plants produced in 2012 WS by backcrossing to increase the recovery of the repetitive parental genome were planted in the field in 2013 DS. The F1 plants were established in the field and subjected to target gene testing in 2013 WS. Hybrid rice is currently cultivated in the Philippines and continues to gain significance given its yield advantage over inbred cultivars.
Backcrossed maintenance and restoration lines of Mestizo 1 and Mestiso 3 were established in the field and morpho-agronomic data such as plant height, panicle number and grain yield were collected (Table 17). Original and improved CMS lines of Mestizo 1 and Mestiso 3 were established in the field and crossed with their corresponding improved maintenance lines for AB seed production and with their corresponding AR recovery lines for seed production of improved hybrids with blight resistance (Table 18 and Figure 19). The improved Mestiso 3 parent lines (CMS, maintenance and recovery lines) are currently included in the hybrid breeding pipeline.
Introgression of bacterial resistance genes into the maternal lines of two-line hybrid system was performed in 2013. Two populations of TGMS maternal lines in F2 generation designated as H028 (PRUPTG101/IRBB54) and H029 (PRUPTG102/IRBB54) were established in the field at NEUST in Gabaldon for backcrossing. F1 plants with invasive bacterial blight, tungro and insect resistance genes and QTLS were planted in the field in 2013 WS.
AxR seed production of improved Mestiso 3 in the Science City of Muñoz, Nueva Ecija (2013 DS). Improved Mestiso 3 with two bacterial disease resistance genes in MYT in Science City of Muñoz, Nueva Ecija (2013 DS). The number of lines selected is also shown in Table 22 and this will be planted for further evaluation in the nursery of origin.
Rice tungro disease (RTD) is considered the most serious viral disease of rice in the Philippines and in South and Southeast Asia in terms of major yield losses. In past years, PhilRice breeding programs used ARC11554 as the RTD resistance donor, but focused on the insertion of a fragment of chromosome 4. Recently, dela Cruz et al. 2013, in press) verified the presence of only GLH resistance on the short arm of rice chromosome 4, while associating RTSV resistance in ARC11554 with the tsv1 gene on chromosome 7.
While a significant difference was observed in the use of 5 versus 15 GLH in RTSV inoculation (Table 24), it did not significantly affect the %RTSV infection of the respective genotypes (Table 23). Individual and combined effects of resistance to GLH and RTSV on rice infection with RTD (RTSV+RTBV) in the current tungro hotspot area.
