**7. QTL associated with cooked kernel elongation ratio**

A QTL was identified on chromosome 8 for kernel elongation [39]. Rani [40] found that a functional marker targeting an SNP in the GS3 is associated with kernel elongation. Tian *et al*. [36] detected 3, 2, and 2 QTLs for water absorption, volume expansion and cooked rice elongation, respectively in a DH population.

Amarawathi *et al.* [41] identified a QTL (*elr11–1*) for linear elongation ratio in chromosome 11 in the marker interval of RM1812 – RM209. Mallikarjuna *et al.* [42] reported that 1 QTL on chromosome 3 in *Oryza nivara* × Swarna derived backcross populations in the marker interval RM55–RM520. Two QTLs were identified for KLAC and both were derived from *O. nivara*, and these were located on chromosomes 5 and 12. Dewei *et al.* [43] identified 12 QTLs for rice elongation traits were detected on chromosomes 3, 4, 6, 8, 9, 10, and 11, among which two QTLs for MRL were located on chromosome 3, one QTL for MRL on chromosome 8, four QTLs for CRL on chromosome 3, 6, 8, and 9, and five QTLs for CRE on chromosome 4, 6, 9, 10, and 11.

Acga *et al.* [44] identified two QTLs for grain elongation on chromosome 2, designated *qGE-2-1* and *qGE-2-2*. The *qGE-2-1* mapped to the interval RM53-RM174, while *qGE-2-2* was mapped to the marker interval RM525-RM6, One QTL for grain elongation was previously reported on chromosome 2 in the marker interval R2510 - RM211 in the study conducted by Ge *et al*. [35]. Chen [45] reported that RM44 is associated with kernel elongation. Sathyasheela [46] reported that RM 209 was associated with LER. Liu *et al.* [47] detected three CRE QTLs on chromosome 4, 5, and 12, respectively, and the *qCRE-4* on chromosome 4 near *qER-4* was detected in this study. Li *et al.* [48] mapped a CRE QTL on chromosome 3, with the favorable allele obtained from the African rice *O. glaberrima*. Using a RIL population, Wang *et al.* [10] identified four CRE QTLs on chromosome 3, 6, 7, and 8, respectively.

### **8. Applications of CRISPR/Cas9 for rice grain quality improvement**

Rice grain quality improvement through targeted genome editing is a fast, sustainable and cost effective approach. Conventional plant breeding methods depends on naturally existing germplasm variations. The introgression through backcrossing requires much time and screening of large population by marker assisted selection requires more energy. The reverse genetic approaches enhance the speed of plant breeding through targeted genome modifications [49] (**Figure 2**).

*Breeding for Grain Quality Improvement in Rice DOI: http://dx.doi.org/10.5772/intechopen.95001*

**Figure 2.** *An illustration of rice grain quality improvement through the CRISPR/Cas9 system.*
