**2.2 Characterization and stack effective** *R* **genes in hybrid rice**

Following the clone of resistant genes and the development of related functional molecular makers, marker screening has been widely applied on resistance identification and innovation of parents of hybrid rice. Up to now, molecular makers of blast resistance genes, *Pi2*, *Pi9*, *Pi1*, *Pib*, *Pita*, *Pid2*, *Pikh*, *Pigm*, and *Pish*, have been developed and used on detecting the related *R* genes [17–25]. In Jiangsu, a total of 544 rice materials were assessed for blast resistance and resistance genes distribution by inoculation and marker screening; results showed that 968, Xiushui 134, Jia 58, Jindao 263, Huaidao 20, Yandao 10, and Gumei 4 contained the majority of resistance genes; and *Pi5*, *Pita*, *Pi9*, and *Pib* exhibited high resistance to six major blast races [14]. In South China, with functional marker of *Pi1*, *Pik-p*, *Pikh*, *Pi2*, *Pi9*,


**29**

**Table 2.**

**Figure 1.**

*The Utilization of Rice Blast Resistance Genes in Hybrid Rice Breeding in China*

make breeders directly utilize related resistance resources on purpose.

*Piz-t*, *Pita*, and *Pii*, 328 hybrid rice combinations were screened, in which *Pita* and *Pii* were found in high frequency, but *Pi2* and *Pi1* displayed highly effective resistance contribution to local rice [26]. In Sichuan Province, with molecular markers closely linked to *Pi-9*, *Pi-2*, *Pi-kh*, and *Pi-km*, general rice parents of hybrid rice were analyzed and selected for the resistance resources [27]. The *R* gene screening

The hybridization, backcross, and marker-assisted selection (MAS) were the general method for the introduction of *R* genes into the restorer line, maintainer line, and sterile line of hybrid rice. MAS conduced to selectively breeding based on the genotype and accelerate the breeding course [28]. The procedure for MAS was shown in **Figure 1**. As we know, *R* genes, such as *Pi9*, *Pi2*, *Pi1*, and *Pigm*, have been reported to show relatively high resistance in different districts in China [29–31]. Hence, these *R* genes were often used for improvement of rice blast

**R genes used Variety improved Variety type Reference** *Pi9* Yandao 6 Hao General cultivar [32] *Pi25* Xiangwanxian 13 General cultivar [33] *Pi1, Pi2* and *Pi33* Jin 23B Maintainer line [34] *Pi1* and *Pi2* Rongfeng B Maintainer line [35] *Pid*(t)*, Pib* and *Pita* G46B Maintainer line [36] *Pi9* R599 Maintainer line [37] *Pi9* R288 Maintainer line [38] *Pi9* Shuhui527, Minghui 86, and Minhui 3301 Restorer line [39] *Pigm(*t) Chunhui 350 Restorer line [40] *Pi9* and *Pi49* Chuang 5S Sterile line [41] *Pi25* Zhenda A Sterile line [42] *Pi47* and *Pi48* C815S Sterile line [43] *Pi9* 03S Sterile line [44] *Pi1* GD-8S Sterile line [45] *Pi1* and *Pi2* Peiai64S Sterile line [46]

*DOI: http://dx.doi.org/10.5772/intechopen.83617*

*The breeding course with marker-assisted selection and backcross.*

*The improved rice varieties of different types with MAS technique.*

## **Table 1.**

*Selected rice varieties with different resistant resources to blast in China.*

*The Utilization of Rice Blast Resistance Genes in Hybrid Rice Breeding in China DOI: http://dx.doi.org/10.5772/intechopen.83617*

*Piz-t*, *Pita*, and *Pii*, 328 hybrid rice combinations were screened, in which *Pita* and *Pii* were found in high frequency, but *Pi2* and *Pi1* displayed highly effective resistance contribution to local rice [26]. In Sichuan Province, with molecular markers closely linked to *Pi-9*, *Pi-2*, *Pi-kh*, and *Pi-km*, general rice parents of hybrid rice were analyzed and selected for the resistance resources [27]. The *R* gene screening make breeders directly utilize related resistance resources on purpose.

The hybridization, backcross, and marker-assisted selection (MAS) were the general method for the introduction of *R* genes into the restorer line, maintainer line, and sterile line of hybrid rice. MAS conduced to selectively breeding based on the genotype and accelerate the breeding course [28]. The procedure for MAS was shown in **Figure 1**. As we know, *R* genes, such as *Pi9*, *Pi2*, *Pi1*, and *Pigm*, have been reported to show relatively high resistance in different districts in China [29–31]. Hence, these *R* genes were often used for improvement of rice blast

#### **Figure 1.**

*Protecting Rice Grains in the Post-Genomic Era*

resistance breeding.

**2. The utilization of rice blast resistance genes**

The resistance level of parents is directly related with the resistance performance

Following the clone of resistant genes and the development of related functional molecular makers, marker screening has been widely applied on resistance identification and innovation of parents of hybrid rice. Up to now, molecular makers of blast resistance genes, *Pi2*, *Pi9*, *Pi1*, *Pib*, *Pita*, *Pid2*, *Pikh*, *Pigm*, and *Pish*, have been developed and used on detecting the related *R* genes [17–25]. In Jiangsu, a total of 544 rice materials were assessed for blast resistance and resistance genes distribution by inoculation and marker screening; results showed that 968, Xiushui 134, Jia 58, Jindao 263, Huaidao 20, Yandao 10, and Gumei 4 contained the majority of resistance genes; and *Pi5*, *Pita*, *Pi9*, and *Pib* exhibited high resistance to six major blast races [14]. In South China, with functional marker of *Pi1*, *Pik-p*, *Pikh*, *Pi2*, *Pi9*,

**Province Resistance resource Reference**

Dongnong 415, Songjing 9, Longdao 12, Hejiang 23, and Wuyoudao 3

610, Hanyou 983, Lvyinzhan, Bingyou C278, Yuenongsimiao, and

Guangdong Sanhuangzhan 2 Hao, Qingliuai 1 Hao, Jingxian 89, IR36, and 28 Zhan [9] Hunan Xiangzao 143, Fengyuanyou 299, Jinyou 207, Liangyou 222, Quanfengyou

[6, 7]

[8]

[10, 11]

[12, 13]

[14, 15]

[16]

Sichuan IR99–35, Miyang 46, IR 1544, Tetep, Gumei 2, 6326, Suhui162, and Suhui

Hubei Zhenke, Jinlong 1, Fanyu 1, Ningwan 1, Sanqizao, Nanjing 15, Aiyinnuo,

Fujian Yixiangyou 673, Dyou 15, Gangyou 148, Guyou 527, Jiafuzan, and Teyou

Jiangsu Longjing 968, Xiushui 134, Jia 58, Jindao 263, Huaidao 20, Yandao 10, and

Jinzao 47, Yunjin 23, and Quanzhen 10

Heilongjiang Suijing 12, Mudanjiang 26, Longdun 105, Longjing 20, Longjing 31,

527

627

Gumei 4

*Selected rice varieties with different resistant resources to blast in China.*

Zhuoliangyou 249

of hybrid rice. The resistance evaluation for breeding lines is a very important prerequisite work for resistance breeding of hybrid rice. For traditional breeders, field nursery or artificial inoculation with blast isolates in greenhouse was normally used for resistance identification. Amounts of rice lines with middle or high resistance have been identified in different provinces with diverse ecology. The detailed information was listed in **Table 1**. These identified rice materials provided rich selection as parents or resistant resource for hybrid rice breeding. As we know, genetic mechanism of rice blast resistance followed the gene for gene interaction. It was unclear about background and resistant genes in these materials, and the presence of one *R* gene masked another *R* gene; and also, the stationary field nursery only can stand for limited ecological districts. Hence, blast evaluation cannot identify any particular resistance gene, and it will lead to huge uncertainty in resistance of later generations in breeding. Phenotype identification cooperated with precise analysis of resistant genes will more effectively serve for hybrid rice

**2.2 Characterization and stack effective** *R* **genes in hybrid rice**

**2.1 Identification of the resistant rice parents**

**28**

**Table 1.**

*The breeding course with marker-assisted selection and backcross.*


### **Table 2.**

*The improved rice varieties of different types with MAS technique.*

resistance (**Table 2**). Recently, a new class resistance gene *Ptr* just cloned encoded an atypical protein and conferred broad-spectrum disease resistance and will provide diverse selection for resistance improvement [47]. To breeding rice cultivars with durable blast resistance, stacking several resistance genes still was the most effective method. To stack resistance gene purposefully, spectrum of each resistance gene must be determined, and also, the identification of differential blast races/isolates that distinguished each resistance gene in different districts was critical for ensuring the effectiveness of resistance gene stacking [48].

## **3. Conclusions**

With identification in the rice blast field nursery or functional marker detecting of major *R* genes, the amount of blast resistance resources was identified and provides diverse selections for hybrid rice resistance breeding. However, the recent finding showed that *Pita* required *Ptr* to function revealed that part of single *R* gene may be not functional as we thought originally [47], and further function analysis of more *R* genes may be necessary.

For conventional rice breeding, all blast *R* genes must be stacked into breeding lines to be effective, whereas hybrid rice can stack blast *R* genes into two parents. For hybrid rice breeding, blast resistance was only a part of index, and other agronomic traits also need to be considered. Lines of Chuang 5 S stacked *Pi9* and *Pi49* have been found obvious differences on plant height, spike length, spike number and stigma exertion rate with the receptor, even though the blast resistance has improved [41]. Hence, blast resistance breeding for hybrid rice was a synthetic work that contained resistance innovation and excellent agronomic trait selection.

In this chapter, it introduced the progress on identification of resistance resources and the utilization of blast resistance genes. Traditional cross technique, combined with MAS, has been used to transfer different major *R* genes into parent's lines to improve the resistance of hybrid rice and achieved remarkable results. Following the improvement of blast resistance of the authorized varieties, it gratefully contributed to decrease the damage of rice blast disease and played important function on protection of rice production safety in China.

### **Acknowledgements**

This work was supported by Hunan Provincial Science and Technology Department (CN) (2018NK1020), Hunan Academy of Agricultural Science and Technology Innovation Project (2018ZD01-7), Hunan Academy of Agricultural Science and Technology Innovation Project (2017JC03), and Hunan Provincial Natural Science Fund Youth Fund (2018JJ3379).

**31**

**Author details**

provided the original work is properly cited.

Junjie Xing\*, Huafeng Deng and Longping Yuan

Hunan Hybrid Rice Research Center, Changsha, Hunan, China

\*Address all correspondence to: xingjunjie@hhrrc.ac.cn

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*The Utilization of Rice Blast Resistance Genes in Hybrid Rice Breeding in China*

*DOI: http://dx.doi.org/10.5772/intechopen.83617*

### **Conflict of interest**

The authors declared that there was no conflict of interest.

*The Utilization of Rice Blast Resistance Genes in Hybrid Rice Breeding in China DOI: http://dx.doi.org/10.5772/intechopen.83617*
