*2.2. Development of BC3F4 Pyramided Lines Using Marker-Assisted Breeding*

The BC2F3 pyramided rice genotypes were evaluated for their resistance to BB in the field conditions using the Taiwanese *Xanthomonase oryzae* strain isolate, XF89-b. The resistance donor IRBB66, containing five BB resistance genes, showed shorter lesion lengths (mean lesion length of 0.43 cm), while the susceptible checks, TN1, TCS10, IR24 and TNG82, exhibited a range of longer lesion lengths, between 6.75 and 12.56 cm (Table 1, Figure 4). The genotypes having either BB resistance genes alone or more than two genes pyramided were shown to be moderately resistant, resistant, and highly resistant to the BB disease (Figure 5). In addition, the five-gene-pyramided BC2F3 genotypes exhibited a range of shorter lesion lengths, between 0.37 and 0.46 cm (Table 1). The five-gene-pyramided lines displayed higher levels of disease resistance and a broader resistance spectrum compared to both the parental rice variety, TNG82 and the genotypes possessing a single gene.

**Table 1.** The results of TNG82/IRBB66 BC2F3 lines after incubating the *Xoo* strains XF89-b in the field at the first crop season in 2016.



**Table 1.** *Cont.*

† Mean ± standard error. ¥ HR <sup>=</sup> highly resistant (lesion length <sup>&</sup>lt; 1 cm); R <sup>=</sup> resistant (1 cm <sup>&</sup>lt; lesion length <sup>&</sup>lt; 3 cm); MR = moderately resistant (3 cm < lesion length < 6 cm); MS = moderately susceptible (6 cm < lesion length < 10 cm); S = susceptible (10 cm < lesion length). Means with none or the same letter of a row are not significantly different at 5% level by least significant difference (LSD) test.

**Figure 4.** The leaf lesion length of TNG82/IRBB66 BC2F3 genotypes after 21 days inoculum of bacterial blight pathogen XF89-b in the field at the first crop season in 2016. Susceptible cultivar: TCS10, IR24, and TN1; Parental: TNG82 and IRBB66.

**Figure 5.** The leaf lesion photo of TNG82/IRBB66 BC2F3 genotypes after 21 days inoculum of bacterial blight pathogen XF89-b in the field at the first crop season in 2016. Susceptible cultivar check: TCS10, IR24, and TN1; Parents: TNG82 and IRBB66.
