Evaluation of hybrid rice parental lines against bacterial blight disease and detection of resistant gene (s) by gene‐specific, linked markers

Abstract

Bacterial blight (BB) disease, caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the major bottlenecks of rice (Oryza sativa) production. The present study was undertaken to identify BB‐resistant parental lines of hybrid rice based on pathogenicity tests and molecular screening. Three virulent races of Xoo, i.e. BXo93, BXo822 and BXo887 were used to evaluate the 66 maintainers and 200 elite restorer lines against BB. Based on the pathogenicity test, none of the maintainer lines was found resistant, whereas 16 restorers were resistant against the three races and 15 restorers were resistant to a single race (Bxo93). These 31 restorer lines were selected to detect the presence of major bacterial blight resistance genes, i.e. Xa4, xa5, Xa7, xa13, Xa21 and Xa23 using molecular markers. Thirteen restorer lines carried the Xa4 gene but were not resistant to all three races of BB. Fourteen restorers and one restorer had two (Xa4 + xa5; Xa4 + Xa7; Xa4 + Xa21 and Xa7 + Xa21) and three (Xa4 + xa5 + Xa7) BB resistance genes, respectively. Genotypes having Xa21, Xa7 + Xa21 or Xa4 + Xa21 had reduced lesion lengths that ranged from 1.4 cm (against BXo93)–3.0 cm (against BXo887), 1.6 cm (against BXo93)–2.0 cm (against BXo822 and BXo887) and 2.5 cm (against BXo887)–3 cm (against BXo822), respectively, and were found to be the most effective resistance genes against bacterial blight. The restorer lines having the Xa21, Xa7 + Xa21 or Xa4 + Xa21 could be used as parental lines for the development of bacterial blight‐resistant hybrid varieties.

Pyramiding of bacterial blight resistance genes into promising restorer BRRI31R line through marker-assisted backcross breeding and evaluation of agro-morphological and physiochemical characteristics of developed resistant restorer lines

“…It was noted that BRRI31R had the Xa4 gene by default and for this reason, finally, five homozygous pyramided restore lines were selected with four BB resistance genes, Xa4 + xa5 + xa13 + Xa21 from the cross combination, BRRI31R × IRBB60 in BC 3 F 5 progenies. Though Xa4 is not effective against the BB pathogen of Bangladesh but combination of this gene might enhance the function of other resistance gene and combination of these four genes were also found as very effective against the diverse isolates of BB pathogens [ 23 , 25 , 33 , 61 , 64 ]. These gene combinations also gives long-lasting and broad-spectrum resistance in the R8012 restorer line for Chinese CMS Zhong-9A restoration [ 65 ].…”

“…Following 14 days of inoculation, eight (8) infected leaves per hill were collected from the field for lesion length measurement. The disease response was graded using the modified scale of Akter et al, [ 25 ]. Briefly, disease data was categorized into six scales (0 to 9) i.e., 0-Highly resistant (HR, lesion length <0.5 cm), 1-Resistant (R, lesion length 0.5–3.0 cm), 3-Moderately resistant (MR, lesion length 3.1–5.0 cm), 5-Moderately susceptible (MS, lesion length 5.1–10.0 cm), 7-Susceptible (S, lesion length 10.1–15.0 cm) and 9-Highly susceptible (HS, lesion length >15.0 cm).…”

“…But till now, no effective chemical control measure is suggested to combat the disease. So far, 237 hybrid rice varieties have been released in Bangladesh but no variety has any resistance characteristics because all hybrid parental lines are susceptible to available races of Xoo [ 25 ].…”

“…Therefore, stacking resistance genes into hybrid parental lines is a durable strategy to manage bacterial blight disease [ 25 ]. Moreover, by adopting conventional breeding it is tough to introgress more than one genes into the single lines and sometimes dominance and epistasis effects make it more difficult to identify the effective gene (s) [ 26 , 27 ].…”

“…Among them, Xa4 , xa5 , Xa7 , xa13 , Xa21 , and Xa23 genes have been extensively deployed and incorporated into rice cultivars for the development of BB resistant cultivars [ 32 ]. Resistance genes i.e., xa5 , xa13 and Xa21 were found effective for the bacterial blight pathogens of Bangladesh [ 23 , 25 , 33 , 34 ]. Moreover, molecular markers of these resistance genes are widely used in breeding programs to develop bacterial blight resistant rice varieties [ 9 , 35 , 36 ].…”