Bacterial blight resistance gene B5 has received little attention since it was first described in... more Bacterial blight resistance gene B5 has received little attention since it was first described in 1950. A near-isogenic line (NIL) of Gossypium hirsutum cotton, Ac B5, was generated in an otherwise bacterial-blight-susceptible ‘Acala 44’ background. The introgressed locus B5 in Ac B5 conferred strong and broad-spectrum resistance to bacterial blight. Segregation patterns of test crosses under Oklahoma field conditions indicated that Ac B5 is likely homozygous for resistance at two loci with partial dominance gene action. In controlled-environment conditions, two of the four copies of B5 were required for effective resistance. Contrary to expectations of gene-for-gene theory, Ac B5 conferred high resistance toward isogenic strains of Xanthomonas citri subsp. malvacearum carrying cloned avirulence genes avrB4, avrb7, avrBIn, avrB101, and avrB102, respectively, and weaker resistance toward the strain carrying cloned avrb6. The hypothesis that each B gene, in the absence of a polygenic ...
Current Plant Science and Biotechnology in Agriculture, 1987
This study employed cotton lines developed by breeding genes for resistance to bacterial blight i... more This study employed cotton lines developed by breeding genes for resistance to bacterial blight into the susceptible background of cultivar Ac 44. Leaves of Ac 44 and of lines containing resistance genes B2, B3, b7, or BN, or a combination of these plus a polygenic complex were each inoculated with six strains of Xanthomonas campestris pv. malvacearum. The strains included two field isolates, one from California and one from Oklahoma, neither of which was virulent against any of the four resistance genes, as judged by visible host reaction. Also included were spontaneous mutants derived from those isolates. Three of the mutants were virulent against B3 and b7 and one was virulent against BN. Final bacterial population densities were significantly lower in incompatible cultivar/race combinations than in compatible combinations (analysis of variance followed by the protected least squares difference test: P<0.002). Accumulation of the sesquiterpenoid phytoalexins 2,7-dihydroxycadalene, lacinilene C, and lacinilene C 7-methyl ether was determined eight days post-inoculation, when compatible and incompatible bacterial multiplication curves had diverged. Phytoalexin levels were in all cases greater in incompatible interactions than in compatible interactions. However, within the incompatible interactions, phytoalexin levels varied greatly and did not correlate with either final bacterial population densities or bacterial growth yields.
Near-isogenic lines of upland cotton (Gossypium hirsutum) carrying single, race-specific genes B4... more Near-isogenic lines of upland cotton (Gossypium hirsutum) carrying single, race-specific genes B4, BIn, and b7 for resistance to bacterial blight were used to develop a pyramid of lines with all possible combinations of two and three genes to learn whether the pyramid could achieve broad and high resistance approaching that of L. A. Brinkerhoff's exceptional line Im216. Isogenic strains of Xanthomonas axonopodis pv. malvacearum carrying single avirulence (avr) genes were used to identify plants carrying specific resistance (B) genes. Under field conditions in north-central Oklahoma, pyramid lines exhibited broader resistance to individual races and, consequently, higher resistance to a race mixture. It was predicted that lines carrying two or three B genes would also exhibit higher resistance to race 1, which possesses many avr genes. Although some enhancements were observed, they did not approach the level of resistance of Im216. In a growth chamber, bacterial populations attai...
Bacterial blight resistance gene B5 has received little attention since it was first described in... more Bacterial blight resistance gene B5 has received little attention since it was first described in 1950. A near-isogenic line (NIL) of Gossypium hirsutum cotton, Ac B5, was generated in an otherwise bacterial-blight-susceptible ‘Acala 44’ background. The introgressed locus B5 in Ac B5 conferred strong and broad-spectrum resistance to bacterial blight. Segregation patterns of test crosses under Oklahoma field conditions indicated that Ac B5 is likely homozygous for resistance at two loci with partial dominance gene action. In controlled-environment conditions, two of the four copies of B5 were required for effective resistance. Contrary to expectations of gene-for-gene theory, Ac B5 conferred high resistance toward isogenic strains of Xanthomonas citri subsp. malvacearum carrying cloned avirulence genes avrB4, avrb7, avrBIn, avrB101, and avrB102, respectively, and weaker resistance toward the strain carrying cloned avrb6. The hypothesis that each B gene, in the absence of a polygenic ...
Current Plant Science and Biotechnology in Agriculture, 1987
This study employed cotton lines developed by breeding genes for resistance to bacterial blight i... more This study employed cotton lines developed by breeding genes for resistance to bacterial blight into the susceptible background of cultivar Ac 44. Leaves of Ac 44 and of lines containing resistance genes B2, B3, b7, or BN, or a combination of these plus a polygenic complex were each inoculated with six strains of Xanthomonas campestris pv. malvacearum. The strains included two field isolates, one from California and one from Oklahoma, neither of which was virulent against any of the four resistance genes, as judged by visible host reaction. Also included were spontaneous mutants derived from those isolates. Three of the mutants were virulent against B3 and b7 and one was virulent against BN. Final bacterial population densities were significantly lower in incompatible cultivar/race combinations than in compatible combinations (analysis of variance followed by the protected least squares difference test: P<0.002). Accumulation of the sesquiterpenoid phytoalexins 2,7-dihydroxycadalene, lacinilene C, and lacinilene C 7-methyl ether was determined eight days post-inoculation, when compatible and incompatible bacterial multiplication curves had diverged. Phytoalexin levels were in all cases greater in incompatible interactions than in compatible interactions. However, within the incompatible interactions, phytoalexin levels varied greatly and did not correlate with either final bacterial population densities or bacterial growth yields.
Near-isogenic lines of upland cotton (Gossypium hirsutum) carrying single, race-specific genes B4... more Near-isogenic lines of upland cotton (Gossypium hirsutum) carrying single, race-specific genes B4, BIn, and b7 for resistance to bacterial blight were used to develop a pyramid of lines with all possible combinations of two and three genes to learn whether the pyramid could achieve broad and high resistance approaching that of L. A. Brinkerhoff's exceptional line Im216. Isogenic strains of Xanthomonas axonopodis pv. malvacearum carrying single avirulence (avr) genes were used to identify plants carrying specific resistance (B) genes. Under field conditions in north-central Oklahoma, pyramid lines exhibited broader resistance to individual races and, consequently, higher resistance to a race mixture. It was predicted that lines carrying two or three B genes would also exhibit higher resistance to race 1, which possesses many avr genes. Although some enhancements were observed, they did not approach the level of resistance of Im216. In a growth chamber, bacterial populations attai...
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Papers by Margaret Essenberg