EXPRESSION AND SEGREGATION OF GENES ENCODING CRYIA INSECTICIDAL PROTEINS IN COTTON

Epistatic and environmental effects on foreign gene expression in cott on (Gossypium hirsutum L.) could influence the breeding, stability and , in the case of pest resistance, efficacy and durability of the forei gn gene, This study was undertaken to characterize the expression and segregation of two foreign cryIA genes in a range of insect-resistant cotton lines derived in three backgrounds. The cryIA genes encoded ins ecticidal proteins from the bacterium Bacillus thuringiensis spp, kurs taki, The transformed cotton lines, MON 81 expressing the cryIA(b) gen e and MON 249 expressing the cryIA(c) gene, were crossed to 14 cotton isolines with five different insect-resistance traits, CryIA gene expr ession and variation were examined in terminal leaves of 2293 F-2 prog eny and subsequently in 12 F-2:4 lines [cryIA(b) only] in field experi ments conducted at two locations in Texas. CryIA gene expression was v ariable and influenced by genetic and environmental factors. Site-of-g ene-insertion and cotton-background effects were significant sources o f variation for the cryIA gene, Significant epistatic and/or somaclona l effects increased plant-to-plant variation and caused cryIA gene exp ression to behave as a quantitative trait. Environmental effects, betw een and within locations and over time, decreased parent-offspring cor relations of mean cryIA gene expression between individuals from the F -2 and F-2:4 generations. Gene dosage at the cryIA lotus influenced in secticidal protein concentration in F-2 populations with the cryIA(b) gene insert-homozygotes produced 14% more CryIA(b) protein than hemizy gotes, The CryIA phenotype segregated as a simple, dominant Mendelian trait, However, non-Mendelian segregation occurred in some lines deriv ed from MON 249. Expression of cryIA genes in cotton lines was influen ced by one or more of the following: site of gene insertion, gene cons truct, background genotype, epistasis, somaclonal mutations, and the p hysical environment, These results indicate that appropriate evaluatio n and selection procedures should be used in a breeding program to dev elop new cotton lines sith pest-resistant traits conferred by foreign genes, Moreover, that a practical backcross breeding program could be used to develop cotton cultivars combining one or more pest-resistant traits from foreign and native gene sources.