A Statistical Study of the Inheritance of Stoneville 20 Resistance to the Bacterial Blight Disease of Cotton in the Presence of Xanthomonas Malvacearum Races 1 and 2.

TILIZING inherently resistant plants is the only known method for adequately U controlling the bacterial blight disease of cotton, which is caused by Xanthomonas malucrcearum (E. F . Sm.) Dowson. For this reason the development of resistant varieties has received considerable attention during the past decade. In 1939 SIMPSON and WEINDLING (1946) found a selection from Stoneville 2A which was resistant to bacterial blight. The selection was designated Stoneville 20. This strain has been the principal source of resistance used in a number of breeding programs in the United States. SIMP SON^ reported that Stoneville 20 resistance was inherited as a simple recessive character with susceptibility being dominant and that a favorable alignment of modifying or minor genes was necessary for the full expression of resistance. BLANK (1949) reported studies which supported SIMPSON’S hypothesis. BIRD ( 1950) conducted experiments involving Stoneville 20 resistance in a segregating population following the second backcross to Stoneville 2B. It was shown that heterozygous plants could be distinguished from homozygous ones and that if dominance was present it was in the direction of resistance. The gene was designated B‘ until its relationship with KNIGHT’S and CLOUSTON’S (1939) factors B, and B, and KNIGHT’S (1944, 1948) factors B, and B, could be ascertained. After studying segregating populations from third backcross generations in Deltapine and Acala material, BIRD and BLANK (1951) concluded that Stoneville 20 resistance was recessive but showed that heterozygous plants tend to be intermediate between the homozygous ones when minor genes were present. KNIGHT (1953), after studying Stoneville 20 resistance in a Sake1 background, concluded that it was inherited as a simple