Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/9/2000
Publication Date: N/A
Interpretive Summary: Many short season cottons grown in the USA are susceptible to a new disease called bronze wilt. Studies were performed to determine whether there was a simple genetic basis for bronze wilt susceptibility and whether sources of resistance are available. Results indicate that susceptibility in 'Stoneville 373' and 'Paymaster 1220 B/R', two varieties widely affected by the disease, is due to homozygous genetic characters which are present in most, but not all, plants of the cultivar. Cotton lines containing certain bacterial blight resistance showed high levels of susceptibility to bronze wilt, whereas lines with other resistance genes were more resistance. The results indicate that manipulation of bacterial blight resistance genes may reduce severity of bronze wilt.
Technical Abstract: The effects of environment and genotype on expression of resistance to bronze wilt was studied using 'Suregrow 125', 'Tamcot Sphinx', and 'Deltapine 50' as resistant cultivars and 'Stoneville 373', 'Paymaster 1220 B/R' and 'Pima S-7' as susceptible cultivars. A standard screening procedure was adapted from the environmental studies. 'Stoneville 373' and 'Paymaster 1220 B/R' commercial seed, were mostly susceptible to bronze wilt also included resistant individuals. Plants that gave uniform susceptiblity or resistance were used for genetic studies. Resistance to bronze wilt caused by Agrobacterium tumefaciens strain 34B was completely dominant or overdominant to susceptibility. Thus, severe bronze wilt occurs only when a homozygous recessive condition is present. Cultivars carrying different bacterial blight resistance genes (B genes) also were evaluated for resistance to strain 34B. Cultivars with the B4, BN, BIn, and B2,B3 genes showed higher levels of resistance than similar cultivars that lacked these genes. The 'DPxP4' and 'S-295' cultivars which have B4 and B12 genes also showed higher levels of resistance to bronze wilt. Cultivars with the B2 or B7 gene were more susceptible to bronze wilt than the corresponding cultivar lacking these genes and behaved similar to 'Hartz 1215.' Both cultivars that carried the B2 gene, alone or combined with B3, showed more blighting and defoliation of lower leaves and recovered more slowly than the 96 other cultivars when returned to temperatures below 33ºC. Reactions of 96 modern cultivars and lines to bronze wilt caused by A. tumefaciens strain 34B in a greenhouse screen are reported.