Submitted to: American Society of Sugar Cane Technologists
Publication Type: Abstract only
Publication Acceptance Date: 5/1/2006
Publication Date: 7/1/2006
Citation: Milligan, S.B., Comstock, J.C. 2006. Inheritance of resistance to ratoon stunting disease and implications for selectin in florida. [abstract]. American Society of Sugar Cane Technologists. 26:52 Interpretive Summary:
Technical Abstract: Ratoon Stunting Disease (RSD) (caused by Leifsonia xyli subsp. xyli (Davis et al.) Evtushenko et al.) may impart major economic yield losses in sugarcane, particularly in ratoon crops. Although control may be obtained by mechanical sanitation and the use of disease-free seed-cane, genetic resistance would add to its control. The germplasm from the sugarcane breeding program based at Canal Point, FL has been evaluated for RSD susceptibility since 1993. Susceptibility to RSD was determined by a serological test specific to RSD. The number of colonized vascular bundles per imprint (CVB) was determined from inoculated tests of Stage 2 and Stage 3 genotypes from the Canal Point breeding program. Stage 2 yields and RSD evaluations are determined from independent, unreplicated tests with about 1500 genotypes. Stage 3 trails consist of replicated tests of about 130 clones at four locations while an independent RSD inoculation test of the germplasm is conducted using a replicated test. We estimated narrow-sense heritabilities of log transformed CVB and yield components using a half-sib parental analysis. The narrow-sense heritability percent for CVB was low (h2 = 7.8%) but similar to that estimated for stalk number and sugar yield. Non-additive genetic variance was not indicated. Within test clonal repeatability analysis of the Stage 3 material indicated that the clonal repeatability was about 0.50 while Spearman correlations of Stage 2 CVB with Stage 3 CVB averaged r = 0.21. This suggested that the within test estimate is significantly inflated by the genotype x year variance. Correlations of CVB with the yield components of germplasm in the Stage 2 and Stage 3 trials indicated very low (r <0.10) to no correlation with any yield component. Among the inoculation tests, the check cultivars often varied as did their responses within the tests, however they tended to fall into three categories: resistant (CVB near 0), moderately susceptible (5<CVB<10), and susceptible (CVB>>10). We simulated selection on the populations by conservatively (CVB=0) or liberally (CVB<10) classifying genotypes as resistant. Approximately 10% of the Stage 3 genotypes and 35% of the Stage 2 genotypes were conservatively classified as resistant, while approximately 70% of the Stage 3 and Stage 2 clones were liberally classified as resistant. There was no consistent trend in apparent resistance among the test years examined. Population means were calculated after removing genotypes classified as susceptible from the analysis. As expected from the poor correlations, simulated selection effected little change on population means. Genotype selection, however, looks for the exception not the average. Given the cultural control options available, selection for RSD resistance should be maintained as practiced, which involves cautious dropping of some susceptible genotypes and consideration when making crosses.