An Evaluation of Methods Used in Screening Progenies for Sugarcane Mosaic Virus Resistance.

The methods used in screening sugarcane (Saccharum sp.) for resistance to sugarcane mosaic virus (SCMV) were studied, with emphasis on greenhouse techniques, natural spread in unselected progenies and screening effectiveness. Greenhouse procedures were studied at Baton Rouge, Louisiana, while field tests were conducted at the St. Gabriel Experiment Station. In greenhouse studies progenies with resistant parents showed the highest resistance to infection by mechanical inoculation, followed by canes with one resistant parent. In natural field spread tests, canes of Resistant x Susceptible parents showed significantly (P \u3c 0.05) less resistance after one test year, and no significant (P \u3c 0.05) differences were found between resistance of any susceptibility classes the second year. The commercial check cane NCo 310 showed highly significant (P \u3c 0.01) susceptibility when compared to canes of the other parental classes or the commercial check CP65-357. Random samples from sixteen crosses, totaling over 3200 screened seedlings, showed that 10.2 percent of these plants showed visual mosaic symptoms when allowed to grow out, unclipped, in another greenhouse. Rio sorghum, which is an indicator host of the virus strains used for inoculation, was used as uninoculated checks, and did not show symptoms. This indicates the clipping of seedlings before field transfer may be a means for virus spread into field populations. More sanitary techniques may have to be devised to accomplish this task. Results of a paired comparison test in 1979-80 showed that populations containing screened seedlings showed significant (P \u3c 0.05) and highly significant (P \u3c 0.01) levels of mosaic over unscreened populations. Mechanical transfer was eliminated wherever possible by minimum tillage, and plots were cut with a sugarcane harvester after plants had been dead for several weeks due to freezing and drying