AbstractIn this report [cf. R.A.M., xviii, p. 477] it is stated that the most important sugar-cane diseases in Hawaii at present are leaf scald (Bacterium albilineans[Xanthomonas albilineans]) and chlorotic streak, with an occasional outbreak of eye spot (Helminthosporium sacchari[Bipolaris sacchari]). On the island of Maui eye spot is the principal disease, while leaf scald and chlorotic streak are only of localized importance. The most serious diseases in Kauai and Oahu are eye spot and brown stripe (Cochliobolus stenospilus) [the ascigerous stage of H. stenospilum], though in the last few months chlorotic streak has become somewhat more serious than before on some varieties in parts of Kauai. Mosaic is becoming of minor importance, as a result of the planting of resistant varieties, selection of healthy planting material, and improved weed control.
In a varietal resistance test, in which healthy and diseased cuttings of 23 varieties were planted, several varieties, including 31-2484 and 31-2510, showed marked tolerance towards chlorotic streak, while others, including P.O.J. 2878, D. 1135, Olaa 3055 and 32-1063 showed little tolerance, as indicated by the depressed growth in the plots planted with diseased cuttings.
Transmission of chlorotic streak occurs by means of cuttings and may be eliminated by hot-water treatment before planting, which also stimulates germination and early growth in cold, wet conditions. In almost every instance, treatment at 52° C. for 20 minutes has given 100 per cent. healthy stands. [In R.A.M., xvi, p. 561, the record of the symptoms of chlorotic streak on elephant grass (Pennisetum purpureum) was given in error as on Typha elephantina.]
Leaf scald varietal resistance tests clearly demonstrated that most of the local varieties are commercially resistant and that very susceptible varieties can easily be detected by the external and internal symptoms which they develop. The disease was less severe than in previous years, and the use of resistant varieties is again suggested.
Red stripe [Bact. rubrilineans] is limited almost exclusively to the Kohala area, and, with the decline of the Tip canes here, is becoming much less serious.