Effect of Stunting Disease on Yield of Some Sugarcane Varieties in Puerto Rico

Abstract

The effect of the ratoon stunting disease virus was studied on yield of cane and sugar per acre of varieties B. 37161, B. 41227, B. 4362, Co. 421, H. 328560, P.O.J. 2878, P.R. 975, P.R. 980, P.R. 1000, and P.R. 1013. A 3-hour hot water treatment at 50° C. did not eradicate the virus in most varieties, assuming that all were initially infected, but this treatment furnished very good control, except in Co. 421. In the combined crop of plant cane and two ratoons, percent sucrose increase due to inoculation was statistically significant in varieties H. 328560 and Co. 421. Tonnage of cane per acre was significantly reduced by inoculation in seven varieties. The canes affected and the percent yield reductions were, respectively, as follows: B. 37161, 14.6; B. 41227, 11.4; B. 4362, 13.4; Co. 421,13.6; H. 328560,16.9; P.R. 980, 20.4; and P.R. 1013, 11.8. Production of sugar per acre per crop was reduced significantly in seven varieties as a result of reduced tonnage. The varieties affected and the percent yield reductions were, respectively, as follows: B. 37161, 12.1; B. 41227, 12.4; B. 4362, 11.2; H. 328560, 12.0; P.R. 975, 9.6; P.R. 980, 16.9; and P.R. 1013, 10.2. There were significant reductions of cane and sugar per acre per crop in some varieties, especially in B. 41227, B. 4362, and P.R. 1013 although detectable infection in the combined crop of these varieties was only 3.6, 5.7, and 6.0 percent, respectively. The absence of symptoms in these canes suggests the presence of masked infections. The production of sugar per acre per crop of varieties Co. 421 and P.R. 1000 was not significantly reduced in the combined analysis in spite of the high disease incidence (78.8 and 57.9 percent infection, respectively). The lack of significance in Co. 421 was attributable to a significant increase in percent sucrose in inoculated cane in addition to infection of the controls. Varieties P.R. 1000 and P.O.J. 2878 are considered tolerant to the stunting disease. It appears that the disease is not responsible for decline in their yield. Varieties H. 328560, P.R. 975, P.R. 980, and P.R. 1013, in all of which occurred significant reductions in sugar per acre due to the stunting disease, are the only ones of the group tested presently being recommended to growers by the Experiment Station on the basis of other desirable qualities. Variety P.R. 980, which occupies 60 percent of the sugarcane acreage, showed a highly significant yield reduction of 42.4 hundredweights of sugar per acre per crop as a result of inoculation with the stunting disease agent. Had this experiment been a commercial operation, profit to the grower would have been reduced by $170 per acre per crop, estimated at the average liquidation price of $6.23 per hundredweight of raw sugar for the 1964-65 crop, when grower participation was 64.7 percent.