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Herbicide Selection of Italian Ryegrass under Different Levels of UVB Radiation

^a IFEVA, Departamento de Recursos Naturales y Ambiente, Universidad de Buenos Aires, Av. San Martin 4453, C1417DSE Buenos Aires, Argentina
^b Departamento de Produccion Vegetal, Facultad de Agronomia, Universidad de Buenos Aires, Av. San Martin 4453, C1417DSE Buenos Aires, Argentina
^c Present address: University of Western Australia, WA Herbicide Resistance Initiative (WAHRI), Department of Plant Science, 35 Stirling Highway, Crawley, WA 6007, Australia

View larger version (57K): [in a new window]   Fig. 1. Overview of the selection protocol and experimental design. (A) Selection cycles conducted during 1996 and 1997; (B) herbicide screening tests conducted in 1998.

View larger version (31K): [in a new window]   Fig. 2. Effect of ultraviolet-B (UVB) radiation on survival of Italian ryegrass seedlings of a parental population when treated with different doses of diclofop-methyl. Bars represent means ± standard errors. Analysis of variance for (A) 1996: UVB light (L), P = 0.18; herbicide dose (D), P = 0.0001; L x D, P = 0.95. Analysis of variance for (B) 1997: L, P = 0.12; D, P = 0.00001; L x D, P = 0.04.

View larger version (38K): [in a new window]   Fig. 3. Effect of ultraviolet-B (UVB) radiation on biomass of seedlings of a parental population of Italian ryegrass surviving treatment with different doses of diclofop-methyl. Bars represent means ± standard errors. Analysis of variance for (A) 1996: UVB light (L), P = 0.13; herbicide dose (D), P = 0.43; L x D, P = 0.76. Analysis of variance for (B) 1997: L, P = 0.39; D, P = 0.10; L x D, P = 0.03.

View larger version (26K): [in a new window]   Fig. 4. The effect of ultraviolet-B (UVB) light on the relationship between reproductive and vegetative biomass per Italian ryegrass plant growing in (A) nontreated (control) plots and (B) herbicide-treated plots. Both parental populations were pooled for analysis. Regression equations: (A) UVB–: y = 0.1354x + 0.0013, R2 = 0.95, P = 0.001, SE of the slope = 0.01; UVB+: y = 0.1102x + 0.0015, R2 = 0.89, P = 0.001, SE of the slope = 0.01; (B) UVB–: y = 0.1011x + 0.0227, R2 = 0.31, P < 0.05, SE of the slope = 0.05; UVB+: y = –0.0461x + 0.0276, R2 = 0.06, P > 0.05.

View larger version (22K): [in a new window]   Fig. 5. The effect of ultraviolet-B (UVB) light on the density-dependent production of reproductive biomass in (A) nontreated (control) plots and (B) herbicide-treated plots. Parental and F1 populations were pooled for analysis. Regression model fitted: y = a exp(–Kx). Parameters for (A) UVB–: a = 0.061, K = 0.017 (SE = 0.01), R2 = 0.88; UVB+: a = 0.045, K = 0.014 (SE = 0.004), R2 = 0.97; parameters for (B) UVB–: a = 0.18, K = 0.12 (SE= 0.055), R2 = 0.47; UVB+: not significant.

View larger version (49K): [in a new window]   Fig. 6. Effect of ultraviolet-B (UVB) radiation on survival of Italian ryegrass seedlings of an F1 population when treated with different doses of diclofop-methyl. Bars represent means ± standard errors. Analysis of variance: UVB light (L), P = 0.17; herbicide dose (D), P = 0.39; L x D, P = 0.02.

View larger version (30K): [in a new window]   Fig. 7. Effect of ultraviolet-B (UVB) radiation on biomass of seedlings of an F1 population of Italian ryegrass surviving treatment with different doses of diclofop-methyl. Parental and F1 populations were exposed to the same UVB light and herbicide environments. Bars represent means ± standard errors. Analysis of variance: UVB light (L), P = 0.0034; herbicide dose (D), P = 0.0007; L x D, P = 0.31.

View larger version (62K): [in a new window]   Fig. 8. Selection of ryegrass populations in different UVB light and herbicide environments as estimated by the survival to herbicide application of F1 seedlings from seeds produced in 1996 and 1997. The figure illustrates the significant interactions between current environment (herbicide screening) and selection history from Table 2. Bars represent means ± standard errors.

View larger version (54K): [in a new window]   Fig. 9. Selection of ryegrass populations in different UVB light and herbicide environments as estimated by the survival to herbicide application to F2 seedlings from seeds produced in 1997. The figure illustrates the significant interactions between current environment (herbicide screening) and two cycles of the same selection history from Table 2. Bars represent means ± standard errors.