Efficacy of Bioindexing for Graft-Transmissible Citrus Pathogens in Mixed Infections

Abstract

Biological indexing for graft-transmissible pathogens of citrus in the presence of additional pathogens was investigated. The probability for symptom expression, the efficacy of the bio-indexing tests, and the number of citrus indicators required for pathogen detection were statistically evaluated. Multiple infections did not preclude symptom expression or reduce the diagnostic efficacy of the primary indexing hosts for Citrus tristeza virus (CTV), Citrus psorosis virus (CPsV), and Citrus tatter leaf virus (Apple stem grooving virus). Symptoms of Citrus vein enation virus (CVEV) and the diagnostic efficacy of Mexican lime were suppressed by the T30 group CTV isolates, but not by other CTV isolates tested. CPsV suppressed symptom expression and diagnostic efficiency of Dweet tangor and sweet orange for concave gum. The application of alternate bioassay hosts for indexing was also investigated. Dweet tangor, sweet orange, and Citrus excelsa are not typically used for bioindexing of CVEV, however, Dweet tangor and C. excelsa detected CVEV in single infections, whereas in sweet orange, CVEV was detected only when CPsV, concave gum, or citrus viroids were present. CTV was readily detected using the alternative indicator C. excelsa, whereas only shock reacting CPsV isolates were effectively indexed by Mexican lime.

Caracterización del Viroide exocortis de los cítricos en diferentes condiciones de indexado

“…La eficiencia del indexado (Ɵ) se determinó como la probabilidad de expresión de síntomas (P) en muestras inoculadas con tejido infectado (n) con un nivel de confianza del 95 %, de acuerdo a la metodología de Vidalakis et al (2004). La eficiencia se calculó con la fórmula Ɵ= 1-(1-P L ) n usando el límite inferior de probabilidad de Clopper y Pearson (P L = 0.7935 calculado para 16 unidades) y n=4 como el número mínimo de muestras recomendado por Roistacher (1991) y Vidalakis et al (2004) para el diagnóstico de CEVd por indexado.…”

“…La eficiencia se calculó con la fórmula Ɵ= 1-(1-P L ) n usando el límite inferior de probabilidad de Clopper y Pearson (P L = 0.7935 calculado para 16 unidades) y n=4 como el número mínimo de muestras recomendado por Roistacher (1991) y Vidalakis et al (2004) para el diagnóstico de CEVd por indexado.…”

“…Indexing efficiency: The indexing efficiency (Ɵ) was determined as the probability of the expression of symptoms (P) in samples inoculated with infected tissue (n) with a level of confidence of 95 %, according to the methodology by Vidalakis et al (2004). Efficiency was calculated with the formula Ɵ= 1-(1-P L ) n using the lower probability limit by Clopper and Pearson (P L = 0.7935 calculated for 16 units) and n= 4 as the minimum number of samples recommended by Roistacher (1991) and Vidalakis et al (2004) for the diagnosis of CEVd by indexing.…”

“…Efficiency was calculated with the formula Ɵ= 1-(1-P L ) n using the lower probability limit by Clopper and Pearson (P L = 0.7935 calculated for 16 units) and n= 4 as the minimum number of samples recommended by Roistacher (1991) and Vidalakis et al (2004) for the diagnosis of CEVd by indexing.…”

Plant health: How diagnostic networks and interagency partnerships protect plant systems from pests and pathogens

“…For each index, technicians maintain adequate positive control plants under the same environmental conditions as the test indicators. The controls serve dual purposes: They provide a comparison for the test plant and also demonstrate that environmental conditions in the greenhouse are optimal for plant growth and symptom expression (Childs 1978;Roistacher 1991;Vidalakis et al 2004). …”