An optimized screening method for identifying levels of resistance to Crinipellis perniciosa in cocoa (Theobroma cacao)

Abstract

The effects of host age, leaf number, host type (clone or seedling), pathogen spore concentration and incubation time on inoculation with Crinipellis perniciosa (witches' broom disease of cocoa) were studied in greenhouse experiments using susceptible cocoa genotypes. Three methods of inoculation (agar-drop, water-drop and spray) were also tested. An optimized inoculation method was selected and tested for its repeatability as well as its ability to discriminate between various levels of resistance to C. perniciosa in cocoa. The optimized method (350 000 viable basidiospores per mL, 60 h incubation, agar-drop technique) produced 100% infection repeatedly, on both clonal and seedling plants of a susceptible genotype. Seedling age (2-12 months) and leaf number did not significantly affect the percentage of plants with symptoms or broom characteristics. This method discriminated effectively between the various levels of resistance in 14 cocoa genotypes and is recommended as an inoculation method to identify levels of resistance in germplasm collections. Symptom severity was shown to be a better measure of resistance than infection success.

Development of an effective screening method for partial resistance to Alternaria brassicicola (dark leaf spot) in Brassica rapa

“…In the cases of B. nigra and B. juncea, 4 Â 10 3 to 5 Â 10 4 conidia ml )1 were used in screenings for response to A. brassicicola and A. brassicae infection (Westman et al, 1999;Sharma et al, 2002). Ideally, use of the optimal inoculum concentration will not only reduce the chance of overlooking susceptible plants, but will also discriminate between various levels of resistance (King, 1994;Surujdeo-Maharaj et al, 2003). Thus, the present study suggests that 5 Â 10 4 A. brassicicola conidia ml )1 is the optimal inoculum concentration at which various levels of resistance in B. rapa genotypes can be effectively distinguished ( Table 2).…”

Evaluation of cacao (Theobroma cacao) clones against seven Colombian isolates of Moniliophthora roreri from four pathogen genetic groups

“…(2001) similarly investigated the resistance of leaves from 18 cacao genotypes when challenged with 10 isolates of P. palmivora from Trinidad and Tobago. Other studies on other pathogens of cacao include Crinipellis perniciosa (Laker, 1990; Wheeler, 1996; Wheeler & Mepsted, 1988; Surujdeo‐Maharaj et al ., 2003) and Oncobasidium theobromae (Bong et al ., 1996), causal pathogens of witches’ broom disease and vascular streak dieback (VSD), respectively. To date, however, there has been no study of this kind for M. roreri .…”

Selección de genotipos de cacao (Theobroma cacao L.) con resistencia a escoba de bruja (Moniliophthora perniciosa) en Los Ríos, Ecuador

“…La escoba de bruja (Moniliophthora perniciosa) es una enfermedad que causa infección en brotes jóvenes, cojinetes florales, yemas vegetativas y en frutos jóvenes; está enfermedad combinada con la monilia del fruto (Moniliophthora roreri), causan pérdidas anuales que superan en ocasiones el 50% del total de frutos producidos y en casos extremos pueden llegar hasta el 90% de pérdidas (Surujdeo-Maharaj, 2003). El uso de genotipos resistentes para el control de las enfermedades es sin duda una herramienta importante para el desarrollo de híbridos con altos niveles de resistencia; por tanto, la obtención de variedades con mayor valor económico, ayudaría a enfrentar este problema, por su efectividad, bajo costo económico y ambiental, como parte de un combate integrado.…”