Pathogenic variability amongst isolates of Crinipellis perniciosa from cocoa (Theobroma cacao)

Abstract

Dry witches' brooms from cocoa were imported from various areas within Bolivia, Brazil, Colombia, Ecuador, Trinidad and Venezuela. Basidiocarps of Crinipellis perniciosa were induced to form on these brooms and seedlings of different types of cocoa were inoculated with basidiospores either on the hypocotyl or cotyledon bud. Host reactions were assessed mainly by recording stem base swelling and broom development at the cotyledon node (hypocotyl inoculations) or the extent of swelling and branching of shoots (cotyledon bud inoculations). Results from 30 experiments indicated considerable diversity amongst isolates in inducing disease symptoms, but suggested that two groups or populations of C. perniciosa exist on cultivated cocoa. One group (A), comprising isolates from Bolivia and Pichilingue (Ecuador) and most isolates tested from Colombia, induced severe symptoms on cocoa with Scavina 6 as one parent; the other group (B), comprising isolates from Brazil, Trinidad and Venezuela, did not. Within these groupings variants could be further distinguished by particular host reactions. Isolates from Ecuador, especially from the Oriente, a centre of diversity for Theobroma cacao, showed a range of pathogenicity comparable to that found amongst isolates from cultivated cocoa over a much wider area.

Dual culture ofCrinipellis perniciosa and potato callus

“…Investigations of the genetic variability of C-biotype isolates, as assessed by somatic compatibility reactions and other parameters [Griffith, 1989;McGeary and Wheeler, 1988;Wheeler and Mepsted, 1988], have shown that populations of this biotype generally consist of a small number of geographically widespread clones ( = somatic compatibility groupings). However, during a detailed study of the C-biotype in Amazonian Ecuador [Griffith, 1989], some local populations were found to consist of several sympatric clones.…”

Cacao yield in different planting densities

“…Presently, both the conditions are rarely fulfilled in cacao farming. The existence of pathogenic races different from C. perniciosa (Laker, 1990) along with the evidence of a differential behaviour of cacao clones to infection by these races (Wheeler and Mepsted, 1982) lead to a weakening of witches'-broom resistance as the cacao trees age. The degree of complexity of this matter was discussed by Dias et al (2000).…”

TEMPORAL GENETIC CHARACTERIZATION OF ISOLATES OF Moniliophthora perniciosa IN SOUTHEAST OF BAHIA, BRAZIL

“…Temporal stability of witches´ broom resistance is a major concern for intensively managed plantations, since pathogenic variation toward resistant families has been reported (Wheeler and Mepsted, 1988). Since the introduction of RAPD analysis (Williams et al, 1990), this technique has been proved to be a very powerful tool in genetic analysis and has been applied to a wide range of organisms.…”