Association among sources of resistance to witches' broom disease for the increment of the level and durability of the character. In: Agrotrópica v. 24 n. 1 p. 27-30, 2012.

Abstract

After the witches’ broom introduction in the South of Bahia, the research structure already established and the knowledge on the resistance of the clone Scavina 6 allowed the promptly indication of new resistant varieties, but most of these varieties had only the Scavina clone as resistant ascendant. Therefore, the central element for the cocoa breeding program in Bahia, is the necessity of including, in the areas of cocoa cultivation, resistance factors different from the used until now and associating different resistance genes, to enlarge the durability of this resistance. In the search for this association of genes and increment in resistance durability and level, some trails were established in a Comstock II design, and, among them, one that was formed by the clones: Scavina 6, CAB 5003-23, Scavina 12, Moq 216, Ca 5, Chuao 120, ICS 1 and SPA 5, as maternal progenitors, and C. SUL 3, CEPEC 90, RB 36, CCN 34, Ma 16, Sgu 26, CC 10 and SIAL 70, as fathers (the clones CC10 and SIAL 70; ICS 1 and SPA are highly susceptible, while the others were selected as resistant). From these trials, considering only the progenies that include Scavina 6 as progenitor, it was verified significant differences among the descendants of the two clones pre-selected as susceptible (CC 10 and SIAL 70) and the descendants of all the clones pre-selected as resistant, for the total number brooms among the years 2001- 2008 (repeated measures analysis). The interaction between father and year was also significant, showing that the progenies have different tendencies through the years: the progenies for whose the only source of resistance was the clone Scavina 6 showed an increment of brooms much more accentuated that the ones verified for the progenies whose fathers were also resistant. These results, considering the evolution of the fungus verified in other studies, indicate that larger resistance durability was obtained and proves a higher level of resistance with the association of different sources of resistance. Plants selected in these and other progenies that associate different sources of resistance are being settled in regional clone trials.