ARS | Publication request: FREQUENCY OF OFF-TYPE PROGENY AMONG THE ORIGINAL ICS1 X SCA6 RECIPROCAL FAMILIES MADE FOR SELECTION FOR DISEASE RESISTANCE IN TRINIDAD

Submitted to: Ingenic Newsletter
Publication Type: Trade Journal
Publication Acceptance Date: July 8, 2004
Publication Date: September 1, 2004
Citation: Schnell II, R.J., Heath, M., Johnson, E.S., Brown, J.S., Olano, C.T., Motamayor, J. 2004. Frequency of off-type progeny among the original ICS1 x SCA6 reciprocal families made for selection for disease resistance in Trinidad. Ingenic Newsletter. 9:34-39.

Interpretive Summary: Cacao breeding has not been very successful. One of the major reasons for this is the misidentification of individuals in breeding trials. While investigating the nature of disease resistance in a historical family in Trinidad (ICS1 x SCA6) and its reciprocal, we discovered a number of misidentified parents and progeny. We were able to do this using DNA markers known as microsatellites. We used 33 different microsatellite markers to fingerprint the parents and all of the progeny and discovered that approximately 30% of the progeny were misidentified. Some of the misidentification arose from pollen contamination during controlled pollination and some resulted from errors in labeling in the nursery. Correctly identifying full-sib families is an important step in the estimation of heritabilities, predictions of genetic gain, and identification of superior parents. As demonstrated in this study, pollen contamination and mislabeling of plant families has been a serious problem in cacao improvement programs and in germplasm management.

Technical Abstract: The genetic integrity of a reciprocal full-sib family of Theobroma cacao L. was investigated using microsatellite markers. Of the 186 putative full-sibs analyzed, 27.9 % of the trees were off-types based on 33 microsatellite loci. Significant differences were observed between the frequency of off-types in the reciprocal families. In the SCA6 x ICS1 family off-types accounted for 14.0% of the seedlings. Among these, two were maternal half sibs (MHS) that most likely arose from pollen contamination during pollination, while 13 individuals were completely unrelated. The ICS1 x SCA6 family was more problematic with 46.8% of the seedlings classified as off-types. Of these, six were selfs of ICS1, 13 were MHS, and 18 were unrelated. The six selfs and 13 MHS most likely arose from pollen contamination. The differences in frequency of offtype seedlings among the two families is striking, with only 2 of 94 (2.1%) for SCA6 x ICS1 vs. 19 of 61 (31.1%) for ICS1 x SCA6. Fifteen clones known to have been used in breeding during the same time period as the crosses being studied were produced were evaluated as parents to determine if a mistake in labeling during pollination occurred. It was not possible to identify any additional parents with certainty from the analysis.