Cacao is an important crop in the tropics, but its breeding has been hampered by a lack of understanding of its genetics. One result of this has been the introduction of “hybrid” trees which did not perform predictably under various environmental conditions. We are studying the inheritance of isoenzyme, RFLP, and Random Amplified Polymorphic DNA (RAPD™) markers in order to estimate the genetic relationships among and between populations. Our objectives include determining if any linkage exists between these molecular markers and witches' broom (Crinipellis perniciosa) resistance, a major disease of cacao.
C.M. Ronning, D.M. Harkins, R.J. Schnell and L.H. Purdy
R.J. Schnell, R.J. Knight, D.M. Harkins and Gary Zill
The ability to eliminate zygotic seedlings from the polyembryonic mango (Mangifera indica L.) rootstock `Turpentine' by visual roguing was investigated. Four selected populations, A) randomly selected plants, B) plants selected as off-types, C) seedlings that were of `Turpentine' phenotype, and D) seeds where a single seedling emerged, were examined using electrophoretic analysis and five enzyme systems. Significant differences (χ2 = 39.63, P< 0.001) were found among the four categories, with 28% of the random, 66% of the off-type, 10% of the true-to-type, and 54% of the monoembryonic seedlings being zygotic. These data indicate that visual selection for trueness-to-type and roguing for off-types is useful in reducing the frequency of zygotic seedlings among `Turpentine' rootstock plants.