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C.M. Ronning, R.J. Schnell and D.N. Kuhn

RAPD markers have been used successfully in genetic analysis of several crop plants. This method poses difficulties with a highly heterozygous species such as Theobroma cacao because of the dominant phenotypic expression of bands. A backcross family derived from ctultivars Catongo and Pound 12 was analyzed to determine the efficacy of RAPD markers in analyzing cacao populations. A preliminary screen of the parents and the F1 plant used as the backcross parent was conducted with 180 RAPD primers; of these, 26% were polymorphic and reproducible and produced 104 storable loci. Genomic DNA from 54 individuals of the backcross population was then amplified with these primers; 68.3 % of the loci segregated as expected in a Mendelian fashion. Separation of RAPD fragments on acrylamide revealed an additional polymorphic locus from one primer that was indistinguishable on agarose. The results demonstrated that RAPD markers can be used to study the cacao genome.

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C.M. Ronning, R.J. Schnell and S. Gazit

The native American genus Annona contains many species that are cultivated for their edible fruit, including the custard apple (A. reticuluta L.), soursop (A. muricata L.), cherimoya (A. cherimola L.), sugar apple (A. squamosa L.), and interspecific hybrids, the atemoyas. RAPD analysis of A. cherimola. `Campa' and `Jete,' A. squamosa `Lessard,' and the atemoyas `Ubranitzki,' `Malali,' and `Kaspi' resulted in very distinctive patterns, indicating that RAPD markers, may be an efficient method of fingerprinting genotypes within and between Annona species. All 15 primers used generated repeatable, polymorphic patterns. An F1 population of `Jete' × `Lessard' was analyzed to determine the inheritance of the RAPD banding patterns. Fifty-two polymorphic loci were identified, which segregated in an expected Mendelian fashion.

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C.M. Ronning, D.M. Harkins, R.J. Schnell and L.H. Purdy

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.

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C.M. Ronning, S.P. Kowalski, L.L. Sanford and J.R. Stommel

The Colorado potato beetle is a serious pest of the cultivated potato. Natural resistance has been found in a few wild species, including Solanum chacoense Bitter, in which resistance is attributed to the presence of foliar specific leptine glycoalkaloids. Production and accumulation of these compounds within S. chacoense varies widely and appears to be inherited in a quantitative fashion, but high leptine producing clones occur rarely. In the present study, 15 different accessions from various locations and altitudes of origination were analyzed for foliar glycoalkaloid content in order to determine the frequency and distribution of genes for leptine production/accumulation, and to see if we could find a center, or core, of leptine production. Leptines were detected in eight of the 15 accessions, and the amounts within each accession varied widely, but none of the individuals produced high amounts of leptine (defined as greater than 62% of total glycoalkaloids). All of the leptine-containing accessions originated from western Argentina. There was no relationship between elevational level and leptine, but there was a negative trend with total glycoalkaloids and elevation; this was due to levels of solanine and chaconine decreasing with increasing elevation. In addition, nine unidentified glycoalkaloids were detected, in very high proportions in some individuals and accessions. AFLP marker frequency and diversity were used to compare subpopulations of these accessions. AFLP markers revealed substantial diversity among clones. The relationship of marker distribution to glycoalkaloid content is discussed. The results raise interesting questions about glycoalkaloid biosynthesis and inheritance, and point the direction for new avenues of leptine and glycoalkaloid research.