Plant, Animal & Microbe Genomes X Conference Plant, Animal & Microbe Genomes X ConferenceJanuary 12-16, 2002
Town & Country Convention Center
San Diego, CA
Workshop: Apomixis
Uniformity of rootstock genotype is essential for reliable citrus performance following budding and orchard establishment. Therefore, one of the most important traits within the breeding programs for citrus rootstock is apomictic reproduction by seed. Garcia et al. (1999) reported the first genetic study of polyembryony and apomixis using molecular marker analysis in a cross between two diploid (2n=18) polyembryonic species (Citrus volkameriana and Poncirus trifoliata), differing in the degree of polyembryony. Since this study presented several possible limitations, a new marker analysis of apomixis has been carried out trying to overcome them by using the Kruskal-Wallis statistical methodology, suitable for non-normal distributed traits, and increasing the number of polymorphic markers up to 73 in P. trifoliata and 97 in C. volkameriana. New markers are 43 SSR loci and 11 IRAPs. Also several changes of variable were considered. Comparing to QTLs previously reported, only few changes are found. As expected from the fact of analysing more markers, two new Apo QTLs are detected in C. volkameriana linkage maps. The strongest effect on apomixis corresponds to Apo 2 (a C. volkameriana QTL), also related to monoembryony/polyembryony. Comparing the QTLs detected in P. trifoliata and C. volkameriana, more QTLs are detected and at higher significance levels when studying C. volkameriana alleles than when studying the segregation of P. trifoliata alleles. The parent with the lowest apomixis value is contributing much more to the genetic variance than the parent with the highest apomixis value. Considering all results and the accumulated knowledge on monoembryony/polyembryony in citrus, an hypothesis on the regulation of apomixis in this genus is formulated.