Genetic analysis of apomixis in Citrus and Poncirus by molecular markers |
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Authors: | R García M J Asíns J Forner E A Carbonell |
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Institution: | (1) Instituto Valenciano de Investigaciones Agrarias (IVIA), Apartado Oficial, 46113 Moncada (Valencia), Spain e-mail: mjasins@ivia.es Fax: +34-961390240, ES |
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Abstract: | Propagation of citrus rootstocks depends upon the production of clonal plants from nucellar seedlings. This makes apomixis
one of the host important traits in breeding programs for citrus rootstocks. The genetic control of apomixis was studied in
a 50-tree progeny derived from the cross C. volkameriana×P. trifoliata using 69 molecular markers and bulked segregant analysis. The proportion of nucellar seedlings was estimated by isoenzymatic
analysis of 25 seedlings per tree for 2 consecutive years. The type of embryony (polyembryonic versus monoembryonic seeds)
was also determined for fruit-yielding trees. Separate genetic maps for each parental species were developed. The integration
and comparison of these maps could be accomplished using common multiallelic segregant loci. Differences in gene synteny between
the two species-specific genetic maps were shown. Important distortions in the segregation of markers at several genomic regions,
some of them also involving differences in the C-methylation pattern, have been observed, especially for the pollen parent.
Analysis of quantitative trait loci (QTLs) revealed the presence of six genomic positions (two in P. trifoliata and four in C. volkameriana) contributing individually up to 24% of the total variation for apomixis. Within the same species, QTLs with positive and
negative allele effects were present, even in the same linkage group. One of the markers associated to apomixis (Apo2) is also associated to embryony type. Therefore, the genetic control of apomictic reproduction found in citrus (nucellar
embryony) is quite complex compared to what has been reported for gametophytic apomixis. Molecular markers linked to QTLs
governing apomixis will be useful to assist selection of future apomictic rootstocks for citrus varieties.
Received: 30 November 1998 / Accepted: 28 December 1998 |
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Keywords: | Linkage groups Non-inbred species QTLs Polyembryony Nucellar embryony Fruit breeding |
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