The two lines were examined for RFLPs with 58 mapped clones in combination with three restriction enzymes, EcoRI, HindIII, and EcoRV. With EcoRI digests, 98.3% of the clones detected identical banding patterns for B14 and B14A; however, only 87.9% of the clones revealed identical patterns with HindIII digests of the two inbreds. Similar observations have been reported for other pairs of inbred lines isogenic for rust resistance (Beckman and Weck, MNL 62:107, 1988).
Nine RFLP clones detected polymorphisms between the two inbreds (Table 1). The clones have been mapped to chromosome one (3 clones), three (2), six (2), seven (1), and ten (1). The Rp1 locus has been mapped to the short arm of chromosome ten (Russell and Hooker, Crop Sci 2:477-480, 1965); however, RFLP clones used in the study did not detect differences between B14 and B14A in that region.
Table 1. RFLP clone-enzyme combinations
that detected differences between B14 and B14A.
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The presence of donor parent (or non-recurrent
parent) HindIII RFLP patterns at a level greater than theoretical
expectations may be attributable to several factors. The unexpected RFLP
patterns could be linked to donor chromosome segments selected during backcrossing;
possibly, they contain genes influencing the response to rust infection
or the segments contain genes which enhance the agronomic performance of
B14. Russell and Hooker (Crop Sci. 5:95-96, 1965) reported significant
differences for grain yield between B14 and B14A single-cross hybrids in
rust-free environments. Mutations in B14 or B14A seem to be an unlikely
source of the variation given the number of clones detecting polymorphisms.
Pollen or seed contamination cannot be eliminated as sources of the variation
until the donor parent has been examined for polymorphisms.
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