RFLP diversity among P39 and four derivatives

--J. T. Gerdes and W. F. Tracy

Purdue 39 (P39) was the most widely used sweet corn inbred line in the 1930's and 1940's. This inbred is reported to be highly mutable, and a number of strains of P39 were previously identified. These strains are thought to be single gene mutations. Four such strains are C30 (a small mutant of P39 and the source of the rd gene), P39M94, P39M96, and IP39 (narrow grained mutant). These inbred strains all closely resemble P39 morphologically, even C30 which looks like a small P39 plant. All four of these inbred strains gained use in hybrid sweet corn production.

P39 and these four strains were subjected to RFLP analysis. Seventy-seven markers spread throughout the genome were scored. Thirty-two of the 77 markers showed differences from P39 for at least one strain. At 14 of these markers, two to all four strains differed from P39. Furthermore, three different alleles were seen at 7 markers among the inbreds. The four strains were compared to P39 and each other for similarity. The differences of the strains from P39 ranged from 9 markers (11.7%) for IP39 to 18 (23.4%) for P39M96 (Table 1). The strains differed from each other by as few as 5 markers (6.5%) for IP39-P39M94 to as many as 28 (36.4%) for C30-P39M96.

Table 1. Number of differences observed among P39 and four inbred strains derived from P39 at 77 RFLP markers.
  P39 C30 P39M94 P39M96 IP39
P39 -- 17 14 18 9
C30   -- 14 28 11
P39M94     -- 23 5
P39M96       -- 21

The exact cause of these differences is not known. Outcrossing is an unlikely explanation because of the strong morphological resemblance of these inbreds along with the historical references of instability. Also residual heterozygosity is not a likely candidate because as many as three alleles were seen at a number of markers. These results raise an interesting question on the origin of variability in maize. (The authors wish to thank the Agrigenetics RFLP Mapping Group for their assistance in RFLP data collection and analysis. Agrigenetics Corporation, Madison, WI.)

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors

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