Registration of 38 Maize ( Zea mays L.) Breeding Populations Adapted to Short‐Season Environments

The 38 maize (Zea mays L.) populations described herein (Reg. no. GP-512–GP-549, PI613059–PI613096) are the result of over 30 yr of population development and improvement by the University of Guelph corn breeding program and were released by the University of Guelph in October 1999 (Table 1). They are adapted to short-season environments [,2800 Ontario Crop Heat Units (OCHU) (Brown and Bootsma, 1993)] [Note that 2800 OCHUs » 95-d relative maturity (RM) rating » 350 FAO rating » 2150 growing degree days (GDDs)]. The populations encompass 24 distinct genetic backgrounds, most of which, based on their initial composition, would be expected to represent extensive genetic diversity. Seven of the 38 populations have not undergone recurrent selection, i.e., are cycle 0 (C0) populations, although three (CG-SynAC0, CG-SynBC0, and CG-Syn C C0) underwent mild mass selection during their development. For 21 of the remaining 31 populations, various recurrent selection procedures were employed including selfed progeny (S), half-sib (HS), reciprocal recurrent selection (RRS), or combined S and RRS (COM) (Table 1). Selection was based on a performance index (PI) of grain yield/grainmoisture which, beginning in the 1980s, included an adjustment for standability (Stojxen and Kannenberg, 1994), although standability per se was also a selection criterion during the early years of the program as well. Visual selection of individual plants and lines was practiced during the development of each cycle. Depending on the response of the germplasm to the environmental conditions during a particular growing season, the number of lines tested per cycle varied from 37 to 100 and the number of selected genotypes to recombine to form the next cycle varied from eight to 30. Generally, higher numbers of lines were tested and recombined from the 1980s on. The objective was to have a selection intensity of around 20%. Also, beginning in the 1980s, the S and RRS procedures were changed to testing of S2 lines instead of S1 lines, and in addition, two generations of recombination were done to establish the subsequent cycle of the population. The half-sib procedure also was changing during this time from modified ear-to-row (ME) (Lonnquist, 1964) to half-sib progeny selection (HS) (Compton andComstock, 1976). Detailed examples of the Guelph selection procedures can be found in Stojxen and Kannenberg (1994) and Sullivan and Kannenberg (1987). The relative combining abilities, stabilities and performances of 12 of the populations are presented in Doersken et al. (2003) and Lee et al. (2003). The remaining 10 of the 38 populations were identified as unadapted germplasm with potential for short-season breeding purposes, and depending on relative maturity, were either subjected directly to mass selection (M) for earliness (PI613093– PI613096), or in the case of the least adapted populations, crossed to a very early maturing source [CG-SynA-NL (described below)] and then mass selected for earliness (PI613087– PI613092) (Table 1). For most of these populations, 60 early flowering segregants of good agronomic type were sib-mated out of a population of approximately 200 plants during each cycle of selection. Seed for these releases was produced through sib-mating the most recent completed cycle of the population. Twenty row nursery blocks were planted (15 plants per row). Approximately 100 to 120 ears were pollinated by bulking pollen from the first ten rows and pollinating ears in the other ten rows reciprocally.