Hallauer’s Tusón: a decade of selection for tropical-to-temperate phenological adaptation in maize

Abstract

Crop species exhibit an astounding capacity for environmental adaptation, but genetic bottlenecks resulting from intense selection for adaptation and productivity can lead to a genetically vulnerable crop. Improving the genetic resiliency of temperate maize depends upon the use of tropical germplasm, which harbors a rich source of natural allelic diversity. Here, the adaptation process was studied in a tropical maize population subjected to 10 recurrent generations of directional selection for early flowering in a single temperate environment in Iowa, USA. We evaluated the response to this selection across a geographical range spanning from 43.05°(WI) to 18.00°(PR) latitude. The capacity for an all-tropical maize population to become adapted to a temperate environment was revealed in a marked fashion: on average, families from generation 10 flowered 20 days earlier than families in generation 0, with a nine-day separation between the latest generation 10 family and the earliest generation 0 family. Results suggest that adaptation was primarily due to selection on genetic main effects tailored to temperature-dependent plasticity in flowering time. Genotype-by-environment interactions represented a relatively small component of the phenotypic variation in flowering time, but were sufficient to produce a signature of localized adaptation that radiated latitudinally, in partial association with daylength and temperature, from the original location of selection. Furthermore, the original population exhibited a maladaptive syndrome including excessive ear and plant heights along with later flowering; this was reduced in frequency by selection for flowering time.

Registration of BS39 Maize Germplasm

“…Exotic accessions of Tusón germplasm were provided by Major Goodman, North Carolina State University, Raleigh, NC. According to Teixeira et al (2015), the five accessions were PI 449556 and PI 583912 (collected from Brazil), NSL 283507 (collected from Cuba), PI 487940 (tentatively) (collected from Ecuador), and PI 498583 (collected from Guatemala). However, caution should be considered for the identifications of PI 487940 and PI 498583.…”

“…Primary emphasis was given to time of silk expression, but attention also was given to ear height, root and stalk strength, and incidence of Ustilago maydis infection. The original work described here supplements the partial description of population development presented in Teixeira et al (2015).…”

Phenology and Biomass Production of Adapted and Non‐Adapted Tropical Corn Populations in Central Iowa

“…Tuxpeño, Suwan, and Tuson were the tropical corn populations chosen based on their importance in tropical corn breeding programs (Hallauer, 1999;Teixeira et al, 2015). The adapted strains had five cycles of selection for adaptation (C5), and the nonadapted strains had one (C1).…”

“…Th e potential of tropical corn has been evaluated mainly for grain production (King et al, 1972;Oyervides-Garcia et al, 1985;Edmeades et al, 1993;Pulam, 2011). Due to lower grain yields compared to U.S. Corn Belt hybrids, tropical populations have been adapted to be a better source of germplasm for U.S. Corn Belt conditions (Hallauer, 1999;Teixeira et al, 2015).…”

Development of a multiple-hybrid population for genome-wide association studies: theoretical consideration and genetic mapping of flowering traits in maize

“…Improving the adaptability of temperate maize largely depends upon the use of tropical maize germplasm, which hosts rich sources of favorable genes and alleles67, particularly for tolerance to abiotic and biotic stresses. A shortcut to the favorable alleles hosting in tropical maize is to develop temperate-tropical hybrids.…”