Measurement of Genetic Diversity among Popular Commercial Corn Hybrids

Abstract

Genetic vulnerability of corn (Zea mays L.) has increased repeatedly since the growing of hybrid corn, single cross hybrids, and popular hybrids. We definite genetic vulnerability as the potential susceptibility of a crop to future attack by some biological or environment stress due to growing large numbers of a uniform biotype over large geographical areas. Genetic diversity, which usually decreases genetic vulnerability, has lacked a good method for measurement. The purpose of this study was to develop and test a method for measuring genetic diversity of corn and to assess genetic vulnerability in the U.S. Corn Belt by comparing genetic diversity of popular hybrids between two major and seed companies. Genetic diversity was estimated by the formula: GD = 1‐[(H‐C)/(H‐S)], where GD equals genetic diversity, H equals the average performance of the two hybrids, C equals the hybrid‐by‐hybrid cross, and S equals the average of the selfed hybrids. The method assumes heterosis is caused by some degree of dominance and epistasis is absent. A higher than average performing cross of two hybrids (less inbreeding depression) indicates more genetic diversity between the hybrids while lower than average performance of the cross (more inbreeding depression) indicates less diversity. Data were collected for grain yield, time to flower, grain moisture, and plant height on five popular hybrids from each of two major seed companies. Results for yield provided more precise estimates of GD than other performance traits measured. Genetic diversity averaged 0.74 and ranged from 0.17 to 1.37 and 0.28 to 1.12 among hybrids within companies. The GD estimate for the two most popular hybrids of 1985, 3732 and T1100 was 0.94. Our results help those needing a method to measure genetic diversity and should also encourage those concerned about genetic vulnerability in corn.

Changes in Pedigree Backgrounds of Pioneer Brand Maize Hybrids Widely Grown from 1930 to 1999

“…Degrees of pedigree relatedness are based on a possibly false assumption that founder lines are unrelated and “bottlenecks” that constrict flow of genetic diversity may not be apparent from observation of pedigree data. Nonetheless, studies of relationships among inbred lines of maize using pedigree data generally concur with results using molecular marker data including restriction fragment length polymorphisms (Smith et al, 1990; Bernardo, 1993; Bernardo et al, 1997), simple sequence repeats (Smith et al, 1997; Bernardo and Kahler, 2001; Lu and Bernardo, 2001), and heterosis data (Troyer et al, 1983, 1988; Paszkiewicz et al, 1986; Smith et al, 1987, 1990). Maize breeders regularly use pedigree data when developing breeding and genetic evaluation strategies.…”

Adaptedness and Heterosis in Corn and Mule Hybrids

“…A successful parent must have some degree of adaptedness to the area where the hybrid is grown. Genetic diversity values between two hybrids can be estimated by scaling their hybrid F1 (the cross of the two hybrids) yield between the average of their two F2 yields and the average of their two per se yields (Troyer et al, 1988). This requires about as much time and effort as evaluating five inbreds on one tester.…”

Simple sequence repeat (SSR) vs. sequence-related amplified polymorphism (SRAP) markers for Cynara cardunculus characterization

“…For this reason, a better knowledge of C. cardunculus genetics and variability is crucial in order to plan new breeding strategies, for efficient germplasm resources utilization and to maintain genetic diversity, which sustains long-term selection responses and reduces vulnerability (Sorrels and Wilson, 1997;Troyer et al, 1998;Jana, 1999).…”