Identifying heterotic groups and testers for hybrid development in early maturing yellow maize (Zea mays) for sub‐Saharan Africa

Abstract

Identification of heterotic groups and efficient testers, which are important prerequisites for the development of outstanding hybrids, has been a major challenge to its success, especially for early and extra‐early germplasm. This study was carried out to (a) identify the most efficient heterotic grouping method for classifying a set of inbred lines and (b) determine the efficiency of testers in classifying inbred lines into heterotic groups. A total of 205 hybrids obtained by crossing 41 inbred lines with five standard testers were evaluated together with five hybrid checks under drought, low soil nitrogen (N), Striga ‐infested and optimal environments in Nigeria between 2014 and 2016. The heterotic group's specific and general combining ability (HSGCA) method was more effective in classifying the inbred lines into heterotic groups. Testers TZEI 17 and TZEI 23 were the most efficient across environments and could be invaluable for classifying other lines into heterotic groups and assessing combining ability of maize inbreds. In addition, these testers and heterotic groups represent an invaluable resource for development of outstanding hybrids in sub‐Saharan Africa (SSA).

Classifying highland quality protein maize in bred lines into heterotic groups

“…The best classification method was identified based on the breeding efficiency proposed by Fan et al (2009) and modified by Badu-Apraku et al (2016). The equation for estimating the breeding efficiency is as shown below according to Annor et al (2020):…”

“…The magnitude of the combining ability effect plays a crucial role in heterotic grouping, since it indicates the types of gene action as a preliminary indicator of heterotic expression (Singode et al, 2017). Maximum heterosis can be exploited if the breeding program uses inbred lines having significant positive GCA effect for grain yield and classified in opposing heterotic group (Annor et al, 2020). Phenotypic descriptors and molecular markers have been widely used in crop diversity studies to measure genetic distances (Darvishzadeh, 2012).…”

Transcriptome Reveals Allele Contribution to Heterosis in Maize

“…The aggregation of favorable alleles from different parents in the hybrids can exhibit much greater effects and may result in elite varieties ( Cai et al, 2014 ). At present, intervarietal hybrid advantage is the main technical term used to describe unknown underlying mechanism(s) responsible for superior hybrid maize characteristics, with few mechanistic clues obtained from past studies that focused on maize germplasm-associated heterosis groups and patterns ( Reif et al, 2003 ; Aguiar et al, 2008 ; Zhang et al, 2018 ; Annor et al, 2020 ). Nevertheless, early maize varieties cultivated in China possessed limited genetic diversity that has hindered attempts to substantially increase hybrid maize yields in recent decades.…”

Improved methods of predicting genetic merit in plant breeding programs using linear mixed models

“…An important requirement of any successful hybrid breeding programme is the availability of efficient testers, which could effectively discriminate and classify inbred lines into appropriate heterotic groups for the development of high-yielding hybrids, see for example Dudley et al (1991), Melchinger and Gumber (1998), Lee and Tollenaar (2007), Annor et al (2020) and others. Crosses need to be made from inbreds that come from large heterotic groups and the number of possible crosses is the product of the number of inbreds within each heterotic group.…”

“…An effective tester for the early stages of hybrid breeding programs should be able to rank inbred lines correctly for performance in hybrid combinations and increase the differences between testcrosses (relative to standard to standard errors) for efficient discrimination (Annor et al, 2020). A good tester should have the capacity to reveal high genetic variance between hybrids but must also be representative of the heterotic group in order to make effective selections.…”