Use of Genomic Estimated Breeding Values Results in Rapid Genetic Gains for Drought Tolerance in Maize

Abstract

More than 80% of the 19 million ha of maize (Zea mays L.) in tropical Asia is rainfed and prone to drought. The breeding methods for improving drought tolerance (DT), including genomic selection (GS), are geared to increase the frequency of favorable alleles. Two biparental populations (CIMMYTAsia Population 1 [CAP1] and CAP2) were generated by crossing elite Asian-adapted yellow inbreds (CML470 and VL1012767) with an African white drought-tolerant line, CML444. Marker effects of polymorphic single-nucleotide polymorphisms (SNPs) were determined from testcross (TC) performance of F 2:3 families under drought and optimal conditions. Cycle 1 (C1) was formed by recombining the top 10% of the F 2:3 families based on TC data. Subsequently, (i) C2 [PerSe_PS] was derived by recombining those C1 plants that exhibited superior per se phenotypes (phenotype-only selection), and (ii) C2[TC-GS] was derived by recombining a second set of C1 plants with high genomic estimated breeding values (GEBVs) derived from TC phenotypes of F 2:3 families (marker-only selection). All the generations and their top crosses to testers were evaluated under drought and optimal conditions. Per se grain yields (GYs) of C2 [PerSe_PS] and that of C2[TC-GS] were 23 to 39 and 31 to 53% better, respectively, than that of the corresponding F 2 population. The C2[TC-GS] populations showed superiority of 10 to 20% over C2[PerSe-PS] of respective populations. Top crosses of C2[TC-GS] showed 4 to 43% superiority of GY over that of C2[PerSe_PS] of respective populations. Thus, GEBV-enabled selection of superior phenotypes (without the target stress) resulted in rapid genetic gains for DT.

Effect of Trait Heritability, Training Population Size and Marker Density on Genomic Prediction Accuracy Estimation in 22 bi-parental Tropical Maize Populations

“…Using recombinant inbred lines derived from a cross between B73 and Mo17, Massman et al ( 2013 ) showed that GS produced from 14 to 50% higher genetic gains for stover and grain yield than marker assisted recurrent selection for several traits in a maize biparental population. This result was then verified in tropical maize (Beyene et al, 2015 ; Vivek et al, 2017 ). Beyene et al ( 2015 ) found that the average genetic gain per year across eight tropical maize populations of GS was three times higher than that of pedigree based phenotypic selection in drought stress conditions.…”

Genomic Selection in Plant Breeding: Methods, Models, and Perspectives

“…Another example of genetic gains from rapid-cycle GS on CIMMYT maize is two biparental maize populations (F 2:3 ) from Asia (CAP1 and CAP2) that were developed and evaluated for testcross performance under drought and optimal conditions [72]. The genetic gains per year for PS versus GS in drought environments were 0.067 t/ha versus 0.124 t/ha, respectively, for CAP1, and 0.076 t/ha versus 0.104 t/ha, respectively, for CAP2.…”

Gains through selection for grain yield in a winter wheat breeding program

“…In another study, negative GEBV for yield were observed for synthetic hexaploid spring bread wheat lines evaluated across heat and irrigated environments [36]. Selection for drought tolerance in maize using GEBV, in contrast, has resulted in rapid genetic gains and positive selection responses through using molecular markers associated with yield under drought stress [37]. While selecting lines based on GEBV alone should be considered with caution, the implementation of genomic selection in breeding programs should help increase the rate of genetic gains through a faster breeding cycle, higher selection intensity, and efficiency of genomic prediction approaches in integrating novel genetic material in wide-crosses and pre-breeding programs [38].…”