Abstract
Most Agropyron Gaertn. species are excellent sources of forage. The derivative lines of wheat-Agropyron cristatum show elite agronomic traits, and some are valuable for wheat breeding. The species of Agropyron Gaertn. was mainly recognized by the spike morphology in traditional taxon. Six traits, including spike length (SL), ear stem length (ESL), the second internodes length (SIL), spikelet number per spike (SNS), floret number per spikelet (FNS), and grain number per spikelet (GNS), are vital to morphology studies and also influences the forage crop yield. To elucidate the genetic basis of spike and stem traits, a quantitative trait locus (QTL) analysis was conducted in a cross-pollinated (CP) hybrid population derived from a cross between two diverse parents, Agropyron mongolicum Keng Z2098 and A. cristatum (L.) Gaertn. Z1842, evaluated across three ecotopes (Langfang, Changli, and Guyuan of Hebei, China) over 3 years (from 2014 to 2016). Construction of a high-density linkage map was based on 1,023 single-nucleotide polymorphism (SNP) markers, covering 907.8 cM of the whole Agropyron genome. A total of 306 QTLs with single QTL in different environments explaining 0.07–33.21% of the phenotypic variation were detected for study traits. Seven major-effect QTLs were identified, including one for ESL on chromosome 3, one for SIL on chromosome 5, three for SL (two on chromosome 2 and one on chromosome 4), and two for SNS on chromosomes 3 and 7. Also, seven stable QTLs, including four for ESL, one for SL, one for GNS, and one for FNS, were mainly mapped on chromosomes 2, 3, 4, 5, and 7, respectively, elucidating 0.25–14.98% of the phenotypic variations. On the use of Agropyron CP hybrid population to identify QTL determining spike and stem traits for the first time, these QTLs for six traits would provide a theoretical reference for the molecular marker-assisted selection in the improvement of forage and cereal crop species.
Highlights
Agropyron Gaertn. is an important wild relative of wheat that has the genome of P: diploid, PP, 2n = 2x = 14; tetraploid, PPPP, 2n = 4x = 28; and hexaploid, PPPPPP, 2n = 6x = 42 (Dewey, 1984; Fordlloyd et al, 2011)
The parents and CP hybrid population of Agropyron had a significant difference in spike morphology (Figure 1)
The parents showed a significant variation in three different environments, and the average of CP hybrid population for most of traits was closer to the female than the male (Table 1; FIGURE 1 | Comparison of the morphology of the parents (A,B) and the F1 hybrid plants of Z2098/Z1842 (C)
Summary
Agropyron species possess a lot of useful characteristics, such as the tolerance to drought (Asay and Johnson, 1990) and cold, resistance to diseases (Lu et al, 2015), and high yield traits (Dong et al, 1992) It is a quality forage for grassland improvement and a valuable genetic resource for wheat. A. mongolicum Keng, a unique species found in China, is mainly distributed in Shaanxi, Ningxia, Inner Mongolia, Gansu, Shanxi, and other areas (Guo, 1987). Both A. cristatum and A. mongolicum are diploids, but the two are very different in general morphology (Dewey, 1981, 1984). A. desertorum (Fisch ex Link) Schlut, A. mongolicum, and A. michnoi Roshev should be offspring species of A. cristatum sharing the same basic genome from the counterpart based on SSR analysis (Che et al, 2015)
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