Cold tolerance in field conditions, its inheritance, agronomic performance and genetic structure of maize lines divergently selected for germination at low temperature

Abstract

Given the importance of early cold tolerance in maize (Zea mays L.), we previously conducted a divergent selection for low (L) and high (H) cold tolerance at germination. The source population was the F 2 of B73 9 IABO78 single cross. Selection was first conducted as recurrent selection (four cycles) and then in inbreeding (three generations). Ten lines were finally selected for L and ten for H; these lines were then evaluated to investigate: (i) their field cold tolerance in the early autotrophic phase and the relationship with the cold tolerance expressed at emergence and in the heterotrophic phase; (ii) the inheritance of these cold tolerance traits; (iii) their agronomic performance as lines per se and as crosses; (iv) their SNP-based genetic characterization. For all cold tolerance traits, the H group of lines was superior to the L group; selection responses were often symmetric, suggesting the prevalence of additive effects. The relationship among cold tolerance traits was appreciable, suggesting a common genetic basis. Differences among testcrosses were largely due to general combining ability effects and the relationship between line per se and testcross performance was high, confirming the prevalence of additive effects. Correlated responses were also obtained for agronomic traits, the H lines being superior to L lines both per se and as crosses. For SNP-marker loci, the B73 allelic frequency was greater in the H group (61.7 %) than in L group (39.7 %). Across field trials, an H line excelled for all traits, thus proving to deserve further investigations.

Registration of Maize Inbred Line Bo23 with High Cold Tolerance and Agronomic Performance for Early Sowing

“…The parent B73, on the other hand, exhibited poor GY performance, indicative of its poor response to early sowing growing conditions. Such poor performance under early sowing conditions was also revealed by the line's slow growth to flowering; in the present study, B73 flowered 8 d later than the average of the other four lines, whereas in the agronomic trials sown approximately 40 d later by Frascaroli and Landi (2016)—thus, with no cold stress—the flowering delay was less, 3 to 4 d. Moreover, B73's GY performance was worsened by its susceptibility to Barley yellow dwarf virus . With respect to other characteristics (herein not presented), the percentage of standing plants (i.e., neither root‐ nor stalk‐lodged) exhibited in three trials by Bo23 was slightly lower than that of B73 (92.7 vs. 97.0%, P ≤ 0.05).…”

“…Concurrently, the S 3:4 to S 7:8 lines were subjected to a 5‐yr investigation aimed at studying the responses to selection for cold tolerance in the germinator and in the field as early sowing, as well as for several agronomic traits. Responses were appreciable for DG and for most of the other investigated traits (Frascaroli and Landi, 2013, 2016). Throughout the investigation, the line H102, henceforth indicated as Bo23, always exhibited excellent results, thus warranting further evaluations for cold tolerance and agronomic traits with early sowing.…”

“…Bo23 and other lines used as checks were tested both per se and in hybrid combination. The check lines for the evaluation per se were the divergently selected H101, H104, L2, L5, and L14, chosen on basis of their high or low cold tolerance level (Frascaroli and Landi, 2016); the two parental inbreds B73 and IABO78; and the two European public inbred lines D23 and EA2087, chosen because of their well‐proven high level of cold tolerance (Bhosale et al, 2007; Revilla et al 2000). These 10 lines were evaluated for 2 yr (2014 and 2015); selected L and H lines were at the S 7:8 and S 8:9 level, respectively.…”

“…Bo23 was tested for agronomic traits along with a restricted group of check lines, H101 and H104 (chosen because of their valuable agronomic performance in Frascaroli and Landi [2016]) and the two parental inbreds B73 and IABO78. These five lines were investigated both per se and in hybrid combination again with the single cross tester Mo17 × H99.…”

“…The inbred line IABO78 (unpublished) was derived from Italian germplasm, has flint kernel, and is characterized by an appreciable level of cold tolerance (Frascaroli and Landi, 2013); IABO78 has never previously been used in applied breeding. We evaluated direct and correlated responses (Frascaroli and Landi, 2013, 2016) and noted a line coded as H102 that showed excellent performance for both cold tolerance in the field and for agronomic traits (Frascaroli and Landi 2016). On the basis of these findings, we conducted further investigations into H102's characteristics expressed as an early‐sown crop.…”