Improvement of early-season cold tolerance in sorghum by introgression of favorable genes from Chinese kaoliang germplasm

Joseph Edward Knoll, Purdue University

Abstract

Cold temperatures in the early growing season are a major limitation to grain sorghum (Sorghum bicolor (L.) Moench) production in temperate regions of the United States. Kaoliang sorghum landraces from China represent a possible source of genes for improvement of early-season cold tolerance in sorghum. A collection of 139 Chinese sorghum accessions was evaluated in the field and growth chamber for early-season traits under cold stress conditions. Field plantings were also evaluated for flowering time and mature plant height. Several accessions were identified with superior early-season performance in both the field and growth chamber. A range of bloom times and mature plant heights was observed in the collection, though most accessions bloomed relatively early and were very tall. The same Chinese sorghum accessions were also genotyped using simple sequence repeat (SSR) markers to characterize the genetic diversity present within the collection. Genetic distance analysis revealed an average pairwise similarity of 61.7%. Subsequent clustering analysis showed that accessions with good early-season cold tolerance were evenly scattered among the clusters. The results of both the field evaluation and genetic diversity analysis indicate the presence of significant variability within the kaoliang germplasm collection. To assess the inheritance of early-season cold tolerance, a recombinant inbred (RI) population was created by crossing ‘Shan Qui Red’ (SQR), a cold-tolerant kaoliang, with SRN39, a cold-sensitive African caudatum. This population was utilized in several studies. To evaluate the field performance of kaoliang-derived sorghum under different planting conditions, SQR, SRN39, 40 recombinant inbred lines, and their 42 hybrids with ‘Wheatland’ (a commercial seed parent) were planted in replicated field trials for three consecutive seasons under early and later plantings. Seedling performance was highly influenced by weather conditions. Early planting was generally associated with reduced emergence and seedling vigor, but hybrids tended to show better emergence and vigor than inbreds, as expected. Some correlations between the performance of inbred lines and of their hybrids with Wheatland were observed. In the early plantings of 2001 and 2003, final stand counts were significantly correlated between inbreds and hybrids. Days to half-bloom and mature plant height were both highly correlated between inbreds and hybrids, but yield was only moderately correlated in two of five plantings. Using this same RI population, quantitative trait locus (QTL) analysis was conducted to identify genetic markers linked to germination in the growth chamber, field emergence, and field seedling vigor under varying conditions. QTL were identified by single marker analysis, simple interval mapping (SIM), and composite interval mapping (CIM). Two QTL for germination were identified: one on linkage group SBI-03a, derived from SRN39, was significant under cold and optimal temperatures. The other, on group SBI-07b, showed greater significance under cold temperatures and was contributed by SQR. A region of linkage group SBI-01a, derived from SQR, showed strong associations with seedling emergence and seedling vigor scores under early and late field plantings. A QTL for both early and late emergence was identified by CIM on group SBI-02 which favored the SRN39 allele. SIM identified a QTL for early vigor on SBI-04 favoring the SQR genotype. Three SSR markers (Xtxp43, Xtxp51, and Xtxp211), representing three major QTL for emergence and vigor in the field, were chosen for further testing in two segregating populations (Tx2794 × SQR F2, and Wheatland × SQR BC1F2) to determine their effects in different genetic backgrounds. F3 or BC1F 3 families from these populations carrying varying numbers of QTL markers were planted in replicated field trials in two successive growing seasons, and were tested for early-season performance and agronomic traits. Statistical analysis confirmed the effects of these markers in these new populations, thus validating their utility as tools for selection for early-season cold tolerance in sorghum.

Degree

Ph.D.

Advisors

Ejeta, Purdue University.

Subject Area

Agronomy|Genetics

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