Mapping of post-flowering drought resistance traits in grain sorghum: association between QTLs influencing premature senescence and maturity

Abstract

The identification of genetic factors underlying the complex responses of plants to drought stress provides a solid basis for improving drought resistance. The staygreen character in sorghum (Sorghum bicolor L. Moench) is a post-flowering drought resistance trait, which makes plants resistant to premature senescence under drought stress during the grainfilling stage. The objective of this study was to identify quantitative trait loci (QTLs) that control premature senescence and maturity traits, and to investigate their association under post-flowering drought stress in grain sorghum. A genetic linkage map was developed using a set of recombinant inbred lines (RILs) obtained from the cross B35 x Tx430, which were scored for 142 restriction fragment length polymorphism (RFLP) markers. The RILs and their parental lines were evaluated for post-flowering drought resistance and maturity in four environments. Simple interval mapping identified seven stay-green QTLs and two maturity QTLs. Three major stay-green QTLs (SGA, SGD and SGG) contributed to 42% of the phenotypic variability (LOD 9.0) and four minor QTLs (SGB, SGI. 1, SGI.2, and SGJ) significantly contributed to an additional 25% of the phenotypic variability in stay-green ratings. One maturity QTL (DFB) alone contributed to 40% of the phenotypic variability (LOD 10.0), while the second QTL (DFG) significantly contributed to an additional 17% of the phenotypic variability (LOD 4.9). Composite interval mapping confirmed the above results with an additional analysis of the QTL x Environment interaction. With heritability estimates of 0.72 for stay-green and 0.90 for maturity, the identified QTLs explained about 90% and 63% of genetic variability for stay-green and maturity traits, respectively. Although stay-green ratings were significantly correlated (r = 0.22, P< or =0.05) with maturity, six of the seven stay-green QTLs were independent of the QTLs influencing maturity. Similarly, one maturity QTL (DFB) was independent of the staygreen QTLs. One stay-green QTL (SGG), however, mapped in the vicinity of a maturity QTL (DFG), and all markers in the vicinity of the independent maturity QTL (DFB) were significantly (P< or =0.1) correlated with stay-green ratings, confounding the phenotyping of stay-green. The molecular genetic analysis of the QTLs influencing stay-green and maturity, together with the association between these two inversely related traits, provides a basis for further study of the underlying physiological mechanisms and demonstrates the possibility of improving drought resistance in plants by pyramiding the favorable QTLs.

QTL mapping and loci dissection for leaf epicuticular wax load and canopy temperature depression and their association with QTL for staygreen in Sorghum bicolor under stress

“…Collocation of QTL for staygreen and those for leaf wax and temperature depression Most Stg QTL are located on SBI-02 and SBI-05 (Xu et al 2000;Haussmann et al 2002;Subudhi et al 2000;Crasta et al 1999). In this study, only the staygreen QTL Stg 1, Stg2, Stg3 and Stg4 were considered as Stg loci (Xu et al 2000;Crasta et al 1999).…”

“…QTL peak position, 1-LOD widths, and the proportion of phenotypic variance explained were extracted from the plots. All QTL were overlaid on the Stg QTL positions previously published (Crasta et al 1999;Subudhi et al 2000;Xu et al 2000) for the same mapping population. These previously mapped Stg loci were derived from a visual phenotypic rating on a to 5 scale.…”

“…In cereal crops like grain sorghum, the staygreen trait has traditionally been defined as the ability of a plant to maintain active photosynthetic processes under water deficit, especially post anthesis (Crasta et al 1999). When defined in terms of green leaf area, staygreen has been scored as a leaf death count (Xu et al 2000) and more recently, leaf area under decline (LAUD) (Kumari et al 2007), compared to a reference genotype (Thomas and Howarth 2000).…”

Stay-green expression in early generation sorghum [Sorghum bicolor (L.) Moench] QTL introgression lines

“…It has a low grain yield under the conditions of this experiment, due to its short plant height, small panicle size, and low grain number. A number of stay-green QTLs have been identiWed by diVerent research groups based on RIL populations derived from crosses involving this line or its derivatives (Tuinstra et al 1996;Crasta et al 1999;Xu et al 2000b;Subudhi et al 2000;Sanchez et al 2002). The recurrent parent, R 16, is a released, high yielding but very senescent, post-rainy (rabi) season variety.…”

“…The trait is likely to be more easily manipulated using a marker-assisted breeding approach, using as selection criteria speciWc alleles at molecular loci linked to genomic regions contributing to the stay-green trait (i.e., quantitative trait loci = QTLs), identiWed in carefully managed, replicated, multi-environment tests. The work of diVerent groups has led to a better understanding of the inheritance of stay-green (Walulu et al 1994;van Oosterom et al 1996;Tuinstra et al 1997), to the mapping of QTLs associated with postXowering drought tolerance in sorghum (Tuinstra et al 1996(Tuinstra et al , 1998Crasta et al 1999;Tao et al 2000;Xu et al 2000b;Subudhi et al 2000;Kebede et al 2001;Sanchez et al 2002;Haussmann et al 2002) and identiWcation of markers linked to these QTLs (Hash et al 2003;Harris et al 2007).…”