Pyramided QTL underlying tolerance to Phytophthora root rot in mega-environments from soybean cultivars ‘Conrad’ and ‘Hefeng 25’

Abstract

Phytophthora root rot (PRR) of soybean (Glycine max (L.) Merr.) is the second most important cause of yield loss by disease in North America, surpassed only by soybean cyst nematode (Wrather et al. in Can J Plant Pathol 23:115-121, 2001). Tolerance can provide economically useful disease control, conditioning partial resistance of soybean to PRR. The aims of this study were to identify new quantitative trait loci (QTL) underlying tolerance to PRR, and to evaluate the effects of pyramided or stacked loci on the level of tolerance. A North American cultivar 'Conrad' (tolerant to PRR) was crossed with a northeastern China cultivar 'Hefeng 25' (tolerant to PRR). Through single-seed descent, 140 F2:5 and F2:6 recombinant inbred lines were advanced. A total of 164 simple sequence repeat (SSR) markers were used to construct a genetic linkage map. The percentage of seedling death was measured over 2 years (2007 and 2008) in the field at four naturally infested locations in Canada and China following additional soil infestation and in the greenhouse following inoculation with Phytophthora sojae isolate. A total of eight QTL underlying tolerance to PRR were identified, located in five linkage groups (F, D1b+w, A2, B1, and C2). The phenotypic variation contributed by the loci ranged from 4.24 to 27.98%. QPRR-1 (anchored in the interval of SSR markers Satt325 and Satt343 of LG F), QPRR-2 (anchored in the interval of Satt005 and Satt600 of LG D1b+w), and QPRR-3 (anchored in the interval of Satt579 and Sat_089 of LG D1b+w) derived their beneficial allele from 'Conrad'. They were located at chromosomal locations known to underlie PRR tolerance in diverse germplasm. Five QTL that derived beneficial alleles from 'Hefeng 25' were identified. The QTL (QPRR-1 to QPRR-7) that were detected across at least three environments were selected for loci stacking and to analyze the relationship between number of tolerance loci and disease loss percentage. The accumulation of tolerance loci was positively correlated with decreases in disease loss percentage. The pyramid of loci underlying tolerance to PRR provided germplasm useful for crop improvement by marker-assisted selection and may provide durable cultivar tolerance against the PRR disease.

Transcriptomic evidence for the control of soybean root isoflavonoid content by regulation of overlapping phenylpropanoid pathways

“…As mentioned earlier, Conrad and AC Colombe are also favored for their increased resistance to P. sojae (Poysa, personal communication) and other soybean pathogens [28, 29]. Therefore, the differential expression of genes involved in stress response, localized to the root hairs could be suggestive of a mechanism underlying the improved resistance to pathogen infection.…”

“…Four soybean cultivars were chosen for this study: two with increased resistance to stem and root rot disease caused by Phytophthora sojae , Conrad and AC Colombe; two with susceptibility to P. sojae , AC Glengarry and Pagoda (Poysa, personal communication). Multiple sources have cited increased resistance in Conrad soybeans to a broad range of pathogen infection ( Fusarium graminearum and P. sojae ) [28, 29]. …”

Quantitative trait locus analysis of saturated fatty acids in a population of recombinant inbred lines of soybean

“…The cumulative effects of QTL pyramiding have been proved previously in soybean (Li et al 2010;Njiti et al 2001Njiti et al , 2002) and other crops (Huang et al 1997;Jiang et al 2007;Richardson et al 2006). In this study, we analyzed the cumulative effects of QTL for the saturated fatty acids by a group comparison of different QTL combinations for multiple loci based on the results of ANOVA (Jiang et al 2007).…”

Quantitative trait locus analysis of unsaturated fatty acids in a recombinant inbred population of soybean

“…The cumulative effects of QTL pyramiding have been proven previously in soybean (Li et al 2010;Njiti et al 2001Njiti et al , 2002 and in other crops (Huang et al 1997;Jiang et al 2007;Richardson et al 2006). Li et al (2010) analyzed Phytophthora root rot tolerance in a RIL population and evaluated the cumulative effects of the detected QTL. Their results indicated that the plant tolerance to Phytophthora root rot was correlated with the number of loci carrying resistance alleles.…”