Abstract
Crop wild species are increasingly important for crop improvement. Peanut (Arachis hypogaea L.) wild relatives comprise a diverse genetic pool that is being used to broaden its narrow genetic base. Peanut is an allotetraploid species extremely susceptible to peanut root-knot nematode (PRKN) Meloidogyne arenaria. Current resistant cultivars rely on a single introgression for PRKN resistance incorporated from the wild relative Arachis cardenasii, which could be overcome as a result of the emergence of virulent nematode populations. Therefore, new sources of resistance may be needed. Near-immunity has been found in the peanut wild relative Arachis stenosperma. The two loci controlling the resistance, present on chromosomes A02 and A09, have been validated in tetraploid lines and have been shown to reduce nematode reproduction by up to 98%. To incorporate these new resistance QTL into cultivated peanut, we used a marker-assisted backcrossing approach, using PRKN A. stenosperma-derived resistant lines as donor parents. Four cycles of backcrossing were completed, and SNP assays linked to the QTL were used for foreground selection. In each backcross generation seed weight, length, and width were measured, and based on a statistical analysis we observed that only one generation of backcrossing was required to recover the elite peanut’s seed size. A populating of 271 BC3F1 lines was genome-wide genotyped to characterize the introgressions across the genome. Phenotypic information for leaf spot incidence and domestication traits (seed size, fertility, plant architecture, and flower color) were recorded. Correlations between the wild introgressions in different chromosomes and the phenotypic data allowed us to identify candidate regions controlling these domestication traits. Finally, PRKN resistance was validated in BC3F3 lines. We observed that the QTL in A02 and/or large introgression in A09 are needed for resistance. This present work represents an important step toward the development of new high-yielding and nematode-resistant peanut cultivars.
Highlights
Arachis hypogaea L., with a common name of peanut or groundnut, is an important oil, food, and fodder crop cultivated worldwide with an annual production of 66.3 million tons and grown on 34.1 Mha (FAOSTAT, 2021)
Four generations of marker-assisted backcrossing (MABC) for introgression of peanut root-knot nematode (PRKN) resistance from A. stenosperma were completed in two locations, Athens, GA, and Tifton, GA under greenhouse conditions (Figure 1)
Transferring wild beneficial alleles requires an additional step of developing peanut compatible wild-derived synthetic allotetraploids (Suassuna et al, 2020)
Summary
Arachis hypogaea L., with a common name of peanut or groundnut, is an important oil, food, and fodder crop cultivated worldwide with an annual production of 66.3 million tons and grown on 34.1 Mha (FAOSTAT, 2021). Peanut is an allotetraploid species (AABB, 2n = 4x = 40), with a recent and unique polypoid origin, which occurred 5 to 10 thousand years ago (Bertioli et al, 2019, 2020) This narrow genetic base and limited gene flow with its genetically diverse diploid wild relatives resulted in a lack of strong resistance alleles for pests and diseases in the primary gene pool. One important pest is the peanut root-knot nematode (PRKN) (Meloidogyne arenaria) (Holbrook and Stalker, 2003) It causes yield losses greater than 50% in infested fields, and at times, 100% losses in heavily infested areas of fields have been reported (Dickson and De Waele, 2005; Timper et al, 2018). The use of high-yielding and nematode-resistant cultivars in combination with rotation is the most efficient and effective way to control nematode populations and maintain yield while reducing the use of nematicides
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