Abstract
Introgression of desirable traits from wild relatives plays an important role in crop improvement, as wild species have important characters such as high resistance to pests and pathogens. However, use of wild peanut relatives is challenging because almost all wild species are diploid and sexually incompatible with cultivated peanut, which is tetraploid (AABB genome type; 2n = 4x = 40). To overcome the ploidy barrier, we used 2 wild species to make a tetraploid with the same allotetraploid genome composition as cultivated peanut. Crosses were made between 2 diploid wild species, Arachis valida Krapov. and W.C. Greg. (BB genome; 2n = 2x = 20) and Arachis stenosperma Krapov. and W.C. Greg. (AA genome; 2n = 2x = 20). Cuttings from the diploid F1 AB hybrid were treated with colchicine to induce chromosome doubling thus generating an induced allotetraploid. Chromosome counts confirmed polyploidy (AABB genome; 2n = 4x = 40). We named the new allotetraploid ValSten. Plants had well-developed fertile pollen, produced abundant seed and were sexually compatible with cultivated peanut. ValSten exhibits the same high resistance to early and late leaf spot and rust as its diploid parents. Notably, we observed morphological variations, including flower width and branch angles in the earliest generation (S0) of allotetraploids. A SNP array was used to genotype 47 S0 allotetraploids. The great majority of markers showed the additive allelic state from both parents (AABB). However, some loci were AAAA or BBBB, indicating homeologous recombination. ValSten provides a new, vigorous, highly fertile, disease resistant germplasm for peanut research and improvement.
Highlights
Peanut or groundnut (Arachis hypogaea L., AABB genome type, 2n = 4x = 40) is an important oil and food crop worldwide
The creation of ValSten are intended for use as a source of valuable alleles in breeding
They have the advantage of being directly sexually compatible with cultivated peanut, and of having identified DNA markers linked to a subset of their alleles
Summary
Its production is frequently challenged by pests and pathogens including bacteria, fungi, nematodes and viruses that can cause severe yield loss. Early and late leaf spot diseases caused by the fungi Passalora arachidicola Cersospora arachidicola, teleomorph Mycosphaerella arachidis) and Northopassalora personata Cercosporidium personatum, teleomorph Mycosphaerella berkeleyi) and rust, caused by Puccinia arachidis, can cause over 50% pod yield losses in some areas where fungicides are used rarely or inappropriately (Waliyar 1990; Ouedraogo et al 1994). In Georgia, the major peanut producing state in USA, more than 35 million dollars was spent on leaf spot control in 2015. The losses caused by leaf spots alone was about 8.6 million dollars (https://secure.caes.uga.edu/extension).
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