Fine Mapping Of Qpl.zass-3,a Major QTL Governing Pod Length In Asparagus Bean And Development Of Linked Caps Markers

Cowpea,originating from West Africa and widely distributed in the tropical and subtropical regions of the world,is an important annual leguminous crop.There are two main subspecies of cultivated cowpea,which are the asparagus bean（V.unguiculata ssp.sesquipedialis）and the common cowpea（V.unguiculata ssp.unguiculata）.Asparagus bean is one of the most important summer vegetables in China,which is cultivated nation-wide except for a few extremely cold regions.The pods are the most important economic organs of asparagus bean,and pod length is the most important agronomic trait of pods.Pod lengths in asparagus beans vary remarkably,from less than 10 cm to more than 120 cm.Thus far,there are only a few reports on the study of pod length in cowpea,and the genes controlling pod length in cowpea remain uncloned.Previously,we mapped a major QTL,Qpl.zaas-3,to LG3 of cowpea,which controls pod length.It the current study,we used a large F₂ population comprising 2153 offspring of the cross of“ZN016”（a landrace cowpea）and ZJ282（a commercial cultivar）,to precisely map Qpl.zaas-3.A regional saturate genetic linkage map was constructed based 490 new SNP makers designed from analysis of the cowpea 60K i Select Consortium SNP Array and genome re-sequencing of the two parents.According to the results of QTL fine-scanning,SNP closely linked the trait gene were developed to CAPS.The main results are as follows:1.Statistical analysis found that the pod length in the F₂ population showed a near-normal distribution.The mean pod length value was 40.6 cm,which fell between the two parental values.The length distribution ranged from 24.6 to 62.3 cm,demonstrating an obvious transgressive segregation and is indicative of interactions between-or with-QTLs.2.A total of 490 new SNP markers were developed by analyzing the cowpea 60K i Select Consortium SNP Array and genome re-sequencing of the two parents.The number of technically working SNPs were 433.3.A regional saturate genetic map was constructed.In the previously mapped Qpl.zaas-3interval,there were 150 SNP markers with the average marker distance being only 0.00867c M.4.In QTL scanning,Qpl.zaas-3 was re-mapped to a 0.132 c M interval between the markers 2＿25214 and 2＿49346.The phenotypic variance it explained was 22.2373%.A physical interval of 130 kb was determined through comparison with the cowpea genome in the Phytozome database.There were seven predicted genes in tis physical interval.5.Based on a Hpa II enzyme recognition site in the flaking sequence of the SNP marker2＿49346,this marker SNP marker was successfully converted to the PCR-based CAPS marker CAPS2＿49346,which is more user-friendly to breeders.