A linkage map for Cucurbita maxima based on Randomly Amplified Polymorphic DNA (RAPD) markers

Abstract

Linkage information is needed for marker-assisted selection in squash and pumpkin breeding programs involving Cucurbita ecuadorensis, a source of resistance to many diseases. A mapping population was produced by backcrossing an inter-specific cross of C. maxima x C. ecuadorensis to C. maxima. One hundred RA PD primers were used to survey the parental polymorphism, and 42 of these found to be polymorphic between the parents were used for construction of a linkage map. The 42 primers generated 122 distinct and reproducible bands for 55 plants of the BC1F1 population. A linkage map consisting of 102 markers on 22 linkage groups was produced with an approximate length of approximately 1195.2 cM. The segregation of most of these markers did not deviate from the expected 1:1 ratio. Some terminal markers on several linkage groups displayed significant deviation from a 1:1 ratio. Only two linkage groups (12 and 22) had a majority of markers that exhibited significant segregation distortion. A total of 20 RAPDs remained unmapped, and nine of these displayed highly distorted (P< 0.01) segregation ratios, suggesting that they were not single sequences segregating genetically. Thus this first linkage map for C. maxima appears to give good coverage of the genome. Predominant normal segregation of most markers suggests significant homology between C. maxima and C. ecuadorensis genome, and that much of the useful traits of C. ecuadorensis could be introgressed into C. maxima.