SSR Marker-Assisted Pyramiding Of Verticillum Wilt Resistant QTL In Upland Cotton

Verticillium wilt is one of the major destructive diseases during cotton production. In recent years, the very disease has become epidemic in China's three cotton production regions, causing severe agricultural consequences to cotton production. The severeness of this cotton pathogen is not only determined by its own invasion type, hypha density within soil, but also closely related with several environmental factors such as ambient temperature and humidity. Since the main way to combat with this cotton disease lies in breeding cultivars with broad-spectrum Verticillium wilt resistance, great research efforts have been made toward this mission by Chinese crop breeders. However, few bona fide Verticillium wilt resistant cotton cultivars are available to date. The main obstacles are the lack of disease resistant Germplasm, and low narrow disease resistant level in upland cotton. The strategy of molecular marker-assisted breeding (MAS) can pyramid multiple target QTL efficiently, shedding light on creating new upland cotton breeding materials with higher disease resistant performance.Two resistant upland cotton cultivars 5026 and 60182, being obtained from our lab with decades of breeding efforts, had previously been characterized by method of QTL analysis. This study is based on the construction of F2 and F2:3 populations that derived from 5026 and 60182. All polymorphism SSR markers that linked to target resistant QTL were selected for F2 and F2:3 populations screening, aiming at pyramiding QTL combinations.Results:1, F2 population including about 1000 individuals plants was derived by crossing two resistant upland cotton cultivars 5026 and 60182. Based on previous QTL analysis on the two upland cotton cultivars,72 SSR markers from the two parents that linked to Verticillium wilt resistant QTL were selected for polymorphism screening between their donors. Among the 28 polymorphism SSR markers,19 polymorphism markers come from 5026, spanning on A5, A8, Al 1, D6, D9 linkage groups, the remained 9 markers come from 60182, spanning on D7, D9, Al 1 linkage groups. These 28 SSR markers were used for polymorphism screening in F2 population, then 41 heterozygous and 10 homozygous selfing lines representing different QTL combinations were selected to construct F2:3 population. Again by screening F2:3 population,25 homozygous selfing lines were available.2, The V991 was utilized for prelimary greenhouse inoculation test toward these 25 pure lines. The 5026 and 60182 cultivars were served as resistant comparison groups, while the Li-8 and Jun-1 were adopted as susceptible comparison groups. Upon the third cotton leaf disease index (DI) analysis, we found that 5026 holded better resistant performance than 60182, while Li-8 is more susceptible than Jun-1. Compared with 5026, 10 test lines showed higher V991 resistant performance. These 10 lines can shed light for future disease-resistant cotton breeding research.