Fidelity of Sugarcane Crosses Assessed with SSR Markers

Abstract

Sugarcane (Saccharum hybrids spp.) is a wind-pollinated species that bears very small yet complete flowers. During crossing, a lack of pollen control (trimming off dehisced florets and hot water treatment) may result in both self-pollination (selfs) and unintentional pollination from stray pollen (off-types). Due to this uncertainty, it is important to estimate the percentage of intentional paternal hybridizations to better understand and possibly improve the crossing process. In this study, six pairs of simple sequence repeats (SSR) primers were used to assess the fidelity of 343 bi-parental crosses made at three U.S. breeding stations in 2002, 2003, 2004, 2005, and 2006. By comparing the SSR fingerprints between the two parents and 20 random progenies, three types of progenies were identified, namely, hybrids, selfs, and off-types. Hybrids had only SSR fingerprints found in either parent; selfs had only SSR fingerprints of the maternal parent; and off-types had SSR fingerprints that were not found in either parent. The fidelity of the 343 crosses fluctuated from 100% hybrids to 100% off-types. Multinomial analysis indicated that the ratio of hybrids from intentional hybridization to selfs and off-types fluctuated by year and location. Selfing rates (−30.5%) and off-type rates (−9.2%) were lower in crosses from which superior progenies were selected and advanced through 10-year field evaluation and testing, but off-type rates were not significant indicating that selfing may reduce advancement rates more than the off-types. Hot water treatment reduced off-types by 27% and selfing by 20%. This research demonstrates the utility of SSR markers for measuring hybridization rates and highlights the importance of pollen control measures through trimming and hot water treatment of sugarcane flowers.

Keywords

• sugarcane breeding
• cross fidelity
• <i>saccharum hybrids</i> spp.
• ssr