Fertility and Progeny Ploidy of Triploids in China Rosa Germplasm

Abstract Background Although triploid plants are often assumed to be sterile, in Rosa, triploids appear to have been important in both species evolution and breeding. A better understanding of the fertility of China Rosa triploids and their behavior when used in interploidy crosses will not only improve gene introgression from China triploid roses to modern roses, but also enhance our understanding of male and female fertility mechanism with triploids. The objective of this study was to evaluate the usefulness of five triploid China roses for breeding by measuring the pollen size, quantifying the fertility and following the ploidy transmission of interploidy crosses. Results In the five triploids, the pollen grain size of Rosa multiflora var. cathayensis Rehd ‘Fen Tuan Qiang Wei’ followed a normal distribution, suggesting that 1 mainly ploidy level pollen grain were produced, while the pollen size of other 4 triploids followed skewed, flattened, and slightly bimodal distributions, indicating a wide range of chromosome numbers. Although none of the 5 triploids produced hips as females, 3 gave good hip and seed production on the tetraploid mother plant when used as the pollen parents. Based on the ploidy level analysis of their progeny, ‘Fen Tuan Qiang Wei’ produced 1n viable pollen whereas ‘Chun Shui Lü Bo’ and ‘Yu Shi Zhuang’ produced 2n viable pollen. In the meiosis of triploids, the triads, pentads and microcyte in the meiosis products indicated the objective triploid production of euploid pollen grains. Conclusions In this study we reported 1 China triploid rose produces 1n viable pollen, and 2 China triploid roses produce 2n viable pollen, and no anueploid progeny was produced. Our results indicate that the triploids contribute significantly to tetraploids formation in the crossing system of Genus Rosa, and it is possible for breeders to create novel rose types with valuable triploids in the future. With the special triploid resources found in this experiment, Genus Rosa will be an excellent material to study the mechanism of triploids in the future.