Estimation of Outcrossing Rate in Napier Grass

Abstract

Napier grass [Cenchrus purpureus (Schumach.) Morrone], also known as elephant grass, is an important tropical forage that has the potential to become an alternative feedstock for energy production. Knowledge about the mode of reproduction and outcrossing rate is essential to select the best strategy to apply in breeding programs to develop new cultivars for application in energy and forage production systems. The objective of this work was to evaluate the outcrossing rate in two Napier grass breeding populations. Six microsatellite markers were used to genotype 28 half‐sibling families totaling 588 individuals, and pollen viability was checked by fluorescein diacetate test (FDA) methodology. A total of 14,603 pollen grains were assessed; 7751 (53%) were considered viable, and 6852 (47%) were considered sterile. Forty‐two alleles were found among all evaluated individuals, and analysis of molecular variance results showed that 14% of variance occurred among half‐siblings and 86% occurred within half‐siblings. Comparison of molecular data among parental and half‐sibling populations found 95.3% of seeds derived from outcrossing, indicating that Napier grass is predominantly allogamous. Currently, directional crosses and hybrid formation in Napier grass depend on the inflorescence protection and pollen collection of selected individuals. Since our results suggest that the self‐fecundation rate is very low (5%), other strategies like unprotected directional crosses can be applied to implementation of large‐scale hybrid production.