Insect Pollinators in CGMS Hybrid Seed Production of Cajanus cajan

Pigeonpea [Cajanus cajan (L.) Millspaugh] is the only shrubby food legume crop with drought tolerance in the world. Insect pollinators are essential to flower pollination in cytoplasmic genetic male sterility (CGMS) pigeonpea lines, and the species, abundance, and visiting frequency of insect pollinators are the key factors for pigeonpea hybrid production. More than 46 species of insects have been reported to be flower visitors in the open field for pigeonpea production outside China, of which Megachile spp. are the major pollinators. In this study, the species, abundance, and visiting frequency of flower-visiting insects at flowering stage, as well as hybrid yield of pigeonpea, were investigated in the pigeonpea hybrid production field in Yuanmou County, Yunnan Province, China, using CGMS-based ICPH2671 hybrid. A total of 25 species of flower-visiting insects were detected, including 5 major pollinator species, Megachile velutina Sm., Megachile sp-5, Xylocopa tenuiscapa Westw., Apinae sp-1, and Megachile sp-2. At the blooming stage, the flower-visiting insects visited each primary branch at a frequency of 2.8 times per 10 min for the CGMS male sterile line, while at a frequency of 5.2 times per 10 min for the CGMS restorer line. This indicated the preference of flower-visiting insects to the flowers of restorer line. This significant difference between the male sterile and the restorer lines resulted in very similar dry seed yields of the male sterile line (383.7 g per plant) and the restorer line (357.0 g per plant). Therefore, enough pollens can been transported from the restorer line to the male sterile line by insect pollinators, even much less visiting frequency on the flowers of male sterile line compared to that of the restorer line.