MODERN MAIZE HYBRIDS CAN IMPROVE GRAIN YIELD AS PLUS-HYBRIDS BY THE COMBINED EFFECTS OF CYTOPLASMIC MALE STERILITY AND ALLO-POLLINATION

A cytoplasmic male-sterile (CMS) maize (Zea mays L.) hybrid is referred to as a Plus-Hybrid when it is grown in mixture with an unrelated pollinator, i.e. when it is allo-pollinated. It often leads to higher grain yields than the corresponding sib-pollinated male-fertile hybrid. To improve breeding processes, more knowledge of Plus- Hybrid effects with modern plant material must be ac- quired. The Plus-Hybrid abilities of 12 modern European hybrids from diverse breeders, representing all three types of CMS, were evaluated in a field study at three lo- cations in Switzerland in 2005; their suitability as pollen receptors and pollen donors were tested by combining their male-sterile and male-fertile forms with two respec- tive known tester hybrids. The variations caused by the CMS effect on the yield of a specific genotype in a given environment ranged from -8 to +8%. These variations did not depend on the type of male-sterile cytoplasm. The Plus-Hybrid effect for a specific combination was consis- tent among locations, but the extent of the effect depend- ed on the environment. The test pollinator induced an av- erage Plus-Hybrid effect of +6.9% on the grain yield of the set of CMS hybrids. After allo-pollination, the yield of seven of the 12 CMS hybrids increased by more than +8% (mainly due to a higher thousand kernel weight). Al- though the impact of the type of cytoplasm was not sig- nificant, hybrids with C and T cytoplasm showed a stronger response to allo-pollination than hybrids with S cytoplasm. Five very responsive CMS hybrids and one good pollinator, originating from different European breeders, were identified among the set of 12 hybrids tested in these field trials.