Wide Crosses in Cereals

I NTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . 117 AGRONOMIC TRAITS OF INTEREST IN WIDE CROSSES. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 118 FLOWER STRUCTURE IN THE CEREALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 PREFERTILIZATION BARRIERS IN WIDE CROSSES .. . . . ....... ... . ...... .. 122 Intraspecies Incompatibility 122 Interspecies Incompatibility . .. . . . . . . . . . . . . . . .... .... .... 124 POSTFERTILIZATION BARRIERS IN WIDE CROSSES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Chromosome Dqubling Overcomes Sterility of FI Hybrid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Tissue Culture Can Rescue Hybrid Embryos Showing Failure of Endosperm Development . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Selective Chromosome Elimination Can Limit the Recovery of Hybrids .... . . . . . . . . . .. 128 BARRIERS TO GENE EXPRESSION IN PROGENY FROM WIDE CROSSES . . . . . . . 129 MANIPULATION OF ALIEN CHROMATIN INTRODUCED INTO CEREALS BY WIDE CROSSES . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Recombination Induced by Removal of the Controls on Homologous Pairing ....... 131 Chromatin Breakage/Repair Induced by Ionizing Irradiation ... .. ... . . . . ... .. . . ... ...... 132 Cell Culture 133 THE INTRODUCTION OF DNA INTO CEREALS BY TRANSFORMATION OF TISSUES OR PROTOPLASTS .. ...... . . . .. ... . ..... . . ....... .. .... .. . ..... ..... 133 MONITORING ALIEN INTROGRESSIONS . ..... . . ..... . . . .. . . . . ......... ... ... . . ... . . ...... . 136