Genetic analysis of mutants, histological study of apomictic reproductive physiology, and molecular mapping of disease resistance genes in pearl millet (Pennisetum glaucum (L.) R.Br.);

Genetic analyses of a radiation-induced mutation (stubby head) in pearl millet were performed on F{dollar}sb2{dollar}, F{dollar}sb3{dollar}, and BC{dollar}sb1{dollar} populations of plants to determine the number of genes involved. Ratios for standard genetic models were tested. Linkage analyses showed that the mutant phenotype was controlled by two loci linked in coupling 29 centimorgans (cM) apart. Analyses also showed that a second mutant (female sterile), while having similar developmental characteristics, was not an allele at one of the stubby head loci. A second study was undertaken to identify the cause of seed set failure in a BC{dollar}sb3{dollar} apomictic pearl millet derivative (169-46). Various procedures were pursued including sectioned and stain-cleared ovaries to examine the failure of endosperm development. Embryo sacs in 169-46 mostly produced binucleate, unreduced central cells which, when fertilized by a reduced sperm, would be expected to abort due to endosperm imbalance, unlike its apomictic parent which most often produced mononucleate central cells. These results have implications for transfer of apomixis to crop or forage species. A third study to identify molecular markers linked to pyricularia leaf spot and rust resistance genes in pearl millet was established. More than 500 RAPD primers and 40 RFLP probes (including 13 RFLP probes from rice) were used to identify eight markers linked to the disease resistance genes (4 RAPD and 4 RFLP). The previously mapped RFLP probes allowed assignment of rust resistance genes in pearl millet to specific linkage groups (the {dollar}Rrsb1{dollar} gene to linkage group 3 and unnamed rust resistance genes in Tift 89D{dollar}sb2{dollar} and ICMP 83506 to linkage group 4). A single RAPD marker linked to pyricularia leaf spot resistance was identified but no linkage group location could be assigned.