REGULATION OF POLLEN FERTILITY IN THE „9E‟-CMS-INDUCING CYTOPLASM OF SORGHUM: INTERACTION OF PLANT GENOTYPE WITH ENVIRONMENT pp. 157-177
Authors: (L.A. Elkonin, M.I. Tsvetova, V.V. Kozhemyakin, O.P. Kibalnik, Agricultural Research Institute for South-East Region of RAAS, Saratov, Russia, and others)
Abstract: Restoration of pollen fertility in plants with cytoplasmic male sterility (CMS) is known to be controlled by specific nuclear fertility-restoring genes that suppress functioning of aberrant mitochondrial genes, expression of which destroys pollen development. Usually, these genes are dominant and manifest in the F1 generation. In sorghum, pollen fertility restoration in some CMS-inducing cytoplasms (A4, ‗9E‘, ‗M35-1A‘) has aberrant mode of inheritance: it is stably expressed in self-pollinated progenies of F1 hybrids with restored fertility but unstably manifested in new hybrid genome (F1 or test-cross hybrids to CMS lines with the same cytoplasm type). We found that in the ‗9E‘ cytoplasm this phenomenon is caused, evidently, by environmental conditions during test-cross hybrid plant development, namely water-availability and photoperiod. Experimental data testify to strong sensitivity of fertility-restoring genes to plant water-availability conditions at microspore- and gametogenesis: at high level of water availability these genes are dominant and can express in heterozygous state (in test-cross hybrids), while in drought conditions fertility-restoring genes are recessive and can function only in homozygous state. In addition, reduced photoperiod at photoperiodically-sensitive stage of sorghum plant ontogenesis also increased percentage of male-fertile F1 plants, perhaps, by ‗activation‘ of fertility-restoring genes, and these genes expressed in the next generation. Changes of environmental conditions during male-sterile hybrid plant ontogenesis can ‗activate‘ expression of fertility-restoring genes. Cytological analysis revealed significant polymorphism of pollen grain (PG) types in CMS-lines with the ‗9E‘ cytoplasm and in the F1 hybrids with restored male fertility.