A1 Cytoplasm Research Articles

Effect of type of sterile cytoplasm on manifestation of economically valuable traits in sorghum-sudangrass hybrids

A comparative analysis of sorghum-sudangrass hybrids produced on the basis of isonuclear alloplasmic sorghum lines with different sterile cytoplasm types has revealed significant differences between them with respect to economically valuable traits. Hybrids produced with the use of A3 cytoplasm are characterized by low initial growth and narrow leaves; A4 cytoplasm, by more intensive initial growth and high carotene content; and 9E cytoplasm, by a lower green mass yield and wider leaves.

Fodder yield and quality in forage sorghum: scope for improvement through diverse male sterile cytoplasms

Cytoplasmic male sterility (CMS) has proved to be an effective and efficient genetic tool in sorghum (Sorghum bicolor (L.) Moench) hybrid breeding programs. The A1 (milo cytoplasm) CMS type has been widely exploited to produce both commercial grain and forage sorghum hybrids. To explore the possibility of using alternative CMS (non-milo cytoplasm) sources, we studied the effect of cytoplasm on forage yield and quality in sorghum. Nine female (CMS) lines (representing three each in A1, A2, and A3 cytoplasms) and five male lines were used to generate 45 hybrids, which were evaluated in three environments. Cytoplasm and its first-order interaction with location and male and female lines showed the presence of a cytoplasmic effect on the majority of fodder yield and quality traits examined. The CMS lines possessing A3 cytoplasm (A3N213 and A3N193) were good combiners for important fodder yield and quality traits. For hydrocyanic acid, the CMS lines possessing A1 cytoplasm were good combiners. Mean performance of hybrids and combining ability analysis of parents revealed that A3 cytoplasm can be used along with the widely used A1 cytoplasm, which helps in the diversification of the male sterile base of forage sorghum hybrids.

Registration of Twelve Sorghum Germplasm Lines Tolerant to Greenbug Feeding Damage

The biotypic diversity of the greenbug [Schizaphis graminum (Rondani)] and development of lines with tolerance to greenbug feeding are ongoing concerns of sorghum [Sorghum bicolor (L.) Moench.] breeding programs in the United States. The genetic male sterile population KP7B and four germplasm sources (IS 25246, IS 27002, IS 27834, and IS 27903) were used in population improvement for tolerance to greenbug feeding. Differences in tolerance were quantified by estimating the chlorophyll content of leaf tissues using a SPAD chlorophyll meter following a 7‐d period of greenbug feeding on leaves. Twelve sorghum germplasm lines KS 121 (Reg. No. GP‐718, PI 651584), KS 122 (Reg. No. GP‐719, PI 651585), KS 123 (Reg. No. GP‐720, PI 651586); KS 124 (Reg. No. GP‐721, PI 651587), KS 125 (Reg. No. GP‐722, PI 651588), KS 126 (Reg. No. GP‐723, PI 651589), KS 127 (Reg. No. GP‐724, PI 651590), KS 128 (Reg. No. GP‐725, PI 651591), KS 129(Reg. No. GP‐726, PI 651592), KS 130 (Reg. No. GP‐727, PI 651593), KS 131 (Reg. No. GP‐728, PI 651594), and KS 132 (Reg. No. GP‐729, PI 651595) with enhanced tolerance to greenbug feeding were developed and released by the Kansas Agricultural Experiment Station in October 2007. These lines are three‐dwarf (dw1, Dw2, dw3, dw4) in height, photoperiod‐insensitive, and possess unique combinations of plant color and tolerance to damage by greenbug biotypes E, I, and K. All 12 lines restore fertility in the A1 cytoplasm system and hence can be used as R‐lines in breeding programs to develop new hybrids with greenbug feeding tolerance.

Influence of types of sterile cytoplasm on the resistance to sorghum shoot fly (Atherigona soccata)

With 2 figures and 3 tables Shoot fly Atherigona soccata (Rondani) is one of the most important insect pests affecting sorghum during early stages of crop growth. Commercial production of hybrid seed in sorghums relies on a single source of male sterility (A1) resulting in restricted nuclear genetic diversity of male-sterile (A) as well as restorer (R) lines. Alternative cytoplasms should be exploited to avoid insect pest outbreaks that might be related to the use of single source of cytoplasm. Therefore, this study was carried out to identify the non-milo cytoplasms that are less susceptible to shoot fly. Four isogenic lines in four male-sterile backgrounds, viz. A1, A2, A3 and A4, and their corresponding maintainer (B lines) lines were studied using a fishmeal technique across rainy and postrainy seasons of 2006–07. The A4 cytoplasm was found to be least susceptible to shoot fly as it was comparatively less preferred for oviposition and had lower deadheart formation across seasons than the other cytoplasms tested and thus can be exploited for developing shoot fly-resistant hybrids.

Registration of 34 Sorghum Germplasm Lines Resistant to Acetolactate Synthase–Inhibitor Herbicides

Sorghum [Sorghum bicolor (L.) Moench] germplasm lines designated KS201 through KS234 (Reg. No. GP‐684, PI 659520 to Reg. No. GP‐717, PI 659553) were developed and released by the Kansas Agricultural Experiment Station, Manhattan, KS in 2007. The donor of the herbicide resistance gene, Tailwind, was crossed to adapted‐seed and pollinator‐parent lines. The progenies were treated with the target herbicide, and resistant individuals were repeatedly backcrossed to the adapted parents. Backcrossing was performed until the undesirable wild characteristics from the donor parent were eliminated. Lines KS201 through KS218 are R lines and restore fertility in A1 cytoplasm system; lines KS219 through KS234 are B lines and do not restore fertility in A1 cytoplasm. All lines possess a unique genetic resistance to acetolactate synthase (ALS)–inhibitor herbicide families and are useful breeding materials for the development of commercial hybrids with ALS resistance. The lines are all of combine‐harvester height and reach 50% flowering 60 to 82 d after planting at Manhattan, KS. A majority of the lines are pigmented plant types and have variable grain color and seed sizes within the range common to existing public inbreds.

Mapping and characterization of Rf 5 : a new gene conditioning pollen fertility restoration in A1 and A2 cytoplasm in sorghum (Sorghum bicolor (L.) Moench)

With an aim to further characterize the cytoplasmic male sterility-fertility restoration system in sorghum, a major fertility restoration gene was mapped along with a second locus capable of partial restoration of pollen fertility. The major fertility restoration gene, Rf(5), was located on sorghum chromosome SBI-05, and was capable of restoring pollen fertility in both A(1) and A(2) male sterile cytoplasms. Depending on the restorer parent, mapping populations exhibited fertility restoration phenotypes that ranged from nearly bimodal distribution due to the action of Rf(5), to a more normalized distribution reflecting the action of Rf(5) and additional modifier/partial restoration genes. A second fertility restoration locus capable of partially restoring pollen fertility in A(1) cytoplasm was localized to chromosome SBI-04. Unlike Rf(5), this modifier/partial restorer gene acting alone resulted in less than 10% seed set in both A(1) and A(2) cytoplasms, and modified the extent of restoration conditioned by the major restorer Rf(5) in A(1) cytoplasm. In examining the genomic regions spanning the Rf(5) locus, a cluster of pentatricopeptide gene family members with high homology to rice Rf (1) and sorghum Rf (2) were identified as potential candidates encoding Rf(5).

Line x tester analysis across locations and years in Sudanese x exotic lines of forage sorghum

Combining ability in forage sorghum [Sorghum bicolor (L.) Moench] was not as much investigated as in grain sorghum. In the present study, 4 local stocks (Testers) and 7 exotic stocks in A3 cytoplasm were crossed in line x tester fashion to investigate combining ability in forage sorghum. The hybrids and their parents were evaluated across two years (2002 - 2003) and at two locations in Khartoum State, Sudan. Forage yield, days to flower, plant height, leaf to stem ratio and stem diameter were studied. Significant general (GCA) and specific combining ability (SCA) effects in desirable direction were detected for most traits. The best general combiners for forage yield and earliness in flowering were identified. Both additive and non-additive gene actions were important in the expression of all characters with the preponderance of additive actions for days to flower, forage yield, stem diameter, leaf to stem ratio and non-additive actions for plant height. GCA effects were more stable over years than specific ones. Selection in early generations was suggested for characters predominately controlled by additive genes. Heterosis breeding was recommended for forage yield improvement. For leaf to stem ratio, selection must be based on more genetically diverse materials. Key words: A3 cytoplasm, additive, ankolib, combining ability, islang, hybrid sorghum, shambat.

Seed parent breeding efficiency of three diverse cytoplasmic-nuclear male-sterility systems in pearl millet

Pearl millet (Pennisetum glaucum (L.) R. Br.) hybrids, grown widely in India and to some extent in the US, are all based on an A1 CMS source, leaving the pearl millet hybrids vulnerable to potential disease or insect pest epidemics. A comparison of this CMS system with two additional CMS systems (A4 and A5) in the present study based on isonuclear A-lines (seed parents) and their isonuclear hybrids showed that A-lines with the A4 cytoplasm had much fewer pollen shedders and much reduced selfed seed set in visually assessed non-shedding plants as compared to those with the A1 cytoplasm. A-lines with the A5 cytoplasm had neither any pollen shedders nor did they set any seed when selfed. This showed that the A5 CMS system imparts complete and most stable male sterility, followed by the A4 and A1 CMS systems. The frequency of maintainers, averaged across a diverse range of 26 populations, was highest for the A5 CMS system (98%), followed by the A4 (59%) and the A1 (34%) system indicating the greatest prospects for genetic diversification of A-lines lies with the A5 cytoplasm, and the least with the A1 cytoplasm. Mean grain yield of hybrids with the A1 cytoplasm was 5% more than the A4-system hybrids, while there was no difference between the mean grain yield of hybrids based on A1 and A5 CMS systems. Based on these results, it is suggested that seed parents breeding efficiency will be the greatest with the A5 CMS system, followed by the A4 CMS system, and least with the currently commercial A1 CMS system.

Fertility Restoration of the Sorghum A3 Male-Sterile Cytoplasm through a Sporophytic Mechanism Derived from Sudangrass

Fertility restoration of sorghum [Sorghum bicolor (L.) Moench] lines carrying the IS1112C (A3 group) male-sterile cytoplasm has been documented as a two-gene gametophytic mechanism involving complementary action of restoring alleles designated Rf3 and Rf4, as derived from IS1112C. Fertility restoration capability has also been reported from sudangrass (S. bicolor subsp. drummondii) populations. We describe characteristics of a fertility restoration system derived from sudangrass, in which male-sterile individuals were observed at high frequency in backcross and F2-F3 segregating populations. Segregation analyses were consistent with a sporophytic restoration system involving two complementary genes. Pollen iodine staining in fertile progeny indicated that the restorers were not efficacious, and fertility was decreased in progeny of backcrosses. Silencing of restoring alleles through paramutation might be operative in these examples. Sudangrass-derived fertility restoration did not involve enhanced transcript processing of the chimeric mitochondrial open reading frame orf107 Thus male sterility induced by the A3 cytoplasm can be restored through different mechanisms.

Effect of cytoplasm and cytoplasm-nuclear interaction on combining ability and heterosis for agronomic traits in pearl millet {Pennisetum glaucum (L) Br. R}

Cytoplasmic male sterility (CMS) is considered an efficient genetic tool in pearl millet hybrid breeding. Of the several CMS sources available in pearl millet, A1 is the only CMS widely exploited to produce commercial hybrids in India. To explore the possibility of using alternate CMS sources, we studied the cytoplasmic effects of different CMS sources on agronomic characters in pearl millet. Five CMS (A) lines representing A1, A2, A3, A4 and A5 cytoplasms, their respective maintainer (B) lines and eight restorer (R) lines were used to generate 40 A × R and B × R experimental crosses. The experimental material was evaluated at two different locations in India. Analysis of combining ability and heterosis revealed that A4 and A5 cytoplasms had desirable effects for earliness. The A5 CMS was found to be particularly promising, as compared to other CMS sources for improving grain yield. The study also indicated that the cytoplasmic effects on general combining ability (GCA) for various agronomic characters were largely non-significant. However, cytoplasmic effects on specific combining ability and heterosis were found to be modulated by cytoplasmic-nuclear interactions and influenced by the environmental conditions. The study also demonstrated the advantage of utilizing diverse male-sterile and restorer combinations in maximizing the productivity as well as for genetic and cytoplasmic diversification of hybrids in pearl millet.

Combining ability and heterosis as influenced by male-sterility inducing cytoplasms in sorghum [Sorghum bicolor (L.) Moench

An investigation was carried out to assess the efficiency of A2 cytoplasmic-nuclear male-sterility (CMS) system in comparison to the widely used A1 cytoplasm in terms of general combining ability (gca) effects of male-sterile (A-) lines and mean performance, specific combining ability (sca) effects and mid-parent heterosis of hybrids for days to 50% flowering, plant height and grain yield at International Crops Research Institute for the Semi-Arid Tropics, Patancheru, Andhra Pradesh, India in 2001 and 2002 rainy seasons. The material for the study consisted of six pairs of iso-nuclear, allo-plasmic (A1 and A2) A-lines and 36 iso-nuclear hybrids produced by crossing these A-lines with three dual restorer (R-) lines. The results revealed that cytoplasm and its first-order interaction with year, R- and A-lines did not appear to contribute to variation in iso-nuclear hybrids for plant height and grain yield. Cytoplasm had limited effect on gca effects of A-lines and on sca effects and mid-parent heterosis of iso-nuclear hybrids for days to 50% flowering, plant height and grain yield. The mean days to 50% flowering, plant height and grain yield of A2 cytoplasm-based hybrids were comparable with those of widely used A1 cytoplasm-based hybrids. The relative frequency of the occurrence of the A1- and A2-based hybrids with significant sca effects and mid-parent heterosis indicated that A2 CMS system is as efficient as A1 with a slight edge over A1 for commercial exploitation. The implications of these results are discussed in relation to opportunities for broadening not only cytoplasm base but also nuclear genetic base of both the hybrid parents.

Genetic and epigenetic regulation of male fertility restoration in the 9E, A4 and M35 CMS-inducing cytoplasms of sorghum

The use of new CMS-inducing cytoplasms significantly increases the genetic variability of cultivated sorghum hybrids. The aim of the research was to study the inheritance of fertility restoration in new types of male-sterile cytoplasms (A4, 9E, M35) and to explore the reasons for its instability. Genetic analysis revealed that the restoration of male fertility was controlled by dominant genes, whose expression was strongly dependent on a sufficient level of water availability to plants during anther and pollen formation. An epigenetic mechanism for “switching on” fertility-restoring gene expression in F1 hybrids is proposed, which is regulated by water availability to plants. This “active” state of fertility-restoring genes is stably expressed in self-pollinated progenies of restored hybrids, irrespective of their water availability conditions, but is not transmitted to testcross hybrids grown under arid conditions.

Relative susceptibility of different male-sterile cytoplasms in sorghum to shoot fly, Atherigona soccata

The shoot fly, Atherigona soccata is an important pest of sorghum, and host plant resistance is one of the most effective components for managing this pest. Most of the hybrids grown in India based on milo cytoplasm (A1 cytoplasm) are highly susceptible to shoot fly. Therefore, the present studies were undertaken to evaluate different male-sterile cytoplasms (CMS) for their relative susceptibility to sorghum shoot fly. Oviposition and deadheart formation were significantly lower on the maintainer lines as compared to the corresponding male-sterile lines. Among the cytoplasms tested, A4M cytoplasm showed antixenosis for oviposition and suffered lower deadheart formation than the other cytoplasms tested. The A4G1 and A4M cytoplasms suffered lower deadhearts in tillers than the other cytoplasms. Recovery following shoot fly damage in A4M, A3, and A2 cytoplasms was better than in the other cytoplasms tested. The larval and pupal periods were longer and male and female pupal weights lower in A4M and A4VzM CMS backgrounds compared to the other CMS systems. Fecundity and antibiosis indices on CMS lines were lower than on the B-lines. The A4M cytoplasm was found to be relatively resistant to sorghum shoot fly, and can be exploited for developing shoot fly-resistant hybrids for sustainable crop production in future.

Use of A3 Cytoplasm to Reduce Risk of Gene Flow through Sorghum Pollen

A critical impediment to field testing and deployment of transgenic sorghum [Sorghum bicolor (L.) Moench] is the threat of gene flow to weedy relatives through pollen. A technique using sorghum with A3 cytoplasmic male sterility to control transgene flow through pollen while using nontransgenic pollinators is described and an experiment was designed to evaluate the risk of viable pollen flow using A3 hybrids under field conditions. Seed set under pollinating bags (an indicator of fertile pollen) was evaluated at the University of Nebraska Field Laboratory at Ithaca, NE, in 2001 and 2002 on selfed F2 progeny grown from open pollinated seed of 12 F1 hybrids produced in A1 and A3 cytoplasm. The F2 seed was produced in hybrid yield trials in 1997 and 1998 at Ithaca, NE. In each evaluation year, the experimental design was a split‐split plot with seed production year the main plot factor, hybrid as the subplot factor, and cytoplasm as the sub‐subplot factor. Cytoplasm effects were highly significant, with percent seed set on A1 F2 individuals averaging 74%, and on A3 F2 individuals averaging 0.04%. Upper confidence limits (P = 0.05) for percent seed set were 1.32% or less for the progeny from all A3 hybrids. Polymerase chain reaction (PCR) analysis confirmed that four male fertile individuals (from a population of 1007) were detected with A3 cytoplasm. These results support the hypothesis that gene flow through pollen can be severely restricted but not eliminated in sorghum by the use of A3 cytoplasmic male sterility.

Effect of Cytoplasm on the Agronomic Performance of Grain Sorghum Hybrids

Hybrid sorghum [Sorghum bicolor (L.) Moench] seed production relies exclusively on cytoplasmic male sterility (CMS) systems and almost all hybrid sorghum seed is produced using the A1 CMS system. However, the reliance on a single CMS system increases the vulnerability of the crop to diseases and stresses that may attack that particular CMS system. Alternative CMS systems have been described and even used on a limited basis for hybrid seed production, but a direct comparison of the agronomic effects of different cytoplasms has not been possible because male‐sterile lines with a common genetic background (and different cytoplasm) were not available. The recent development of isocytoplasmic A‐lines allows more direct comparison of cytoplasmic effect on agronomic performance. The purpose of this study was to determine by means of a set of isocytoplasmic hybrids if cytoplasm per se influences agronomic performance. Twelve hybrid genotypes were created in three different cytoplasms (A1, A2, and A3 for a total of 36 hybrids), and they were evaluated for plant height, days to anthesis, and grain yield at Weslaco and College Station, TX, in 1998 and 1999. As expected, significant differences existed among hybrids for plant height, days to anthesis, and grain yield. Cytoplasm type had no effect on plant height and was of minimal practical effect on days to anthesis, but a significant reduction in yield was observed in A3 cytoplasm hybrids as compared with A1 and A2 cytoplasm hybrids. The specific reason for the reduced yield of A3 hybrids is not known, but seed set data indicated that it was not associated with fertility restoration. The results indicate that hybrids created in A2 cytoplasm yield comparably to the commonly used A1 cytoplasm and therefore, the A2 system will provide a suitable alternative for hybrid seed production should problems be encountered in the A1 CMS system.

Expression of Susceptibility to Fusarium Head Blight and Grain Mold in A1 and A2 Cytoplasms of Sorghum bicolor.

Panicle diseases are among the major constraints to sorghum (Sorghum bicolor) production in the northern Great Plains; host plant resistance is the primary management option. However, essentially all commercial sorghum hybrids contain A1 cytoplasm, which raises the concern about increased disease risk as a result of cytoplasmic genetic uniformity. To determine the influence of cytoplasmic background on the expression of susceptibility to panicle diseases, F1 hybrids with four nuclear genotypes in each of two cytoplasms (A1 and A2) were planted in three environmentally diverse geographic locations in Nebraska. Fusarium head blight ranged in incidence from 13 to 100% across locations. Grain mold, caused primarily by species of Alternaria, Fusarium, and Cladosporium, ranged in incidence from 5 to 100% across locations. There was a significant effect of nuclear genotype on the incidence and severity of both head blight and grain mold across the three locations. Cytoplasm had no effect on head blight incidence or severity, or on grain mold severity. Cytoplasm had a significant effect on grain mold incidence, with A1 exhibiting slightly lower incidence than A2 (64 versus 70%). Although the cytoplasm effect for grain mold incidence was statistically significant, most of the variation in grain mold incidence was attributable to nuclear genotype. The slight increase in grain mold incidence attributable to A2 cytoplasm should be overcome easily by selection of nuclear genotypes with grain mold resistance. The use of A2 cytoplasm to incorporate genetic diversity into grain sorghum hybrids should not increase the risk of head blight or grain mold in commercial grain production.

Analysis of Resistance to Ergot in Sorghum and Potential Alternate Hosts

Ergot (caused by Claviceps africana Frederickson, Mantle & de Milliano) of sorghum [Sorghum bicolor (L.) Moench] recently has become a global disease problem and is a major threat to hybrid seed production. Host-plant resistance is one option for control; however, the genetic and physiological bases for ergot resistance are poorly understood. The objective of this study was to evaluate resistance to C. africana in 18 genetically diverse sorghum lines, including cultivated landraces and wild accessions, as well as in potential alternate hosts, including grassy weeds and range grasses commonly found in sorghum-producing areas in the central Great Plains of the USA. These entries were evaluated for ergot resistance in the greenhouse following spray inoculation with conidial suspensions during flowering. The results of this analysis indicated that only Sorghum ssp. were susceptible to ergot; however, within the sorghum germplasm pool, several wild accessions were identified with resistance to ergot. Two of these resistant entries, IS14131 and IS14257, were characterized further in male-sterile (A3 cytoplasm) genetic backgrounds to evaluate the physiological basis for their resistance. Parent lines, male-sterile hybrids, and susceptible checks were evaluated for ergot resistance following spray inoculation with ergot in experiments in a winter nursery at Guayanilla, Puerto Rico, and in a greenhouse at Manhattan, KS, during the winter and spring of 2000. The expression of ergot resistance in IS 14131 and IS14257 and in corresponding male-sterile hybrids suggests that these sorghums may harbor genes for resistance to ergot.

Dynamic Multiline Population Approach to Resistance Gene Management

ABSTRACT The dynamic multiline population breeding strategy integrates principles from the gene stacking and multiline approaches and allows application of the multiline strategy to cross-pollinated hybrid crops. Experiments were conducted to evaluate the effectiveness of the breeding approach. Backcross derivatives of pearl millet Tift 23DB were developed with rust resistance from 18 Burkina Faso landraces, 3 Pennisetum glaucum subsp. monodii accessions, and 2 elite inbreds (1 from India and 1 from the United States). Four cycles of open pollination were made, the last two in the field in rust epidemics. Cytoplasmic male-sterile (CMS) counterparts of the populations in the A(4) cytoplasm were included and advanced simultaneously with the B population. Hybrids with Tift 383 were produced on CMS cycles 1 (C1) through C4. Frequency of hybrid seedlings with resistance increased with each cycle, and frequencies averaged 18 to 38% in C1 to C4 hybrids, respectively, when inoculated with five single-uredinium isolates of Puccinia substriata var. indica. The hybrid populations and Tifleaf (TL)1 and TL2 were evaluated in three yield trials in 1998 to 1999. Disease-free forage dry matter yields did not differ among hybrids. Across trials, area under the disease progress curve (AUDPC) of TL1 and TL2 averaged 1,307, C1 and C2 averaged 914, and C3 and C4 averaged 604. Final severities of TL1 and TL2 averaged 67%, C1 and C2 averaged 47%, and C3 and C4 averaged 30%. When analyzed by regression analysis, AUDPC was reduced 12.2%, final rust severity was reduced 13.3%, and digestible biomass was increased 4.1% per cycle.

Nuclear genes from Tx CMS maintainer lines are unable to maintain atp6 RNA editing in any anther cell-type in the sorghum bicolor A3 cytoplasm.

RNA editing and cytoplasmic male sterility are two important phenomena associated with higher plant mitochondria. We recently have shown a potential function of RNA editing in CMS development. The frequency of atp6 RNA editing was specifically reduced in anthers of male-sterile Sorghum bicolor, which increased in frequency in partially restored progeny. Here we present data that show that the loss of RNA editing capability also occurs in a second nuclear background that allows the expression of male sterility. Loss of RNA editing thus appears to be associated with unique combinations of male-sterile cytoplasm and non-restoring nuclear backgrounds. In addition, the reduction of RNA editing affects both gametophytic and sporophytic anther cell-types but not other floral tissues. An analysis of F(2) plants exhibiting different levels of fertility indicates a co-segregation of fertility restoration and atp6 RNA editing. The atp6 transcript abundance is similar in seedlings and anthers of male-sterile, partially restored, and male-fertile lines and thus is not associated with loss of atp6 RNA editing in anthers. A model for RNA editing and male sterility based on the data available is presented. Functional correlations with other CMS systems are also discussed.

Nuclear-cytoplasmic interactions in restoration of male fertility in the ‘9E’ and A4 CMS-inducing cytoplasms of sorghum

The genetics of male-fertility restoration in sorghum in the “9E” and A4 CMS-inducing cytoplasms, was studied by crossing a number of fertility restorer lines of A1 cytoplasm to CMS lines [9E]T×398 and [A4]T×398 and the line [9E]Milo-10, which was obtained by backcrossing Milo-10 to [9E]T×398. It was revealed that both A4 and “9E” cytoplasms are characterized by a sporophytic mode of restoration of male fertility. Depending on the nuclear background of the male parents, fertility restoration was controlled by one or two dominant genes. Fertility-restorer genes of one of the tester lines, KVV-114, were effective in [9E]T×398 but could not restore [9E]Milo-10. A fertile line obtained from the fertile hybrid [9E]T×398/KVV-112, with “9E” cytoplasm, also failed to restore [9E]Milo-10. In a number of hybrid combinations with both A4 and “9E” cytoplasms a novel and unusual phenomenon of gradual restoration of male fertility in subsequent backcross generations was observed. Pollen from the fertile revertants did not transmit fertility restoration in progeny from crosses with the original CMS line and was poorly transmitted in sib-crosses. The appearance of fertile revertants and the different reactions of different CMS lines with the same cytoplasm in test-crosses may be caused by the action of recessive nuclear genes of the recurrent male parents that were accumulated during backcrossing; these may induce changes in cytoplasmic genes controlling CMS.