Stable Male Sterility Research Articles

Characterization and inheritance of a novel thermo-sensitive restoration of cytoplasmic male sterility in Capsicum annuum

Thermo-sensitive male sterility can be used for two-line hybrid production, if the fertility can be manipulated by temperature shifting. In this study, we investigated a novel thermo-sensitive cytoplasmic male-sterile (TCMS) line of pepper. The TCMS line was sterile at temperatures above 15°C but their fertility was restored when night temperatures were below 13°C. To elucidate the cellular mechanism acting in the TCMS line, histological analysis was performed using light microscopy and transmission electron microscopy (TEM). We demonstrated that stable male sterility in pepper might be induced due to the abnormal development of tapetal cells whereas defects of callose wall biosynthesis seemed to be the main reason for male sterility in TCMS plants. Meiotic cell division in sterile TCMS plants proceeded to the last stage, whereas normal sterile plants were arrested at the meiotic stage. Further analysis using TEM revealed that abnormal development and failure of timely programmed cell death of the tapetum led to secretory dysfunction of tapetal cells. Consequently, this secretory defect may have influenced callose wall deposition and pollen wall formation in sterile TCMS. To reveal genetic mechanisms influencing TCMS, inheritance and marker analysis was performed. Cytoplasmic male sterility (CMS)-associated marker tests showed that the TCMS line contains CMS cytoplasm. Inheritance patterns and Rf-linked marker analysis suggested that TCMS is controlled by an allele named RfTCMS located at the Rf locus. Restoring experiment at low temperature showed that the thermo-sensitive restorer, RfTCMS, may be another allele located on the Rf locus and is recessive to Rf and dominant to rf.

Development of Novel Cytoplasmic Male Sterile Source from Dongxiang Wild Rice (Oryza rufipogon)

This study was conducted to develop and characterize a novel cytoplasmic male sterile (CMS) source which was identified from Dongxiang wild rice (Oryza rufipogon) by crossing Dongxiang wild rice as female with Zhongzao 35, an indica inbred variety, as male and continuous backcrossing with Zhongzao 35. Observation under optical microscope manifested that this novel CMS belonged to typical abortion type with less pollen compared with wild abortive type cytoplasm (CMS-WA). Sequential planting showed that this novel CMS has complete and stable male sterility. Testcross experiment showed that all the 24 tested materials including maintainer and restorer lines of CMS-WA and Honglian type cytoplasm (CMS-HL) and other indica inbred varieties are the maintainers with complete maintaining ability, suggesting that this novel CMS has fertility restoration totally different from CMS-WA and CMS-HL and belongs to a novel type of CMS. So far, we only discovered a unique fertility restoration source for this novel CMS. Inheritance analysis showed that the fertility restoration of this CMS was governed by three pairs of independent dominant genes. Prospect for application of this novel CMS system in hybrid rice breeding was also discussed.

Identification of a single nucleotide deletion causing frameshift mutation in OsDFR2A in a genic male sterile mutant of rice and its possible application to F1 hybrid breeding

Stable genic male sterility (GMS), which is not influenced by environmental factors, has not been used for F1 hybrid seed production because male-sterile inbred lines cannot be developed and male-sterile plants must be selected from segregating populations every time. However, the stability of male sterility may provide a reliable system for F1 seed production without contamination of selfed seeds. A genic male-sterile mutant in rice (Oryza sativa L.), C204, which was selected from progeny of the cultivar ‘Koshihikari’ irradiated by gamma rays, has shorter and whiter anthers than those of ‘Koshihikari’ and has no pollen grains. Segregation analysis of C204 suggested the male sterility of this mutant to be controlled by a recessive allele of a single gene. Linkage analysis of a mutated gene responsible for the male sterility revealed the gene to be in a region of ca. 75 kb on the long arm of chromosome 9. The nine genes predicted in the 75-kb region were sequenced, and compared with the published Nipponbare genome sequences. A single-base deletion was found in the first exon of a C204 allele of Os09g0493500, which encodes an NAD-dependent epimerase/dehydratase family protein, resulting in a frameshift causing a premature stop codon. A dot-blot single nucleotide polymorphism marker for detection of the single-base deletion in Os09g0493500 was developed. We herein propose an F1 hybrid seed production system using stable GMS with a simple selection method of GMS plants.

Studying comparative suitability of CMS lines

Parental lines constitute the first and foremost step in a hybrid breeding program. In this context, developing a commercially viable cytoplasmic male sterile (CMS) line is considered to be a highly cumbersome process. In fact, the belated success of hybrid rice technology in India was basically due to the nonavailability of a CMS line suited to the tropics. Over the years, a large number of male sterile lines with different cytosterility sources have been developed in India and elsewhere. Only a few-such as IR58025A and IR62829A-are now used commercially in India. They possess all the essential traits-complete and stable male sterility, high outcrossing rate, better grain quality, easy restorability, good combining ability, and adaptability-of a commercially viable CMS line. Some 64 CMS lines from India, China, Malaysia, and IRRI were evaluated along with IR58025A, IR62829A, and standard checks in the wet season of 1995 and 1996 and dry season of 1994 and 1995 to assess their comparative suitability for commercial use.

Xingxiangyou 77, a high-yielding and fine-quality semi-aromatic hybrid rice

Xingxiangyou 77 was developed at HHRRC using aromatic cytoplasmic male sterile line Xingxiang A and nonaromatic restorer line Minghui 77. It was extensively tested and approved for release to farmers by the Hunan Provincial Crop Variety Release Committee in February 1997. Xingxiang A, improved from the first aromatic CMS line Xiangxiang 2A, is another aromatic CMS line developed by HHRRC. The new line has stable male sterility and better outcrossing characteristics than Xiangxiang 2A. Minghui 77, developed by the Sanming Agricultural Institute, Fujian, China, is a popular strong restorer line with good grain quality. The cross between these two parents was first made in 1993. In 1994, the hybrid was tested in the Hunan Rice Variety Multilocational Trial and yielded 6.9 t ha -1 on average at all five locations, 5.5% higher (significant at 5% level) than check Weiyou 64. In the same year, it gave a mean yield of 5.9 t ha -1 at six locations in the trial of new commercial fine-quality rice varieties of Hunan Province with a yield advantage of 2.9% over check Xiangwanxian 1. Tested in the Hunan Rice Variety Regional Trials of 1995 and 1996, it gave a mean grain yield of 6.8 t ha -1 over 14 and 12 locations, respectively, with yields of 2.3% and 5.6% higher than those of check Weiyou 64 (Table 1). In the on-farm trials and demonstration plots, it generally yielded 6.8 to 7.7 t ha -1 when grown as late rice in a double-cropping system.

Production and characterization of an alloplasmic and monosomic addition line of Brassica rapa carrying the cytoplasm and one chromosome of Moricandia arvensis

Intergeneric hybridization was performed between Moricandia arvensis and four inbred lines of Brassica rapa following embryo rescue. Three F1 hybrid plants were developed from three cross combinations of M. arvensis × B. rapa, and amphidiploids were synthesized by colchicine treatment. Six BC1 plants were generated from a single cross combination of amphidipolid × B. rapa ‘Ko1-303’ through embryo rescue. One BC2 and three BC3 plants were obtained from successive backcrossing with B. rapa ‘Ko1-303’ employing embryo rescue. Alloplasmic and monosomic addition lines of B. rapa (Allo-MALs, 2n = 21) were obtained from backcrossed progeny of three BC3 plants (2n = 21, 22 and 23) without embryo rescue. An alloplasmic line of B. rapa (2n = 20) degenerated before floliation on 1/2 MS medium due to severe chlorosis. Allo-MALs of B. rapa (2n = 21) showed stable male sterility without any abnormal traits in vegetative growth and female fertility. Molecular analyses revealed that the same chromosome and cytoplasm of M. arvensis had been added to each Allo-MAL of B. rapa. This Allo-MAL of B. rapa may be useful material for producing cytoplasmic male sterile lines of B. rapa.

Fine mapping of a gene for non-pollen type thermosensitive genic male sterility in rice (Oryza sativa L.)

The thermo-sensitive genic male sterility (TGMS) lines play a crucial role in two-line hybrid rice production. For a practical TGMS line, the stability of male sterility is one of the most important technical indicators. In this study, XianS, a spontaneous mutant with stable male sterility from an indica rice cultivar Xianhuangzhan, was classified as a non-pollen type TGMS line. The critical non-pollen sterility point temperature of XianS was determined as 27 degrees C. Genetic analysis demonstrated that the non-pollen sterility in XianS was controlled by a single recessive gene. Using SSR markers and bulked segregant analysis, the TGMS gene in XianS was fine mapped to a 183 kb interval between RMAN81 and RMX21 on chromosome 2. Two markers, 4039-1 and RMX14 completely cosegregated with this gene. Allelism test indicated that the non-pollen phenotype in seven non-pollen type TGMS lines from different sources, XianS, AnnongS-1, Q523S, Q524S, N28S, G421S, and Q527S is caused by the same TGMS gene. Although the location of TGMS gene in XianS is close to the gene OsNAC6, a previously identified candidate gene of tms5 in AnnongS-1, the sequence of OsNAC6 and its promoter region was identical in TGMS line XianS, AnnongS-1, and wild-type Xianhuangzhan. These results suggest that the non-pollen type TGMS trait probably be controlled by the same TGMS gene in different TGMS rice lines, but its real candidate gene still need to be further studied and identified.

Stability of Cytoplasmic Male Sterility in Maize under Different Environmental Conditions

ABSTRACTCytoplasmic male sterility (CMS) is a maternally transmitted trait, whereby a plant is unable to produce viable pollen. Studies have revealed that this trait is a tool for enabling efficient and reliable coexistence between genetically modified (GM) and non‐GM cultivation by biocontainment of GM maize (Zea mays L.) pollen. Maize has three types of male‐sterile cytoplasm (T, S, and C), the fertility of which can be restored by nuclear rf genes or by interactions with the environment. Twenty‐two CMS versions of modern European maize hybrids were evaluated in 17 environments in Switzerland, France, and Bulgaria, with two or three sowing dates, in 2005 and 2006. Stable and unstable male sterility occurred in all three CMS types. T‐cytoplasm hybrids were the most stable, while S‐cytoplasm hybrids often showed partial restoration of fertility. C‐cytoplasm was similar to T‐cytoplasm with regard to maintaining male sterility. Climatic factors, especially air temperature, evapotranspiration, and water vapor, during the 10 d before anthesis as well as during anthesis, were correlated positively or negatively with the partial reversion to male fertility of CMS hybrids, indicating an interaction between genetic and climatic factors. This study illustrates that T‐ and C‐cytoplasm in particular open up viable prospects for containing transgenic pollen, especially for Bt‐maize.

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.

Male sterility systems for hybrid seed production in Brassica crops.

Abstract Brassica crops are important sources of edible oil, leafy vegetables and renewable energy. In addition, some Brassica crops inhibit potato pests and have the potential to become cash crops from the potato rotation land for potato growers, if these crops yield well. One effective approach to increase Brassica crop productivity per unit land is through the use of the heterosis in hybrids prepared with male sterility systems. In Brassica crops, various male sterility systems have been identified or developed, including endogenous nuclear male sterility (NMS: recessive NMS, dominant NMS, interactive NMS), cytoplasmic male sterility (CMS: endogenous CMS, alloplasmic CMS) and transgenic male sterility. Both environmentally stable and sensitive male sterility systems are available and in use. The chlorosis associated with allochloroplasts in several alloplasmic CMS systems has been largely eliminated by organelle-selective protoplast fusion. Several mitochondrial CMS genes and a CMS fertility restorer gene ( Rfo ) have been identified and sequenced. The cloning of NMS genes and additional CMS fertility restorer genes is underway. The difficulty in maintaining NMS uniformity in populations has been partly solved by the interactive NMS (INMS)-based approach (epistatic suppressors for either recessive or dominant male sterility genes). INMS has become one of the most useful MS systems. This critical review focuses on the types, genetic analysis and technological breakthroughs of Brassica plant male sterility systems for their use in the large-scale hybrid-seed production.

Genetic characterization of a new cytoplasmic male sterility system (hau) in Brassica juncea and its transfer to B. napus

A novel cytoplasmic male sterility (CMS) was identified in Brassica juncea, named as hau CMS (00-6-102A). Subsequently, the male sterility was transferred to B. napus by interspecific hybridization. The hau CMS has stable male sterility. Flowers on the A line are absolutely male sterile, and seeds harvested from the line following pollinations with the maintainer gave rise to 100% sterile progeny. The anthers in CMS plants are replaced by thickened petal-like structures and pollen grains were not detected. In contrast, in other CMS systems viz. pol, nap, tour, and ogu, anthers are formed but do not produce viable pollen. The sterility of hau CMS initiates at the stage of stamen primordium polarization, which is much earlier compared with the other four CMS systems. We have successfully transferred hau CMS from B. juncea to B. napus. Restorer lines for pol, ogu, nap, and tour CMS systems were found to be ineffective to restore fertility in hau CMS. Sixteen out of 40 combinations of mitochondrial probe/enzyme used for RFLP analysis distinguished the hau CMS system from the other four systems. Among these sixteen combinations, five ones alone could distinguish the five CMS systems from each other. The evidence from genetic, morphological, cytological and molecular studies confirmed that the hau CMS system is a novel CMS system.

Discovery of new male-sterile cytoplasm sources and development of a new cytoplasmic-nuclear male-sterile line NJCMS3A in soybean

Most of the cytoplasmic-nuclear male-sterile (CMS) lines of soybean were developed only from a limited cytoplasm sources and performed not as good as required in hybrid seed production, therefore, to explore new male-sterile cytoplasm sources should be one of the effective ways to improve the pollination and hybridization for a better pod-set in utilization of heterosis of soybeans. In the present study, total 80 crosses between 70 cultivated and annual wild soybean accessions and three maintainers (N2899, N21249, and N23998) of NJCMS1A were made for detecting potential new sources with male-sterile cytoplasm. The results showed that in addition to the crosses with N8855.1 (the cytoplasm donor parent of NJCMS1A) and its derived line NG99-893 as cytoplasm parent, there appeared three crosses, including N21566 × N21249 and N23168 × N21249, with male-sterile plants in their progenies. According to the male fertility performance of backcrosses and reciprocal crosses with the tester N21249, the landrace N21566 and annual wild soybean accession N23168 were further confirmed to have male-sterile cytoplasm. Accordingly, it was understood that the source with male-sterile cytoplasm in soybean gene pool might be not occasional. The results also showed that the genetic system of male sterility of the newly found cytoplasm source N21566 was different from the old cytoplasm source N8855.1, while N23168 was to be further studied. Based on the above results, the derived male-sterile plants from [(N21566 × N21249) F1 × N21249] BC1F1 were back-crossed with the recurrent parent N21249 for five successive times, and a new CMS line and its maintainer line, designated as NJCMS3A and NJCMS3B, respectively, were obtained. NJCMS3A had normal female fertility and stable male sterility. Its microspore abortion was mainly at middle uninucleate stage, earlier than that of NJCMS1A and NJCMS2A. The male fertility of F1s between NJCMS3A and 20 pollen parents showed that 7 accessions could restore its male fertility and other 13 could maintain its male sterility. The male sterility of NJCMS3A and its restoration were controlled by one pair of gametophyte male-sterile gene according to male fertility segregation of crosses between NJCMS3A and three restorers. The nuclear gene(s) of male sterility in NJCMS3A appeared different from the previously reported CMS lines, NJCMS1A and NJCMS2A. The development of NJCMS3A demonstrated the feasibility to discover new CMS system through choosing maintainers with suitable nuclear background.

Stable male sterility induced by the expression of mutated melon ethylene receptor genes in Nicotiana tabacum

A major concern about genetically modified crops is transgene flow through pollen dispersal. We previously demonstrated that overexpression of the mutated melon ethylene receptor genes Cm-ETR1/H69A or Cm-ERS1/H70A induces pollen abortion and altered flower architecture, resulting in sterility or reduced fertility in transgenic tobacco plants. To investigate the stability of these traits, three transgenic tobacco lines in which Cm-ETR1/H69A or Cm-ERS1/H70A confer sterility or reduced fertility were grown in a greenhouse with environmental conditions that changed, depending on the outside conditions. During the growth of the plants, the temperature ranged from 31°C at the beginning of September to 17°C at the beginning of November. The light provided was natural sunlight. The first group of plants flowered in late September, and the second group flowered in late October. The wild-type plants showed the homostyly type of floral architecture, whereas, three transgenic lines showed the heterostyly type. The floral architecture was stable during the different flowering periods. Pollen production was significantly reduced in two transgenic lines and completely aborted in one transgenic line, and these traits were also stable during the different flowering periods. These results suggest that the sterility or reduced fertility induced by the expression of mutated melon ethylene receptor genes in transgenic tobacco plants is stable under varying environmental conditions.

Photoperiod-sensitive male-sterile mutant in tomato and its potential use in hybrid seed production

SummaryThe current practice of manual emasculation of tomato ¯owers for hybrid seed production is labour-intensive and contributes signi®cantly to the high cost of seed. Here we report on a photoperiod-sensitive, single gene male-sterile mutant (7B-1) in tomato which is 100% male sterile in long days (LD, minimum of 12.h daylength) in summer ®eld conditions, but produces many male-fertile ¯owers in short days (SD, 8.h). In LD, 7B-1 ¯owers contain stamens that are pale, short and in the anthers microspore mother cells are differentiated but meiosis does not occur, i.e. microspores and pollen grains are not formed. Unlike the wild type ¯owers, the style and stigma of 7B-1 ¯owers are well exposed and this allows for ready access for pollination without emasculation. In SD, mutant ¯owers possess normal-looking orange-yellow anthers that enclose the stigma and produce normal viable pollen, which when used for pollination of 7B-1 ¯owers yield good fruit- and seed-set. The 7B-1 seed in turn generate a 100% population of male-sterile plants all of which can be used as female parents for hybrid seed production. The female fertility is not affected in 7B-1 ¯owers in both LD and SD conditions. The 7B-1 mutant has been grown in various ®eld locations including, Saskatoon, California, Florida and in Chile, and at all locations it has shown stable male sterility. The 7B-1 mutant is a simple, natural and costeffective system that has a strong potential for use in commercial-scale production of tomato hybrid seed.

Commercial viability of alternative cytoplasmic-nuclear male-sterility systems in pearl millet

Commercial viability of three cytoplasmic-nuclear male sterility (CMS) systems (A4, A5 and Av) as potential alternatives to the most widely used A1 system in pearl millet (Pennisetum glaucum (L.) R.Br.) was evaluated in terms of stability of complete male sterility of four isonuclear A-lines (81A1, 81A4, 81A5 and 81Av) and the level and stability of male fertility restoration of their 44 single-cross hybrids. Lines 81A4 and 81A5 had no pollen shedders (PS), and there were very low frequency of non-PS plants of these A-lines that had a maximum of 1–5% selfed seedset (SSS). In 81A1 and 81Av,there were, albeit low frequency (<1%) of PS plants, and relatively higher frequency of the non-PS plants in these two lines, the more so in 81Av,had 1–5% and even greater SSS. Some hybrids made on each of the three A-lines (81A1, 81A4 and 81Av) had high and stable male fertility, while others made on the same three A-lines displayed large variation in SSS across the environments, the more so in case of hybrids made on 81Av. These results indicate that the A4 CMS system provides a better alternative to the A1 CMS system, while the Av system does not. On the basis of highly stable male sterility and the highest frequency of pollinators behaving as maintainers, the A5 CMS system appeared to be the best for A-line breeding. The commercial viability of this CMS system in breeding R-lines of grain hybrids, however, still remains to be ascertained as no hybrid on it was fully male fertile in any environment.

Identification of stable maintainer and fertility restorer lines for 'Polima' CMS in Brassica campestris

'Polima' cytoplasmic male sterility (CMS) was transferred from 'Polima' Brassica napus ISN 706' to five different cultivars of Brassica campestris ('Pusa kalyani', Pant toria', 'Candle', Tobin' and 'ATC 94211') by repeated backcrossing. It was observed that, while 'Polima' CMS manifested complete and stable male sterility in the nuclear backgrounds of Pusa kalyani', Pant toria', and Tobin', the cultivars Candle' and 'ATC 94211' possessed the restorer gene for this CMS in the heterozygous condition. An analysis of F 1 and F 2 generations of Polima' Pusa kalyani' × Candle' and 'Polima' 'Pusa kalyani' x 'ATC 94211' revealed that restoration is controlled by a single dominant gene. Identification of stable maintainers and restorers of Polima' CMS could facilitate the development of hybrid varieties in B. campestris.

Agro-morphological characterization of ovary culture-derived plants of rice (Oryza sativa L.)

Plants derived from unpollinated ovary culture of ten rice genotypes showed significant variability in agro-morphological characteristics. The ovary-derived plant (H1) populations were completely haploid, doubled haploid or haploid-doubled haploid mixture. Haploids had very drastic reduction in plant height, panicle length, grain length, breadth and number and spikelet fertility (0.0%–2.1%). Doubled haploids from the hybrid of UPRI 95–121 × UPRI 95–165 were normal with fertility ranging between 69.6% and 97.7%. A genetic segregation in ratio of 1:1 was observed for five pigmentation characters in the H1 population derived from hybrid UPRI 95–122 × UPRI 95–165. Plant height showed the largest coefficient of variability (28.5%) followed by the number of spikelets per panicle (24.2%), number of grains per panicle (22.0%), percent seed set (9.2%) and panicle length (9.0%). The range of variation in the H1 population from fully fertile hybrid PMS 2A (CMS) × IR 31802 (restorer) was similar to its corresponding F2 population for plant height, spikelet fertility and number of grains/panicle. A single clone of plants from the cultivar BG 1321 exhibited complete male sterility but normal female fertility when pollinated with other varieties. Ovary-derived plants from the CMS lines PMS 2A and IR 58025A showed stable male sterility and those from thermosensitive genetic male sterile line UPRI 95–140 showed thermosensitive genetic male sterility. These lines have potential in the hybrid breeding program and are being currently exploited.

Detection and characterization of two new CMS systems in faba bean (Vicia faba) *

AbstractWide crosses were made to identify new cytoplasmic male sterility (CMS) systems in faba beans, based on the interaction of cytoplasm with restorer and maintainer alleles. A total of 330 F1 hybrids were produced in both reciprocal forms. Male sterile segregates were observed in one reciprocal version in the F2 generation of six crosses. Two of these crosses with female parents originating from Afghanistan and Egypt expressed stable male sterility in subsequent backcross generations. Based on the female parents of the two crosses, these two CMS systems were designated CMS 199 and CMS 297. CMS 199 was more stable than CMS 297 during backcross generations and across different environments. Maintainer and restorer lines for both CMS systems were identified. Lower expression of male sterility occurred in CMS 297 in the greenhouse during the winter generations than in isolation cages during the summer generations, which may be utilized to maintain male sterile lines by selfing. Regarding practical applications, the CMS 199 shows great promise for hybrid breeding in faba beans.

A male sterile line with dominant gene (Ms) in cabbage (Brassica oleracea var. capitata) and its utilization for hybrid seed production

A male sterile plant, 79-399-3, was identified from a spring cabbage line 79-399 in 1979. Light-microscopic studies with paraffin section indicated that meiotic division stopped at the tetrad stage. The ratio of male sterile plants to fertile plants in the progenies of test crosses was 1:1 in five experiments conducted in 1982 and 1991–1994. However, some male sterile plants were sensitive and developed a very low number of viable pollen grains. When sensitive male sterile plants were selfed, the progenies segregated into male sterile and fertile plants at a ratio of 3:1. The male sterile plants from selfing of sensitive male sterile plants were propagated by tissue culture and crossed with different inbred lines. From the progenies of the crosses, populations with 100% male sterile plants were observed. The results indicated that homozygous dominant male sterile (MsMs) plants segregated from the selfed progenies. Populations with 100% male sterile plants and stable male sterility were developed as male sterile lines. Several favorable combinations were also selected by crossing the male sterile lines with inbred lines with high combining ability for desirable horticultural characters.

A Second Source of Cytoplasmic Male Sterility in Maize Induced by the Nuclear Gene Iojap

Cytoplasmic male sterility (cms) was found in plants derived from the F2 progeny of fertile, normal cytoplasm plants of the inbred R181 pollinated with a genetic stock carrying the recessive nuclear gene, iojap. The male sterile plants were maintained by back-crossing with the inbred W182BN which maintains all known sources of cytoplasmic male sterility. The new male sterile progeny were found to exhibit stable male sterility under field conditions in two environments. However, they were partially fertile in the hot, dry summer of 1983 at Aurora, NY. It was found that these lines were restored by lines that characteristically restore cms S group cytoplasms. Pollen phenotype studies indicated that the restoration was gametophytic in nature, also characteristic of the cms S group. Agarose gel electrophoresis of undigested mitochondrial DNA (mtDNA) from these steriles indicated that these lines have the S-1 and S-2 episomes characteristic of the cms S group. Restriction endonuclease digest patterns of mtDNA from these sterile lines digested with BamH I indicated that these steriles fit into the CA subgroup of the cms S group. The new source of cms has been designated cms Ij-1.