Male-sterile Parents Research Articles

The Dark Side of the pollen: BSA-seq identified genomic regions linked to male sterility in globe artichoke

Globe artichoke (Cynara cardunculus var. scolymus; 2n = 2x = 34) is a food crop consumed for its immature flower heads. Traditionally, globe artichoke varietal types are vegetatively propagated. However, seed propagation makes it possible to treat the crop as annual, increasing field uniformity and reducing farmers costs, as well as pathogens diffusion. Despite globe artichoke’s significant agricultural value and the critical role of heterosis in the development of superior varieties, the production of hybrids remains challenging without a reliable system for large-scale industrial seed production. Male sterility (MS) presents a promising avenue for overcoming these challenges by simplifying the hybridization process and enabling cost-effective seed production. However, within the Cynara genus, genic male sterility has been linked to three recessive loci in globe artichoke, with no definitive genetic mechanism elucidated to date. A 250 offsprings F2 population, derived from a cross between a MS globe artichoke and a male fertile (MF) cultivated cardoon (C. cardunculus var. altilis) and fitting a monogenic segregation model (3:1), was analyzed through BSA-seq, aiming at the identification of genomic regions/genes affecting male sterility. Four QTL regions were identified on chromosomes 4, 12, and 14. By analyzing the sequence around the highest pick on chromosome 14, a cytochrome P450 (CYP703A2) was identified, carrying a deleterious substitution (R/Q) fixed in the male sterile parent. A single dCAPS marker was developed around this SNP, allowing the discrimination between MS and MF genotypes within the population, suitable for applications in plant breeding programs. A 3D model of the protein was generated by homology modeling, revealing that the mutated amino acid is part of a highly conserved motif crucial for protein folding.

Combining ability of carrot genitors for root yield traits and leaf blight tolerance

The market demand for uniformity and productivity of commercial carrot roots has prioritized hybrid materials over open-pollinated varieties. In this sense, the objective of this work was to estimate the combining ability of carrot genitors for root productivity and resistance to leaf scorch. The experiments were conducted in Gama, DF, in the agricultural years 2012/13 and 2013/14. We evaluated 33 carrot hybrids, originated from crosses between three male-sterile populations, with 11 male-fertile S2 lines, all the genitors being of tropical origin. At 90 days after sowing, the severity of the leaf blight disease was estimated in the plots. At 100 days after sowing, harvesting was performed and root yield characters were evaluated. Analysis of variance and partial diallel analysis were performed for each year and jointly for both years. It was found that additive and non-additive genes are important in the manifestation of root yield and leaf blight resistance traits in carrot hybrids. The male-sterile parents with higher overall combining ability for root productivity are strains LM-649 and LM-650 and, among the male-fertile, strain LM-555-2-2. The best hybrids for root yield and leaf blight resistance are LM-649 × LM-555-11-1, LM-650 × LM-555-7-1 and LM-650 × LM-554-8-1.

Genetic Improvement of Chinese Jujube for Disease Resistances: Status, Knowledge Gaps and Research Needs

Chinese jujube is one of the earliest domesticated fruit trees in the world. This fruit crop is becoming increasingly popular globally for its outstanding adaptability to marginal land and a broad range of climate conditions. There is a growing demand by growers and consumers for new cultivars with improved yields, earliness, resistance to biotic and abiotic stresses and fruit quality attributes. Breeding jujube for disease resistance is still in its infancy despite the consensus that disease is the top-ranking production constraint and growing disease resistant cultivars is the most sustainable and cost-effective approach for diseases management. Major knowledge gaps remain to be filled in the current breeding scheme for enhancing disease resistance. These knowledge gaps include, but are not limited to (1) a lack of understanding of jujube pathogens in terms of their taxonomy, epidemiology and genetic diversity; (2) a lack of standardized screening methods to identify host resistance; (3) a high rate of germplasm mislabeling; and (4) ineffective production of hybrid progenies. Nonetheless, recent progress in utilization of male sterile parents in controlled crosses, coupled with mounting genomic information on both pathogens and jujube, will likely speed up the combination of host resistance with other horticultural traits. This article reviews the status of jujube disease resistance breeding and suggests future research needs for developing disease resistant cultivars of Chinese jujube. Although the review focuses on jujube breeding programs in China, the summarized information should be useful to researchers in the international jujube community as well.

Floral traits to enhance outcrossing for higher hybrid seed production in rice: present status and future prospects

High seed cost is a major factor limiting the adoption of hybrid rice in South and Southeast Asian countries. A practical way to improve hybrid seed production is to increase the outcrossing rate in rice. Several studies reveal that perennial wild Oryza species have a higher outcrossing rate than annual species. Among various traits that influence outcrossing, pistil characteristics are the most crucial in improving the seed set on the male sterile parent in hybrid seed production. Wild species are known to have wide genetic variability for stigma length, anther length, and percent stigma exsertion. This review establishes the need to exploit new genetic resources, through both classical and molecular breeding approaches, to improve seed production. It also reviews the genetic variability of floral characteristics, the genetics of floral traits that influence outcrossing, and progress made in understanding these traits using biotechnological approaches, the effect of environment on floral traits and the resulting prospects for improving hybrid rice seed production.

Nectar phenolics drive cross visits between dimorphic flowers by honey bees

SummaryBroccoli (Brassica oleracea) is widely grown. For hybrid seed production, farmers use a hermaphrodite parent, conventionally called “male”, to cross with a male sterile parent, or “female”. We fed Apis mellifera colonies with 30 % sucrose solution with (P-fed) and without (S-fed) para-hydroxybenzoic acid (a phenolic acid commonly found in nectar), and compared the number of pollen foragers between the P- and S-fed colonies. As compared to the S-fed colonies, the P-fed colonies had higher proportions of foragers visiting the male plants for pollen. Also, they had higher proportions of pollen foragers that switched to visit the female plants. Our study suggests that nectar phenolics may be adaptively suited to augment outcrossing pollination by honey bees.

Registration of ‘Bearpaw’ Wheat

‘Bearpaw’ (Reg. No. CV‐1083, PI 665228) hard red winter (HRW) wheat (Triticum aestivum L.) was developed and released by the Montana Agricultural Experiment Station in September 2011. Bearpaw is of unknown pedigree, derived from a composite of five crosses made to the same F1 male sterile parent in 1999: Dominant male sterile (DMS)/‘Rampart’//‘Pronghorn’/3/2*Rampart, DMS/Rampart//Pronghorn/3/Rampart/4/MTW9806, DMS/Rampart//Pronghorn/3/Rampart/4/‘Nuplains’, DMS/Rampart//Pronghorn/3/Rampart/4/MT9513, DMS/Rampart//Pronghorn/3/Rampart/4/MT98113. Bearpaw was developed using a modified bulk‐breeding method and selected as an F5:6 headrow. Bearpaw was tested under the experimental number MTS0721 from 2007 to 2011 in Montana. Quality has been evaluated in multilocation Montana trials since 2007. Bearpaw is a high‐yielding, solid‐stem, semidwarf (Rht‐B1b) HRW wheat cultivar with medium maturity, medium to high test weight and grain protein, and acceptable milling and baking quality. Bearpaw was released for its host‐plant resistance to wheat stem sawfly (Cephus cinctus Nort.) conditioned by stem solidness, along with short stature and improved yield potential relative to existing solid‐stem cultivars adapted to Montana.

A novel hybrid seed system for plants

A two-component hybrid seed system has been developed that is broadly applicable and provides for effective generation and maintenance of the male-sterile parent, hybrid seed production and full restoration of fertility in the hybrid seed. The technology is based on the functional interaction of two loci that are inserted in the same position on two homologous chromosomes, and thus are 'linked in repulsion', and that jointly code for male sterility and herbicide resistance, both traits being expressed in heterozygous plants only. The localization to the same locus on a chromosome is achieved by the genetic transformation of plants with a construct containing both genetic elements (loci), and subsequent derivatization from the primary pro-locus of the two precursor lines using site-specific deletions. The functional interaction of the two loci is achieved through intein-based trans-splicing of two pairs of complementary protein fragments that provide for male sterility and herbicide resistance. Unlike the hybrid seed systems that are currently in use, the technology relies on the genetic modification of just one parent, and is therefore much simpler to develop and use. Arabidopsis has been used for the proof of principle presented here, but the essential elements of the technology are generic and have been shown to work in many crop species.

Molecular Characterization of Mitochondrial Genomes of Rice Lines Containing Wild Abortive (WA) Male Sterile and Fertile Cytoplasms

Indian rice breeders have developed hybrid rice using primarily the wild abortive (WA) type cytoplasm for the male sterile parent. In this communication, we report our studies on the molecular characterization of the mitochondrial genomes of male sterile lines possessing this cytoplasm as also the respective maintainer, restorer and restored lines using 16 mitochondrial gene probes. The results show polymorphism in the location of several genes and expression of one of the genes, namely orf 156. Polymorphism in five genes namely coxl, cob, atp 6, rrn18 and orf156 differentiates the sterile cytoplasm from the fertile ones while the RFLPs in coxIII and rps14 can differentiate maintainers and restores from each other. The WA cytoplasm is very different from the Chinsurah boro II cytoplasm as is evident from the transcription patterns of atp6. Of the genes studied, only orf156, which encodes a membrane bound 156 amino acid long polypeptide showed differences In the transcript pattern between the male sterile and fertile cytoplasms. However, it is not clear whether this gene is associated with the CMS trait in WA type of cytoplasm. These studies show the utility of mitochondrial RFLPs to distinguish different cytoplasms existing in the rice lines.

A chimeric and truncated mitochondrial atpA gene is transcribed in alloplasmic cytoplasmic male-sterile tobacco with Nicotiana bigelovii mitochondria

Protoplast fusions were performed between two sexually produced alloplasmic male-sterile tobacco cultivars, with cytoplasms from Nicotiana bigelovii [Nta (big)S] and N. undulata[Nta(und)S], both of which exhibit homeotic-like phenotypes affecting the petal and stamen whorls. Among the fusion products obtained, both novel male-sterile and pollen-producing cybrid plants were identified. Of the pollen-producing cybrid plants, all of which were indehiscent, some had flowers with stamens that appeared normal when compared to male-fertile tobacco plants. Other hybrid plants were incompletely restored as they exhibited petaloid structures on the anther-bearing pollen-producing stamens. In this study, gel-blot analyses with mitochondrial geneprobes were conducted comparing the mitochondrial DNA of cybrids and male-sterile parents. It was found that the flower morphology typical of the Nta(big)S parental plants, as well as of the novel male-sterile cybrids, coincided with the presence of a chimeric atpA gene copy where an open reading frame of unknown origin was found to be linked in-frame to the 3'-end of a truncated atpA gene. RNA gel-blot hybridizations revealed the presence of atpA transcripts in the malesterile parent Nta(big)S and novel male-sterile cybrids, but which were absent in cybrids capable of pollen production.

Observations on Inheritance of Male Sterility in Apricot

Male sterility is defined as the deviant condition in normally bisexual plants when no viable pollen is formed (Frankel and Galun, 1977). Male sterility has been exploited as an effective tool to aid hybrid seed production in many crops. Using this trait, seed producers can transform one inbred from a planned hybridization into a “female” line, thereby ensuring seed of hybrid origin on the male-sterile parent (Janick, 1972). However, male sterility is an undesirable characteristic in scion cultivars of Prunus to be used for fruit production because this trait would restrict yield in large monocultural production blocks. From the viewpoint of an apricot breeding program, male sterility is a characteristic to be avoided (Scott and Weinberger, 1944). A review of apricot (Prunus armeniaca L.) pollen fertility (Burgos, 1991) indicated that only two cases of male-sterile apricot cultivars (‘Arrogance’ and ‘Colorao’) have been described (Garcia et al., 1988). In this paper we show where several male-sterile trees were observed in progenies from controlled hybridizations in P. armeniaca, and we propose a preliminary inheritance model of the trait. Nine different crosses with a total of 378 trees were scored for the male sterility trait. Male-sterile anthers can be distinguished visually from normal fertile anthers during the bloom period. Shrunken, discolored anthers are indicative of male-sterile pollen and provide a sharp contrast to the swollen, yellow appearance of normal pollen-fertile anthers (Connors, 1927). Several samples of shrunken, discolored anthers were chosen randomly to

Modifications of Mitochondrial DNA Cause Changes in Floral Development in Homeotic-like Mutants of Tobacco.

To investigate the influence of mitochondrial genes on stamen development of higher plants, protoplasts from three different, male-sterile tobacco cultivars were fused. The fused cells were cultured individually into calli, from which plants were regenerated. Cybrid plants were obtained that exhibited flowers with recombined biparental male-sterile morphology and with novel male-sterile stamens that differed from any types from sexual or somatic hybridizations described previously. The male-sterile morphologies of these cybrids and their parents support the hypothesis that nuclear-mitochondrial interaction occurs at several stages in tobacco floral development and that several mitochondrial genes are necessary for normal stamen and corolla development. Analysis by restriction endonuclease digestion of mitochondrial DNA of male-sterile cybrids and their parents revealed that the mitochondrial DNA of male-sterile cybrids with parental floral morphology was unchanged when compared with parental mitochondrial DNA. Cybrids that were morphologically similar to one parent's male-sterile phenotype had mitochondrial DNA almost identical to that parent, whereas cybrids with recombined biparental or novel male-sterile phenotypes contained mitochondrial DNA different from both male-sterile parents and from each other. A set of mitochondrial DNA fragments could be correlated with split corollas, a feature found in several tobacco male-sterile cultivars. DNA gel blot analysis using a number of mitochondrial genes confirmed the conclusions based on ethidium bromide staining of mitochondrial DNA restriction digests.

Modifications of floral development in tobacco induced by fusion of protoplasts of different male-sterile cultivars

Protoplasts derived from different cytoplasmic male-sterile cultivars of Nicotiana tabacum were fused. Nearly 200 cybrid calli were regenerated into plants and their flower morphologies were examined. Most cybrids exhibited parental-type male-sterile morphologies. Some, however, showed novel male-sterile phenotypes or phenotypes which combined traits of both male-sterile parents in a new combination. Others were restored to fertility, with stamens which produced functional pollen.

On the mechanism of cytoplasmic male sterility in the 447 line of Vicia faba

The trait of cytoplasmic male sterility, expressed in plants bearing the 447 cytoplasm of Vicia faba, is uniquely and positively correlated with the presence of a linear double-stranded RNA molecule (dsRNA) 16.7 kb in size. Restriction enzyme digestion profiles of mitochondrial DNA isolated from fertile and cytoplasmic malesterile (CMS) lines do show a limited number of specific differences in fragment intensities and mobilities. However, mitochondria isolated from the progeny of the cross CMS × Restorer line contain DNA with an identical restriction profile as the male-sterile parent: moreover, subsequent generations are completely and permanently fertile, even upon segregation of the nuclear restoration gene. Southern hybridizations, using cDNA clones as probes, reveal homology between the CMS-associated dsRNA and the nuclear genome of both sterile and fertile lines. The regions cloned, representing approximately 22% of the total dsRNA sequence, show no homology to organelle DNA. We have not been able to stably transmit the dsRNA to fertile lines of V. faba or any other plant species, using a variety of standard virological techniques.

Fusion-mediated combination of Ogura-type cytoplasmic male sterility with Brassica napus plastids using X-irradiated CMS protoplasts

X-irradiated protoplasts of a Brassica napus line carrying the Ogura Raphanus sativus male sterile cytoplasm were fused to protoplasts of male fertile B. napus cv. Olga. Plants were regenerated from six out of 34 randomly selected clones. In one clone, Bn(RS)26, a plant with male sterile flowers was obtained. Mitochondria of this plant are non-parental as revealed by DNA-DNA hybridization using a species specific probe. Its chloroplasts, however, derive from the fertile parent which results in loss of the sensitivity to low temperatures associated with R. sativus plastids in the male sterile parent. The novel cytoplasm of the Bn(RS)26 cybrid was transmitted through seed.

Influence of Tetracycline on the Expression of Cytoplasmic Male Sterility (cms) in Chives (Allium schoenoprasum L.)

AbstractTo influence the expression of cytoplasmic male sterility (cms), different clone members of male sterile genotypes of chives were treated with different chemicals, especially antibiotics which are known to act as protein synthesis inhibitors. A remarkable number of male sterile plants turned to partial or full male fertility after the treatment with tetracycline HCl and tetracycline base. Pollen grains produced by tetracycline on male sterile plants were viable and able to fertilize the egg cells. By using the perennial nature of Allium schoenoprasum L. it could be shown that the fertility induced on male sterile plants by tetracycline is reversible. This could be of practical importance for the multiplication of male sterile parents in hybrid breeding. None of the chemicals had any effect on the fertility of male fertile plants. Differences in reaction indicated that genetic differences exist between male sterile plants responding to tetracycline and those which do not.The results are discussed in view of the influence of tetracycline on the mitochondrial protein biosynthesis.

DISTANCE FROM POLLEN SOURCE AND YIELDS OF MALE STERILE SUNFLOWER AND SORGHUM

Efficient production of hybrid sunflower (Helianthus annuus L.) and sorghum (Sorghum bicolor (L.) Moench) seed requires a minimum but adequate proportion of the land for pollinator rows and that the male sterile and pollinator rows accommodate production machinery. The objective of this research was to determine the effect of distance from pollen source on male sterile seed yield and if presently used ratios of male sterile to pollinator rows could be increased without reduction in seed yield of the male sterile parent from the land area occupied by both parents. Seed was harvested from male sterile rows located from 1 (76 cm) to 40 (30 m) rows from the pollen source. Correlations and regression analyses showed that yield per row declined linearly with distance from the pollinator rows. However, yield of the male sterile parent per hectare of area occupied by both parents was increased by including up to at least six male sterile and two pollinator rows per strip. Male sterile to pollinator row ratios of 12:1 for sunflower and 7:1 for grain sorghum did not differ significantly from the commonly used 3:1 ratio in yield of male sterile parent per hectare of area occupied by both parents.Key words: Helianthus annuus L., Sorghum bicolor (L.) Moench, hybrid seed production, plant breeding

Male‐Fertility Restoration in Crosses of R5 with Soft Red Winter Wheats1

The inheritance of male‐fertility restoration was studied in crosses of the spring wheat restorer germplasm line R5 with cms ‘Monon’ and cms ‘Redcoat’ soft red winter wheat (Triticum aestivum L.) cultivars with T. timopheevii Zhuk. cytoplasm. Two greenhouse cycles of Fl's, F2's, BC1's, along with the restored parent, and malesterile parents, were grown to provide two sets of data. Genetic hypotheses were postulated as expected ratios of fertile: semi‐sterile: sterile plants and data were tested for goodness of fit by chi‐square analyses. The BC1F2 populations and F3 populations were grown in the field to determine the proportion of families segregating for sterility. Results from the cms Monon/R5 crosses indicated the presence of two partially dominant complimentary restorer factors in the greenhouse and field environments. Complete fertility restoration was expressed only when both dominant factors were present to either the homozygous or heterozygous condition. Results from the cms Redcoat/R5 crosses suggested the presence of three dominant factors in the greenhouse environment, but segregation in the field environment suggested that only two factors were involved.The complete restoration of fertility of F1 plants in the environments tested suggests that R5 is a valuable source of restorer factors for developing R‐lines for hybrid soft red winter wheats.

Asynchrony of Floral Events and Other Differences in Pollinator Foraging Stimuli between Fertile and Male-sterile Carrot Inbreds1,2

Abstract The inability to achieve adequate pollination of seed parents has slowed the development of hybrid carrots (Daucus carota L.) and dampened industry acceptance. Thus, cytoplasmically male-sterile inbreds and F1 seed parents were compared with their fertile counterparts for synchrony of floral events and character of pollinator foraging stimuli. Usually, but not always, male-sterile plants were visually different, bloomed later, and exhibited delayed nectar and aroma production compared to male-fertiles. The quality and quantity of nectar and aroma were also different, with male-sterile flowers often inferior to fertile flowers in amounts of nectar produced. Successful use of any cross-pollinated entomophilous hybrid crop system should involve selection for similar floral characteristics early in the breeding program to insure maximum transfer by insects of pollen from male-fertile to male-sterile parents.

Some aspects of cross-pollination in wheat (Triticum aestivum L.) 1. Pollen concentration in the field as influenced by variety, diurnal pattern, weather conditions and level as compared to the height of the pollen donor

For the large-scale production of hybrid seed the cross-fertilizing capacity of wheat must be increased. Breeding good pollinators is, therefore, a necessity. Five spring wheat varieties were examined for differences in pollen shedding capacity under normal field conditions. The examination was carried out by collecting pollen on object slides every hour from 06.00 till 20.00 h during flowering. In general, the variety Peko proved to be the best shedder of pollen, while Opal was the worst. Gaby, Jufy I and Orca were intermediate. Consistent results were hard to obtain mainly due to varying weather conditions. It was established that pollen is released throughout the whole period of daylight. The maximum release of pollen, however, occurred from 08.00 till 11.00 h. A less pronounced and much smaller peak was noticed from about 15.00 till 18.00 h. Most pollen appeared to be released at a temperature of 16–20°C and a relative humidity of 70–75%. Although there seems to be some relationship between the diurnal pattern of the pollen release and the indicated values of these meteorological factors, one cannot say that the former is entirely determined by the latter. It has been suggested in the literature that a male-sterile parent that is shorter than its pollinator would be most likely to produce good seed set in the hybrid wheat seed production field. Investigations showed that a greater concentration of pollen was found below the ear level of pollinator plants than at or above ear level.

Heterosis for Yield and Yield Components in Rice

It is important to know the degree and direction of hybrid vigor for its commercial exploitation. Heterobeltiosis and standard heterosis were studied in 14 crosses between rice (Oryza sativa L.) cultivars (improved and landraces) and three wild aborted male sterile parents. These crosses showed marked variations in the expression of heterobeltiosis and standard heterosis for yield and yield components. Grain yield manifested highly significant heterobeltiosis and standard heterosis in five crosses. Heterobeltiosis ranging from –55 to 139% and standard heterosis from –11 to 369% were observed. Highest heterotic effect among the yield components was for panicle number plant-1 followed by spikelet number and panicle length. With appropriate choice of parental lines, it is possible to develop F1 rice hybrid possessing distinct yield superiority over the best-inbred lines.Key words: F1; Heterobeltiosis; Hybrid vigor; Oryza sativa; Standard heterosisDOI: http://dx.doi.org/10.3126/narj.v4i0.4857Nepal Agriculture Research Journal Vol. 4&5, 2001/2002Page: 6-12Uploaded date: 8 June, 2011