Functional male sterility in tomato (Lycopersicon esculentum Mill.) and its application in hybrid seed production

Advantages and disadvantages in using functional male sterility (positional sterile — ps, positional sterile 2 — ps 2, and excerted stigma — ex) in tomato hybrid seed production and attempts to elaborate systems for their more efficacious use in breeding were discussed in this review. It was concluded that the application of one of these types of sterility, (ps 2) in practice, although in a limited number of countries, showed the functional male sterility in tomato was a potential not to be underestimated in developing approaches that aimed at reducting the time and cost associated with hybrid seed production.     

Genetic load,nutrient limitation,and seed production in Lupinus texensis (Fabaceae)

The interaction of mating system and nutrient limitation in determining seed production was investigated in the annual, self-compatible plant Lupinus texensis (Fabaceae). Abortion of developing seeds is a major factor limiting seed production in natural populations (17-28%). Selfing rates are generally low (0.02-0.21), suggesting that deleterious recessive genes may be maintained at significant levels in natural populations. The average inbreeding depression associated with seed development is δ = 0.24. Nutrient limitation reduced seed output across experimental treatments by a factor of 0.22 through decreased production of inflorescences, flowers, and ovules, and by a factor of 0.29 through increased abortion of fruits and of seeds within fruits. Competition for resources among fruits increased the frequency of seed abortion. Moreover, a greater proportion of selfed seeds were aborted as the overall abortion rate increased. Estimates of genetic load may therefore only be appropriate if undertaken in the field, and inbreeding depression may vary from year to year simply due to changes in environmental conditions rather than to underlying genetic changes in populations. The existence of inbreeding depression and the high frequency of abortions suggest that selective abortion favoring outcrossed progeny occurs in natural populations of L. texensis.     

A straight-forward seed production technology system for foxtail millet (Setaria italica)

For autogamous crops, a precondition for using heterosis is to produce sufficient pure male-sterile female parents that can be used to produce hybrid seeds. To date, cytoplasmic male sterility(CMS)and environment-sensitive genic male sterility(EGMS) have been used commercially to exploit heterosis for autogamous species. However, neither CMS nor EGMS has been established for foxtail millet(Setaria italica). Here, we report on the establishment and application of a seed production technology(SPT)...     

Antisense inhibition of a nuclear gene,BrDAD1, in Brassica causes male sterility that is restorable with jasmonic acid treatment

Male sterility is widely used for the production of hybrid seeds, but the use of genic male sterility is rather limited because of difficulty in maintaining homozygous male sterile plants. Recently, the DEFECTIVE IN ANTHER DEHISCENCE 1 (DAD1) gene, which encodes a phospholipase A1 involved in the first step of the jasmonic acid (JA) biosynthesis pathway, was isolated from a male sterile Arabidopsis mutant. To utilize this gene in Brassica crops, we characterized the BrDAD1 gene, the putative ortholog of DAD1 in Brassica rapa. Out of 25 plants transformed with an antisense gene constructed from the BrDAD1, 3 plants showed a defect of anther dehiscence at the flower bud opening stage and produced inviable pollen. One of the three showed male sterility only, but the other two showed a delay or a lack of flower opening in addition to male sterility. The male sterile and flower-opening phenotypes were rescued by the application of JA as well as linolenic acid. Furthermore, all these characteristics were inherited to the next generation. The present results demonstrate a novel control system for hybrid seed production by the use of nuclear genes.     

CRISPR/Cas9‐mediated knockout of Ms1 enables the rapid generation of male‐sterile hexaploid wheat lines for use in hybrid seed production

The development and adoption of hybrid seed technology have led to dramatic increases in agricultural productivity. However, it has been a challenge to develop a commercially viable platform for the production of hybrid wheat (Triticum aestivum) seed due to wheat's strong inbreeding habit. Recently, a novel platform for commercial hybrid seed production was described. This hybridization platform utilizes nuclear male sterility to force outcrossing and has been applied to maize and rice. With the recent molecular identification of the wheat male fertility gene Ms1, it is now possible to extend the use of this novel hybridization platform to wheat. In this report, we used the CRISPR/Cas9 system to generate heritable, targeted mutations in Ms1. The introduction of biallelic frameshift mutations into Ms1 resulted in complete male sterility in wheat cultivars Fielder and Gladius, and several of the selected male‐sterile lines were potentially non‐transgenic. Our study demonstrates the utility of the CRISPR/Cas9 system for the rapid generation of male sterility in commercial wheat cultivars. This represents an important step towards capturing heterosis to improve wheat yields, through the production and use of hybrid seed on an industrial scale.     

EXTRAFLORAL NECTARIES AND PLANT GUARDING IN IPOMOEA PANDURATA (L.) G. F. W. MEY. (CONVOLVULACEAE)

Throughout the range of Ipomoea pandurata in North and South Carolina, ants and wasps are attracted to the pedicellar extrafloral nectaries. These hymenopterans are aggressive toward phytophagous insects that visit the plants. Protection of the plant is afforded by these pugnacious hymenopteran nectar feeders.     

Indian Potato (<Emphasis Type="Italic">Ipomoea pandurata</Emphasis>, Convolvulaceae)—A Record of Confusion<Superscript>1</Superscript>

Indian Potato ( Ipomoea pandurata , Convolvulaceae)—A Record of Confusion. Once European explorers began sending back plants from distant lands, confusion developed regarding their identities. Among these was Ipomoea pandurata, which native peoples in the eastern United States considered to be a purgative. Unfortunately, edible plants like potatoes were confused with I. pandurata, and by the early 1900s Americans and Europeans began writing that indigenous peoples also ate its roots. The literature for the late 1900s into the 2000s mostly reports that I. pandurata is edible. Although no documented use for food by pre-European cultures in the Americas has been found, the myth persists that the roots were eaten on a regular basis.     

Induction of male and female sterility in isabgol (<Emphasis Type="Italic">Plantago ovata</Emphasis>) due to floral infection of downy mildew (<Emphasis Type="Italic">Pernospora plantaginis</Emphasis>)

Downy mildew (Peronospora plantaginis) caused two different types of infection in the floral parts of isabgol (Plantago ovata). Systemic infection resulted in long spikes bearing weak and sterile florets, which later turned black due to saprophytic growth. Localised infection produced various symptoms ranging between normal flower opening and failure to bloom. Different parts of infected flowers such as sepal, petal, filament and anther were reduced in size compared to healthy flowers. However, gynoecium was elongated in localised infection. P. plantaginis induced gradual sterility of isabgol flowers. Androecium was affected more than the gynoecium was. Pollen number, pollen viability and germination reduced drastically due to localised infection. On the contrary, there were no significant differences between healthy and locally infected flowers in terms of stigma receptivity. In systemically infected spikes, bud development was arrested leading to sterility. When localised disease severity was high, secondary systemic infection caused similar symptoms. Microscopic observations showed presence of the pathogen in different parts of the flowers. Downy mildew adversely affected seed yield and quality; producing seeds, which were smaller and lighter than the healthy ones and later, became black. Seed yield was reduced by as much as 73.45 percent. Husk content per unit seed mass increased relatively as the total surface area of infected seeds increased.     

Genetic characterization and fine mapping of a novel thermo-sensitive genic male-sterile gene tms6 in rice (Oryza sativa L.)

The application of genetic male sterility in hybrid rice production has great potential to revolutionize hybrid seed production methodology. The two-line breeding system by using thermo-sensitive genic male sterility (TGMS) has been discovered and successfully developed as a breeding strategy in rice. One TGMS gene was investigated by a spontaneous rice mutant line, Sokcho-MS, originated from a Korean japonica variety. It was shown that Sokcho-MS is completely sterile at a temperature higher than 27°C and/or lower than 25°C during the development of spikelets, but fertile at the temperature ranging from 25 to 27°C regardless of the levels of day-length. Genetic analysis and molecular mapping based on SSR, STS and EST markers revealed that a single recessive gene locus involved the control of genic male sterility in Sokcho-MS. By using an F₂ mapping population derived from a cross between Sokcho-MS and a fertile indica variety Neda, the new TGMS gene, designated as tms6, was mapped primarily to the long arm of chromosome 5 of Oryza sativa at the interval between markers E60663 (2.0 cM) and RM440 (5.8 cM). Subsequently, tms6 was fine mapped to the interval between markers RM3351 (0.1 cM) and E60663 (1.9 cM). As tms6 appeared to be independent of other mapped TGMS genes in rice, the genetic basis of Sokcho-MS was further discussed.     

Polyploidy and sterility in relation to sex in Dioscorea alata L. (Dioscoreaceae)

Chromosome numbers and fertility studies of 73 male and 30 female flowering germplasm accessions of Dioscorea alata L. were carried out. All males were tetraploids showing the same chromosome number (n=20 or 2n=40) and were pollen fertile (10.9–96.2%), most of them being highly fertile. Among the female the majority were higher ploids (hexa-and octoploids; 2n=60 and 80) and sexually completely sterile. There were only two tetraploid female accessions which were sexually fertile. Pollination studies revealed that seed sterility in D. alata was due to female sterility associated with the occurrence of higher levels of ploidy. The female sex-limited occurrence of higher polyploidy and sterility observed in D. alata is a curious situation among dioecious higher plants.     

Variation of sterility and fertility in Utricularia australis f. australis in Hokkaido, northern Japan

Seed-production ability was studied in Utricularia australis R. Br. f. australis Komiya and Shibata through field observation, pollination experiment, pollen culture, and isozyme analysis for populations in various regions of Hokkaido, northern Japan. Utricularia australis f. australis has previously been postulated to be sterile in Japan, however, in the present study, fertile populations were found in eastern Hokkaido. Bisexual sterility and male sterility were suspected to be present in populations in the western part of Hokkaido. There was also a strain that seemed to produce no seed because of intra-clonal inbreeding depression or self-incompatibility. Isozyme analysis of three enzyme systems indicated a uniformity of multienzymatic phenotype (MEP) in each population or region. The MEP grouping of populations corresponded to the type of sterility and fertility revealed by pollination and pollen culture experiments. These experiments suggested that each regional strain had its own sterility or fertility type.     

中国球兰属一新记录种——缅甸球兰

首次报道了萝藦科(Asclepiadaceae)球兰属(Hoya)的1个中国新记录种——缅甸球兰(Hoya burmanica Rolfe),该种原记载产自缅甸和印度,2017年在中国西南部的云南铜壁关省级自然保护区内发现有分布。缅甸球兰与琴叶球兰(Hoya pandurata Tsiang)最为相似,但前者叶三角形或卵状披针形,中脉在叶背面微凸起,花冠杯状,二者容易区别。     

Reproductive system and fitness of Vriesea friburgensis,a self‐sterile bromeliad species

Reproductive biology and plant fertility are directly related to many aspects of plant evolution and conservation biology. Vriesea friburgensis is an epiphytic and terrestrial bromeliad endemic to the Brazilian Atlantic rainforest. Hand‐pollination experiments were used to examine the reproductive system in a wild population of V. friburgensis. Plant fertility was assigned considering flower production, fruit and seed set, seed germination, and pollen viability. Self‐sterility observed from spontaneous selfing and manual self‐pollination treatments may be the consequence of late‐acting self‐incompatibility. Hand‐pollination results indicated no pollen limitation in the population studied. Floral biology features such as a few daily open flowers, nectar production, and sugar concentration corroborate hummingbirds as effective pollinators, although bees were also documented as pollinators. Components of fitness such as high flower, fruit, and seed production together with high seed and pollen viability indicate that this wild population is viable. From a conservation point of view, we highlight that this self‐sterile species depends on pollinator services to maintain its population fitness and viability through cross‐pollination. Currently, pollinators are not limited in this population of V. friburgensis. Conversely, the maintenance and continuous conservation of this community is essential for preserving this plant–pollinator mutualism.     

Genetic structure, population size, and seed production of Pulsatilla vulgaris Mill. (Ranunculaceae) in Central Germany

Pulsatilla vulgaris Mill. (Ranunculaceae) is a rare and rapidly declining grassland community species that was once widespread at a time when Central Germany was covered by steppe vegetation. Through the course of this study, the patterns of random-amplified polymorphic DNA (RAPD) variation among 11 populations of varying size were analysed to assess any possible local differentiation, in relation to spatial isolation, resulting from random genetic drift brought on by reduced population size and lack of migration between geographically isolated populations. Following results attained from methods including: multivariate analysis based on asymmetric Soerensen similarity, φ_ST-statistics, and analysis of molecular variance, we were able to conclude that there is a high within-population variability (84.4%) and a weak, but significant, differentiation among populations (φ_ST=0.17). A matrix correlation between genetic and geographical distances revealed that geographical differentiation was reflected in the RAPD profile (Mantel test: r=0.47,p=0.002). Further significant correlations were noted between population size and both percentage of polymorphic loci (p=0.02) and genetic diversity (p=0.03). An additional analysis of seed production showed that mean seed set, seed number, and mean seed mass per population could be attributed to differences in population size, whereas only seed mass was related to genetic variation.     

Breeding systems and hybridization inPetrorhagia sect.Kohlrauschia (Caryophyllaceae)

In the diploid speciesP. prolifera, the evolution of autogamy has resulted in the presence of distinct selfing and outcrossing races. The change in breeding system toward autogamy is associated with a reduction in the size of floral features and a lower pollen production. The outbreeding populations have only been found in Greece, while the selfing populations have colonized much of Europe. The two races appear to be reproductively isolated from one another. —Petrorhagia sect.Kohlrauschia contains four species.P. glumacea is outbreeding and shows unilateral incompatibility with the small-flowered race ofP. prolifera and interfertility with the large-flowered race; althoughP. glumacea is sympatric with the large-flowered race, they do not appear to hybridize in the wild. Amongst the allopatric species, internal breeding barriers are also found. These may take the form of hybrid sterility or seed incompatibility.P. velutina is autogamous and reproductively isolated from all the other species of the section regardless of whether they are sympatric or allopatric. It is suggested that the evolution of autogamy has been an important factor in the spread ofP. velutina, the tetraploidP. nanteuilii, and the small-flowered race ofP. prolifera in Europe.     

Expression of <Emphasis Type="Italic">Aprotinin</Emphasis> in Anther Causes Male Sterility in Tobacco var <Emphasis Type="Italic">Petit havana</Emphasis>

Expression of many proteinases has been documented during anther development. Although their roles are not completely understood, their inhibition could possibly result in impairment of anther development leading to male sterility. We proposed that such an impairment of anther development can be engineered in plants resulting in male sterile plants that can be used for hybrid seed production. Here, we report that anther-specific expression of Aprotinin gene (serine proteinase inhibitor) in tobacco has resulted in male sterility. Southern analysis and zymogram analysis confirmed the integration and expression of Aprotinin gene in the anthers of the transgenic plants. Transverse sections of anthers of transgenic male sterile plants showed damaged tapetum. The pollen germination in the transgenic plants ranged between 2% and 65% that confirmed the impairment in pollen production leading to male sterility and low seed yield. Thus, inhibition of serine proteinases that are expressed during anther development has resulted in impaired pollen production and male sterility, though the exact role of these proteinases in anther development still has to be elucidated.     

Genic markers for wild abortive (WA) cytoplasm based male sterility and its fertility restoration in rice

Commercial exploitation of heterosis is essential for enhancing productivity of rice. The use of cytoplasmic male sterility (CMS) and fertility restoration system greatly facilitates large scale production of hybrid seed. The wild abortive (WA) cytoplasm is most widely used for hybrid seed production in rice. The present study was undertaken to develop molecular markers for both WA cytoplasm based male sterility and its fertility restoration for use in efficient hybrid breeding. High degree of genetic differentiation of WA-cytoplasm from its normal fertile counterpart was observed due to DNA rearrangements involving five (coxI, coxIII, cob, atp6 and rps3) mitochondrial genes. Cleaved amplified polymorphic sequence (CAPS) markers based on five mitochondrial genes namely, coxIII, cob, atp9, rps3 and 18SrRNA polymorphic between CMS and maintainer line were developed. The utility of these informative markers was demonstrated in purity testing of the CMS line Pusa6A being used in commercial hybrid seed production. Fertility restoration was found to be controlled by a major locus in the Basmati restorer line PRR78, which was mapped to a short marker interval of 0.8 cM and a physical interval of 163.6 kb on rice chromosome 10. A total of 13 pentatricopeptide repeat (PPR) motif containing genes were predicted in a 1.66 Mb region on the long-arm of this chromosome of which, four were present in the marker interval containing the fertility restorer gene. High degree of conservation of gene order was observed between japonica and indica for the predicted PPR genes. A sequence tagged site (STS) and a genic non-coding microsatellite (GNMS) marker were designed based on one of the candidate PPR motif containing genes present in the marker interval, which were validated using F₂ population and other known restorer lines. The candidate gene based marker identified in the present study would be useful in marker assisted selection (MAS) for fertility restorer gene in hybrid breeding programme based on WA-CMS of rice.     

A biotechnology‐based male‐sterility system for hybrid seed production in tomato

Incorporating male sterility into hybrid seed production reduces its cost and ensures high varietal purity. Despite these advantages, male‐sterile lines have not been widely used to produce tomato (Solanum lycopersicum) hybrid seeds. We describe the development of a biotechnology‐based breeding platform that utilized genic male sterility to produce hybrid seeds. In this platform, we generated a novel male‐sterile tomato line by clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR‐associated protein 9 (Cas9)‐mediated mutagenesis of a stamen‐specific gene SlSTR1 and devised a transgenic maintainer by transforming male‐sterile plants with a fertility‐restoration gene linked to a seedling‐colour gene. Offspring of crosses between a hemizygous maintainer and the homozygous male‐sterile plant segregated into 50% non‐transgenic male‐sterile plants and 50% male‐fertile maintainer plants, which could be easily distinguished by seedling colour. This system has great practical potential for hybrid seed breeding and production as it overcomes the problems intrinsic to other male‐sterility systems and can be easily adapted for a range of tomato cultivars and diverse vegetable crops.     

REPRODUCTIVE ISOLATION BARRIERS TO GENE EXCHANGE BETWEEN SOLANUM CHACOENSE AND S. COMMERSONII (SOLANACEAE)

In contrast to the general intercompatibility of diploid species of tuber-bearing potatoes of South America, Solanum chacoense Bitter and S. commersonii Dunal have well-established internal barriers to gene exchange. Pollen tubes of S. commersonii are inhibited in growth down the style of S. chacoense. While S. chacoense pollen tubes are not inhibited in S. commersonii stylar tissue, seed development is abnormal, resulting in production of large numbers of seeds that are not filled out. Even the apparently normal F₁ seed germinated poorly; approximately 0.1 germinable seeds were set per cross as compared with over 30 seeds per cross following intraspecific crosses. Lowland S. chacoense, including populations sympatric with S. commersonii, were not more effectively isolated from S. commersonii than were highland S. chacoense populations, over 500 km from the nearest S. commersonii. The F₁ hybrids produced were vigorous and highly fertile. Crosses between unrelated S. commersonii-chacoense F₁ hybrids produced only 1.3 germinable seeds per cross. This reduction resulted from low numbers of berries set, few seeds per berry, and low seed germination. The F₂ progeny were vigorous, but while many were both male and female fertile there were indications of an increase in sterility over that of the parents and F₁'s. The data were interpreted as indicating that the isolation barriers result from polygenic differences between the parent species and are composed principally of genes that function in several of the processes of seed setting. The accumulation of genes that keep these species isolated was interpreted as not having developed as a result of selection for such isolation in the region of overlap (Wallace effect), but rather as a byproduct of divergence that occurred during their allopatric evolution.