Treatments of Pollen with Different Solvents Affect the Seed Setting Rate of Rice(Oryza sativa L.)

This study aimed to investigate the effects of treatments of rice pollen with different solvents on the seed setting rate.Rice pollen was treated with ultrapure water,0.5%dimethyl sulfoxide,ethanol(1%,5%,and 8%),and 0.5%dimethyl sulfoxide+8%ethanol,and the pollen without treatment was taken as the control.Then,crossing was conducted with the treated rice plants as the male parents and plants subjected to emasculation by warm water as the female parents.The seed setting rates of the male and female parents were then recorded.The results showed that the treatments with different solvents significantly decreased the seed setting rates of both male and female parents.The treatment with 1%ethanol resulted in the highest seed setting rates for both male and female parents,while the treatment with 0.5%dimethyl sulfoxide resulted in the lowest seed setting rates for both parents.Although these solvents affected the seed setting rate of rice,they served as intermediate solvents to dissolve chemicals used in the induction of rice haploids.This study layed a technical foundation for subsequent chemical induction of rice haploids.

Effect of Extreme Natural High Temperature on Seed Setting Rate of Rice(Oryza sativa L.) at Heading and Flowering Stage

The seed setting rates of total 198 rice cultivars （lines） at heading and flowering stage were investigated under the condition of extreme natural high tem- perature in 2013 so as to analyze the effect of extreme natural high temperature on seed setting rate of different rice cultivar （line）. The results showed that the contin- uous high temperature showed certain effects on the seed setting rates of tested materials, and significant differences were shown in seed setting rate among differ- ent rice cultivars （lines）. The seed setting rates differed significantly among indica F1 hybrids derived from different sterile and restorer lines, indicating that the sterile and restorer lines had great effects on heat tolerances of different F~ hybrids. The cor- relation analysis showed that the seed setting rates of conventional indica restorer lines and conventional japonica rice cultivars （lines） were negatively related to the daily highest temperature （P〉0.05）, and the seed setting rates of indica F1 hybrids were positively related to the seed setting rates of their restorer lines. Total four in- dica restorer lines, including Ninghuiguangkangzhan, Shuhui 527, Chenghui 3203 and Xianyin-8, and four new japonica rice cultivars （lines）, including Wuyinjinghui （B2）, Nanjing 4//W3660/Nanjing 44 （B12） and Wuyun 2330/JD6011 （B22） were pre- liminarily screened, and their seed setting rates were all close to the normal level （90%）. The screened rice cultivars （lines） showed higher heat tolerances.

Effect of Enhanced UV-B Radiation on Seed Setting Rate and 1 000-grain Weight of Indica Hybrid Rice Restorer Lines

[Objective] This study was to investigate the effect of enhanced UV-B radiation on seed setting rate and 1 000-grain weight of hybrid rice combinations. [Method] The seed setting rate and 1 000-grain weight of 10 new sterile indica restorer lines planted in pots under enhanced UV-B radiation and fluorescent lamps （control） were respectively measured, and the differences were compared. [Result] The enhanced UV-B radiation significantly reduced the seed setting rate of indica restorer lines, and the differences between that UV-B radiation treatment and control all reached extremely significant level. In addition, the enhanced UV-B radiation reduced the 1 000-grain weight of most indica restorer lines, and compared with that of control the difference achieved significant or very significant level. However, the effect of enhanced UV-B radiation on seed setting rate and 1 000-grain weight differed to different indica restorer lines, and the differences among restorer lines tested were significant or very significant, which indicated the possibility to screen antiUV-B radiation rice materials and combinations. Finally, the indica restorer lines 09R-14, Luhui 37 and 10R-7703 which were strongly resistant to UV-B radiation were screened out. [Conclusion] This study laid foundation for breeding hybrid rice varieties resistance to UV-B radiation.

Studies on Seed Setting Stability in Associated with Temperature for a Two-Line Hybrid Rice,Liangyoupeijiu

When being planted in wide areas in southern China (23°23' - 33°23' N, 98°35' - 120°19' E, sea level above 2.7 - 1285 m), Liangyoupeijiu (LYPJ), a two-line hybrid rice combination, showed a seed setting rate of 75.2 - 77.2%, which was lower by 4.3 - 7.5 percent point than that of an indica hybrid rice Shanyou 63 (CK), with similar values of grain yield and coefficients of variation to CK. Sowing during 5-25th of May in Nanjing (32°3' N, 118°48' E), China, LYPJ headed before 4th September, and gave a seed setting rate of 75 - 90%, and grain yield over 1 kg/m2. If the sowing date was delayed to 14 - 15th, June, its heading date would be as late as 17th - 21st September, and seed setting rate would be declined by 10 - 15% in comparison with that on a suitable sowing date. When flowering took place at an average daily temperature range of 13.7 - 28.5℃ for five days, the spikelet fertility (SF) would be increased by 1.9- 10.7%, for each increment of 1℃. The suitable (SF≥90%) and safe (SF≥75%) temperatures for flowering stage were indicated to be 26.5℃ and 22.9℃, respectively. To get a high and stable seed set in cultivating LYPJ, it was recommended that LYPJ would be planted in the areas south of 34癗, and the favorable average daily temperature during flowering stage should be at 26 - 28℃.

Mapping of three QTLs for seed setting and analysis on the candidate gene for qSS-1 in rice(Oryza sativa L.)

The lower seed setting is one of the major hindrances which face grain yield in rice. One of the main reasons to cause low spikelet fertility （seed setting） is male sterility or pollen abortion. Notably, pollen abortion has been frequently observed in advanced progenies of rice. In the present study, 149 BC2F6 individuals with significant segregation in spikelet fertility were generated from the cross between N040212 （indica） and Nipponbare （japonica） and used for primary gene mapping. Three QTLs, qSS-1, qSS-7 and qSS-9 at chromosomes 1, 7 and 9, respectively, were found to be associated with seed setting. The recombinant analysis and the physical mapping information from publicly available resources exhibited that the qSS-1, qSS-7 and qSS-9 loci were mapped to an interval of 188, 701 and 3741 kb, respectively. The seed setting responsible for QTL qSS-1 was further fine mapped to 93.5 kb by using BC2F7 population of 1 849 individuals. There are 16 possible putative genes in this 93.5 kb region. Pollen vitality tests and artificial pollination indicated that the male gamete has abnormal pollen while the female gamete was normal. These data showed that low seed setting rate relative to qSS-1 may be caused by abnormal pollen grains. These results will be useful for cloning, functional analysis of the target gene governing spikelet fertility （seed setting） and understanding the genetic bases of pollen sterility.

Factors Influencing the Outcrossed Seed-Setting Obstacles of Photo-thermo Sensitive Genie Male Sterile Rice

Using photo-thermo sensitive genie male rice (PTGMS) Pei' ai 64S, W7415S, W6154S, N26S, Annong S, Nongken 58S, 7001S and 5088S as female parents and conventional indica lines 8258 and U89 as male parents, the factors affecting outcrossed seed-setting were analyzed. The PTGMS had obstacles in outcrossed seed setting influenced by inheritance and environment at varying degrees. Environmental temperature was regarded as the main factor that resulted in the outcrossed seed-setting obstacles. The sensitive stage was at the early stage of grain filling for outcrossed seed setting. There existed remarkable differences at the sensitivity stage, the duration of sensitive period, the sensitive level and the effective level of outcrossed seed-setting obstacles caused by environmental temperature among different PTGMS lines. Therefore, attention should be paid to outcrossed seed-setting obstacles in selection and utilization of PTGMS lines.

Molecular mechanisms controlling seed set in cereal crop species under stress and non-stress conditions

Maximizing seed yield is the ultimate breeding goal in important cereal crop species. Seed set is a key developmental stage in the process of seed formation, which determines grain number, seed mass, and realized yield potential, and can be severely affected by abiotic and biotic stresses. However, seed set can also be substantially reduced by genetic factors even under optimal fertilization conditions. The underlying molecular genetic mechanisms are still obscure. In this review, we elucidate the process of seed set of cereal crop species in detail, including development of floral structures, formation of viable gametes, double fertilization, seed development, and abortion. We discuss how genetic and non-genetic factors affect seed set in different development stages. Finally, we will propose novel strategies to study genetic mechanisms controlling seed set and exploit genetic resources to improve seed set in cereal crop species.

Research on Flowering Habits and Fertility of Gaozhou Common Wild Rice (Oryza rufipogon) in Lingshui of Hainan Province

[Objective] The paper was to explore the flowering habits and fertility of Gaozhou common wild rice （Oryza rufipogon Griff.） in Lingshui of Hainan Province. [Method] The flowering habits, pollen fertility and seed setting rate of Gaozhou common wild rice in Lingshui of Hainan Province were studied, and compared with the flowering habits of common wild rice in Hainan Province. [Result] Gaozhou common wild rice was able to flower twice a year. The first flowering stage was from mid-April to mid-June for about 60 d, and the daily peak flowering dates were from May 13 to May 22. The daily flowering time was mainly between 11：20 and 13：00, and the peak flowering was at 11：30. The second flowering stage was from late August to late October for about 45 d, and the peak flowering dates lasted from September 8 to September 18. The daily flowering time was mainly from 11：15 to 12：50, and the daily peak flowering was at 11：30. In both flowering stages, the panicles had the same flowering characteristics. The stigma exsertion reached a high value of 95.37% with single （46.23%） and dual （49.14%） stigmas exsertion respectively. A spikelet remained open for 1.5-2.5 h, the angle of spikelet opening varied from 29.9° to 32.4°. At the two flowering stage the average pollen fertility rates were 89.67% and 85.62%, the average seed setting rates were 58.81% and 55.79%, respectively. Hainan population flowered only once （from mid-October to mid-December）, this had significant difference with the performance of Gaozhou common wild rice which flowered twice a year. [Conclusion] The results provided basis for the research on gene flow frequency from transgenic rice to wild rice and its relationship with flowering habits of common wild rice.

Floral traits and pollination system of Zygophyllum xanthoxylum in the managed and wild populations in an arid region of Northwest China

Zygophyllum xanthoxylum, which belongs to Sarcozygium of Zygophyllaceae, is one of the ecologically important species in Northwest China. In order to understand the pollination system of Z. xanthoxylum, we investigated the following characteristics of this species in the Urat Desert-grassland Research Station in western Inner Mongolia of China： flowering dynamics, pollen viability, pollen limitation, floral visitors and breeding system. The results showed that the flowering period and flowering peak were different between the wild and managed popula- tions, being longer in the managed population. Z. xanthoxylum was pollen-limited, and pollen limitation was more intense in the wild population than in the managed population. Chalicodoma deserticola （Hymenoptera） was found to be the most frequent pollinator in the wild population, while Anthophora fulvitarsis （Hymenoptera） was the most frequent and effective visitor in the managed population. Out-crossing was dominant in the breeding system and self-pollination just played an assistant role to assure the reproduction of Z. xanthoxylum.

Responses of Yield Characteristics to High Temperature During Flowering Stage in Hybrid Rice Guodao 6

By sowing at different dates during 2005 and 2006 both in paddy fields and greenhouse, a super hybrid rice combination Guodao 6 and a conventional hybrid rice combination Xieyou 46 （as control） were used to analyze the differences in heat injury index, seed setting rate, grain yield and its components. Guodao 6 showed more stable yield and spikelet fertility, and lower heat injury index than Xieyou 46. Further studies indicated that the spikelet sterility is positively correlated with the average daily temperature and the maximum daily temperature, with the coefficients of 0.8604 and 0.9850 （P〈0.05） respectively in Guodao 6. The effect of high temperature injury on seed setting caused by maximum daily temperature was lower than that by average daily temperature during the grain filling stage.

Abnormal Structure of Embryo Sac in Autotetraploid Rice

The structures of mature embryo sacs in 13 genetic stock lines of autotetraploid rice （Oryza sativa L.）, including indica, japonica and javanica, were studied by using the whole-mount stain-clearing laser scanning confocal microscopy （WCLSM）. Among the 13 autotetraploid rice, the majority of ovaries possess normal polygonum-type embryo sacs, while a few ovaries were characterized by abnormal embryo sacs. The abnormalities of embryo sacs could be classified into six categories, i. e. no female germ unit, abnormal polar nuclei, embryo sac degeneration, no egg apparatus, small embryo sac and ＇double set＇ of embryo sacs. The frequency of abnormal embryo sac in japonica （26.6%） was higher than that in indica （19.34%）. In addition, the major abnormalities in each autotetraploid line varied, suggesting that the abnormalities may be related to the genotypes of the varieties.

Pollen Grain Germination and Pollen Tube Growth in Pistil of Rice

The germination of pollen grain in vitro and the growth of pollen tube in the pistil of rice were observed with a microscope. The stigma was removed at different time points after pollination to study its effect on seed setting rate. The rice pollen grain started to germinate at 2 min after pollination and the pollen tube penetrated stigma into style in 5-10 min, 30 min later the end of pollen tube reached the bottom of ovary, and only some pollen tubes arrived at embryo sac at 40 min after pollination. Meanwhile, a small amount of callose began to deposit in the pollen tubes, a great deal of callose was observed at 50 min after pollination, whereas the pollen grain began to shrink. The growing rates of pollen tube in the rice stigma, style and ovary were 1500, 5000, and 5400 μm/h, respectively. The seed setting rate was quite low when the stigma was removed at about 10-15 min after pollination, gradually increased when it removed at 20 min to 50 min after pollination, and over 60% when it removed at 50 min after pollination and finally tended to be stable.

Distribution of the Classification Traits in the F_2 Progeny of Two Crosses of indica/japonica in Rice (Oryza sativa)

Comparison of seed setting rate, plant height and Cheng's morphological traits were made between the F_2 progeny of indica-japonica hybrids, 02428/Pei'ai 64 and Taichung 65/Teqing. There existed resemblance normal distribution in plant height, and the distribution had no relationship with the seed setting rate and plant height in F_1 progeny, suggesting that there were no gametic selection for the plant height in the F_2 progeny of indica-japoniea hybrids. An average seed setting rate of the F_2 was equal to the F_1 populations in the recombination of 02428/Pei'ai 64 in which there was an excellent cross compatibility, but the remarkable increase in the seed setting rate from the F_1 to F_2 in Taichung 65/Teqing, indicating that gametic selection only took place in the indica-japonica crosses with low cross compatibility while null or little in the hybrids with high compatibility. There were many intermediate types among the leaf pubescence, color of hull at heading, and length of the first and second panicle internode, and these Cheng's morphological traits was distributed normally; there were also a little intermediate types in hull hairness and phenol reaction with bi-peak distribution; while length to width ratio of grain was inclined to the japonica types obviously showing a skewed distribution in the F2 population. Although Cheng's morphological traits in F_2 populations had inconsistent distribution types, Cheng's morphological traits index showed normal distribution, which suggested that intermediate types, i.e. indicalinous or japonicalinous, were primary in F_2 population.

Studies on the Growth Habits and Characteristics of Two Polyploid Indica-Japonica Hybrid Rice with Powerful Heterosis

Based on a series of polyploid indica-japonica hybrid plant lines obtained from a new breeding strategy of using double predominance of wide cross and polyploidization to breed super flee, two polyploid indica-japonica hybrids, PSR073 and PSR120 were studied in their growth periods to show the powerful heterosis in a larger scale and to study the characteristics of polyploid indica-japonica hybrids more elaborately. The leaf age, tiller growth, flowering habits, and agronomic traits of them were observed to analyze their growth habits and characteristics. The results showed that the.agronomic traits of PSR073 and PSR120, such as the plant height, panicle length, grain length, grain width, and 1000-grain weight, all acquired obvious predominance of polyploidy, and that the seed setting rate was more than 83%. No significant difference was observed between the two tetraploids and common diploids in the leaf age, tiller growth, and flowering habits. It was concluded that the characteristics of the two powerful heterosis polyploid hybrids were different from those of the polyploid rice reported earlier. Wide cross and polyploidization had no negative effects on their growth habits and characteristics; on the contrary these had powerful heterosis. This had provided theoretic and practical evidences for their application to agricultural production.

Viability of Stigmas of Pistils in Winter Rape： Peculiarity of Samples with Different Origins

The researches have been carried out in 2011-2012, in the experimental fields of Yuryev Plant Production Institute Kharkiv, Ukraine. The forms of ＂00＂ type （a low content of erucic acid and glucosinolates） and self-pollinated lines--110M-10, 127M-10, 132M-10 were studied; the forms of＂0＋＂ type--selfed lines 124-10, 221-10, 305-10; the forms of＂＋0＂ type--cultivars Victor, Janus, Emerald; forms of ＂＋＋＂ type--cultivars Fyedorovskiy, Marens, Uspikh, as well as, self-incompatible forms 5C, 15C-10, 32C-10 and the original sterile form of mutant origin were used. Viability in stigmas of the pistil lasted 3-7 days, in the forms of ＂＋0＂, ＂＋＋＂ type, 7-15 days in the cultivars and forms of ＂0＋＂, ＂00＂ type, 14-21 days in the self-incompatible and sterile forms. A fast loss of sensitivity to pollen by pistil＇s stigma was observed in the forms of＂＋0＂ and ＂＋＋＂ types. On the contrary, in self-incompatible and sterile forms was observed a gradual increase of sensitivity of pistil＇s stigma to pollination and then its gradual fall. A maximum of sensitivity of a pistil＇s stigma to pollen in ＂00＂ and ＂0＋＂ forms was on the 3rd-6th day after castration.

Pollen and resource limitations to lifetime seed production in a wild population of the endangered plant Disanthus cercidifolius var.longipes H.T.Chang(Hamamelidaceae)

Disanthus cercidifolius Maxim.var.longipes H.T.Chang,a plant species that only occurs in a few counties in Hunan,Jiangxi and Zhejiang Provinces and with a relatively small number of individuals,is ranked as a second Class endangered species for conservation in China.We have studied the effect of pollen and resources available to female reproduction,and the reproductive mechanism of“excess flowers with low fruit set”in Disanthus cercidifolius Maxim.var.longipes H.T.Chang was discussed.Results are as follows:Pollen from different sources has significant effects on fruit set and seed set of Disanthus cercidifolius Maxim.var.longipes H.T.Chang.The pollen source rather than pollen numbers significantly affected reproduction of this species.In wild populations,producing one fruit needs about 54.8 flow-ers,and one satiation seed needs about 6.60 flowers or 83.19 ovules.After fertilizing,which was propitious to flower develop-ment,the abortion rate of flower buds was decreasing,but the flowering rate was increasing.The fruit set and seed set was also significantly increasing,while abortion rate of fruit was significantly decreasing.With the increasing percentages of cutting leaves,the fruit set decreased,but the abortion rate of fruit shows no significant differentiation among treatments.After cutting branches that were puny,broken and insect-infested branches,the flower number seemed to be decreas-ing,but the fruit set and seed set all increased significantly.After removing some flowers,the fruit set was calculated with respect to the number of flowers remaining after the treatment increased with increasing of percentages of flower removal,whereas fruit set calculated with respect to the initial number of flowers remained constant,and the mean weights of per fruit and per seed all decreased significantly.Sufficient spatial or temporal heterogeneities in nutrient levels might allow limitation of seed set by resources and pollen in a natural population,while supplying resources may indirectly affect pollination by increasing attraction of the flowers to pollinators.There were very low fruit and seed sets in natural populations of Disanthus cercidifolius Maxim.var.longipes H.T.Chang.Different factors may have interacted to effect a low fruit set.A joint adoption of the“selection abortion hypothesis”,“ovary reserve hypothesis”and“male function hypothesis”seems to be the most likely explanation for the reproductive strategy of“excess flowers with few fruit sets”in Disanthus cercidifolius Maxim.var.longipes H.T.Chang.

Molecular mechanisms underlying the negative effects of transient heatwaves on crop fertility

Transient heatwaves occurring more frequently as the climate warms,yet their impacts on crop yield are severely underestimated and even overlooked.Heatwaves lasting only a few days or even hours during sensitive stages,such as microgametogenesis and flowering,can significantly reduce crop yield by disrupting plant reproduction.Recent advances in multi-omics and GWAS analysis have shed light on the specific organs(e.g.,pollen,lodicule,style),key metabolic pathways(sugar and reactive oxygen species metabolism,Ca2+homeostasis),and essential genes that are involved in crop responses to transient heatwaves during sensitive stages.This review therefore places particular emphasis on heat-sensitive stages,with pollen development,floret opening,pollination,and fertilization as the central narrative thread.The multifaceted effects of transient heatwaves and their molecular basis are systematically reviewed,with a focus on key structures such as the lodicule and tapetum.A number of heat-tolerance genes associated with these processes have been identified in major crops like maize and rice.The mechanisms and key heat-tolerance genes shared among different stages may facilitate the more precise improvement of heat-tolerant crops.

Sugar Input, Metabolism, and Signaling Mediated by Invertase： Roles in Development, Yield Potential, and Response to Drought and Heat

Invertase （INV） hydrolyzes sucrose into glucose and fructose, thereby playing key roles in primary metabolism and plant development. Based on their pH optima and sub-cellular locations, INVs are categorized into cell wall, cytoplasmic, and vacuolar subgroups, abbreviated as CWlN, CIN, and VlN, respectively. The broad importance and implications of INVs in plant development and crop productivity have attracted enormous interest to examine INV function and regulation from multiple perspectives. Here, we review some exciting advances in this area over the last two decades, focusing on （1） new or emerging roles of INV in plant development and regulation at the post-translational level through interaction with inhibitors, （2） cross-talk between INV-mediated sugar signaling and hormonal control of development, and （3） sugar- and INV-mediated responses to drought and heat stresses and their impact on seed and fruit set. Finally, we discuss major questions arising from this new progress and outline future directions for unraveling mechanisms underlying INV-mediated plant development and their potential applications in plant biotechnology and agriculture.

From the floret to the canopy:High temperature tolerance during flowering

Heat waves induced by climate warming have become common in food-producing regions worldwide,frequently coinciding with high temperature(HT)-sensitive stages of many crops and thus threatening global food security.Understanding the HT sensitivity of reproductive organs is currently of great interest for increasing seed set.The responses of seed set to HT involve multiple processes in both male and female reproductive organs,but we currently lack an integrated and systematic summary of these responses for the world’s three leading food crops(rice,wheat,and maize).In the present work,we define the critical high temperature thresholds for seed set in rice(37.2℃±0.2℃),wheat(27.3℃±0.5℃),and maize(37.9℃±0.4℃)during flowering.We assess the HT sensitivity of these three cereals from the microspore stage to the lag period,including effects of HT on flowering dynamics,floret growth and development,pollination,and fertilization.Our review synthesizes existing knowledge about the effects of HT stress on spikelet opening,anther dehiscence,pollen shedding number,pollen viability,pistil and stigma function,pollen germination on the stigma,and pollen tube elongation.HT-induced spikelet closure and arrest of pollen tube elongation have a catastrophic effect on pollination and fertilization in maize.Rice benefits from pollination under HT stress owing to bottom anther dehiscence and cleistogamy.Cleistogamy and secondary spikelet opening increase the probability of pollination success in wheat under HT stress.However,cereal crops themselves also have protective measures under HT stress.Lower canopy/tissue temperatures compared with air temperatures indicate that cereal crops,especially rice,can partly protect themselves from heat damage.In maize,husk leaves reduce inner ear temperature by about 5℃compared with outer ear temperature,thereby protecting the later phases of pollen tube growth and fertilization processes.These findings have important implications for accurate modeling,optimized crop management,and breeding of new varieties to cope with HT stress in the most important staple crops.