Divergent recurrent selection for cold tolerance in two improved maize populations

Maize (Zea mays L.) production has significantly expanded into very short-season environments where germination and growth in cooler environments is essentially a pre-requisite. Therefore, an important goal for maize breeders is to improve local germplasm sources of inbred lines that are able to grow under these challenging conditions. The objective of this research was to evaluate direct and correlated responses in two improved early maturing maize populations [NDSCD(M)C10 and BS22(R)C7] after two cycles of S₁ and full-sib intra-population recurrent selection for cold tolerance. The S₁ and full-sib progenies were obtained by self-pollinating 100 random plants and by intercrossing 200 random plants, respectively. Ten percent of the families were selected, based on an index that included emergence percentage, seedling vigor, and root lodging percentage, and recombined at the same time in a summer nursery based upon data across northern North Dakota locations. The essential benefit of this breeding methodology was to achieve one year per cycle of selection based upon progenies. However, direct response to selection was not significant while some correlated responses were significant. We decided to report these results in order to encourage other scientists the evaluation of additional sources of germplasm, the screening at various dates, and the selection of target environments with more intensive cold stress before initiating long-term selection programs for cold tolerance. In addition, further research on the current and alternative long-term selection methods for cold tolerance is recommended for continuous genetic improvement of advanced cycles in the northern U.S. Corn Belt. Part of the thesis submitted by B. Sezegen in partial fulfillment of the requirements for a MS degree at North Dakota State University.     

Mass selection for improved cold and density tolerance of two maize populations

Summary Data of planting and plant density are two cultural practices influencing grain yield of maize (Zea mays L.). Our study was designed to evaluate the usefulness of a mass selection scheme to improve cold and density tolerance of the BS2 and BS3 maize populations. Populations were planted at an early planting date and a high plant density, and three cycles of mass selection for well-filled ears on erect plants were conducted at earch of three Corn Belt locations (i.e., Waseca, MN; Ames, IA; Portageville, MO).Results showed that selection improved cold tolerance traits of BS3, but not of BS2. Mass selection did not increase density tolerance of either population at any location. Selection did not improve response to planting dates, although the early planting date did improve agronomic performance and grain yield of all entries. We concluded that mass selection at high plant densities and early planting dates at diverse geographical locations did not produce cycles adapted to specific environmental conditions.     

Genetic structure and association mapping of cold tolerance in improved japonica rice germplasm at the booting stage

Cold tolerance at booting stage is one of the major determinants for a stable yield of rice (Oryza sativa L.) in many high elevation or high latitude regions. Understanding the genetic basis of cold tolerance is crucial for the improvement of cold tolerance through breeding. In this study, association mapping was performed in 347 rice accessions worldwide with different statistical models in order to identify the genetic marker loci/QTL associated with cold tolerance traits at the booting stage. The evaluation of cold tolerance for all the traits was conducted under natural low temperature in Yunnan and cold water irrigation in Jilin. The 148 SSRs were used for the genotyping. Population structure analysis identified three main subpopulations for the accessions that corresponded to major geographic origins. The relative kinship analysis revealed a weak or no relationship for most of the individual pairs. Model comparisons indicated that the Q+K model controlling both population structure (Q) and the relative kinship (K) was performed better than other models in association mapping. In total, 24 markers were identified that were significantly associated with cold tolerance, including five markers in Yunnan and 19 markers in Jilin. Moreover, RM282, RM252, RM335 and RM6824 were identified in multiple environments or years. Many of these identified markers were located either in or nearby the regions where the QTLs have been reported for cold tolerance at booting stage. These results highlighted the targeted regions for future studies and might be subsequently used in breeding programs to trace and select the useful alleles by MAS.     

Parameters of cold tolerance in common vetch

Summary The cold tolerance of 16 common vetch (Vicia sativa L.) strains was assessed by means of survival rate after direct freezing. Additionally, several seed and seedling parameters, germination in solution with osmotic pressure, and electrolyte exosmosis from shoots and from roots of seedlings were determined. The U.S. cv's Nova II, Vanguard and Warrior and the Turkish cv. Sari Elçi exhibited survival rates higher than 75% after direct freezing test, compared to less than 40% in the remaining entries. Simple correlation analysis showed that only electrolyte exosmosis from shoots after freezing was negatively correlated with survival rate.     

Evaluation of maize plant introductions for cold tolerance

Summary We evaluated cold-tolerance responses of 144 plant introductions (PI) of maize (Zea mays L.), attempting to include in our sample at least one PI adapted to each of the countries or ecological zones respresented in the maize germplasm collection at the North Central Regional Plant Introduction Station at Ames, Iowa, USA. Plant introductions were grown for 42 days in plastic boxes (26 cm long × 19 cm wide × 10 cm deep) in a growth chamber maintained at 10±1 °C. Cold-tolerance responses of each PI were evaluated by three traits: 1) percentage emergence (recorded 30 days after planting), 2) emergence index, an estimate of rate of emergence, and 3) seedling dry weight (sampled 42 days after planting). Estimates of variances and heritabilities for these three traits were large, suggesting that genotypic variation for cold tolerance in the maize germplasm collection would be sufficient to permit selection advance. Furthermore, genotypic correlations among the three traits were high: therefore, improvement by index selection should be possible. Correlations between the cold-tolerance traits and days from planting to 50% silk emergence (an estimate of maturity obtained at Ames. Iowa, USA) were low. Days from planting to 50% silking emergence for the 25 most cold-tolerant PI's ranged from 46 for PI 214279 from Canada to 106 for PI 331440 from Ethiopia. It should be possible, therefore, to develop cold-tolerant genotypes adapted to all latitudes.Contribution from the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011, and the Agricultural Research Service, U.S. Department of Agriculture, cooperating. Journal Paper No. J-8780 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Projects No. 1018 and 2152     

Use of barley seed vigour to discriminate drought and cold tolerance in crop years with high seed vigour and low trait variation

Seed vigour is a precondition for early and homogenous field emergence of barley, in addition to effective malting. This study aimed to assess the selection of barley varieties by using seed vigour as the indicator. Seed vigour of barley (quantified as the germination percentage) was evaluated under drought (?0.2 MPa) and temperature stress (10°C). At two locations over a 3‐year period, 1 population of 133 Derkado × B83‐12/21/5 doubled haploid (DH) lines (and parents) was evaluated for seed vigour, of which 108 DH lines were assessed for three malting parameters. The relatively high values of vigour during the 3‐year period (overall average 94–95%) probably impeded high variations in genetic potential. A total of 27 DH lines of the 133 evaluated showed transgression for vigour (up to 98%) in comparison with the parents (Derkado: 96%; B83: 92%). In conclusion, caution should be applied when selecting for seed vigour, even in good crop years with high levels of seed vigour and low trait variations. Such selection might improve vigour, particularly in crop years with unsuitable weather conditions.     

Creating cold resistant strawberry via interploidy hybridization between octoploid and dodecaploid

Strawberry cultivars showed limited cold resistance in the Northeast of China, while we obtained a synthetic dodecaploid strawberry hybrid ‘YH15-10’ (2n = 12x = 84) which showed sufficient cold resistance in this area. The reciprocal crosses between F. × ananassa cv. ‘Allstar’ (2n = 8x = 56) and ‘YH15-10’ (2n = 12x = 84) were carried out to select cold resistant strawberry in this study. The 134 seedlings were obtained from the cross of Allstar × YH15-10, while failed in its reciprocal cross. The 30 randomly selected seedlings were examined in terms of morphological characters, chromosome numbers and cold resistance. Most morphological characters were widely separated among F1 progeny with a high broad-sense heritability, which showed that these variations mainly resulted from genetic effect. Some hybrids exhibited heterosis, especially in growth vigor and runner production. Among the 30 tested hybrids, 28 decaploids (2n = 10x = 70), one octoploid (2n = 8x = 56) and one enneaploid (2n = 9x = 63) were observed. The 63.3% hybrids demonstrated higher cold resistance than that of ‘Allstar’ at P < 0.05. These high polyploidy strawberries have potential values in commercial production and modern cultivar improvement.     

Signatures of divergent selection for cold tolerance in maize

Divergently selected genotypes can be used for detecting the genomic regions affecting the selected trait (selection signature). Moreover, the genetic distances (GDs) among divergently selected lines can be correlated with the agronomic performances of the crosses among them. Using as source the maize F₂ of B73?×?IABO78, we previously conducted four cycles of divergent recurrent selection and three cycles of divergent selection in inbreeding for cold tolerance at germination. We finally obtained 10 lines selected for low (L) and 10 lines selected for high (H) cold tolerance, which exhibited a notable divergence for both the selected and associated traits. Herein, we investigated the 20 lines and the 28 single diallel crosses among eight random lines (four L and four H); the main objectives were to identify the putative regions controlling the selected and associated traits and to study the relationships between crosses performances and GDs among their parental lines. Allele frequencies at 932 recombination blocks based on 19,220 polymorphic SNPs were obtained for the two lines’ groups; the F _ST calculated across sliding windows indicated 18 regions highly divergent between groups. The increasing alleles for cold tolerance were contributed by both parents, consistently with the transgressive segregations previously found. Several regions associated to DG also affected various agronomic traits. The cross performances showed some relationships with the genetic distances among parental lines for traits affected by dominance, provided that all crosses were considered, while these relationships vanished when only L?×?H crosses were examined.     

Genetic variation of germination cold tolerance in Japanese rice germplasm

Low temperatures at the initial stages of rice development prevent fast germination and seedling establishment and may cause significant productivity losses. In order to develop rice cultivars exhibiting cold tolerance, it is necessary to investigate genetic resources, providing basic knowledge to allow the introduction of genes involved in low temperature germination ability from accessions into elite cultivars. Japanese rice accessions were evaluated at the germination under two conditions: 13°C for 28 days (cold stress) and 28°C for seven days (optimal temperature). The traits studied were coleoptile and radicle length under optimal temperature, coleoptile and radicle length under cold and percentage of the reduction in coleptile and radicle length due to low temperature. Among the accessions studied, genetic variation for traits related to germination under low temperatures was observed and accessions exhibiting adequate performance for all investigated traits were identified. The use of multivariate analysis allowed the identification of the genotypes displaying cold tolerance by smaller reductions in coleoptile and radicle lenght in the presence of cold and high vigour, by higher coleoptile and radicle growth under cold.     

Associations of PCR markers with freezing tolerance and photosynthetic acclimation to cold in winter barley

Associations of PCR markers with freezing tolerance and acclimation of photosynthetic apparatus to cold were tested on 28 winter barley cultivars and advanced breeding forms to select alleles for practical application in marker assisted selection (MAS). We found significant associations between freezing tolerance evaluated with field-laboratory method (FLM) and markers located on 5H chromosome in region of gene Fr-H2 (bin9-10: Xbmag812, Xmwg2230) and region of gene Fr-H1 (bin11: Xmwg514, HvBM5, Xmwg644). Additionally, significant associations with photochemical quenching of chlorophyll a fluorescence (q_P) were found for PCR markers Xpsr115 and Xmwg2062. In our study variation in the promoter region of Vrn-H1 (HvBM5) was directly connected with freezing tolerance of plants partially de-acclimated in the field. The results obtained here showed that different loci of freezing tolerance may play role in variable selection pressure of winter conditions.     

Kalanchoe blossfeldiana transformed with rol genes exhibits improved postharvest performance and increased ethylene tolerance

Kalanchoe blossfeldiana transformed with rol genes, termed root-inducing (Ri) lines, which had been produced through transformation using Agrobacterium rhizogenes wild-type strain ATCC15834, were tested for their postharvest performance. Flower longevity, ethylene sensitivity and display quality varied among control and chemical growth retarded plants and the Ri lines. Both chemical growth retardation and transformation with rol genes reduced the number of flowers in comparison to control plants. Detached single flowers of the two Ri lines tested, Ri line 306 and 331, had a longevity, defined as the stage where the flowers were 70% open, of 32 and 34 d, respectively, whereas chemical growth retarded and control plants had a longevity of 28 and 26 d, respectively. Ri line 331 had the significantly longest display life of 34 d to reach the stage of losing the ornamental value of the whole plant, defined as 10% wilted flowers. The corresponding display life of control and chemical retarded plants and plants of Ri line 306 was 25 d. The opening of the flowers was more synchronous in the Ri lines than control plants. Exposed to ethylene, the flowers of the Ri lines exhibited reduced responsiveness whereas chemical growth retarded and control plants were sensitive. Possible mechanisms behind the improved postharvest performance of plants transformed with rol genes are discussed.     

Production of mutants with high cold tolerance in spring canola (<Emphasis Type="Italic">Brassica napus</Emphasis>)

A major factor affecting spring canola (Brassica napus) production in Canada is killing frosts during seedling development in the spring and seed maturation in the fall. The objective of this study was to explore the possibility of producing spring canola lines with mutations that have altered biochemical pathways that increase cold tolerance. The approach was to generate UV point mutations in cultured microspores followed by chemical in vitro selection of individual mutant microspores or embryos resulting in measurable alterations to various biochemical pathways with elevated levels of key defense signaling molecules such as, salicylic acid (SA), p-Fluoro-d,l-Phenyl Alanine (FPA), and jasmonic acid (JA). In addition, since proline (Pro) is known to protect plant tissues in the cold-induced osmotic stress pathway, mutants that overproduce Pro were selected in vitro by using three Pro analogues: hydroxyproline (HP), azetidine-2-carboxylate (A2C); and, 3,4-dehydro-d,l-proline (DP). Of the 329 in vitro selected mutant embryos produced, 74 were identified with significant cold tolerance compared to their donor parents through indoor freezer tests at −6°C, and 19 had better winter field survival than winter canola checks. All chemically selected mutant doubled haploids with increased cold tolerance compared well with parent lines for all seed quality and agronomic parameters. Development of increased frost tolerant cultivars should allow for spring canola to be produced in western Canada without compromising seed quality.     

玉米种质苗期耐冷性状的遗传分析

摘要：早春低温冷害是黑龙江省主要的自然灾害之一,已成为影响本区域玉米产量水平提高的重要因素。本研究选择不同耐冷玉米种质8份,按Griffing Ⅱ的设计组配,分析低温逆境下玉米出苗及幼苗期性状的遗传规律。相关分析表明,相对出苗指数、相对出苗率、相对苗干重、相对根干重两两相关,相对出苗率与相对根总长相关,上述性状适合作为玉米幼苗耐冷性鉴定的指标。不同亲本的GCA方差、不同组合的SCA方差在相对出苗率、相对发芽指数、相对苗干重、相对根干重、相对根总长等性状上的差异显著。非加性基因效应在相对出苗率、相对发芽指数、相对苗干重、相对根干重、相对根总长中起到重要作用,且狭义遗传力普遍较低,各性状均低于50%,高低次序为相对发芽指数>相对出苗率>相对根干重>相对苗干重>相对根总长,上述性状选择适宜在中晚代进行选择。     

Feasibility of selection for traits associated with cold tolerance in rice under rapid generation advance method

Summary Variability of the hybrid population can be preserved through generations during the process of rapid generation advance (RGA). Effective selection can be done in an early generation for those traits having high heritability value like growth duration and plant height. But selection is not advantageous for traits having low heritability. Thus, selection for panicle exsertion, cold tolerance at seedling stage and panicle length would not be wise during the early generations. However, in the low temperature areas growth duration and plant height are two important factors which determine varietal suitability. As selection of these two characters are possible through RGA, it should be a standard parctice during RGA to eliminate the plants with long growth duration and select plants with optimum plant height.     

Association of molecular markers with cold tolerance and green period in zoysiagrass (Zoysia Willd.)

Cold tolerance and the green period are key traits in the breeding of zoysiagrass (Zoysia Willd.). Identification of molecular markers associated with cold tolerance and the green period of zoysiagrass will contribute to efficient selection of elite cultivars. These two traits were measured in 96 zoysiagrass accessions in 2004 and 2005–2006, respectively. The mapping population was screened with 29 pairs of simple sequence repeat (SSR) primers and 54 pairs of sequence-related amplified polymorphism (SRAP) primers. A multi-loci in silico mapping approach implemented with an empirical Bayes method was applied for association mapping of cold tolerance and green period. We detected 254 SSR polymorphic loci and 338 SRAP polymorphic loci, among which three SSR loci (Xgwm131-3B-187, Xgwm469-6D-194 and Xgwm234-5B-244) and one SRAP locus (Me11Em7-406) were significantly associated with cold tolerance with effect values of 57.83%, 38.05%, 36.92% and 37%, respectively. Three SSR loci (Xgwm132-6B-225, Xgwm111-7D-34 and Xgwm102-2D-97) and two SRAP loci (Me19Em5-359 and Me16Em8-483) were significantly associated with the green period with effect values of 79.54%, 62.59%, 99.04%, 49.01% and 82.57%. These markers will be useful for genetic improvement of the cold tolerance and green period of zoysiagrass by marker-assisted breeding.     

寒地优质粳稻新品种区域适应性及丰产性研究

通过对15个品种丰产性、适应性和抗逆性进行综合比较.结果表明垦稻11号、垦粳2号、三江一号、龙粳20号、垦稻18号、龙粳17号、龙粳21号、龙粳24号综合性状表现良好,连续3年试验产量表现稳定,在栽培中注意各品种的自身特点,加强管理.可以搭配空育131种植.     

Genetical and morphological characterization of cold tolerance at fertilization stage in rice

Cold temperature during the reproductive phase leads to seed sterility, which reduces yield and decreases the grain quality of rice. The fertilization stage, ranging from pollen maturation to the completion of fertilization, is sensitive to unsuitable temperature. Improving cold tolerance at the fertilization stage (CTF) is an important objective of rice breeding program in cold temperature areas. In this study, we characterized fertilization behavior under cold temperature to define the phenotype of CTF and identified quantitative trait loci (QTLs) for CTF. A wide variation in CTF levels has been identified among local cultivars in Hokkaido, which is one of the most northern regions for rice cultivation in the world. Clear varietal differences in pollen germination, and pollen tube elongation due to cold temperature have been observed. These differences may confer a degree of CTF among this population. We conducted QTL analysis for CTF using 120 backcrossed inbred lines derived from a cross between Eikei88223 (vigorous CTF) and Suisei (very weak CTF). Three QTLs for CTF were identified. A clear effect by QTL, qCTF7, for increasing the level of CTF was validated using advanced progeny. These results will facilitate marker-assist selection for desirable QTLs for CTF in rice breeding program.     

福建乌龙茶品种资源抗寒性鉴定与评价

福建地处我国东南沿海,地跨南亚热带与中亚热带,属亚热带海洋性季风气候,全年气候温和,日照充足,雨量充沛,雨热同期,温暖湿润.年平均气温17℃～21℃,≥10℃积温达5500℃～7700℃,无霜期240～330d,年降雨量1300～1900mm茶树品种资源极为丰富,同时又是我国乌龙茶品种资源的分布、保存中心地带.本文通过对福建乌龙茶品种资源抗寒性鉴定与评价,也为乌龙茶的抗寒育种、抗寒栽培、省内外引种及推广提供依据.     

Cytoplasmically controlled cold tolerance in a cytoplasmic-genetic male sterile line of rice

Summary The cytoplasmic-genetic male sterile line, Krishna-A with Kalinga-I cytoplasm was developed in rice through repeated backcrossing the completely pollen sterile F₁ of the cross Kalinga-I/Krishna with the recurrent male parent cv. Krishna. The germination percentage and root-shoot length in Krishna-A at 12°C and 9°C indicated a higher degree of tolerance to low temperature than the cold tolerant female parent Kalinga-I. The high yielding cold tolerant variety Kalinga-I was developed from a cross involving the cold tolerant variety Dunghansali and the high yielding variety IR 8. It is inferred that tolerance to low temperature during germination in Krishna-A was inherited from the cytoplasm of cv. Dunghansali through Kalinga-I besides male sterility. The cytoplasmic control of cold tolerance is reported here for the first time in rice literature. The male sterile line Krishna-A because of its tolerance to low temperature would be suitable for the development of hybrid rice especially for areas where low temperature is a problem during germination.