Improvement of resistance to Fusarium head blight by recurrent selection in an intermating breeding spring wheat population using the dominant male-sterile gene ms 2

Four cycles of recurrent selection for FHB resistance were conducted in an intermating wheat breeding population using the dominant male-sterile gene ms ₂ during 1987–1991.Five cycles of phenotypic mass selection for male-sterile plants were evaluated using the soil-surface inoculation method in Experiment I. Experiment II evaluated changes in FHB scores during five cycles of progeny selection for fertile plants using the single-floret inoculation method. In Experiment I, the average level of FHB response increased to MR level in C₄, compared to MS level in C₀. The numbers of infected spikelets and diseased kernels decreased 0.32 and 2.68 per cycle, respectively. In Experiment II, the average level of FHB response increased to R level in C₄F₁. The numbers of infected spikelets and diseased kernels decreased 0.93 and 4.58 per cycle, respectively. In both experiments, the largest selection gains were realized in the first cycle. The frequencies of R and MR individuals were increased significantly. The frequencies of individuals with FHB response equal and/or superior to Sumai 3 were increased to 5–8% in C₄ and 25% in C₄F₁after the fourth cycle. Agronomic traits tended to be slightly improved in selected populations. Compared to 2% in C₀, about 34% of lines superior in both FHB resistance and agronomic traits in C₄F₁ were selected to enter the conventional breeding program for further evaluation. Sixty three semidwarf lines superior in both FHB resistance and yield potential were selected from the F₅ generations derived from C₁F₁ to C₄F₁. From them, two resistant cultivars with high-yielding potential were developed and commercialized in the Lower Yangtze Valley. Recurrent selection appears to be highly effective and feasible in shifting the average FHB response of the intermating population in the desirable direction, thereby enhancing the frequency of resistant individuals. This revised version was published online in July 2006 with corrections to the Cover Date.     

小麦抗赤霉病基因库研究 Ⅵ.轮选品系与原始亲本的综合分析与比较

用２６个来自基因库的轮选品系或抗源材料和１９个原始亲本，在赤霉病单花接种条件下，对抗性和１６个农艺性状进行综合分析与比较。平均而言，从接种后１６－１７到２６－２７天，病小穗数和病小穗率的扩增值，轮选品系比原始亲本分别少１．３２个和７．１１％。     

表型轮回选择和混合选择改良小麦群体效应的研究

在吴兆苏等(1984)创建的小麦基础群体中,采用不同的选择方案,对不育株和可育株分别进行两轮选择。结果表明两轮选择显著地降低了可育株和不育株群体的株高。可育株群体株高的下降速率大于不育株群体。单株产量和单株穗数没有得到显著的改良。相关性状穗长、千粒重等出现负向间接选择效应。轮回选择通过选株间的互交,维持了不     

Variation for reproductive and agronomic traits among T. repens × T. nigrescens third generation backcross hybrids in the field

Interspecific hybridisation with Trifolium nigrescens Viv. is a possible strategy to improve the reproductive potential of white clover (Trifolium repens L.). Following the development of a fertile F1 hybrid, three generations of backcrossing have been carried out usingT. repens as the recurrent parent. Vegetative characteristics, stolon growth and seed yield components of the backcross (BC) 2 and 3 generations, as well as the parental species were measured on spaced plants grown in the field. Leaf size and plant spread of the BC2 and BC3 generations were less than T. repens but there was no difference in plant fresh weight. Numbers of inflorescences per plant and florets per inflorescence of the backcrosses were greater than T. repens however this was not reflected indifferences in seed yield per plant asT. repens had more seeds per floret and per plant than the backcrosses. Differences in stolon length, the proportion of flowering nodes and the pattern of axillary bud development were observed between T. repens and the backcrosses. Significant variation among the BC 3 generation for vegetative and reproductive traits was observed. Individual plants among the BC 3 generation were identified that combine high forage yield, substantial inflorescence production and good fertility, and these will form the basis of further selection. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phenotypic recurrent selection in common bean (Phaseolus vulgaris L.) based on performance of S2 progenies

Summary The effect of a recurrent selection procedure for improving seed yield per plant was evaluated in common bean. Progress was registered after three cycles of recurrent selection with S2 progeny evaluation performed on the grain yield/plant. Gain from selection was estimated by field testing 45 random S2 lines from each of the C0, C1 and C2 populations. Response to selection for seed yield/plant was 6 g from C0 to C1 and 4.4 g from C1 to C2. The seed yield improvement was due principally to an increase in pods/plant; little contribution was provided by the 1000-seed weight and seeds/pod traits. Broad-sense heritability and genotypic variance for grain yield remained high in all cycles which suggests further gain from additional selection cycles. Grain yield/plant is significantly correlated to pods/plant and seeds/pod traits in all cycles, indicating that plants with favourable combinations of these traits could be identified. The proposed recurrent selection procedure appears to be effective in improving the population and extracting superior genotypes for varietal development.     

Insect-mediated cross-pollination in soybean [Glycine max (L.) Merrill]: II. Phenotypic recurrent selection

Recurrent selection is a method for population improvement which has been used in soybean [Glycine max (L.) Merrill] to modify traits such as grain yield, seed-protein content, seed-oil content, tolerance to iron-deficiency chlorosis, and seed size. Nuclear male-sterility with insect-mediated cross-pollination has been successfully used in recurrent selection schemes in soybean. However, little attention has been given to selection to increase the agronomic performance of male-sterile plants per se. The objective of this study was to evaluate the response of male-sterile lines segregating for male-sterile alleles ms2, ms3, ms6, ms8, and ms9 to phenotypic recurrent selection for increased seed-set after 3 cycles, using a selected group of male parents. Bees halictidae, anthophoridae, andrenidae, and megachilidae were utilized as the pollinator vector. The results indicated that recurrent selection in a favorable environment was successful to increase the number of seeds per male-sterile plant. Although a differential response was observed among populations, the seed-set observed would justify the use of some specific male-sterile selections as female parents in a hybrid soybean seed production system.     

Recurrent selection using male sterility and hydroponic tiller culture in pedigree breeding of wheat

A procedure for recurrent selection based on the male sterility gene, Ms3, was implemented. To facilitate the production of large numbers of hybrid progeny, a simple hydroponic system was developed in which male‐sterile tillers cut at the flowering stage can be pollinated and maintained for about 8 weeks‐long enough to produce a large quantity of viable hybrid seeds. The recurrent selection steps were integrated with a pedigree breeding programme employing different selection cycles for male and female plants. F₁ female plants are subjected to a single screening for seedling resistance. In addition to F₁ seedling screening, F₂‐F₄ male families are field‐selected for disease resistance, agrotype and quality in a pedigree programme before being used in crosses.     

Stability analysis over seasons and locations of multilines of wheat (Triticum aestivum L.)

Summary Three multilines each of Kalyansona and PV 18 varieties of wheat were compared for their stability of yield and agronomic characters and disease resistance against the respective recurrent parents. The experiments were conducted for four years at nine locations.The multilines had more tillers and bolder seeds than the recurrent parents. There were, however, no differences for plant height, ear length and number of spikelets per spike.The genotypes x years x locations interaction was much more important than genotypes x years or genotypes x locations interaction as well as the main effects for genotypes. It is suggested that the number of test locations should be increased while decreasing the number of years.The stability parameters indicated that the multilines had a higher mean yield in the case of Kalyansona multilines whereas the yield of multilines of PV 18 was not significantly inferior to that of the recurrent parent. The regression coefficients were very close to unity except for KSML 3 (b=1.132). The deviations from regression were much larger for the multilines than for the recurrent parents.For rust resistance the multilines were superior over the varieties Kalyansona and PV 18.This is publication No. 9 of the series Studies on multilines in wheat (Triticum aestivum L.)     

Induction of an alloplasmic male-sterile Brassica oleracea by substituting cytoplasm from ‘Early Scarlet Globe’ radish (Raphanus sativus)

Summary Alloplasmic male-sterile Brassica oleracea L. was synthesized in a backcrossing program through amphidiploid Raphanobrassica by using Early Scarlet Globe radish (Raphanus sativus L.) as the donor of cytoplasm and B. oleracea broccoli and cabbage as recurrent pollen parents. Persistence of radish chromosomes and high female sterility were encountered in the first four backcrosses. Following use of colchiploid 4x broccoli as pollen parent, a BC₅ plant was obtained that had 2n=3x+1=28 chromosomes, improved seed set, and no radish traits. The BC₆ with recurrent 2x broccoli contained male-sterile plants with 2n=18 or 19 chromosomes, increased seed set, and broccoli morphology. Subsequent generations segregated for male-sterile and restored male-fertile plants, some with variable development of stamens and pollen. Leaf color of the alloplasmic plants, especially seedlings, was lighter green than normal.     

Recurrent selection for resistance to Verticillium dahliae in pepper

Summary Two cycles of recurrent selection were performed in a population including 7 small fruited varieties of pepper (Capsicum annuum) with low resistance level to Verticillium and resistance to other soilborne pathogens. The collaboration of 7 plant breeders in this work and the use of 2 artificial methods of inoculation allowed screening of numerous plants for resistance to V. dahliae under different conditions. The population was simultaneously improved for resistance to V. dahliae and for resistance to Phytophthora capsici, and at each cycle, intercrosses were performed between all these plants. The general level of resistance to V. dahliae increased continuously during the 2 cycles of seles of selection. Selfed progenies of plants from the 2 cycles displayed a higher resistance than the original parents, whatever the method of inoculation used. This gave evidence of transgressions for resistance. Crosses involving parents that did not seem resistant by themselves also produced transgressive lines, indicating that resistance genes were present but not active in these varieties. The transgressive lines with polygenic resistance to V. dahliae were included into a further breeding program to introduce genes of agronomic value.     

Direct and indirect selection for yield in chickpea

Summary The efficiency of indirect selection for seed yield was compared with direct selection for yield per se in chickpea. A total of 2500 single F₂ plants, derived from 50 crosses with 50 plants from each cross, were divided into five sub-populations (SP1 to SP5) of 500 plants each by including 10 plants from each of the 50 crosses. The five sub-populations were advanced upto F₆ by exercising 10% selection intensity for four successive generations for number of pods per plant in SP1, number of seeds per pod in SP2, seed weight in SP3, seed yield in SP4 and random selection in SP5. The efficiency of direct and indirect selection for yield was evaluated by comparing groups of 50 F₆ lines from each sub-population. SP1 and SP3 F₆ lines showed higher mean grain yield than the other three methods. SP1 and SP3 were found to be almost equally efficient in developing F₆ lines which were significantly superior to the check. This suggests that indirect selection for yield via pod number and seed weight is more efficient than direct selection for yield.     

The development of Raparadish (x Brassicoraphanus, 2n=38), a new crop in agriculture

Summary Raparadish, x Brassicoraphanus, the amphidiploid hybrid between Brassica rapa (syn. B.campestris) and Raphanus sativus (fodder radish) was made by Dolstra (1982). Primary hybrid plants grew vigorously, suggesting that the amphidiploid AARR might be useful as a fodder crop. Three populations of this new material were studied, with special attention to improvement of fertility and resistance to beet cyst nematode (Heterodera schachtii), whilst preserving genetic variability. For lack of progress one of the populations was abandoned after the fourth generation. The other two populations were observed through nine or ten generations. Apart from the last two generations mass selection for seed set was carried out on the basis of single plants. This led to a considerable increase in average seed production, without losing a wide variation for this trait. Thus more progress is being expected. Five cycles of mass selection for resistance to beet cyst nematodes led to a considerable increase of the level of resistance of both populations. The prospects of this new agricultural crop are discussed.     

圆锥小麦四排穗性状基因的遗传及分子标记分析

四排穗(four-rowed spike, FRS)性状是超数小穗(supernumerary spikelets, SS)性状的一种类型,表现为在一个穗轴节片上近垂直地着生2个无柄小穗,从而增加了小穗数和穗粒数,对提高产量有一定的潜力。为了解圆锥小麦0880 FRS性状的遗传特征,将0880与正常穗(normal spike, NS)圆锥小麦0879杂交,构建了遗传群体,并对0880 (FRS) × 0879 (NS)与0879 (NS) × 0880 (FRS) F₁、F₂及F_2:3植株的穗部性状进行了调查。结果显示,正反交组合的F₁植株均表现为正常穗,F₂群体中正常穗与四排穗符合3∶1的分离比例,表明0880的四排穗性状由隐性单基因控制,将该基因定名为frs1;细胞质对frs1无显著影响。采用已定位于普通小麦A组与B组的SSR分子标记并结合混合分组分析法(BSA), 筛选出32个在双亲及F₂单株构建的四排穗型池和正常穗型池都具有多态性的SSR分子标记,利用JoinMap4.0软件构建了与frs1连锁的2A染色体11个SSR分子标记遗传图谱,其中SSR标记Xwmc598和Xwmc522位于frs1基因两侧,与该基因的遗传距离分别为4.0 cM和2.4 cM。利用2A染色体缺失系对这11个SSR进行物理定位,Xwmc598和Xwmc522均被定位在2A染色体短臂FL0.00~0.78区域。本研究的结果为frs1基因的精细定位及分子标记辅助选择奠定了基础。     

Breeding strategy in foxtail millet,Setaria italica (L.P. Beauv.), following interspecific hybridization

Summary An interspecific cross between foxtail millet Setaria italica and its wild relative Setaria viridis was undertaken in order to introduce from the latter triazine resistance in the cultivated plant. Four backcross generations obtained with S. italica as recurrent parent were studied. Results show that only two backcross generations associated with selection are enough to eliminate weedy characters and to return to the cultivated type. S. viridis could thus be an interesting source for improvement of foxtail millet without a complex and time consuming breeding strategy.     

Breeding transgressive lines of pepper for resistance to Phytophthora capsici in a recurrent selection system

Summary In order to increase the resistance level of pepper (Capsicum annuum) to Phytophthora capsici the main sources of genetic resistance were intercrossed. The parents included 7 varieties from different origins of partial resistance to P. capsici and to other soilborne pathogens. Two cycles of recurrent selection were performed by 7 plant breeders who screened the plants at two developmental stages with various isolates and at two temperatures. Analysis of data revealed a strong influence of the testing conditions on the evaluation of the plants. The level of resistance of the progenies further depended on the pathogen isolate used to screen the plants. Improvement of the whole population was more significant during the first cycle and lines with enhanced level of resistance as compared to the parents i.e. transgressive lines were fixed from the two cycles. These lines were resistant to much higher inoculum concentrations than the original parents and the expression of resistance was stable at high temperature (32°C). These new sources of polygenic resistance were included into a new breeding program to improve the agronomic characters.     

小麦轮回选择的初步实践

利用太谷核不育小麦,开展以抗锈和矮秆丰产为主要目标的轮回选择,选择压分别为5.6%和4.7%.抗锈群通过一轮混合选择,条锈病反应型0—1级的抗病株率和严重度25%以下的轻病株率较基础群体分别提高12.5%和5.1%.矮秆丰产群采用两种轮选方案.经两轮选择看出,改良半姐妹法其群体的株高比基础群体明显降低6.2厘米,其余性状有向选择目标集中的趋势;混合选择法其群体除穗粒数外,其余性状进展趋势与上相同.     

Single-gene resistance to powdery mildew in zucchini squash (Cucurbita pepo)

Cucurbita pepo (pumpkin, squash,gourd) is an economically important species that is susceptible to the cucurbit powdery mildew fungus, Podosphaera xanthii(syn. Sphaerotheca fuliginea). ‘True French’, an open-pollinated cultivar of the Zucchini Group of C. pepo, was crossed with an unnamed powdery-mildew resistant straight neck-type accession, the resistance of which was apparently derived from an interspecific cross with a resistant wild species of Cucurbita,and resistant plants were selected in the F₂ generation. This was followed by six cycles of backcross-pedigree selection for resistance, and resulted in the development of an accession true-breeding for resistance to powdery mildew and nearly isogenic to ‘True French’. The resistant and susceptible near-isogenics were crossed and seeds of the filial and backcross generations were produced. Plants of the parental accessions and their progenies were grown together in a controlled-environment chamber, exposed to the pathogenic fungus, and scored as resistant, partially resistant, or susceptible 27–33 days after sowing. The results indicated that resistance is conferred by a single incompletely dominant gene, designated Pm-0. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pedigree selection for Gibberella ear rot resistance in maize

The pedigree method is often used for developing inbred lines in maize (Zea mays L.). This study was conducted to assess the effectiveness of pedigree selection for improving resistance to Gibberella ear rot in four maize populations. Selection was based on the severity of ear rot symptoms after inoculation with macroconidial suspensions of Fusarium graminearum (Schwabe) into the silk channel (for two populations) and into the developing kernels (for two other populations). Samples of the selfed families (S₁ to S₅), recovered from remnant seed from the selection programs, were evaluated for disease resistance during three years, using inoculation and evaluation protocols similar to those used during selection. Among-family selection was effective in both of the populations selected after silk inoculation and in one of the populations selected after kernel inoculation. Responses to selection were more evident in later than in earlier generations for both types of inoculation. Changes in the estimated genetic gain over generations were consistent with changes in the variances among families, which tended to increase in early generations and to decrease in later generations. Selection after kernel inoculation seemed to have been more effective than selection after silk inoculation in developing families with more stable resistance. Based on the results obtained here, it seems that responses to family selection could be accelerated without increasing operational costs by increasing selection intensity in later generations and inoculating fewer plants per family.     

小麦抗倒性影响因子和产量因子的遗传与相关研究

旨在为小麦育种和生产上预防倒伏、提高稳产能力提供参考。以来源于野生二粒小麦远缘杂交组合的82个高代系为试材,在西北农林科技大学试验站测定并分析抗倒性影响因子和产量性状的相关性。结果表明,（1）株高与抗倒性呈负相关关系,成熟期茎壁厚与抗倒性呈正相关关系,各个性状的抗倒性排序为株高>成熟期茎壁厚度>单穗重>单株重;（2）粒宽、穗粒数和单穗重呈极显著正相关关系(0.413^**、0.767^**);（3）倒伏引起千粒重、单穗重下降,导致减产;（4）小穗数、小穗粒数及穗粒数等产量因子及抗倒影响因子的杂种分离世代都出现小于低亲值的遗传特点,分离子代产量接近高亲值的单株占1.5988%,杂交育种中分离世代最低群体需在120株左右。选择茎壁厚、植株高度适中、增加粒宽（饱满大粒）和穗粒数（大穗、多花结实性好）,有望筛选出高产抗倒品种。     

Increasing resistance to Fusarium crown and root rot in asparagus by gametophyte selection

In garden asparagus, Fusarium crown and root rot is the main cause of crop decline. Since chemical treatments are inefficient, efforts should focus on the development of resistant cultivars to control the disease. Toxic culture filtrate (TCF) of F. oxysporum has affected asparagus pollen germination and tube growth. Consequently, gametophyte selection was evaluated to ascertain if the application of selective agents at this level could increase selection efficiency. Two susceptible pistillate plants and one tolerant and one susceptible staminate plants were used in controlled crosses. Before pollination, a drop of a germination vehicle with TCF or without it was applied to the stigmas. Some pollinated pistils were fixed and analyzed by fluorescence microscopy; the rest were left on the plant for seed production. Fifty to 200 seeds were obtained per treatment combination (staminate plant x pistillate plant x pollination vehicle). The derived plantlets were inoculated in vitroand evaluated for disease symptoms. The application of TCF to stigmas reduced pollen germination and tube growth compared with untreated controls,regardless of the genotypic combination. Pollen germination and tube growth was poorer for the tolerant staminate genotype than for the susceptible one. When the TCF was applied, the number of seeds per pollination in comparison with the controls diminished only when the susceptible genotype was the pollinator. The percentage of affected root area of the progenies obtained after applying the TCF was lower than in the controls only when the tolerant genotype was the pollinator. Increasing Fusarium resistance in asparagus by means of gametophyte selection seems feasible. This revised version was published online in August 2006 with corrections to the Cover Date.