Quantitative trait loci for adventitious and lateral roots in rice

The mass of a root is determined by two underlying morphogenetic factors: (1) the length of the main root axis (root axis length: RAL), and (2) the amount of lateral root development generated by a unit length of the axis (branching index: BI). The mass of a rice adventitious root was partitioned into these two factors at the quantitative trait locus (QTL) level, using ‘Akihikari’ (a lowland cultivar as a recurrent parent) × ‘IRAT 109’ (an upland cultivar) backcross inbred lines. Four QTLs were detected for the dry weight of individual adventitious roots (root dry weight: RDW), which were associated with a QTL for RAL (chromosomes 1 and 9) or a QTL for BI (chromosomes 6 and 11). For BI, an additional QTL was detected on chromosome 1. The absence of co‐located QTLs suggested that RAL and BI are under separate genetic control. Despite its small population size and few replications, this study suggests that the partitioning of root mass into these underlying components could be useful for understanding the complexity involved in the genetic control of root growth.     

以热量指数表示北疆棉区棉花延迟型冷害指标的研究

应用乌兰乌苏农业气象试验站棉花试验的生育期、产量及旬气温资料,计算出棉花不同播期和不同生长阶段的热量指数,研究分析不同播期棉花产量、霜前花率与棉花不同生长阶段的热量指数之间的关系发现:1)随播种期推后,棉花生长前期热量指数明显增加,而棉花生长后期的热量指数则呈现出明显的下降趋势。2)现蕾—开花阶段的热量满足状况很好,热量指数稳定。3)分期播种的单产与棉花生长后期的热量指数具有很好的线性关系,霜前花率也与棉花生长后期的热量指数关系密切,生长后期的热量指数变化对棉花品质的影响较产量更加敏感。4)以减产幅度为标准,在棉花开花期以前热量充足的情况下,后期生长热量指数低于64为一般延迟型冷害年指标,低于61.8为严重延迟型冷害年指标。5)以霜前花率为标准,在棉花开花期以前热量充足的情况下,后期生长热量指数低于 70.9 会出现一般冷害年,低于63.2,会出现严重冷害年。     

Fertility Improvement in Autotetraploids of Pea — Selection for Seed-Set and Disjunction Index

Four seed-set groups of plants, viz. unselected ‘general’ and selected ‘high’, ‘medium’ and ‘low’ were constituted in C₁ generation from randomly selected autotetraploids of two pea cultivars, T 163 and 5064-S. In C₂ generation, ten plants were selected at random in each of the four groups. Two seeds each from selected autotetraploids were drawn and bulked to make 20 seeds in each of the four groups to raise C₃ generation. Selection resulted in a gradual shift in seed-set, though the magnitude and nature varied with the group and generation. Improvement in the seed-set from C₁ to C₃ generation was associated with the increase in bivalents per cell, disjunction index and total chiasmata. Increase in total chiasmata was mostly due to an increase in proximal ones. Increase in seed-set was reflected in improvement of grain yield per plant.     

Comparison of some selection procedures and objectives in faba beans (Vicia faba L.). I. direct and index selection for seed yield

Summary Starting with two heterogeneous F₂ populations, each based on 20 cross combinations, different selection procedures were applied for four consecutive selection cycles. Three of the selection procedures involved seed yield per plant (SYP): (i) direct selection for SYP (DSY); (ii) indexselection for SYP (ISY) with plant length, the ratio of the vegetative top to plant length, end of grain filling and duration of the generative stage as auxiliary characters and finally; (iii) independent culling levels selection (ICL) for the index described above and crude protein content. For ICL-selection the attention is focussed on SYP in this paper.For all three selection procedures, predicted and realized responses were calculated and expressed as percentage of a corresponding non-selected population. The intensities of selection differed over selection methods and generations, mostly due to practical constraints.As far as predicted responses are concerned, ISY-selection seemed to be slightly superior to DSY-selection and DSY-selection to ICL-selection. This order may partly be due to differences in selection intensity. However, none of the predictions was very accurate, but the predictions of ICL-selection seemed to be the most accurate. This has been ascribed also to the relative mild selection intensity applied in ICL-selection. It is concluded that a decision in favour of a complicated selection procedure like index selection based on predicted responses only cannot be defended. As far as realized responses are concerned, DSY-selection seems to be slightly superior to the other two selection procedures, as it is the only procedure that resulted in a more or less stable positive response to selection.The auxiliary characters, especially plant length, showed a marked correlated response to all three selection procedures. In case of direct selection for SYP this seemed paradoxical with the inefficiency of index selection, but, it may reflect the differences in the genuine genotypic correlations and the estimated genotypic correlations.     

系祖轮配对维持并提高豫州褐壳蛋鸡Ⅲ系生产性能的研究

对豫州褐壳蛋鸡Ⅲ系采用系祖间轮配的选配方法，经过连续3个世代的选育，开产日龄推迟5．72d，开产平均蛋重减少0．87g，72周龄平均蛋重增加2．82g、蛋数增加8．62枚，蛋品质维持在较高水平，蛋壳颜色变深。说明对已育成的纯系采用系祖间轮配的选配方法，可以维持并提高其生产性能。     

Transgressive segregation in inter and intraspecific crosses of barley

Summary Six populations of F₂-derived lines of barley and their parents were evaluated for heading date, plant height, grain yield, bundle weight, and harvest index in a replicated experiment in the field. These data were used to estimate the minimum number of effective factor pairs segregating for each trait, the number of favorable factors contributed by each parent in a cross, and the frequencies and magnitudes of transgressive segregates.Heading date, plant height, and harvest index were controlled by three to four effective factor pairs, whereas grain yield and bundle weight were controlled by five or more.All three H. spontaneum strains used in our study contributed one or more useful genes for each of the traits, grain yield, heading date, plant height, bundle weight, and harvest index. Therefore, it seems that H. spontaneum can be a useful source of favorable genes for quantitative traits, especially for grain yield, which could be incorporated into barley varieties readily by backcrossing. Transgressive segregates for grain yield in the interspecific crosses may provide the basic materials for improving the productivity of cultivated barley varieties.Journal Paper No. J-9760 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project 2227. Supported in part by a grant from the Science and Education Administration-Cooperative Research, United States Department of Agriculture.     

Use of index selection in recurrent selection programs in maize

Summary Phenotypic and genotypic correlations were examined for four traits in seven populations of maize (Zea mays L.) undergoing recurrent selection. Correlations among grain yield and percentage of grain moisture, root lodging, and stalk lodging were low (|r|<0.3) except for the correlation between grain yield and stalk lodging, which was high and negative. The phenotypic and genotypic correlations agreed well from cycle to cycle within populations. Variation of correlations among populations was not significantly larger than variation among cycles. Heritabilities of these traits generally were high (h²>0.5). Two indices, one that used heritabilities as index weights and one that used relative economic weights (base index) as index weights, were compared with the Smith-Hazel index (optimim index). Relative efficiencies of the two indices, in terms of predicted gains for the individual traits and the composite trait, compared with the Smith-Hazel index, were high. The use of an index in which heritabilities were used as index weights was recommended because:1) the heritabilities were the same as the optimum weights when the traits were uncorrelated, and for the data examined the correlations were low; and 2) heritabilities were computed in routine data analyses and were available at no additional cost.Joint contribution: USDA-SEA-AR and Journal Paper No. 10152 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project 2194.     

Selection in segregating generations of autogamous species. I. Selection response for combined selection

Summary The response to selection is determined by the genetic and nongenetic variance, the selection intensity, and the size of the experiments. If, in pure line breeding, selection starts in segregating generations, the gain depends on the relation of additive to epistatic variance. The gain can be increased if an index is constructed using the information from relatives. From animal breeding this kind of selection is known as combined selection. In this paper the optimal number of families and subfamilies is determined that will maximise the selection response by combined selection for a fixed total size of experiments. The composition of the genetic variance has a imited influence on the optimal size of the progenies. If epistatic variance is important, then the number of F₂ families has to be reduced and the number of F₃ families and F₄ families must be increased. The same is true if the nongenetic variance is increased.     

以湖南和湖北大豆[Glycine max（L.）Merr.]为例分析影响遗传多样性评价的因素

以不同来源大豆种质为材料进行基因组SSR分析，探讨大豆遗传多样性研究方法，旨在为科学评价大豆种质资源提供参考。当取样比例相同时，湖北大豆的遗传丰富度显著高于湖南大豆，但两省大豆遗传多样性指数之间没有显著差异。当取样量相同时，利用随机取样法比较，湖南大豆的遗传多样性显著高于湖北，而利用聚类取样比较，两省大豆的遗传多样性没有显著差异。在遗传多样性指数相同情况下，湖北大豆的遗传丰富度显著高于湖南大豆。取样数与三个遗传多样性评价参数（等位变异数、Shannon指数、He）之间均达到显著和极显著相关。以湖南大豆为例，估算出在大豆SSR遗传多样性分析中，至少需要50~60个样本，即占总体9.0%~10.8%的取样比例，才能代表总体的遗传变异。提出在评价大豆遗传多样性时，应用大豆样本数对其遗传多样性指数计算公式进行修正，建议将Shannon指数计算公式改为H＝－lnN ∑P_i lnP_i (N为样本数)。根据修正公式分析，结果表明，湖北大豆的遗传多样性高于湖南大豆。     

Study on the Changes of the Amount of Microorganism and Microbial Biomass Carbon in Soil of Greenhouse Cropping

通过对四川省温江、双流两地不同设施种植年限土壤中微生物数量及其生物量碳的研究,结果表明,不同设施种植年限大棚土壤中的微生物数量是露地的1.63~3.50倍,且大棚土壤中好气性微生物总数随种植年限的增加有逐渐降低的趋势,三大微生物数量占微生物总数的比例中,细菌表现为随设施种植年限的增加而增加;放线菌和真菌表现为下降;露地土壤微生物多样性指数分别是设施年限为1a、2a和4a的大棚土壤的1.29倍、2.28倍和3.45倍,前者明显高于后者。随设施年限的增加,土壤微生物生物量碳、有机碳及微生物对有机碳的利用率都表现