Family Outcrossing Rates of Pinus caribaea Morelet var. caribaea in Seed Orchard and Natural Populations

Family outcrossing rates of Pinus caribaea var. caribaea populations that differed in origin and management were estimated by using isozyme markers. The family outcrossing rates were estimated by (1)fixing the probability of pollen gene frequency (p); (2) allowing pollen gene frequency to vary among families. The estimates of family outcrossing rates for all the populations varied widely among families (clones of the seed orchard), ranging from 0.39 to 2.0. The average family outcrossing rates of both methods were greater than the     

Genetic variability and inheritance of aluminium tolerance as indicated by long root regrowth in lucerne (Medicago sativa L.)

The objective of this study was to quantify the genetic variability and determine the inheritance of Al tolerance in lucerne (or alfalfa) using a 4-parent diallel mating design. Regrowth root length (RRL), along with root length (RL) and total root length (TRL), was measured to indicate relative Al stress response using a hydroponic system in a 3 μM Al solution at pH 4.5. A diallel analysis indicated the significance of general combining ability (gca) variance for RRL but not the specific combining ability (sca) variance; the same result was obtained for TRL but not for RL. For both RRL and TRL, genetic variance appeared to be more important than the environmental variance. For RRL, a strong but non-significant correlation was indicated between parental performance and their gca effects; while mid-parent heterosis and/or over-dominance were detected, as associated with the expressed sca effects in several combinations. These results suggest the complex genetic nature and expression of Al tolerance in the 4-parent diallel crossing system tested. Al-tolerant parent, GAAT‘S’, was the most promising parent, conferring the highest gca effects for RRL as well as for other two characters. The existence of significant gca variance in RRL may also suggest the feasibility of improving Al tolerance through enhanced root regrowth using phenotypic recurrent mass selection to pyramid desirable Al-tolerant genes, focussing on parental lines and/or elite individual plants expressing long regrowth roots.     

Mating system in an experimental garden composed of cassava (Manihot esculenta Crantz) ethnovarieties

Crossing patterns were investigated in an experimental garden of ethnovarieties ofManihot esculenta (Euphorbiaceae) inPiracicaba, São Paulo, Brazil. A model of evolutionary dynamics for cassava presupposes genetic recombination by means of crossing within cassava gardens as a source that amplifies genetic diversity. Quantitative analysis of mating system parameters was performed using progeny arrays assayed for eight allozyme markers. The multilocus outcrossing rate (t _m)estimate (0.915±0.04)revealed that outcrossing was prevalent, but that a low level of self-pollination also occurred. The multilocus outcrossing rate ranged from 0.69 to 1.00 among eight varieties. The high value found for the outcrossing rate indicates that the ethnovarieties studied are preferentially allogamous. Genetic recombination occurred through crossing within the cassava garden, in agreement with an assumption of the model of evolutionary dynamics for this species.     

Evaluation of Potato Hybrids Obtained from Tetraploid-Diploid Crosses II. Progeny Analysis

A total of 45 tetraploid-diploid (4x—2x) hybrid progenies were obtained by crossing each of ten diploid parents as males to each of five tetraploid parents. Means of six traits of the 45 progenies obtained from a two-year experiment were used in progeny analysis. A new mathematical model is developed for analyzing the incomplete two-way table. It is modified from the conventional model for factorial mating design. The aim of the model is to evaluate the potential of 2x parents in terms of their mean effects (μ_i) and sensitivity measures (B_i) to the 4x parents. The 4x parents were treated as testers in the model. They were compared by the estimates of the magnitude of tester effects (g_i). The mean effects of 2x parents showed a dominant influence on variation of tuber number and mean tuber weight of the hybrid progenies. They also demonstrated a substantial influence on the variation of total and marketable yield, chipping score and specific gravity. The linear response of 2x parents to 4x parents, however, also showed a substantial influence on the variation of the latter traits. The information on μ_i and B_i are useful in terms of choosing superior 2x parents and, together with gj of 4x parents, 4x—2x progenies for specific traits. The μ_i and B_i estimates of the six traits showed a complicated interrelationship to each other.     

The frequency of natural cross-fertilisation in sequential sowings of winter barley

Summary Estimations of random mating frequency were computed for a series of sequential autumn sowings of populations of winter barley. The estimations were by means of the maximum likelihood scoring method and three varieties, each carrying a recessive genetic marker, provided three independent estimations for each population. High levels of out-crossing were found in sowings made early in September, and a trend towards absence of out-crossing in populations sown in late November was evident. Although fluctuations in this trend could be accounted for by fluctuations in meteorological factors, a more profound underlying effect was evident in that the three marker varieties behaved similarly, though to different degrees. It is postulated that the principle effect of sowing date, as it affects out-crossing, is upon the development of the flowering apex, and that environmental conditions at flowering time merely modify flowering behaviour.     

Modified full-sib selection and best linear unbiased prediction of progeny performance in a European F2 maize population

Four cycles of modified recurrent full‐sib (FS) selection were conducted in an intermated F₂ population of European flint maize. The objectives of our study were to monitor trends across selection cycles in the estimates of population mean, inbreeding coefficients and variance components, and to investigate the usefulness of best linear unbiased prediction (BLUP) of progeny performance under the recurrent FS selection scheme applied. We used a selection rate of 25% for a selection index, based on grain yield and dry matter content. A pseudo‐factorial mating scheme was used for recombination. In this scheme, the selected FS families were divided into an upper‐ranking group of parents mated to the lower‐ranking group. Variance components were estimated with restricted maximum likelihood (REML). Average grain yield increased 1.2 t/ha per cycle, average grain moisture decreased 20.1 g/kg per cycle, and the selection index relative to the F₂ check entries decreased 0.3% per cycle. For a more precise calculation of selection response, the four cycles should be tested together in multi‐environmental trials. We observed a significant decrease in additive variance in the selection index, suggesting smaller future selection response. Predictions of FS family performance in Cn + 1 based on mean performance of parental FS families in Cn were of equal precision as those based on the mean additive genetic BLUP of their parents, and corresponding correlations were of moderate size for grain moisture and selection index.     

抗药性根瘤菌基因工程菌的构建与应用

用三亲本杂交的方法将外源抗药性质粒导入到高效固氮的根瘤菌 Tal377中,外源质粒在 Tal377中能正常表达,但不影响其原有的固氮结瘤能力。利用此抗药性根瘤菌所携带的抗药性,在接种此根瘤菌的同时结合施加一定浓度的抗菌素,抗药性根瘤菌与出发菌株相比表现出一定程度地提高其结瘤固氮能力和占瘤率。     

培养条件对银耳孢子产交配信息素的影响

研究了培养条件对银耳孢子产交配信息素的影响。结果表明银耳孢子产交配信息素的较佳培养基为 :蔗糖 2 0 g/L ,(NH4) 2 SO41.5 84 g/L(含N 2 4mmol/L) ,MgSO4·7H2 O 0 .2 5 g/L ,KH2 PO4·3H 2 O 0 .5 g/L ,VB10 .2mg/L ,ZnSO4·7H2 O 2mg/L ,CaCl2 ·2H2 O 0 .5 g/L ,钼酸铵 0 .0 2mg/L。最佳发酵条件为培养基 pH 6 .5 ,2 3℃ ,14 0r/min摇瓶培养 4d。     

农药亚致死剂量对优姬蜂交配行为影响的研究

用１００×１０－６％农梦特和空白农梦特乳油，以及０．０１×１Ｏ－６％氯氰菊酯处理寄生于小菜蛾幼虫的优姬蜂雄蜂，观察农药亚致死剂量对优姬蜂交配行为的影响。结果表明，受农梦特处理的雄蜂只有６８．１８％在遇到雌蜂时引起翅膀扇动。在农梦特和氯氰菊酯处理中，雄蜂对雌蜂在交配行为上的反应迟钝，它们从试验开始到扇动翅膀的时间显著地比对照和空白农梦特乳油的推迟，其交配率分别为２７．２７％和５５％，交配抑制率分别为５３．６８％和３２．０６％。     

玉米小斑病菌(Drechslera maydis)与玉米圆斑病菌(Drechslera carbonum)种间杂交的初步研究

研究相关种内控制有性机制的遗传体系,可以对进化的方向和形式提供重要的信息。研完交配机制中,遗传上的相似之处和不同之处,是确定属内各个种的进化地位和相互间关系的重要方法。研究种间杂交的频率和程度,以及种间杂交和种内交配可育也有利于进行生物评定。本实验通过D.maydis种内交配和D.maydis与D.carbonum种间杂交的初步研究结果,对D.carbonum的分类地位提出一些初步看法。