QUANTITATIVE GENETICS OF SEQUENTIAL LIFE-HISTORY AND JUVENILE TRAITS IN THE PARTIALLY SELFING PERENNIAL,AQUILEGIA CAERULEA

We determined the genetic basis of several traits related to overall fitness of Aquilegia caerulea, a perennial herb of the Rocky Mountains in western North America. To obtain measures of heritability relevant to the evolutionary potential of wild populations, we performed full and partial diallel crosses and studied progeny performance in the field. Based on a joint analysis of two designs with a total of 18 parents and 102 crosses, we detected significant maternal variance for seed mass and emergence time, but this component was negligible for later-expressed traits. Low heritability and evidence that maternal effects on seed mass are largely environmental suggest that in this population there is little evolutionary potential for change in seed mass under conditions experienced during the study. Seed mass varied depending on particular combinations of parents and cross direction. Such an interaction can have several different biological interpretations, including that particular maternal parents selectively provision embryos sired by particular pollen genotypes. Width of the first true leaf after 4 wk of growth and leaf size of juvenile plants at years one and two were significantly heritable and positively genetically correlated. Juvenile survival exhibited significant dominance variance, as expected from evidence of inbreeding depression in this trait. In contrast, for other traits that exhibit inbreeding depression in this population (seed mass and third-year leaf size), dominance variance was negligible.     

Cassava breeding: opportunities and challenges

Although cassava is a major food crop, its scientific breeding began only recently compared with other crops. Significant progress has been achieved, particularly in Asia where cassava is used mainly for industrial processes and no major biotic constraints affect its productivity. Cassava breeding faces several limitations that need to be addressed. The heterozygous nature of the crop and parental lines used to generate new segregating progenies makes it difficult to identify parents with good breeding values. Breeding so far has been mainly based on a mass phenotypic recurrent selection. There is very little knowledge on the inheritance of traits of agronomic relevance. Several approaches have been taken to overcome the constraints in the current methodologies for the genetic improvement of cassava. Evaluations at early stages of selection allow for estimates of general combining ability effect or breeding values of parental lines. Inbreeding by sequential self-pollination facilitates the identification of useful recessive traits, either already present in the Manihot gene pool or induced by mutagenesis.     

3×3完全双列杂交F1不同阶段生长特点的分析

为了了解鲤杂交F1不同组合、不同阶段生长性状的变化情况,研究以建鲤、黄河鲤和黑龙江野鲤3个鲤品种双列杂交F1为试验材料,通过组合、组合内性别间、性别、不同时期体重、体增重以及协方差分量的分析,来确定完全双列杂交F1生长性状的变化特点,以及在此过程中起重要作用的影响因素。结果表明:不同时期各个组合体重不同,不同时期组合内性别间体重差异不同;不同时期不同性别间体重差异不同;不同协方差分量,同一组合PIT标记17个月时的体重的最小二乘估计值不同,同一个协方差分量,9个组合中极值估计值出现的组合也不同;除PIT标记17个月后的体厚作为协方差分量外,性别之间体重没有差异,其余分量均是雌鱼体重显著高于雄鱼体重。这些说明选取合适的协方差分量对组合的选择和育种的结果有重要影响。     

The quantitative genetics of fluctuating asymmetry: a comparison of two models

The genetic basis of fluctuating asymmetry (FA), a measure of random deviations from perfect bilateral symmetry, has been the subject of much recent work. In this paper we compare two perspectives on the quantitative genetic analysis of FA and directional asymmetry (DA). We call these two approaches the character-state model and the environmental responsiveness model. In the former approach, the right and left sides are viewed as separate traits whose genetic coupling is manifested by the genetic correlation. This model leads to the relationship, h2(DA) = h2[(1-rA)/(1-rp)), where h2 is the heritability of each component trait (assumed to be the same), rA and rp are the genetic and phenotypic correlations between traits, respectively. Simulation shows that, under this model, the heritability of FA is considerably less than that of DA, except when heritabilities are very close to zero. The environmental responsiveness model permits genetic variance in FA even when the genetic correlation between traits is + 1. Simulation shows that under this model the heritability of FA can be uncoupled from that of DA. The additive and nonadditive components of the component (right and left) traits, their DA and FA values are estimated using a diallel cross of seven inbred lines of the sand cricket, Gryllus firmus. Four leg measurements were made and both the individual DA and FA values and the compound measures DASUM and CFA estimated. The heritabilities of the compound measures are slightly larger than the individual estimates. Dominance variance is observed in the individual traits but predicted to be an even smaller component of the phenotypic variance than the additive genetic variance. The estimated values confirm this, although a previous study has demonstrated that dominance variance is present. Because the heritabilities of FA are generally larger than those of DA, which never exceed 0.02, the environmental responsiveness model is more consistent with the data than the character-state model. A review of other data suggests that both sources of variation might be found in some species.     

CL系列甘蔗亲本的遗传力及配合力分析

为探讨CL系列甘蔗品种作杂交亲本的遗传特点,采用3×3不完全双列杂交(NCⅡ)遗传设计,估算了7个产量和品质性状的遗传方差、一般配合力(GCA)和特殊配合力(SCA)。结果表明:锤度的遗传主要受母本加性基因效应控制,株高的遗传主要受父母本加性基因控制,而锤重的遗传主要受非加性基因效应所制约;CL83-1163作为母本,糖分配合力高,且能把高糖特性传递给后代,CL88-4730为父本,产量和品质性状的配合力大,其杂交后代表现高产高糖;根据配合力总效应(TCA),综合表现好的组合有CL83-1364×CL88-4730、CL83-1900×CL84-3152、CL83-1163×CL88-4730,可用于今后的甘蔗有性育种计划。     

Heritability and correlation structure of nectar and floral morphology traits in Nicotiana alata

The heritability and genetic basis of nectar traits have been rarely studied in the field, where plants are exposed to environmental factors that could mask underlying genetic effects. Heritabilities and variance components were estimated for nectar and morphological traits of Nicotiana alata , using a partial diallel design. The main experiment was conducted in a Missouri experimental garden using a randomized block design with three plant density treatments, whereas a smaller experiment was conducted near native Brazil habitat to compare the environmental variance in traits between Missouri and Brazil. Significant heritability was detected for nectar volume and energy content, and for corolla tube length. Phenotypic correlations were significant between all traits investigated, whereas significant genetic correlations were only found between nectar volume and energy and between corolla limb width and mouth diameter. There were no significant family-by-density interactions detected in the Missouri field environment. All traits differed significantly between Missouri and Brazil environments, but significant genetic by environment (G × E) interactions between Missouri and Brazil were detected for only one trait. This study shows that nectar traits can be heritable despite considerable environmental variation.     

The Analysis of Partial Diallel Crosses

The analysis of offsprings from the partial diallel crosses is presented. In considered type of crossing, p parental forms into H separate groups are devided. Single crosses among parental forms, from separate groups only, are performed. The analysis for experiments laid out in efficiency balanced block designs is given.     

A Study of Maternal and Maternal Interaction Effects in Diallel Crosses

The analysis of diallel crosses by including the components due to maternal effect and maternal interaction effects have been presented for Griffing method—1 (random effect model) and Griffing method—3 (fixed and random effect model). Wherever exact test of significance is not possible, testing procedure using Satterthwaite (1946) approximation has been presented.     

Genetic effect on uptake of selected nutrients in some rice (O. sativa L.) varieties in phosphorus deficient soils

The influence of genes on the uptake by rice plants of certain macro- and micronutrients (calcium, magnesium, iron, manganese and zinc) was studied, by diallel (7 × 7) analysis, in P deficient upland soil. Both additive and dominant gene effects, with a preponderance of the former, were found to be responsible for the uptake of all the elements studied. Local varieties were found to be not only good yielders but also much more efficient in element uptake. Heterotic effects were observed in various crosses with respect to the uptake of all the aforementioned nutrients. Statistical analysis indicated that while the uptake of iron and zinc were negatively correlated, the uptake of manganese and calcium, manganese and zinc, calcium and magnesium and calcium and zinc were positively correlated.     

Inheritance studies of low-phosphorus tolerance in maize (Zea mays L.), grown in a sand-alumina culture medium

Inbred lines of maize selected as tolerant and intolerant to low-P stress using a sand-alumina culture medium were used to obtain F₁ hybrids and advanced generations to be evaluated in diallel mating schemes and generation means analyses for the inheritance studies. Sand-alumina, a solid culture medium, which simulates a slow release, diffusion-limited P movement in soil solution was used in the inheritance studies. Tolerance to low-P stress conditions in maize seedlings is controlled largely by additive gene effects, but dominance is also important.