GENETICS OF PHYTOPATHOGENIC FUNGI. XI. A GENETIC STUDY OF AVIRULENCE DUE TO AUXOTROPHY IN PENICILLIUM EXPANSUM BY MEANS OF THE PARASEXUAL CYCLE

Nine color and 35 auxotrophic mutants were tested for their virulence, using the ‘Jonathan’ variety of apple; only mutants requiring methionine were avirulent. One tested arginine-requiring and the methionine-requiring mutants were avirulent for the ‘Red Delicious’ variety. In vitro and in vivo, supplementation studies indicated that the avirulence was probably related to the relatively low concentration of the required amino acids at the site of inoculation. One heterocaryon and the corresponding diploid, involving 2 avirulent methionine-requiring mutants, were virulent. Six mutant loci in 3 diploid strains could be assigned to 2 linkage groups by means of the parasexual cycle.     

GENETICS OF PHYTOPATHOGENIC FUNGI. V. HETEROCARYONS INVOLVING FORMAE OF FUSARIUM OXYSPORUM

Garber , E. D., Ellen G. Wyttenbach , and T. S. Dhillon . (U. Chicago, Chicago, Ill.) Genetics of phytopathogenic fungi. V. Heterocaryons involving formae of Fusarium oxysporum. Amer. Jour. Bot. 48(4): 325–329. 1961.—Heterocaryons involving mutant strains of 4 formae of Fusarium oxysporum were studied; the strains differed in nutritional requirements, resistance to acriflavine, and colonial morphology and color. Spores from the heterocaryons gave colonies on minimal medium which resembled one component strain in morphology and color; spores from heterocaryons involving f. pisi yielded colonies on complete medium containing a concentration of acriflavine inhibitory to the other component strain.     

THE GENETICS OF ADAPTATION: THE GENETIC BASIS OF RESISTANCE TO WASP PARASITISM IN DROSOPHILA MELANOGASTER

There have been very few genetic analyses of “natural” adaptations, that is, those not involving artificial selection or responses to human disturbance. Here we analyze the genetic basis of geographic variation in Drosophila melanogaster's resistance to parasitism by a wasp, Asobara tabida. Our results suggest that population differences in ability to encapsulate parasitoid eggs have a fairly simple genetic basis: 60% of the D. melanogaster genome plays no role in differences between resistant and susceptible populations. Instead, resistance gene(s) are restricted to chromosome two, and may be further restricted to the centromeric region of this chromosome. This finding suggests that natural adaptations—like many responses to artificial selection and human disturbance—sometimes have a simple genetic basis.     

壳聚糖对几种植物病原真菌的作用

在马铃薯葡萄糖琼脂 ( PDA)上测定了酸溶性壳聚糖 ( S- )和 2种水溶性壳聚糖 ( S- 和 S- )对 15种植物病原真菌的作用 ,结果表明 ,三种壳聚糖对供试的 15种植物病原真菌均有一定程度的抑制作用 ,抑制强度因壳聚糖的理化性质以及不同的病原真菌而有较大差异。水溶性壳聚糖 S- 可明显抑制水稻恶苗病菌分生孢子的萌发。壳聚糖的抑菌作用机制与其增加菌丝细胞膜的透性有关。     

GENETICS OF PHYSIOLOGICAL AND BEHAVIORAL RESISTANCE TO HOST FURANOCOUMARINS IN THE PARSNIP WEBWORM

Depressaria pastinacella, the parsnip webworm, feeds almost exclusively on the flowers and fruits of Pastinaca sativa, the wild parsnip. Resistance to webworms in wild parsnip populations is largely attributable to genetically based variation in furanocoumarin chemistry; by differentially reducing fruit set among chemical phenotypes, parsnip webworms may act as selective agents on wild parsnip populations. To determine whether wild parsnip chemistry can act as a selective agent on webworm populations, it is necessary to establish that resistance mechanisms in the webworm to furanocoumarins are genetically based. In this study, we estimated the amount of genetic variation in behavioral and physiological responses of webworms to parsnip furanocoumarins. Virtually no variation was found among webworm families for feeding preferences for diets varying as much as fourfold in furanocoumarin content. Nor was significant variation found for mean furanocoumarin intake over the assay period, except in one case, in which maternal effects may account for differences among families. In contrast, substantial familial variation existed for cytochrome P450–mediated metabolism of bergapten and xanthotoxin, two host furanocoumarins. The presence of additive genetic variation in metabolism, and the absence of such variation in discriminative feeding behavior, suggests that adaptation to changes in furanocoumarin chemistry, resulting either from changes in the distribution of chemical phenotypes in parsnip populations or from shifts to new chemically different host plants, is likely to be facilitated by physiological rather than behavioral means.     

GENETICS OF HORIZONTAL RESISTANCE TO DISEASES OF CROPS

(1) Horizontal resistance (HR) to diseases of crops has the following leading features: it is polygenically controlled and must be studied by biometrical-genetic methods; it is pathotype-non-specific and essentially ‘durable’; it has several components (e.g. infection rate, latency period, sporulation potential) which tend to be correlated; its use is relevant to the control of all classes of pathogen (fungi, bacteria, viruses, insects, nematodes); though often unrecognized, it is very common and generally the means by which ‘minor’ diseases remain minor. HR may be contrasted with ‘vertical resistance’ (VR) which is procured by major genes and is pathotype-specific. VR has uses in particular circumstances but has often failed against airborne epidemic pathogens such as many rusts; hence the importance of understanding HR. (2) In this review the genetic evidence of HR is reviewed and examples are summarized in appendices. Very diverse crops, places and pathogens are represented. So far as may be judged, HR is indeed universal, and found or constructable wherever sought. The most important genetic evidence is based on generation mean and variance analysis, general and specific combining ability, offspring-parent regression and response to selection. Useful supplementary evidence comes from historical observations, continuity and repeatability of resistance and yield-related effects. (3) The main conclusions are that HR is universally available, usually highly heritable and responsive to selection, already keeps a host of crop diseases down to acceptably low levels and has socio-economically attractive features that are likely to increase its use in the future. In particular, it offers long-term stability of performance that must be valuable to small farmers in the Third World and is environmentally attractive because successful breeding programmes minimize the need for environmentally damaging chemical protectants. ‘Green’ pressures are likely to favour HR and some relevance to public policy is thereby implied.     

GENETICS OF RESISTANCE OF SALIX SERICEA TO A DIVERSE COMMUNITY OF HERBIVORES

We measured resistance of Salix sericea, the silky willow, to a diverse assemblage of 12 herbivores. We investigated the potential for multispecies coevolution among these herbivores by measuring genetic correlations between pairs of herbivores interacting within the component community. After measuring herbivore attack on half-sib families of potted S. sericea during three years, we found significant narrow-sense heritabilities of resistance to Phyllonorycter salicifoliella and Phyllocnistis sp. in 1991. Thus, there is the potential for selection on resistance to these two herbivores. Despite the many significant phenotypic correlations between herbivore abundances within a year, most genetic correlations between herbivore abundances within a year were not significant. The genetic and phenotypic correlation structure varied from year to year in this three-year study. Thus, it appears that there is the potential for evolution of resistance to the two herbivores for which we found significant heritabilities, but multispecies coevolution seems unlikely.     

THE GENETICS OF CENTRAL AND MARGINAL POPULATIONS OF DROSOPHILA SERRATA. I. GENETIC VARIATION FOR STRESS RESISTANCE AND SPECIES BORDERS

A selection experiment was used to determine if levels of genetic variance in an ecologically important trait, desiccation resistance, were different in central and marginal populations. Four populations of Drosophila serrata were sampled from central and marginal areas of its distribution, along a 3000-km stretch of Australia's east coast. Rainfall patterns along this stretch of coastline change from a tropical cycle in the north to a temperate cycle in the south. Replicate lines from the four populations underwent selection for desiccation resistance for 14 generations. Realized heritabilities calculated after 10 and 14 generations of selection indicated that the four populations differed significantly in the level of genetic variation for desiccation resistance available to selection. Populations from the more southern marginal areas had lower realized heritabilities than more northern central populations. However, a corresponding increase in mean desiccation resistance toward the margin was not found. A mechanism by which D. serrata seemed to have responded to selection was a reduction in the extent that metabolic rate was increased when flies were exposed to low humidity. This response indicates genetic variation for the control of metabolic rate. In contrast, increased desiccation resistance was not associated with lipid or glycogen levels. Increased resistance to desiccation was accompanied by increased starvation resistance, but radiation resistance was not affected. Selection did not affect the degree that replicate lines or populations had diverged.     

粟长蠕孢菌的原生质体转化

本文报道了利用具有潮霉素抗性标记的质粒(pAN7-1)对粟长蠕孢菌原生质体进行转化的结果。经pAN7-1质粒DNA转化处理的粟长蠕孢菌原生质体在含潮霉素(200μg/ml)的选择性培养基上出现两类转化子。一类是正常转化子,其转化率为2个转化子/μg DNA;另一类是流产转化子,其产生频率为500—600个转化子/μg DNA。DNA杂交分析结果表明,在正常转化子中质粒DNA以首尾相接、重复排列的形式整合入受体菌染色体DNA。初筛获得的转化子多数以异核状态存在,经单孢分离纯化后可通过有丝分裂稳定传代。     

GENETIC BASIS OF A BETWEEN-ENVIRONMENT TRADE-OFF INVOLVING RESISTANCE TO CADMIUM IN DROSOPHILA MELANOGASTER

In a replicated, laboratory, natural selection experiment Drosophila melanogaster populations were maintained for 20 generations either on unpolluted medium or on polluted medium containing cadmium chloride at a concentration of 80 μg/ml. Lines maintained on polluted medium evolved resistance. In comparison with unpolluted lines, their juvenile survivorship increased from 35% to 46%, developmental period decreased from 13.7 days to 13.0 days, and fecundity increased from 3 to 29 eggs per two-day period. Emergence weights, however, did not change. By contrast the “environmental” effect of moving susceptible flies onto polluted medium was that after two generations survivorship fell 62%, developmental period increased 40%, and fecundity fell 97%. Emergence weights fell 31% in females and 28% in males. Resistant lines paid a fitness cost in unpolluted environments, with fecundity being reduced by 44% and emergence weights being reduced by 4% in females and 6% in males. Developmental period, however, was unaffected. Analyses of crosses and backcrosses between the lines suggested that the evolved cadmium resistance was due to a single sex-linked gene. Levels of dominance were calculated, and in each life-history character the resistant allele was found to be completely dominant. Because the life-history effects appear to be produced by a single gene, it is probable that they all depend on the same metabolic pathway. Metallothionein production is a likely candidate because this is known to be controlled by genes on the X-chromosome. The study adds to a small number of examples of single or closely linked genes with large antagonistic pleiotropic effects on life histories. The result here is a between-environment trade-off, allowing animals increased fitness in polluted environments, but only at the cost of reduced growth and reproduction in unpolluted environments.     

RESISTANCE OF GENETIC CORRELATION STRUCTURE TO DIRECTIONAL SELECTION IN DROSOPHILA MELANOGASTER

The genetic covariance and correlation matrices for five morphological traits were estimated from four populations of fruit flies, Drosophila melanogaster, to measure the extent of change in genetic covariances as a result of directional selection. Two of the populations were derived from lines that had undergone selection for large or small thorax length over the preceding 23 generations. A third population was constituted using flies from control lines that were maintained with equivalent population sizes as the selected lines. The fourth population contained flies from the original cage population from which the selected and control lines had been started. Tests of the homogeneity of covariance matrices using maximum likelihood techniques revealed significant changes in covariance structure among the selected lines. Prediction of base population trait means from selected line means under the assumption of constant genetic covariances indicated that genetic covariances for the small population differed more from the base population than did the covariances for the large population. The predicted small population means diverged farther from the expected means because the additive genetic variance associated with several traits increased in value and most of the genetic covariances associated with one trait changed in sign. These results illustrate that genetic covariances may remain nearly constant in some situations while changing markedly in others. Possible developmental reasons for the genetic changes are discussed.     

QUANTITATIVE GENETICS OF RESPONSE TO COMPETITORS IN NEMOPHILA MENZIESII: A GREENHOUSE STUDY

To determine the potential for adaptation to a local biotic environment, we examined the magnitude and nature of genetic variation in response to neighboring plants within a natural population of the native California annual, Nemophila menziesii. A total of 22 plants from a natural population were crossed in three reciprocal factorials. The progeny were grown in a greenhouse in nine treatments that varied in conspecific density and in the density of a naturally co-occurring grass species, Bromus diandrus. Increasing the density of each species significantly reduced individual survival, fruit number, and dry weight. Among survivors, we found small to moderate heritability of dry weight within treatments. Additive genetic correlations (r_A) of dry weight between competitive regimes were generally large and positive. In no case were they significantly different from 1, as expected under the null hypothesis that the relative performance of the genotypes under consideration is the same in all environments. On the basis of these results, we cannot conclude that the structure of genetic covariation within this population would promote genetic differentiation in response to locally varying conditions of density of these two species. Aspects of the experiment that may have compromised our ability to detect r_A differing from 1 are discussed.     

RAPD应用于遗传多样性和系统学研究中的问题

在研究银杉（Ｃａｔｈａｙａ ａｒｇｙｒｏｐｈｙｌｌａ）的遗传多样性时,对ＲＡＰＤ 产物的影响因素进行了大量的实验探索,结果表明：逐级纯化的ＤＮＡ 模板的ＲＡＰＤ结果一致, 因而模板制备过程中的很多纯化步骤是不必要的; ＲＮＡ 对扩增产物无影响; 模板浓度在一个相当大的范围内不影响扩增结果; 从干叶和鲜叶中提取的ＤＮＡ 可获得一致的扩增产物; 从而证明ＲＡＰＤ 产物具有很好的重复性。进而讨论了ＲＡＰＤ产物分析及数据分析中的一些问题。通过对升麻属（Ｃｉｍ ｉｃｉｆｕｇａ） ５ 种、类叶升麻（Ａｃｔａｅａ ａｓｉａｔｉｃａ）及松潘乌头（Ａｃｏｎｉｔｕｍ ｓｕｎｇｐａｎｅｎｓｅ）的ＲＡＰＤ 结果分析,认为ＲＡＰＤ 方法可用于种间乃至近缘属间的系统学研究, 但有一定的局限性     

棉铃虫对溴氰菊酯的抗性遗传及其生化机理

用经室内诱导的抗溴氰菊酯棉铃虫Helicoverpa armigera(Hubner)种群与室内饲养多年的敏感种群进行杂交,研究了棉铃虫对溴氰菊酯的抗性遗传规律。结果表明：杂交后的显性度(D)分别为0.34和0.35,F₁与亲本回交的期望值与实际值在比值是1 ∶1时差异显著,回交平台在35%～45%,棉铃虫对溴氰菊酯的抗性可能是一个以上主基因的不完全显性遗传。生化分析表明,抗性种群的。-乙酸萘酯酶活力与敏感种群的差异显著,这可能是棉铃虫对溴氰菊酯产生高抗药性的重要解毒酶之一。     

GENETIC CORRELATION BETWEEN RESISTANCE TO OXIDATIVE STRESS AND REPRODUCTIVE LIFE SPAN IN A BIRD SPECIES

Evolutionary theories propose that aging is the result of a trade‐off between self‐maintenance and reproduction, and oxidative stress may play a crucial role in such a trade‐off. Phenotypic manipulations have revealed that a high investment in reproduction leads to a decline in the organism's resistance to oxidative stress, which could in turn accelerate aging. Here, by using quantitative genetic analyses as a tool to disentangle genetic effects from phenotypic variances, the relationship between resistance to oxidative stress at sexual maturity and two key reproductive life‐history traits (i.e., number of breeding events during life and age at last reproduction) was analyzed in cross‐fostered zebra finches. The age of last reproduction had high narrow‐sense heritability, whereas the number of breeding events and oxidative stress resistance showed medium and low heritabilities, respectively. We detected positive genetic correlations between early resistance to oxidative stress and both life‐history traits, suggesting that the efficiency of the antioxidant machinery at maturity may be related to individual reproductive investment throughout lifetime, possibly by influencing the pattern of cellular senescence. Genes encoding for resistance to oxidative stress would have pleiotropic effects on reproductive capacity and aging. Further work is required to confirm this assert.     

GENETICS OF BRASSICA RAPA. 3. COSTS OF DISEASE RESISTANCE TO THREE FUNGAL PATHOGENS

Genetic costs of resistance to pathogens may be an important factor maintaining heritable variation for resistance in natural populations. Pleiotropic fitness trade-offs occur when genetic resistance causes reduction in other components of fitness. Although costs of resistance have an important influence on plant-pathogen interactions, few previous studies have detected pleiotropic costs of resistance in the absence of confounding effects of linkage disequilibrium. To avoid this potential problem, we performed artificial selection experiments on resistance to two fungal pathogens, Leptosphaeria maculans, and Peronospora parasitica, and compared growth rates of resistant and susceptible genotypes of Brassica rapa in the absence of pathogens. Leptosphaeria resistance had no effect on growth rate, indicating cost-free defense. In contrast, Peronospora-resistant genotypes grow 6% slower than Peronospora-susceptible genotypes in pathogen-free environments, indicating a significant genetic fitness cost to Peronospora resistance. Such genetic trade-offs could maintain genetic variation in the wild. Another factor that might explain heritable variation for resistance is ecological trade-offs, in which genetic resistance to one species causes susceptibility to another. Such ecological trade-offs do not exist for the pathogens studied in this system.     

丝状真菌遗传转化系统研究进展

丝状真菌是自然界中普遍存在的 ,并具有重要经济价值的一类真核微生物。近年来 ,对其分子生物学的研究取得了长足进展。本文对丝状真菌遗传转化系统的最新研究进展进行了综述 ,主要包括以下几个方面 :转化方法、载体、选择性标记、整合机制以及转化在丝状真菌研究中的应用。