Genetic analysis of salt tolerance during germination in Lycopersicon

Summary The salt-tolerant cultivated tomato (Lycopersicon esculentum) accession, PI174263, and a sensitive cv, UCT5, were crossed to develop reciprocal F₁, F₂ and BC₁ populations for genetic analysis of salt tolerance in tomatoes during seed germination. Variation was partitioned into embryo, endosperm and maternal (testa and cytoplasmic) components. Generation means analysis indicated that there were no significant embryo (additive, dominance or epistatic) effects on germination performance under salt stress. Highly significant endosperm additive and testa dominance effects were detected. The proportion of the total variance explained by the model containing these two components was R²=98.2%. Variance component analysis indicated a large genetic variance with additive gene action as the predominant component. Furhter inspection indicated that this variance was attributable to endosperm additive effects on germinability under salt stress. Narrow-sense heritability was estimated as moderately high. Implications for breeding procedures are discussed.     

Genetic architecture of adaptive differentiation in evolving host races of the soapberry bug,Jadera haematoloma

To explore genetic architecture and adaptive evolution, we conducted environmental and genetic experiments with two recently (ca. 100 generations) diverged, geographically adjacent races of the soapberry bug. One race occurs on a native host plant species, the other on an introduced host. We focused on three traits: length of the mouthparts, body size and development time. The first experiment was an environmental manipulation, comparing individuals of each population reared on one or the other host species (cross-rearing) and estimating three evolutionary rates for each trait. The first rate, evolutionary path compares ancestral-derived populations when both were reared on the introduced host. The second, current ecological contrast compares populations with each reared on its natal host. The third, evolved tradeoff compares the two races when reared on the native host. Differences among these rates are striking and informative. For example, development time, which appears to be relatively undifferentiated phenotypically, has actually evolved very rapidly via countergradient selection. The pattern differs for each trait, and clear developmental tradeoffs have evolved as quickly as adaptation to the new host in each. The second experiment was a two-generation line cross study. With joint-scaling analyzes, we compared purebred, hybrid and backcrossed individuals to describe genetic architecture. Additive genetic variance for mouthpart length was consistently large (ca. 60%), but the interaction of dominance, maternal effects and epistasis was important in the other traits. Rearing host strongly affected genetic architecture. There was no clear relationship between genetic architecture and rate of evolution. Selection has produced both additive and nonadditive differentiation between the host races with surprising speed, consistent with theoretical predictions about evolution in fitness-associated traits.     

Generation means analysis for productivity in two diverse peanut crosses

Summary Utilization of exotic germplasm resources for population improvement in peanut (Arachis hypogaea L.) has increased as the need to increase genetic diversity among peanut cultivars was recognized. Progeny of crosses of two unadapted germplasm lines (GP-NC 343 and FESR-11-P11-32) with an adapted cultivar (NCV11) of peanut were evaluated for the genetic factors influencing the inheritance of yield and fruit characters in crosses among diverse lines. Objectives were to (1) estimate the relative importance of additive and nonadditive genetic effects in the inheritance of yield and fruit characters in two diverse peanut crosses; (2) determine the proportion of exotic germplasm that gave the optimum combination of mean productivity and genetic variability for each of the crosses; (3) relate the results to theories regarding the transfer of desirable alleles from exotic germplasm into adapted breeding populations. Crosses and backcrosses were made to generate germplasm lines (ten generations) ranging from 0 to 100% exotic germplasm for each cross. The populations were evaluated in replicated field trials. Yield and six fruit characters were measured, and a weighted analysis of variance was conducted to determine if significant differences existed among generations. Generation means analyses were performed for each trait measured in each of the crosses using both three- and six-parameter models, which were tested for goodness-of-fit with a joint-scaling test. Significant differences were detected among generations for most traits measured in both crosses. Estimates of additive genetic effects were significant for pod weight and seed weight in cross 1 (NC-V11 x GP-NC 343) and for all traits in cross 2 (NC-V11 x FESR-11-P11-32) except seedpod ratio. Significant estimates of dominance effects were found for pod length, pod width, and pod weight in cross 1 and for pod length in cross 2. No significant estimates of digenic effects were observed in cross 1, whereas in cross 2 estimates of additive x dominance epistatic effects were significant for yield and pod length, while estimates of additive x additive effects were significant for seed number. Regression of trait means on generations showed a curvilinear response for all traits in cross 1 except seed weight, which gave a linear response. For all traits in cross 2, the relationship between productivity and proportion of unadapted germplasm was effectively linear. Based on generation means and variances, progeny from the first or second backcross generation to the recurrent parent should be expected to give an optimum combination of mean productivity and relative variability in the population.The research reported in this publication was funded in part by the North Carolina Agricultural Research Service     

Fine mapping of a malting-quality QTL complex near the chromosome 4H S telomere in barley

Malting quality has long been an active objective in barley (Hordeum vulgare L.) breeding programs. However, it is difficult for breeders to manipulate malting-quality traits because of inheritance complexity and difficulty in evaluation of these quantitative traits. Quantitative trait locus (QTL) mapping provides breeders a promising basis with which to manipulate quantitative trait genes. A malting-quality QTL complex, QTL2, was mapped previously to a 30-cM interval in the short-arm telomere region of barley chromosome 4H in a Steptoe/Morex doubled haploid population by the North American Barley Genome Project, using an interval mapping method with a relatively low-resolution genetic map. The QTL2 complex has moderate effects on several malting-quality traits, including malt extract percentage (ME), -amylase activity (AA), diastatic power (DP), malt -glucan content (BG), and seed dormancy, which makes it a promising candidate gene source in malting barley-cultivar development. Fine mapping QTL2 is desirable for precisely studying barley malting-quality trait inheritance and for efficiently manipulating QTL2 in breeding. A reciprocal-substitution mapping method was employed to fine map QTL2. Molecular marker-assisted backcrossing was used to facilitate the generation of isolines. Fourteen different types of Steptoe isolines, including regenerated Steptoe and 13 different types of Morex isolines, including regenerated Morex, were made within a 41.5-cM interval between MWG634 and BCD265B on chromosome 4H. Duplicates were identified for 12 Steptoe and 12 Morex isoline types. The isolines together with Steptoe and Morex were grown variously at three locations in 2 years for a total of five field environments. Four malting-quality traits were measured: ME, DP, AA, and BG. Few significant differences were found between duplicate isolines for these traits. A total of 15 putative QTLs were mapped; three for ME, four for DP, six for AA, and two for BG. Background genotype seemed to make a difference in expression/detection of QTLs. Of the 15 QTLs identified, ten were from the Morex and only five from the Steptoe background. By combining the results from different years, field environments, and genetic backgrounds and taking into account overlapping QTL segments, six QTLs can be conservatively estimated: two each for ME and AA and one each for DP and BG with chromosome segments ranging from 0.7 cM to 27.9 cM. A segment of 15.8 cM from the telomere (MWG634–CDO669) includes all or a portion of all QTLs identified. Further study and marker-assisted breeding should focus on this 15.8-cM chromosome region.     

Use of recombinant inbred lines of wheat for study of associations of high-molecular-weight glutenin subunit alleles to quantitative traits

Summary Recombinant inbred lines (RILs) derived by single plant descent to F₈ from a hybrid of Anza, a low-quality cultivar, and Cajeme 71, a high-quality cultivar, differed in alleles at three high-molecular-weight glutenin (HMW-glu) seed storage protein loci. The 48 RILs were classified by SDS-PAGE for the Anza alleles Glu-Alc (null), Glu-B1b (subunits 7 + 8), and Glu-D1a (subunits 2 + 12) and for Cajeme 71 alleles Glu-A1a (sub-unit 1), Glu-B1I (subunits 17 + 18), and Glu-D1d (subunits 5 + 10). All RILs and parents were grown in a replicated field trial with three levels of nitrogen (N) fertilization. Additive and additive x additive gene effects for the three loci were detected by orthogonal comparisons of means for each of six wheat end-use quality traits. Each HMW-glu genotype was represented by three to ten RILs so that variability among RILs within each HMW-glu genotype could be examined. N effects were consistently small. All traits except flour yield were highly correlated with predictor traits studied earlier. Flour protein content, baking water absorption, dough mixing time, bread loaf volume, and bread loaf crumb score were all correlated, suggesting similar gene control for these traits; however, specific additive locus contributions were evident: _B for flour yield; _B and _D for flour protein; and _B for absorption, but differing in sign; all three loci for mixing time, but _B was negative; and all three loci were positively associated with loaf volume. Digenic epistatic effects were significant for flour yield (_AD), flour protein (_AB), and absorption and mixing time (_AD, _BD). Only flour yield showed a trigenic epistatic effect. Six of seven epistatic effects were negative, thus showing how progress in breeding for high quality may be impeded by interaction of genes which, by themselves, have strong positive additive effects. Considerable genetic variance among RILs within a HMW-glu genotype was detected for all traits, and the summation of effects accounted for a mean of 13% of the parental differences for the six traits examined in this study. Clearly, further resolution of the genetics of wheat quality would be desirable from a plant breeding point of view.     

Diallel analysis of submergence tolerance in rice,Oryza sativa L.

Summary The genetics of submergence tolerance in rice was studied in a 10 × 10 half-diallel cross set involving 10 lowland rice varieties, four of which were tolerant (FR13A, FR43B, Kurkaruppan, and Goda Heenati) and the remaining six were nontolerant (RD19, IR42, IR17494-32-1, IR19672-24-3, Jagannath, and CR1009). Estimates of genetic parameters following Hayman's method showed significant additive and nonadditive gene action and the latter appeared to be solely due to dominance. Narrow sense heritability (0.70) indicated that additive gene effects were more important in the inheritance of the trait. Tolerance was dominant over nontolerance and the average dominance was within the range of incomplete dominance. Dominant alleles were more concentrated in the three tolerant parents, FR13A, Kurkaruppan, and FR43B in that order. Wr/Vr graphic analysis suggested the involvement of both major and minor genes. Combining ability analysis by Griffing's method also indicated significance of both additive and nonadditive effects, and the former appeared to be more important than the latter. The hybrids involving FR13A with RD19, IR42, and IR17494-32-1, and those of Kurkaruppan with RD19 and CR1009 appeared to be promising for incorporating an adequate level of tolerance to submergence into lowland rice cultivars.     

Genetic analysis of certain in vitro and in vivo parameters in pigeonpea (Cajanus cajan L.)

Summary Studies on callus growth and shoots/cotyledon, using seven different genotypes of pigeonpea and their hybrid progenies, revealed continuous variation for these traits. Hence, the type of gene action influencing in vitro cell proliferation and differentiation has been investigated in a diallel analysis of seven pigeonpea genotypes. Highly significant average heterosis was recorded for callus growth and seed yield/plant. In general, the F₁ hybrids which showed heterosis for callus growth also exceeded their better parent for yield/ plant. Combining ability analysis revealed both additive and non-additive gene effects for callus growth, while number of shoots/cotyledon was mostly governed by non-additive gene effects. The genotype, ICP 7035, was the best general combiner for callus growth and shoot forming capacity of cotyledons. Two cross combinations, 7186×6974 and 7035×T-21, showed maximum SCA effects for callus growth and shoots/cotyledon. Callus dry weight was positively correlated with seed yield/plant and seedling weight. The strong positive association of callus growth with seed yield indicates the possibility of using this system for mass screening and selection of superior hybrids.     

Inheritance of heading date,plant height,ear length and spikelets per spike in an intervarietal cross of wheat

Summary A study to obtain information on early segregating generations of an intervarietal cross WG 357 X Tobari 66 in spring wheat on the genetics of days to heading, plant height, ear length and spikelets per spike was conducted. WG 357 has amber, hard and lustrous grains and is a well adapted high yielding variety of North India whereas Tobari 66 is red grained introduction from CIMMYT.The parental F₁, F₂, B₁, B₂, biparentals, F₃ (parents of biparentals), F₃ bulk and F₄ bulk generations were studied in order to provide analysis of generations means (Mather 1949; Hayman 1958) and variance component analysis (Kearsay 1965; Perkins and Jinks 1970).There were highly significant differences among the generations for all the characters studied. There were significant differences among the F₃ lines as well as among the biparental progenies. Only in case of ear length was the contrast between the two also significant. The mean value of most of the generations arising from the cross fell between the parental range.The three-parameter model failed to account for the variation in generation means in the case of days to heading. This character was concluded to be influenced by linkage and higher order interactions. For the other characters the three parameter model was adequate. For all characters, additive gene effects were most important as compared to dominance gene effects.The analysis of gene action as provided by the generation variance indicated that additive variance was much more pronounced as compared to dominance variance. The heritability was high for days to heading (71 per cent for narrow sense and 80 per cent in broad sense) and plant height (62 and 93 per cent in narrow and broad sense respectively.The implications of the results in breeding programmes have been discussed.     

Evidence for maternal effect in the inheritance of grain protein in crosses between cultivated and wild tetraploid wheats

Summary Reciprocal crosses were made between cultivated wheat (Triticum turgidum var. durum) and a high-protein line of wild tetraploid wheat (T. turgidum var. dicoccoides). F₁ grains (on maternal spikes) were very similar to the selfed grains on the maternal parent in protein percentage, weight and protein content. These traits were also analyzed in F₃ grains developed on F₂ spikes of segregating populations derived from reciprocal crosses between the same cultivated parent and another high-protein line of var. dicoccoides. No significant differences in the mean values of these traits were found between the reciprocal crosses, indicating no cytoplasmic effect. It has been concluded that these grain characteristics are largely determined by the maternal plant.Recipient of Sir Charles Clore Postdoctoral FellowshipThe Marshall and Edith Korshak Professor of Plant Cytogenetics     

Genetic evaluation with autosomal and X-chromosomal inheritance

Summary At present, genetic evaluation in livestock using best linear unbiased prediction (BLUP) assumes autosomal inheritance. There is evidence, however, of X-chromosomal inheritance for some traits of economic importance. BLUP can accommodate models that include X-chromosomal in addition to autosomal inheritance. To obtain BLUP with autosomal and X-chromosomal additive inheritance for a population in which allelic frequency is equal in the sexes, and that is in gametic equilibrium, we write y _i = x_i + a_i + s_i + e_i, where y _i is the phenotypic value for individual i, x_i, is a vector of constants relating y _i to fixed effects, is a vector of fixed effects, a _i is the additive genetic effect for autosomal loci, S _i is the additive genetic effect for X-chromosomal loci, and e _i is random error. The covariance matrix of a _i's is A _A ² , where A is the matrix of twice the co-ancestries between relatives for autosomal loci, and _A ² is the variance of additive genetic effects for autosomal loci. The covariance matrix of s _i's is S _F ² , where S is a matrix of functions of co-ancestries between relatives for X-chromosomal loci and _F ² is the variance of additive genetic effects for X-chromosomal loci for noninbred females. Given the covariance matrices of random effects a _i, s_i, and e _i, BLUPs of autosomal and of X-chromosomal additive effects can be obtained using mixed model equations. Recursive rules to construct S and an efficient algorithm to compute its inverse are given.Dedicated to the memory of Dr. C. R. Henderson, whose encouraging comments stimulated the research in this paper. Supported in part by the Illinois Agricultural Experiment Station, Hatch Project 35-0367, Estimation of Genetic Parameters.     

Inheritance of resistance to blackmold (Alternaria alternata (Fr.) Keissler) in two interspecific crosses of tomato (Lycopersicon esculentum ×L. cheesmanii f.typicum)

Inheritance of resistance to blackmold, a disease of ripe tomato fruit caused byAlternaria alternata, was studied in two interspecific crosses. The parents, F₁ and F₂ generations of a cross between the susceptibleLycopersicon esculentum Mill. cultivar Hunt 100 and the resistantL. Cheesmanii f.typicum Riley accession LA 422, and the parents, F₁, F₂, F₃, and BC₁ P₂ generations of a cross between the susceptibleL. Esculentum cv. VF 145B-7879 and LA 422 were evaluated. The following disease evaluation traits were used: symptom rating (a symptom severity rating based on visual evaluation of lesions), diseased fruit (the number of diseased fruits divided by the total number of fruit scored), and lesion size (a function derived from the actual lesion diameter). Generation means analysis was used to determine gene action. The data of the Hunt 100 × LA 422 cross fit an additive-dominance model for all three traits. The VF 145B-7879 × LA 422 cross data best fit a model that included the additive × additive and additive × dominance interaction components for the trait diseased fruit, whereas higher-order epistatic models would have to be invoked to fit the data for the traits symptom rating and lesion size. A minimum of one gene segregated for all three traits. Broad-sense heritability estimates ranged from 0.09 to 0.16 for all three traits, indicating that selection for improved resistance to blackmold will require selection on a family performance basis.     

Adoptions expérimentales de larves entre des fourmis de genres différents:Leptothorax nylanderi Förster etSolenopsis fugax Latreille

Résumé En l'absence de son propre couvain,Solenopsis fugax a élevé des larves deLeptothorax nylanderi, à la température de 22°C. Les ouvrières deSolenopsis détruisirent une partie de ces larves mais nourrirent celles qu'elles épargnèrent; ces dernières grossirent lentement pendant cinq à six mois, sans atteindre le stade prénymphe. Lorsque les ouvrières deS. fugax et les larves deL. nylanderi furent soumises ensemble à un hivernage préalable, elles donnèrent les mêmes résultats que sans hivernage. La présence d'une jeune reine deSolenopsis fut défavorable aux larves deLeptothorax.Inversement,L. nylanderi fut capable d'élever, à la température de 22°C, des larves deS. fugax et de les amener jusqu'au stade adulte. En présence de leurs propres larves, les ouvrières deL. nylanderi détruisirent tapidement toutes les larves deS. fugax introduites dans leur nid. D'autre part, un jeune couvain deLeptothorax remplaçait plus ou moins rapidement les larves deLeptothorax enlevées au préalable; sa présence était alors défavorable au développement des larves deSolenopsis. Un hivernage en début d'expérience fut plutôt favorable auxS. fugax, de même que la présence d'une reine féconde deLeptothorax. LesSolenopsis ainsi obtenus n'ont pas vécu plus de sept semaines. Ils étaient tous de caste ouvrière et de taille très petite.

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Summary When its own eggs and larvae missed,Solenopsis fugax bred larvae ofLeptothorax nylanderi, at a temperature of 22°C. TheSolenopsis workers killed some of this larvae and fed the others; these slowly grew bigger during five or six months but never reached the pre-pupa stage. The result was the same if the workers ofS. fugax and the larvae ofL. nylanderi overwintered together or not at all. A youngSolenopsis queen being there was noxious to the larvae ofLeptothorax.On the contrary,L. nylanderi has been able to breed larvae ofS. fugax up to the imago stage, at a temperature of 22°C. When its own larvae were in the nest, together with larvae ofS. fugax, the workers ofL. nylanderi killed the larvae ofS. fugax. On the other hand, new eggs and young larvae ofLeptothorax had to replace, more or less quickly, the larvae which had been taken away, and that was noxious to the growth ofSolenopsis larvae. An overwintering at the beginning of the experiment was rather favourable toS. fugax as was the presence of a fecundLeptothorax queen. TheSolenopsis thus obtained lived no longer than seven weeks. They all were workers and very small.

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S. Fugax L. Nylanderi 22° . Leptothorax , , , , . . S. Fugax Leptothorax.,L. Nylanderi 22° S. Fugax . L. Nylanderi ( )Leptothorax ; S. Fugax Solenopsis, Leptothorax. S. Fugax . .

     

Adoptions expérimentales de larves entre des fourmis de genres différents (II):Myrmica laevinodis Nylander etAnergates atratulus Schenck

Résumé Nous avons fait élever des larves d'Anergates atratulus par des ouvrières deMyrmica laevinodis à 22°C. Pour y parvenir, il n'est pas utile de faire hivernerensemble les larves d'Anergates et les ouvrières deMyrmica. La présence de larves autochtones n'empêche pas lesMyrmica d'élever des larves d'Anergates. Dans toutes les expériences lesMyrmica ont été soumises au fridavant de recevoir des larves d'Anergates. Aucune reine deMyrmica n'a été utilisée dans ces expériences.Sur les 64 larves d'Anergates que nous avons utilisées, 38 se sont transformées en imagos. C'est au début de l'adoption et au moment des métamorphoses que périrent la plupart des 26Anergates perdus. Les femelles vécurent en général 2 ou 3 jours et cherchèrent très tôt à quitter le nid natal. Les mâles vécurent 2 à 3 semaines.

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Summary Larvae ofAnergates atratulus were experimentally reared by workers ofMyrmica laevinodis, at 22°C. An overwintering of both larvae ofAnergates and workers ofMyrmica is not necessary for the success of that experiment. The presence of larvae ofMyrmica does not keep theMyrmica from rearing larvae ofAnergates. The workers ofMyrmica have been cooled, in all the experiments, before receiving larvae ofAnergates. No queen ofMyrmica have been used in that experiments.38 of the 64 larvae ofAnergates used became imagos. Most of the 26 lostAnergates died at the beginning of the adoption and during the metamorphosis. The females lived generally 2 or 3 days and tried, very early, to leave their native nest. The males lived 2 or 3 weeks.

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Anergates atratulus Myrmica laevinodis, 22 . bmecme Anergates Myrmica. Myrmica Anergates. Myrmica Anergates. Myrmica . 64 Anergates , 38 . 26 Anergates 2 3 . 2 3 .

     

Genetic diversity in relation to heterosis and combining ability in spring wheat

Summary Genetic diversity among ten varieties of spring wheat used as parents in a diallel cross was assessed through multivariate analysis (D²-statistics) and then related to heterosis and SCA effects of their hybrids. The parents fell into three groups. Group I contained the varieties, Nobre, Girua and Carazinho; group II contained Sonalika, Lyallpur and Pitic 62 and group III contained Indus 66, Balaka, Sonora 64rs and MSl. The varieties of group I were good general combiners, while the varieties of group III were poor combiners. Significant heterotic and SCA effects for yield and yield components were observed in the hybrids of the parents belonging to different groups but not in the same group. Genetic divergence between the parents had a positive relationship with heterosis and SCA effects of the hybrids.     

Evaluation of an exotic maize population adapted to a locality

Summary An exotic Zea mays L. population (Tuxpeno) was adapted to North Carolina conditions by first introducing genes for adaptability from two North Carolina varieties ([(Jarvis X Indian Chief)Tuxpeno]Tuxpeno) including four generations of intermating, and then selecting for adaptability using maturity as the primary measure. The study evaluated selection for adaptability and the diversity available between adapted Tuxpeno and the local varieties, Jarvis and Indian Chief. Analytical procedures were developed to quantify the diversity between populations and the complementation of local varieties by introduced germ plasms. The analyses utilized the specific effects available from the diallel mating design.Three replicate selections responded similarly under simple recurrent mass selection (1/10) for the earliest disease-free plants initially and additionally for plant types (primarily height) in the final generation. The 1/4 local germ plasm permitted rapid adaptation of Tuxpeno gene pool to local conditions. The adapted Tuxpeno populations yielded similarly to the local populations with an average heterosis for grain yield of 28% when crossed to the local populations used as source of genes for adaptability. The diversity found between adapted Tuxpeno lines and these local varieties based on genes affecting grain yield was 1.5 to 2.5 times that measured between the local varieties (Jarvis and Indian Chief). Diversity lost through intergradation with local material was a reasonable investment. Yield genes introduced from Tuxpeno complemented local gene pools through nonadditive, primarily dominance-associated, gene effects. Reassortment of major gene blocks apparently occurred leading to significant divergence among replicate selections involving both additive-associated and dominance-associated gene effects.Paper No. 6355 of the North Carolina Agri. Res. Ser., Raleigh, NC. Research supported in collaboration with the Rockefeller Foundation and CIMMYT, D.F. (Mexico)     

Epistatic,additive and dominance variation in a triple test cross of bread wheat (Triticum aestivum L.)

Summary Triple test cross progenies resulting from the crossing of three testers (Kloka, UP 368 and an f₁ intermediate between them) and 24 varieties of bread wheat have been studied for plant height (cm), peduncle length (cm), ear length (cm), number of spikelets per spike and harvest index (ratio between economic and total yield). Epistasis was not significant for any of the characters studied. The testers were inadequate for plant height and for peduncle length although the testers varied considerably for these traits. Additive variance played a significant role in the inheritance of all the characters except number of spikelets per spike. The dominance variance was important for plant height, ear length and harvest index. The degree of dominance was in the over-dominance range for plant height. Complete dominance was operative for ear length, number of spikelets per spike and harvest index whereas for peduncle length only partial dominance was observed. The possibility of the isolation of the recombinants with high harvest index has been stressed.     

Inheritance and linkage of isozyme loci in almond

The segregation of seven isozyme marker genes was investigated using eight controlled crosses in almond. The cultivar Nonpareil was the maternal parent in all crosses. Pollination was achieved using eight different cultivars, and a total of 3200 individual kernels were assessed. For each isozyme the goodness-of-fit test was used to test for departure from the expected frequencies assuming Mendelian inheritance. Given a higher than expected number of significant results for individual isozymes, independent segregation between pairs of isozymes was tested using the chi-square statistic on the resulting two-way contingency tables. In all crosses a highly significant association (P value< 0.001) was observed between (1) the AAT- 1 and IDH isozymes loci and (2) the LAP-1 and PGM-2 isozymes loci, which leads to the conclusion that the respective isozyme pairs are linked.In addition, a significant association (P value < 0.001) was observed between LAP-1 and GPI-2 when the pollen sources were Fritz, Mission, or Price, but this could not be tested for the remaining five pollen sources, Carmel, Grant, Keane, Ne plus Ultra, Peerless, because they are homozygous at these loci. If LAP-1 is linked with GPI-2 and PGM-2, it might be expected that we should find evidence of linkage between GPI-2 and PGM-2. The lack of a significant association between these two isozymes suggests that LAP-1 is located centrally on the chromosome. These three pairs of linked loci are the first to be reported in almond.     

Assortative mating and the genetic correlation

Summary The effect of assortative mating on the genetic correlation between traits X and Y is considered. Assortation on trait X changes the magnitude of the genetic correlation but not its sign. There are two situations depending on the signs of the correlation between mates () and of the random mating genetic correlation (): 1) if sign () = sign (), then >, where is the genetic correlation at equilibrium after continued assortation, and 2) if sign () = sign (), then < . However, negative assortative mating is virtually powerless to alter the magnitude of the genetic correlation. The consequences of a mixed assortation model, e.g., high milk production females mated to fast growing males and lesser productive females mated to slower growing sires, were also studied. Mixed positive assortation always increases the genetic correlation, but negative assortation decreases it. The implications of assortative mating on correlated responses to selection and on the equilibrium covariances between relatives for pairs of traits are discussed.     

The inheritance of host plant resistance and its effect on the relative infection efficiency of Magnaporthe grisea in rice cultivars

The inheritance of host plant resistance and its effect on the relative infection efficiency for leaf blast was studied in the crosses IR36/CO39 (partially resistant × highly susceptible) and IR36/IR64 (both partially resistant). On the natural scale, gene action appeared multiplicative. After log transformation, additive effects described most of the genetic variation in the cross IR36/CO39, while additive and dominance effects were about equal in magnitude in the cross IR36/IR64. Dominance was towards increased resistance. No transgressive segregation occurred in the cross IR36/CO39. The number of genes that reduce lesion number was estimated to be zero in CO39 and five or more in IR36. The cross IR36/IR64 showed transgressive segregation in both directions, and IR36 and IR64 each contain at least one gene that is not present in the other cultivar. The heritabilities (narrow sense) in the F₂ were low (range 0.06–0.16), while narrow sense heritabilities based on F₃ lines were much higher (range 0.41–0.68). Lesion numbers in F₃ lines were reasonably correlated with those in F₅ progenies derived from the same F₂ plant (r was±0.6 in both crosses). Partial resistance can be effectively improved by selecting the most resistant plants from the most resistant F₃ lines.     

δ and κ Opiate receptors in primary astroglial cultures from rat cerebral cortex

The effects of , , and receptor-agonists on forskolin stimulated cyclic adenosine-3, 5-monophosphate (cAMP) formation were examined in astroglial enriched primary cultures from the cerebral cortex of newborn rats. Intracellular cAMP accumulation was quantified by radioimmunoassay. Morphine was used as a -receptor agonist, D-Ala-D-Leu-Enkephalin (DADLE) as a -receptor agonist and dynorphine 1–13 (Dyn) as a -receptor agonist. Basal cAMP levels were unaffected by either the opiate agonists or the antagonists used. In the presence of the cAMP stimulator forskolin, morphine had no significant effect on the cytoplasmic cAMP levels. DADLE caused a dose related inhibition of the forskolin stimulated cAMP accumulation. The effects of this receptor stimulation was blocked with the selective antagonist ICI 174.864. In the presence of Dyn, the forskolin stimulated cAMP accumulation was inhibited in a dose related manner. This receptor stimulation was blocked with the selective antagonist MR 2266. Co-administration of DADLE and Dyn resulted in a non additive inhibition of the forskolin stimulated accumulation of cAMP. These findings indicate that astroglial enriched cultures from the cerebral cortex of rats express and -receptors co-localized ont he same population of cells, and that these receptors are inhibitory coupled to adenylate cyclase.