Showing papers in "Crop Science in 1961"

An Evaluation of Effects of Mass Selection and Seed Irradiation With Thermal Neutrons on Yield of Corn1

Abstract: Although the irradiation treatment was detrimental to yield, the irradiated strain significantly outyielded the original variety and yielded only slightly less than the mass-selected control strain after four generations of selection. It is doubtful that irradiation of an already genetically variable population will prove to be particularly valuable as a breeding procedure; yet it is too early to draw definite conclusions. Additional generations of selection are needed. Because of its simplicity and apparent effectiveness, the use of mass selection of individual plants is suggested as a possible method of yield improvement in populations of corn segregating for genes controlling yield. Where the advantages of hybrids other than yield are desired, mass selection is suggested as a possible means of increasing the frequency of favorable genes in segregating populations prior to inbreeding. If over-dominance exists at any locus, mass selection will not be successful in altering gene frequency for that locus after an equilibrium point is reached. Some possible explanations are advanced for the apparent lack of success of early corn breeders using mass- selection and ear-to-row breeding techniques.

Relationship Between Genetic Diversity and Consistency of Performance in Different Environments1

Abstract: M UCH of the genetic improvement in self-fertilized crop plants has come through selecting \"pure-line\" varieties. The origin and reproductive biology of these varieties, plus the manner in which they are maintained by crop improvement associations and by seedsmen, cause them to be highly uniform in appearance--particularly as to size and maturity, resistance to diseases, and quality factors associated with market acceptance. Such varieties can also be very productive. Nevertheless, there is some evidence that mixtures may yield better, and more consistently, than stocks in which variability is kept to the minimum (6, 9, 14; review of older literature in Frankel, 4). Similar observations have been made by maize breeders who find that the highest yields in a particular environment are usually made by single crosses rather than by genetically variable double crosses. However, the same single cross rarely gives the highest yield in different years, or at different locations (13). The consequence is that average performance over a number of environments tends to be poorer for single crosses than for double crosses. According to Jones (10) the success of many double-cross hybrids over very wide areas is the result of their genetic diversity and its presumed consequence--stability and consistency of performance. Thus diversification is widely used in corn production although, as Jones pointed out, double-cross hybrids were originally adopted not for their consistency in production, but to overcome the handicaps that single crosses have in seed production. In self-pollinated crops, however, diversification has been little used since the unconscious cultivation of mixtures was brought to an end by the advent of pure-line varieties in the late nineteenth and early twentieth centuries. According to ~ensen (9), the concept of uniformity was stronger 1952 than ever before, On the other hand Frankel (5) believes that \"a more functional attitude has grown up in recent years, with the recognition of the biological significance of ’purity,’ \" and that ~the trend of development in breeding methods has been to provide a controlled measure of genetic heterogeneity.\" The theoretical advantages of diversity have been discussed repeatedly, and the rational blending of individual lines has been recommended periodically since the nineteenth century. Even so, there are surprisingly few comparisons between the productivity of genetically uniform and genetically diverse populations in self-pollinated crops. There is even less information on the role of genetic diverslty as a yield stabilizer. This paper presents evidence on these points from an experiment in which populations differing in level of genetic diversity were compared over a number of environments.

Implications of Genetic Variances in a Hybrid Breeding Program1

Abstract: FOR many years the use of commercial hybrids has been the standard procedure in corn. More recently, in other crops and in poultry, hybrids have become increasingly important. The breeder needs an objective method of deciding whether or not to produce hybrids. Even after having decided to embark on a hybrid breeding program, he is faced with many practical problems such as the amount of inbreeding needed in the inbred lines; choice of type of cross, single, three-way, or double cross, within which to select; attention that should be given to the order in which the lines are combined; estimation and interpretation of variances among crosses; and prediction of the performance of one type of cross from that of another. A framework is needed for hybrids which will lead to objective decisions. It must properly take account, and consequently must be informative, of the types of gene action. Such a framework is believed to have been developed in a study to be presented here. This study considers the covariances, in terms of genetic variances, between all possible pairs of relatives among single crosses, three-way crosses, and double crosses. Then in terms of the genetic variances and environmental variances, all of which are estimable, one can formulate comparisons. The covariances for hybrids are given and then applied to considerations of the type of cross within which to select, amount of inbreeding needed in the parent lines and the importance of the order in which the lines are combined. Applications to the problems of predicting the performance of one type of cross from that of another and of estimation are to be presented in later papers.

Diurnal Variation and Other Light Effects Influencing the Activity of Nitrate Reductase and Nitrogen Metabolism in Corn 1

Abstract: RECENT work (3, 5) has shown that when cauliflower or corn plants are placed in the dark they rapidly lose their nitrate reductase activity. Corn plants lose approximately 50 and 90% of their nitrate reductase activity within 24 and 48 hours, respectively, after being placed in the dark. The variations in nitrate reductase activity are consistent with the diurnal variation in nitrate content of various plant species (1, 4). These observations would permit the prediction that corn plants will undergo a diurnal variation in nitrate reductase activity under field conditions. Miller (10) grew corn plants to maturity under a series of artificial shade structures that reduced the light intensity, 0, 30, 60, 70, 80, and 90%. The effects of artificial shade on the growth, morphology, and ear set were comparable to the effects of competitive (self) shading obtained increasing plant population. Hybrid Hy2 X Oh7 (recommended for high density planting) is superior in yield to hybrid WF9 )< C103 (not recommended for high density planting) when grown under the artificial shade structures. In subsequent experiments with artificial shade, Knipmeyer (7) found that the nitrate content of young (2 to weeks) corn plants increased in proportion to the decreased light intensity. He also found that the corn plants grown at high planting rates (28,000 plants per acre) tended to have a higher concentration of nitrate (significantly different at the 8 to 10% level) than plants grown at the low (7,000 plants per acre) rate. The accumulation of nitrate by the crowded plants was attributed to the depressing effects of the low light intensity (competitive plane shade) on the nitrate reductase activity (5) and to an adequate (high) soil nitrogen content and sufficient soil moisture to permit free movement of nitrates (7). Precise information concerning the effect of either artificial or competitive plant shading on the level of nitrate reductase activity of corn plants grown under field conditions is not known. The objectives of the work reported herein were to determine (a) if corn plants grown under field conditions would show a diurnal variation in nitrate reductase, nitrate, and water soluble protein content; and (b) if reduction of light intensity by either artificial competitive plant shading would affect nitrate reductase activity.

Carbohydrate Food Reserves and Leaf Area in Regrowth of Orchardgrass 1

Abstract: of Orchardgrass C. Y. Ward and R. E. Blaser ' I HE yield and longevity of stand of adapted varieties •*• of perennial grasses and legumes under favorable soil and aerial environments are often restricted by adverse grazing and mowing practices. The rate of regrowth of perennial forage plants right after mowing or grazing has been largely explained by two factors: (a) leaf area index and concurrent light interception or (b) reutilization of reserve carbohydrates stored in rhizomes, stolons, stubble, and/or roots. The ratio of surface leaf area in square feet per square foot of soil area was named by Watson (12) as the \"leaf area index\" (LAI). Data by Brougham (2) show that for any LAI, regrowth (daily dry matter accumulation) of defoliated ryegrass occurred at a maximum rate where light interception by leaves was near 100%. Closely clipped plants had low LAI's; hence, daily dry matter accumulation was low. Such associations between LAI and daily growth rate have been established by others (1, 3, 4, 5, 6, 12). These writers also showed that the optimum LAI differs with plant species. Accumulation of an LAI beyond that needed to intercept 95 to 100% of the light may result in sufficient self-shading to reduce dry matter accumulation per unit of time.

Photosynthesis Under Field Conditions. I. A Portable, Closed System for Determining Net Assimilation and Respiration of Corn1

Abstract: factors affecting crop yield which occur during the season and vary from day to day or from season to season. It is extremely difficult to evaluate the effect of a particular factor or combination of factors occurring during any specific short period of the season unless data are available describing environments and yields for many years. ’Harvests before and after short-term treatments or observed combinations of environmental factors have not been successful in measuring the net assimilation of corn during such periods. On the other hand, assimilation or respiration of corn growing under field conditions can be determined accurately and almost instantaneously by measuring the amount of carbon dioxide absorbed or released by the plants. The summation of net assimilation over the season should be very nearly equal to total yield and should be related to the economic component of total yield. Therefore, it seemed desirable to measure daytime assimilation and night respiration over short periods. A system capable of determining minute amounts of assimilation or respiration in the field is described in this paper and its accuracy and utility are discussed. In order to determine the change in carbon dioxide concentration within a field plot, it is necessary to isolate the plot in some way. Previously two notable attempts have been made to determine the rate of photosynthesis of growing plants on a field plot scale by a gas exchange technique. Both of these attempts were made in the early 1930’s. Heinicke and Childers (i) enclosed an apple tree of bearing age in a glass covered, wood-framed chamber which measured 7 by 7 by I1.5 feet and determined the rate of photosynthesis during the growing season for periods as short as 5 hours during the day and respiration for a 12hour period at night. Thomas and Hill (3) determined the rate of photosynthesis and respiration of alfalfa, sugar beets, and wheat at 64-minute intervals growing in 6by 6-foot field plots beneath celluloid-covered iron-framework chambers. The same principle of operation was used in both of these studies. Air was continuously drawn into the assimilation chambers, mixed inside the chamber and exhausted through an outlet pipe. A measured subsample was taken of the air at the intake and from the exhaust stream and the difference in concentration of carbon dioxide determined at these two sampling points. The volume of air passing through the chambers was calculated from data on the air stream velocity as measured by an anemometer in the exhaust stream. The carbon dioxide was absorbed in basic solution and determined by titration (’Heinicke and ’Childers) or electrical conductance (Thomas and ’Hill). In recent years the development of infrared gas analyzers suitable for analyzing for carbon dioxide have opened entirely new possibilities in this type of research by allowing rapid and accurate

Cytology of Diploids, Natural and Induced Tetraploids, and Intra‐species Hybrids of Bahiagrass, Paspalum Notatum Flugge 1

Abstract: D IPLO.ID Pensacola bahiagrass (2n = 20), discovered growing wild near Pensacola, Florida, is one of the most popular perennial pasture grasses in Florida and the southern part of the rest of the Gulf States. More limited use has been made in the United States of broader leafed, more palatable but less winterhardy, tetraploid (2n = 40) types such as common bahiagrass and the Argentine variety. The breeding program at Tifton, Georgia, aimed at producing improved bahiagrass pasture varieties, is complicated by the presence of polyploidy and apomixis (at the triploid level and above) in the species. In the past, the apomictic mode of reproduction of desirable tetraploid types and hybrids between sexual diploids and apomictic tetraploids (5) restricted the breeder’s use of the germ plasm in this predominantly tetraploid species. Recently, the apomictic barrier to recombination of characters in natural tetraploids was broken by hybridization with sexual, induced tetraploids of Pensacola bahiagrass (7). Although somatic chromosome numbers have been reported for a number of biotypes and hybrids in this species, very little information regarding their meiotic behavior exists in the literature. The present paper concerns cytological observations on chromosome numbers and meiosis in various plant materials important to the breeding program at Tifton.

Origin and Inheritance of Nectariless Cotton1

Abstract: CULTIVATED Upland cotton, Gossypium hirsutum L., has leaf, extrafloral, and floral nectaries. The nectar secreted attracts many insects and provides an important food for them. A nectary is usually found on the midrib on the lower side of each leaf. (Figure 1). Extrafloral nectaries are commonly found below the bracts (Figure 2) and also between and inside the bracts. Floral nectaries are located between the sepals and petals. (These have not been studied in the plant material reported in this paper.) G. tomentosum Nuttall is a wild cotton species, native to Hawaii, which has no leaf or extrafloral nectaries. G. hirsutum and G. tomentosum, tetraploid species with 2n = 52 chromosomes, produce a fertile Fj hybrid. Among the many interesting genetic markers which appeared in plants derived from hybrids of G. hirsutum X G. tomentosum, the absence of leaf and extrafloral nectaries was selected for transfer to Upland cotton. Rather early in the transfer program, C. E. Rhyne, Jr. suggested that

Heterosis in Intervarietal Crosses in Maize and Its Implication in Breeding Procedures1

Abstract: TN RECENT years there has been an increased interest in -•• heterosis resulting from population crosses of various species (3, 16, 19, 20). There is need for more information relative to the characterization and magnitude of hybrid vigor to provide a basis for more efficient breeding procedures in both plants and animals. Hybrid vigor resulting from Ft crosses of corn varieties was first reported by Beal (2). This led to rather extensive study of variety crosses by plant breeders in an attempt to increase grain yields during the early 1900's. Interest in variety crosses as a practical measure gave way to interest in hybridization of inbred lines derived from varieties after about 1920. Richey (11) presented a summary of 244 reported comparisons between the parental varieties and their F1 crosses as a sample of the results obtained up to that time. His summary showed that 82.4% of the crosses exceeded the parental average, with 55.7% exceeding the higher yielding parent. The lack of consistency of results where different substrains of any given variety were used together with the spectacular results from crosses of selected inbred lines resulted in a loss of interest in varietal crosses of corn at that time. Recently a renewed interest in the type of gene action responsible for heterosis and the expected progress from selection within and among populations has resulted in further study of varietal crosses in corn. Investigations of the relative magnitude of additive genetic and dominance variance in corn varieties (15) led to a study of crosses among southern prolific varieties by this group of workers. The results from a set of diallel crosses among six southern varieties (16) showed the F1 to average 19-9% more than the midparent values and 11.5% more than the high parent. The range in superiority over midparent values was 4.6 to 46.2%. If previous selection had resulted in these varieties being at equilibrium between mutation and selection and if gene frequencies affecting yield were similar from one population to another, the above results would be considered surprising. The fact that corn varieties differ in their underlying genetic constitution is evident from these and earlier data. Many varieties have been preserved by plant breeders since the advent of hybrid corn and have been regrown on a rather small sample basis when necessary to maintain via-

A Summary of Translocation Studies in Barley

Abstract: T HE Fourth American Barley Research Workers’ Conference held at Fargo, North Dakota, February 1 to 4, Break 1960, adopted a system of designating the chromosomes a ..... Previous positions* and the linkage groups of barley. In this system .the Arabic mended numbers 1 through 7 are used to designate both the chrozi-zab K-0°lal° h-~, mosomes and the linkage groups. The correspondence of T1-3a T ert-e \"/~ (b-e) b T ert-c ~ \" the recommended esignations to the linkage groups used c o1365 s by Robertson et al. (15) and to the temporary letter desigd K s TkT5 e nations used by Burnham et al. (2) is presented in Table f vkT6

Genetic Analysis of Energy Production in the Soybean 1

Abstract: W. D. Hansen, R. C. Lefifel, and Robert W. Howell THE emphasis in soybean breeding has been on the production of high yielding, high oil lines; however, a shift in emphasis from oil to protein has been made to obtain a balanced total program. In practice, an increase in oil percentage has been associated with a decrease in protein percentage. The change in percent oil to the change in percent protein is considered to be approximately 1 to 2. The basis for this statement or, for that matter, the basic measures for studying the genetic control of the energy are not clearly defined. The objective of this paper is to quantify the genetics involving the production of energy by the soybean plant and to relate this information with the present breeding program. A plant produces energy by first synthesizing sugar. The energy which is not used for plant metabolism and growth is stored. The form in which the energy is stored and the quality and the quantity of the stored energy is the unique expression of a genotype grown within an environment. Yield components such as seed size, seeds per fruiting unit, and units per plant are genetically controlled but must be considered subservient to the ability of a genotype to produce energy unless storage limitations exist. Two genetic systems should be considered: (i) the genetic potential required to produce total seed energy and (ii) the genetic control of the distribution of energy between seed fractions.

Interaction of Detasseling, Sterility, and Spacing on Yields of Maize Hybrids 1

Abstract: THE influence of detasseling on the performance of corn has been studied since the last decade of the last century. Some of the early research workers found that detasseling decreased yield, while others found that it did not. The early work was reviewed adequately by Grogan. Grogan stated that the removal of immature tassels seemingly results in diversion of some of the energy and nutrients normally expended in pollen production to grain production. He predicted that under the same environment male-sterile plants which produce no pollen would react in a manner similar to their detasseled fertile counterparts.

Influence of Harvest Management on Level of Carbohydrate Reserves, Longevity of Stands, and Yields of Hay and Protein from Vernal Alfalfa 1

Abstract: wilt-resistant variety used widely for hay and pasture in the North Central area of the United States. It consistently has yielded as much or more hay and protein per acre as other varieties in field trials conducted ~chroughout Wisconsin. In addition, Vernal can be cut three times per year at the 1/10-bloom stage in Wisconsin, to obtain high quality hay and silage, without rapidly reducing the longevity or continued productivi~¢ of the stand (9, 10). Stand maintenance of and hay yields from alfalfa are influenced greatly by the number of harvests taken each year, the interval between harvests (5, 7, 8, 10), and the date of the last cutting in the fall of ~:he year (2, 3, 4, 8, 10, 12). Most of the varieties used were susceptible to bacterial wilt but some were very winter hardy. Therefore, it seemed advisable to determine the manner in which Vernal, a very winter-hardy and wik-resistant variety, was affected by frequency of and interval between harvests in relation to its capacity to maintain vigorous and highyielding stands.

Natural Hybridization With and Without Ionizing Radiation in Soybeans1

Abstract: Natural hybridization in soybean varieties with and without ionlzing radiation was measured under field conditions in two widely separated geographical locations, Iowa and Maryland. The different soybean varieties used as pollendonor parents possessed dominant marker genes so that hybrids could be detected in the recessive female recipients. Natural crossing percentages occurring in the controls approximated 1.0% when the genotypes were grown in close contact. On the average, heavy dosages of approximately 2.0 x 10/sup 13/ thermal neutrons or 20,000 r x rays when applied to seed of only female recipients increased natural crossing 4 to 6 times as compared with controls. Within the dosage ranges of irradiation studied, x rays appeared to be just as effective as thermal neutron in causing hybridization. Incidence of natural crossing increased as dosage levels of x rays and thermal neutrons increased, whereas maturity was delayed and seed yield decreased progressively. In the Iowa test, flowers on the upper half of female recipient plants were cross-fertilized more than flowers on the lower half of these same plants with or without irradiation. Insect vector or vectors were believed to be the main reason for hybridization in these tests in both states. The results suggested that naturalmore » crossing in soybeans could be increased more than obtained herein with or without irradiation by better timing of flowering of pollen donors and recipients. The use of irradiation to induce hybridization and its role as a tool for greater genetic recombination in self-pollinated hybrid populations are discussed. The results suggested that if a true index of ionizing radiation-induced mutations is to be obtained, greater than normal precautlons must be taken to lsolate lrradiated material from outside pollen sources. (auth)« less

Inheritance of Protein, Texture, and Yield in Wheat 1

Abstract: FRONDOSA and Frontiera, two varieties of wheat introduced from Brazil, have been widely used in soft red winter wheat breeding programs as sources of leaf rust resistance. Many high-yielding, good agronomic strains have been selected from this material. However, these selections are higher in protein and harder in texture than typical soft wheat. These selections are the dominant varieties of the southeast United States despite objection to these features. Some of the released varieties are Coastal, Atlas 66, Atlas 50, Anderson, Taylor, Taylor 49, Tayland, and Coker 47-27.

Early Generation Testing of Diallel Crosses of Soybeans 1

Abstract: EARLY-GENERATION testing of progenies from crosses between selected parents has been a subject of considerable study in self-pollinated crops, including soybeans. Recent literature reviews on the topic in selfpollinated species, and specifically soybeans, have been presented by Elliott (1) and Johnson (6), respectively. The most general problem has been concerned with the effectiveness of selection for high yield of seed among and within crosses during the early generations after hybridization. Judicious selection of parents has been an accepted part of the breeding procedure, but little information has been obtained on the relative merits of soybean varieties as parents. Possible explanations for the failure to recognize high yielding progenies in early generations include: (1) Genotype-environment interactions, (2) inadequate testing in time and space, (3) heterosis attributable to epistatic or dominance effects of genes which is not obtained or maintained in pure lines, (4) heterozygosity and heterogeneity of genotypes within progenies, and (5) interplant and interplot competition. The studies reported herein were conducted to determine the value of parental and early generation progeny performance in identifying crosses that would

Some Characteristics of Perennial and Annual Ryegrass × Tall Fescue Hybrids and of the Amphidiploid Progenies of Annual Ryegrass × Tall Fescue1

Abstract: TNTERGENERIC hybridization of both annual (Lolium •*• multifiomm L.) and perennial (Lolium perenne L.) ryegrass with tall fescue (Festuca amndinacea Schreb.) is being employed at the Kentucky Agricultural Experiment Station in an effort to improve the palatability and nutritive value of tall fescue. Tall fescue is a productive pasture grass that is widely adapted to the soils and climate of the southeastern United States. It is regarded, however, as relatively low in palatability and nutritive value. On the other hand, perennial and annual ryegrasses are highly nutritious and palatable, but are essentially annual in the southeastern United States. Numerous investigators (2, 4, 8, 10) have succeeded in producing hybrids between Lolium spp. and Festuca spp. but no improved varieties have resulted.

Orienting Linkage Maps on the Chromosomes of Barley 1

Abstract: CYTOGENETIC studies with barley, Hordeum vulgate, have now progressed to the point where it is possible to assign a linkage group to each of the seven chromosome pairs. The extensive genetic data have been summarized at regular intervals (q. v. Robertson et al., 13) and seven linkage groups established. The chromosome morphology has been established from root-tip mitoses by Tjio and Levan (15) and the five nonsatellite chromosomes numbered from 1 to 5 in the order of their decreasing lengths. Of the two satellite chromosomes, the shorter chromosome with the larger satellite is designated as 6 while chromosome 7 is the longer chromosome with a shorter satellite. Sarvella et al. (14) were able to study meiotic pachytene chromosomes in a radiation induced \"short\" chromosome strain but it has not been established that this strain 6arries the normal chromatin arrangement. To correlate .the genetic and cytologic information, Burnham et al. (3) isolated a series of homozygous translocations from X-rayed seed of the variety Mars. By intercrossing translocation stocks, and observing meiotic configurations in F1 plants, they assigned temporary letters a to g to the chromosome pending identification in relation to morphology. Utilizing the fact .that in certain cases the karyotypes of homozygous translocations differed sufficiently from normal to permit identification of the chromosome involved, Hagberg and Tjio (4) and Burnham and Hagberg (2) have established the correspondence between the letter designations and the morphological designations. Kramer et al. (10), using translocation-gene linkages and F, meiotic configurations of translocation intercrosses, concluded that two linkage groups were carried by the same chromosome leaving the g chromosome devoid of assigned genes. They suggested the tentative relationships of the five other linkage groups to the letter designations of Burnham. These conclusions were substantiated by Haus (8) using genetic tests, and by Tsuchiya (16) using associations of linkage groups with trisomics. Recently Swomley,a Ramage and Suneson (12), and Burnham (unpublished) have placed genes on .the remaining chromosome thus finally establishing a linkage group for each chromosome, as given by Ramage t al. (11). All the relationships may be summarized as in Table 1. It is now possible to designate the morphological chromosomes, the chromosomes involved in interchanges, the linkage groups, and the trisomic .types with the same Arabic numerals. A major cytogenetic problem remaining is the orientation of each linkage map on its chromosome with an end

Pollen Abortion in Cytoplasmic Male Sterile Sorghum1

Abstract: SHORTLY after the discovery that the chromosomes of kafir and the cytoplasm of milo (1) interact to produce male sterility, commercial hybrid sorghum became a reality. Cyto-sterile lines had already been well exploited in producing hybrid seeds in corn (9), onions (5), and sugar beets (7). Attempts to develop the effective use of male sterility are still in progress in many other crops including carrot, tomato, wheat, castorbean, cabbage, pearl millet, Capsicum, kinum, and Petunia (4). Though cytoplasmic male sterile lines are being used in many crop plants, the mechanism which causes pollen abortion in plants with sterile cytoplasm is still largely unknown. Jones et al. (6), while analyzing the behavior of the gametophytic and sporophytic tissues in male sterile lines, emphasized the importance of the place of the initiation of the abortion process in determining the mechanism of cyto-sterility.