Showing papers in "Crop Science in 1980"

High Temperature Stress and Pollen Viability of Maize1

Abstract: High temperatures during maize (Zea mays L.) pollination are known to result in poor kernel set, but little is known of the direct effects of temperature on pollen germination. The purpose of this research was to determine how in vitru pollen germination of different maize genotypes is affected by high temperature stress during anthesis. Tassels from field-grown plants were excised at beginning anthesis, placed in water and transferred to growth chambers maintained at daytime temperatures of 27, 32, and 38 C. Nighttime temperatures were maintained 6 C cooler. In vitro germination was measured after 24 and 48 hours in the growth chamber as well as on pollen collected directly in the field. Genotypes differed in their response to temperature. In some genotypes pollen germ. ination steadily decreased as temperature increased. Others either germinated equally well at 27 and 32 C or germinated better at 32 than at 27 C. All genotypes had a lower germination at 38 C than at 32 or 27 C, and several genotypes exhibited no germination after 48 hours at 38 C. After 24 hours in the 38 C chamber, six inbreds widely used in the 1970’s germinated significantly better as a group than inbred.,; widely used in the 1950’s and 1930’s. Growth environment affected the absolute in vitro germination percentage, but in general genotypes retained similar relative responses to increasing temperature. Resuits from this study suggest that prolonged exposure to temperatures above 32 C can reduce pollen germination of many genotypes to levels near zero

Root Growth and Dry Matter Distribution of Soybean as Affected by Phosphorus Stress, Nodulation, and Nitrogen Source1

Abstract: gy reducing nitrate when NO3-N is the source of available N. Thus, for legumes able to form symbiotic associations with Rh izobium, the pattern of dry matter distribution (DMD) within the plant will differ depending upon its mode of N nutrition. The partitioning of dry matter between root and shoot is a heritable characteristic determined by the genotype of the plant (Andrews, 1939; Shank, 1943). Root morphology likewise is considered to be genetically determined (Smith, 1934; Zobel, 1975; Street, 1969). The expression of these characteristics can be altered by environmental conditions. Deficiencies of essential mineral nutrients have been shown to affect both the DMD within the plant and lateral root development. Plants deficient in N or P tend to accumulate relatively more dry matter in their roots than do plants which are adequately supplied (Turner, 1922; Brouwer, 1962). Weisum (1958) demonstrated that root branching in pea (Ptsum sattvum L.) was stimulated by nutrients as follows: NO3-N>P>K> Mg>Ca. Nitrate applied to a discrete root segment increased both the rate of lateral root extension and number of lateral roots per unit length of root (Hackett, 1972; Mdntyre and Raju, 1967; Drew, 1975). The establishment of an active N-fixing nodule system on the roots of a legume complicates these relationships. During the vegetative stage of growth, active root nodules utilize significant quantities of photosynthate for nodule growth and for N fixation (Minchin and Pate, 1972; Herridge and Pate, 1977). Summerfield et al. (1977) found that the root:shoot dry weight ratio in cowpea (Yigna unguiculata L. Walp.) was larger in nonnodulated plants than in nodulated plants grown at equivalent levels of applied N. Experiments with red clover (Trifolium pratense L.) and barrel medic (Medicago tribuloides Desr.) indicate that there is an inverse relationship between nodule number and lateral root formation (Nutman, 1948; Dart and Pate, 1959). Also, there are qualitative observations concerning differences between the root morphology of grain legumes provided combined N and those which are effectively nodulated (Weber, 1966; Wych and Rains, 1978). The purpose of this study was to define the changes in DMD and root development in the soybean plant as influenced by the mode of N nutrition, the magnitude of root nodulation, and P deficiency. ABSTRACT

Computations for Estimating the Genetic Parameters in Joint-Scaling Tests1

Abstract: Weighted least squares has been used to estimate the genetic parameters in Three Parameter Joint Scaling Tests. The principles are presented to generalize the method to any combination of generation means and genetic models including epistasis. The method is adapt. able to computers with matrix algebra programminga nd certain programmabclea lculators.

Mutagenic effects of sodium azide in rice.

Abstract: Seeds of rice cultivar M5 were presoaked in distilled water and treated for 2 or 3 hours with 0, 0.12, 0.50, 0.75, 1.0, 1.25, 1.50, and 1.75 mM sodium azide solutions prepared in 0.1 M phosphate buffer (pH 3). Criteria used to assess the biological effects of azide on rice were germination, seedling height, and seed sterility in the M/sub 1/ generation, and chlorophyll-deficient seedlings and viable mutations in the M/sub 2/ generation. In general, an increase in azide concentration, along with an increase in the post-treatment redrying period, resulted in a decrease in M/sub 1/ germination and seedling height. Azide treatment also induced sterility. The same treatment induced chlorophyll mutations in 98.5% of the M/sub 1/ panicle progenies and in 14% of the M/sub 2/ seedlings. The highest frequency of viable mutations scored in the adult plant stage was 4.64% on an M/sub 2/ plant basis. All azide concentrations were mutagenic.

Classification of Environments and Genotypes in Wheat1

Abstract: Forty-one genotypes (seven cultivars and 34 breeding lines) of winter wheat (Triticum aestivum L.) were planted in eight locations in each of 2 years. Test weight data were used to group locations according to their similarity of genotype ✕ location (G✕L) effects by cluster analysis. The results indicated that deletion of only one location from the variance analysis resulted in a group within which G ✕ L interaction was not significant. Such an analysis would be useful for the selection of testing sites for early generation testing and for development of genotypes with wide or narrow adaptability. The cultivars were also grouped into 10 clusters with respect to their test weight similarity across the 16 environments (2 years and eight locations). Further, stability parameters, i.e., mean, regression coefficient, and deviations from regression were calculated for each genotype. Cluster analysis effectively grouped genotypes according to their stability responses. Three broad categories of genotypes were identified with respect to their stability characteristics. Cluster analysis could be a useful supplementary tool for the analysis of adaptation reactions of wheat genotypes for test weight.

Parent-Progeny Regression in Indiangrass: Inflation of Heritability Estimates by Environmental Covariances

Abstract: Families of two indiangrass [Sorghastrum nutans (L.) Nash] populations were used in this study with a family plot consisting of a parental clone and four half-sib progeny_ The experimental design was a randomized complete block with two replications. The regression of offspring on the parent in the same plot was used to obtain heritability estimates in which environmental covariances might be expected to inflate the parent-offspring covariance. The regression of offspring in one replication with its parent in another replication, and vice versa, was used to obtain heritability estimates whereby environmental covariances should be minimized. Heritability estimates for heading date and plant height, which had high heritabilities, were similar for the two estimation techniques. Heritability estimates for forage yield and in vitro dry matter digestibility (IVDMD) appeared to be influenced by environmental covariances. Mean heritability estimates for forage yield and IVDMD for the three sets of data analyzed were 0.64 and 0.94 respectively, when parents and offspring in the same plot were used in the regression analyses and 0.28 and 0.42 respectively, when parents and offspring in different plots were used. Heritability estimates for forage protein content averaged 0.49 and were similar for both methods of estimation. Additional index words: Sorghastrum nutans, Forage yield, Forage quality, In vitro digestibility, Genetic covariances. 1 Contribution of the Dep. of Agronomy, Univ. of Nebraska, and AR, SEA, USDA. Published as Paper No. 5821, Journal Series, Nebraska Agric. Exp. Stn. Received 26 Sept. 1979. • Research agronomist, AR, SEA, USDA; George Holmes professor of Agronomy, Univ. of Nebraska; and supervisory research geneticist, AR, SEA-USDA, Univ. of Nebraska, Lincoln, NE 68583. R EGRESSION of offspring on parents or on one parent is a method of estimating heritability commonly used by plant breeders. The covariance between a parent and its offspring produced by random mating is an estimate of one-half the additive genetic variance in a population (3, 5). The mean of several offspring is usually used as the offspring value. The covariance between offspring and parents is divided by the phenotypic variance of the parents to obtain the regression coefficient. Because the covariance between offspring and parent is only one-half the additive genetic variance, the regression coefficient is multiplied by two to obtain an estimate of narrow sense heritability (5). Regression of offspring on parents to estimate heritability is based on the following assumptions (3, 4): a) normal diploid and solely Mendelian inheritance, b) no environmental correlations among relatives, c) population in linkage equilibrium or no linkage among genes controlling the traits studied, d) the relatives are noninbred, e) the genetic population is mating at random. Heritability estimates obtained by parent-progeny regression are often used because the estimates obtained are valid both when the parents are selected on some basis and when they are chosen at random from a population (5). The purpose of this paper is to demonstrate the inflationary effect that environmental covariances might have on heritability estimates if the second assumption, i.e., no environmental correlations among relatives, is violated. In 1973, we began a quantitative genetic study on indiangrass, Sorghastrum nutans (L.) VOGEL ET AL.: PARENT-PROGENY REGRESSION IN INDIANGRASS 581 N ash. Our results from this study were used to estimate the effect of environmental covariances on heritabilities based on parent-progeny regression. Indiangrass is a warm-season grass native to the prairies and plains of the United States (9) where it is used in pastures and rangelands for summer grazing. Limited genetic research on this grass has been reported although several varieties have been released. In our study we used two varieties that are adapted to the central Great Plains. 'Holt' was developed by mass selection from ecotypes collected in northeast Nebraska while 'Oto' was developed by mass and progeny selection from ecotypes collected in southeast Nebraska and northeast Kansas (7). MATERIALS AND METHODS In 1973. space-transplanted populations of a Holt X Oto synthetic and Oto indiangrass were sampled at panicle emergence for in vitro dry matter digestibility percentage (IVDMD) and for crude protein. Each nursery contained approximately 1.000 plants_ The Holt X Oto synthetic was established from seed harvested from Holt plants exposed to Oto pollen in an open-pollinated Holt X Oto crossing block. Because Holt flowers 20 days earlier than Oto. it is doubtful if any crossing occurred and the Holt X Oto synthetic will be referred to as Holt. Plants in both nurseries were 2 years old when sampled. The Holt population was located at Lincoln. Nebraska. while the Oto population was located at Mead. Nebr.. which is approximately 55 km northeast of Lincoln. In 1973. seed from open-pollinated plants was harvested from plants sampled from the two populations. In 1974. a twice-replicated. space-transplanted half-sib progeny nursery was established at the Mead Field Laboratory with seedlings grown from open-pollinated seed from 41 Holt and 150 Oto parents that represented the high and low ends of the range in IVDMD. protein percentage. and heading date for the two populations. In 1975. two ramets (propagules) of the parental clones similar in size to the seedlings established the p'revious year were transplanted into the same nursery. A famIly plot consisted of a five-plant row with a parental ramet and four progeny seedlings. The parental ramet was at the end of the plot. Rows and plants within rows were spaced 1.1 m apart. The experimental design was a randomized complete block. Holt and Oto families were randomized together in the ./ same nursery. but because of maturity differences were analyzed .

Comparison of Gains Predicted by Several Selection Methods for Cold Tolerance Traits of Two Maize Populations 1

Abstract: Index selection was developed to help breeders practice simultaneous selection for several traits. Our objective was to compare selection differentials, expected gains, and relative index efficiencies of several indexes constructed to improve cold tolerance of two maize (lea mays L.) populations. Cold tolerance traits were percentage emergence, emergence index (i.e., rate of emergence), and seedling dry weight. Best predicted results for all traits were given by a rank summation index, a multiplicative, weight-free index, and a base index (index weights were reciprocals of phenotypic standard deviations). These indexes were not seriously affected by unequal variances among traits and combined 1) simplicity of use, 2) freedom from need to estimate genetic parameters, and 3) good selection differentials and predicted gains in each trait and in the aggregate genotype. Our results also showed that selection for dry weight/plot identified lines with excellent percentage emergence and seedling dry weight. Additional index words: TLea mays L., Selection index, Selection advance. TpHE goal of many plant breeding programs is simulJL taneous improvement of a crop for several traits. Consequently, plant breeders must consider a number of traits during the selection process. Smith (1936) developed index selection to cope with the complex task of improving breeding material by selecting simultaneously for several quantitative traits. Hazel (1943) later extended index selection procedures by outlining methodology to estimate genetic variances 1 Joint contribution of USDA, SEA, AR and the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011, Journal Paper No. J-9719, Project 2152. Received 4 Feb. 1980. a Assistant professor, Dep. of Agronomy, Iowa State Univ., Ames, IA; director of corn research, Northrup King Co., Stanton, MN 55081; and research geneticist, USDA, SEA, AR, Ames, IA 50011. and covariances and by defining the aggregate genotype (i.e., genetic worth of an individual) as a linear function of genetic values, each weighted by their relative economic weights. The Smith-Hazel approach is considered the optimum index when accurate estimates of variances and covariances are available (Williams, 1962). Plant breeders, however, often do not have reliable estimates of variances and covariances or the information that is needed to assign relative economic weights. Therefore, several researchers have suggested using indexes that are "weight-free" (i.e., do not use relative weighting factors) or are "parameter free" (i.e., do not use genetic variances and covariances). Elston (1963) proposed a multiplicative index without economic weighting factors. Index values for each line are calculated by multiplying phenotypic deviations for each trait in the index (deviations from minimum or maximum values in the experiment also can be used). This index does not use estimates of phenotypic and genotypic variances and covariances. Mulamba and Mock (1978) developed a "parameterfree" index to improve density tolerance in maize (Zea may L.). They constructed a rank summation index (RSI) by summing the ranks of the traits included in the index. Use of RSI also eliminates the need to assign relative economic weights, although weights can be used with RSI. Pesek and Baker (1969) suggested that breeders usually would be better able to specify a desired gain than an economic weight for a trait. The index developed by Pesek and Baker (1969), therefore, uses desired gains to determine relative weights and maximizes expected response in proportion to the gain specified by the breeder. Our objective was to compare selection differentials, expected gains, and relative index efficiencies of several indexes constructed to improve cold tolerance 650 CROP SCIENCE, VOL. 90, SEPTEMBER-OCTOBER 1980 of two maize populations. Cold tolerance traits were percentage emergence at ~0 days after planting, emergence index (a measure of rate of emergence for the 30-day period after planting), and seedling dry weight at 45 days after planting. MATERIALS AND METHODS The data used to compare indexes were collected in a recurrent selection program designed to improve cold tolerance of two maize populations, BS13(SGT) and BSSS2(SCT) (Mock Eberhart, 1979). Each cycle, 100 or 144 Sl-lines from each population were grown in a simple lattice design with two replications at one location. Seeds of each S~-line were planted in one row-plots, 1.52 m long, spaced 76.9 cm. Data were collected for percentage emergence at 30 days after planting, emergence index (a measure of rate of emergence for the 30-day period after planting), and seedl:ing dry weight at 45 days after planting (Mock and Eberharl:, 1972). A selection index was used choose lines with highest percentage emergence and seedling dry weight and lowest emergence index values (k = 1.75). Selected lines were recombined in a diallel to form a new population for the next cycle of selection (Mock and Bakri, 1976). We calculated phenoytpic and genotypic variances and covariances and heritabilities for cold-tolerance traits for CO to C5 cycles of BS13(SCT) and for CO to C4 cycles of BSSSg(SCT). These estimates are biased by genotype × environment interactions, maternal effects, and by 1/4 of the dominance genetic variance. Genotype X environment interactions likely are the most serious source o1.~ bias in our data. Maternal effects probably are more impor’*ant for percentage emergence and emergence index than for seedling dry weight (Grogan, 1970). McConnell and Gardner (1979), however, studied reciprocal crosses of F1 hybrids and concluded that maternal effects were not important for percentage germination and seedling vigor. Grogan (1970) reviewed a number of studies suggesting that cold tolerance traits were controlled primarily by additive, multiplegene systems. One recent study, however, used generation means analyses to show that most genetic variability for percentage germination and seedling vigor in 15 maize crosses was nonadditire (McConnell and Gardner, 1979). Estimates of genetic parameters and S~-line means were used to compare various selection indexes in terms of: 1) selection differentials, 9) predicted gain in each trait, and 3) predicted gain for the aggregate genotype. Selection differentials for each trait were computed by subtracting the cycle mean from the mean of the selections (10% selection intensity) and were expressed as a percentage of the appropriate single-trait differential. The general procedures we used to compute index parameters were outlined by Lin (1978). The selection index (I) aggregate genotype (H) were defined as: I = ~ b, X, =