Improved techniques for the induction and isolation of polyploids in the genus Fragaria

Summary The sensitivity of Fragaria seedlings to colchicine is dependent on the plant organ that is treated. Complete immersion of seedlings in a 1.5% colchicine solution results in total lethality, whereas the survival rates were more than 75% even at concentrations of 3.0% when only shoot apices were treated. High proportions of polyploids were isolated by treating shoot apices of seedlings with a 2.0% colchicine solution for 24–28 h. The dropper method is preferred to the tube method as it involves a minimum of manipulation and requires simple equipment. A differential response to colchicine was observed within and between different diploid species, diploid and tetraploid hybrids.     

Two outcrossing mechanisms in cowpeas,Vigna unguiculata (L.) Walp

Summary Several types of outcrossing mechanisms in cowpeas are observed in breeding plots at IITA. Two of these have been studied. One is genetic male sterility controlled by the simple recessive conditions of a gene designated as ms ₂ ms ₂. The other is mechanical male sterility involving petals constricted in such a way as to provide an opening for stigma and style to emerge at an early, pre-receptive stage of development; while simultaneously restricting stamen development. It is also inherited as a recessive character with the gene symbol designation of Cp-as normal and cp cp as constricted petal. The flower structure is unique and is easily recognized in large populations. Because fruit set is extremely poor it appears less promising than the genetic male sterility at present.     

Methods of overcoming interspecific barriers in Trifolium

Summary Barriers to interspecific hybridization in Trifolium were investigated by manipulation of mentor pollen treatments, ploidy levels, and compatibility and male sterility systems. Crosses involving the addition of mentor pollen produced fewer seeds and hybrids than crosses involving normal pollination. Lower seed set with mentor pollen was deduced to result from the use of less viable pollen, approximately half the pollen having been killed by alcohol. Pollinations at the diploid level resulted in more hybrids than at the tetraploid level, perhaps because genes for male sterility produced higher female sterility in the tetraploids. The self-compatible stock produced more seeds, mostly selfs, than the self-incompatible stock, but produced more hybrids only in one cross, T. pratense L. × T. diffusum Ehrh. The use of male-sterile female parents reduced selfing but produced fewer hybrids than male-fertile female parents. Techniques of this study were designed to affect prefertilization barriers, but the lack of effect may indicate that postfertilization barriers in Trifolium are of greater importance.Journal Article No. 98-3-208 of Kentucky Agricultural Experiment Station. Published with approval of the Director.     

Screening of wild crucifers for resistance to mustard aphid, Lipaphis erysimi (Kaltenbach) and attempt at introgression of resistance gene(s) from Brassica fruticulosa to Brassica juncea

A diverse array of wild and weedy crucifers was screened under laboratory conditions for their resistance to Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae). Among these, Brassica fruticulosa and Brassica montana were found to be the most promising. The availability of a synthetic amphiploid, AD-4(B. fruticulosa × Brassica rapa var. brown sarson) as well as a set of Brassica juncea lines carrying genomic introgressions from B. fruticulosa allowed us to investigate B. fruticulosa resistance in greater detail. This assessment was carried out along with susceptible check B. rapa ssp. brown sarson cv. BSH-1 in a series of choice and no choice experiments. The mustard aphid showed maximum preference for feeding on BSH-1 while least preference was recorded for B. fruticulosa followed by AD-4 as evidenced by the number of aphids that settled on circular leaf bits of these genotypes 24 and 48 h after release in a choice experiment. Brassica fruticulosa exhibited strong antibiosis against mustard aphid in no choice experiment and all the released aphids died within 5–8 days of their release, while the maximum survival (76.7%) was recorded on BSH-1. The survival on AD-4 (40%) was significantly lower than that on BSH-1. Almost similar trend was observed with respect to other demographic parameters of L. erysimi viz. development time, fecundity and longevity. In the screen house studies, there was no seedling mortality in B. fruticulosa and AD-4 after 30 days of aphid release while 80% mortality was observed on BSH-1. Excellent variation for aphid resistance was recorded in B. juncea introgression lines, emphasizing heritable nature of fruticulosa resistance. The biochemical analysis suggested the possibility of high concentration of lectins to be associated with low aphid infestation in B. fruticulosa.     

Assessment of partial resistance to powdery mildew in Chinese wheat varieties

Field trials in two cropping seasons and two locations in central China were conducted on 60 Chinese autumn‐sown wheat varieties to assess their partial resistance to powdery mildew. Mean levels of disease severity ranged from close to 0 to more than 90%. The method of inoculation and the location in which trials were conducted affected the relative performance of the varieties, but these effects were much smaller than the main effect of variety. The area under the disease progress curve was highly correlated with final disease severity, but both were poorly correlated with apparent infection rate. Disease severity was regressed against frequencies of virulence in the Blumeria graminis (syn. Erysiphe graminis) f sp. tritici populations in the trial plots. A vertical distance (D) from the mean mildew severity to the fitted line was calculated for each variety and was used to quantify partial resistance. Five of the 60 varieties, ‘Hx8541’, ‘E28547’, ‘Chuan1066’, ‘Zhe88pin6’ and ‘Lin5064’, consistently expressed relatively low levels of disease despite high frequencies of virulence in the pathogen and had consistently high D‐values. They may therefore have good levels of partial resistance.     

Sensitivity to Drought Stress of Three Soybean Cultivars During Different Growth Stages

Three soybean ( Glycine max L.) culivars, Lee-74, Wright , and Ra 401 , were subjected to 100 % (control), 75 %, and 50 % of field capacity during vegetative (VI), flowering (R2), and pod-filling (R4) stages in greenhouse and field studies. Stress applied at R2 significantly reduced the yield in the greenhouse, while in the field, the maximum reduction was observed when the plants were subjected to stress at R4. Stress during VI reduced the yield components less than stress applied during R2 or R4 stages in both studies. The pod number and seed weight were the yield components most affected by drought stress, and the number of seeds per pod the least affected. Yield stress index was significantly correlated with the yield and its components. The reproductive stage was clearly more sensitive to drought than the vegetative stage. The cultivar Lee 74 had the highest yield and the second highest yield stress index whereas the cultivar Ra 401 had the lowest yield.     

Correlated response to recurrent selection for groat-oil content in oats

Summary One hundred random oat (Avena sativa L.) lines from a base (C₀) and each of three populations (C₁, C₂, and C₃) improved for groat (caryopsis) oil content by phenotypic recurrent selection were evaluated for correlated changes in several unselected agronomic traits. In addition, the parents of the base population and four check varieties were evaluated for the same traits. Phenotypic recurrent selection for high groat-oil content resulted in no significant correlated response in mean expression of any trait. Mean grain yield, biomass, groat yield, and harvest index of the improved populations were equal or superior to the mean of the parents and, with the exception of harvest index, equivalent to the mean of the check varieties. Mean test weight and seed weight of all populations were lower than for parents or check varieties. Selection for high groat-oil content caused a decline in genotypic variance for test weight and groat fraction, but reductions in genotypic variance for heading date and plant height may have resulted from culling for good agronomic type. Broad-sense heritability remained moderate to high for all traits except groat fraction. Phenotypic and genotypic correlation coefficients revealed negative, though mostly nonsignificant, relationships between groat-oil content and several traits, which may reflect a purported bioenergetic limitation to increasing groat-oil content in oats. Oil yield, however, was positively correlated with grain and groat yield, groat fraction, biomass, and harvest index. Results suggest that development of high-oil oat cultivars with current levels of production traits via phenotypic recurrent selection is possible.Journal Paper no. J-13038 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project 2447.     

Chromosome Locations of Additional Barley Enzyme Loci Identified Using Wheat-Barley Addition Lines

Disomic wheat-barley addition lines carrying a full hexaploid set of chromosomes of the wheat cultivar Chinese Spring, plus a pair of either chromosome 1, 2, 3, 4, 6, or 7 from the barley cultivar Betzes, were assayed electrophoretically. Comparisons of zymograms of each addition line with the Chinese Spring wheat and Betzes barky parents of the addition lines gave direct (presumptive in the case of chromosome 5) evidence of the chromosomal locations of nine enzyme loci which have been useful genetic markers in studies of the population genetics, ecogeneties and breeding of barley. Previously reported chromosome locations of several loci were confirmed and evidence was presented for the existence and probable chromosome locations for additional enzyme loci.     

Statistical mapping of tree species over Europe

In order to map the spatial distribution of twenty tree species groups over Europe at 1 km × 1 km resolution, the ICP-Forest Level-I plot data were extended with the National Forest Inventory (NFI) plot data of eighteen countries. The NFI grids have a much smaller spacing than the ICP grid. In areas with NFI plot data, the proportions of the land area covered by the tree species were mapped by compositional kriging. Outside these areas, these proportions were mapped with a multinomial multiple logistic regression model. A soil map, a biogeographical map and bioindicators derived from temperature and precipitation data were used as predictors. Both methods ensure that the predicted proportions are in the interval [0,1] and sum to 1. The regression predictions were iteratively scaled to the National Forest Inventory statistics and the Forest map of Europe. The predicted proportions for the twenty tree species were validated by the Bhattacharryya distance between predicted and observed proportions at 230 plot data separated from the calibration data. Besides, the map with the predicted dominant species was validated by computing the error matrix. The median Bhattacharryya distance in the subarea with NFI plot data was 1.712, whereas in the subarea with ICP-Level-I data, this was 2.131. The scaling did not significantly decrease the Bhattacharryya distance. The estimated overall accuracy of this map was 43%. In areas with NFI plot data, overall accuracy was 57%, outside these areas 33%. This gain was mainly attributable to the much denser plot data, less to the prediction method.     

Factors influencing red expression in autumn foliage of sugar maple trees

We evaluated factors influencing the development of autumn red coloration in leaves of sugar maple (Acer saccharum Marsh.) by measuring mineral nutrient and carbohydrate concentrations, water content, and phenology of color development of leaves from 16 mature open-grown trees on 12 dates from June through October 1999. Mean foliar nutrient and carbohydrate concentrations and water content were generally within the range published for healthy sugar maple trees. However, foliar nitrogen (N) concentrations were near deficiency values for some trees. The timing and extent of red leaf coloration was consistently correlated with both foliar N concentrations and starch or sugar concentrations, which also varied with N status. Leaves of trees with low foliar N concentrations turned red earlier and more completely than those of trees with high foliar N concentrations. Low-N trees also had higher foliar starch concentrations than high-N trees. During the autumn development of red leaf coloration, foliar starch, glucose and fructose concentrations were positively correlated with red leaf color expression. At peak red expression, the concentrations of glucose, fructose, sucrose and stachyose were all positively correlated with red color expressed as a percent of total leaf area.