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studies on the agronomic performance of quince cultivars cultivated in the tropics, especially in humid subtropical climates, which hiders the selection of cultivars with superior agronomic characteristics and the use of this fruit in regions with a mild

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Turkey and the Caucasus. Most of the world's production is based on selections from local wild populations with different cultivars grown in each zone. Most cultivars are single clones, although some, including a few leading Turkish types (e.g., Tombul

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overripe. Because of the continuous interest in developing new strawberry genotypes with improved quality traits, additional data on chemical composition and postharvest behavior of new strawberry breeding selections are necessary. These data facilitate the

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commercial traits are needed to be combined into one plant. The use of a selection index approach as described by Falconer and Mackay (1996) for such multiple-trait selection could offer a solution. This approach, designed to give the most rapid improvement

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Most cells have an active turnover of many of their nucleic acids (particularly some types of RNA) which through degradative processes result in the release of adenine, guanine and hypoxanthine. These free purines are converted to their corresponding nucleotides through salvage pathways. Adenine is converted to its nucleotide form AMP by Adenine phosphoribosyltransferase (APRT) which is one of the enzymes associated with the purine salvage pathway. Since all organisms have a de novo pathway for the formation of AMP, APRT is classified as a `salvage enzyme'. The APRT enzyme, in general, does not show a high degree of specificity for the exact structure of adenine and can also act on cytokinins and adenine derivatives like 2,6-diaminopurine, 2-fluoroadenine and 6-methylpurine. The APRT enzyme can utilize adenine analogues as substrate and convert them into their nucleotide forms which are toxic. Plants that lack APRT activity (APRT-plants) survive in the presense of these analogues. The amount of adenine analogue used for selecting APRT-plants is such that it kills all APRT+ (wild type) plants. APRT+ plants survive when grown in the presense of azaserine and alanosine that block de novo synthesis of AMP. APRT-plants transformed with the wild type cloned gene can be selected from a mixture of transformed and non-transformed plants by selecting in the presense of adenine, azaserine and alanosine. The presense of APRT activity can be confirmed by assaying for the APRT enzyme. APRT activity has been detected in many plant species. The presense of a positive forward and backward selection system can thus allow the use of APRT as a selectable marker in plant gene transfer systems.

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Abstract

Selections were made within ‘Empire’ lettuce (Lactuca sativa L.) to determine whether observed salt tolerance differences were due to microenvironmental influences in salt distribution or to genotypic variation. In a 3-year study conducted in small field plots, selections from ‘Empire’ were tested under high and low salinity conditions. First cycle, pure-line selections for high plant fresh weight (frame) and high head/frame ratios under high salinity were significantly improved in their respective selected characters over the parental line. Further selection within these lines did not substantially improve their respective phenotypes and led to the conclusion that the selected characters were homozygous within the ‘Empire’ cultivar.

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; Gardena, CA) until they were transplanted as described subsequently. Table 1. Half-sib seed family selections of Chinese wingnut ( Pterocarya stenoptera ) used in the study. Inocula. Inocula of P. cinnamomi and P. citricola were grown on a V8 juice

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Abstract

The precision of a 9-plant hill-plot design in which plants were sown 15 cm apart in a 3 × 3 arrangement compared favorably to that of 3-m-row plots containing approximately 75 plants for the estimation of pod yield of snap beans Phaseolus vulgaris L. Quality traits and sieve size distribution based on pod diameter in both plot designs were similar. Using the square design, the entire 9-plant plot can be taken as the unit of selection, or single plant selection can be practiced when the test plant is grown in the center hill surrounded by 8 uniform guard plants. Single plant selection using this design has been used effectively to modify traits of beans having moderate to high heritability. Selection based on family means should be used for traits with low heritability. Efficiency of the hill-plot design is realized in terms of smaller plot size, fewer required seeds per plot and reduced harvest time.

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Agricultural Research Service, nor criticism of similar ones not mentioned. We gratefully acknowledge the technical assistance of Rufus R. Horton, Jr., and the advice on recurrent selection methods of Robert H. Moll. The cost of publishing this paper was

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with reduced oviposition as well as increased mortality and delayed development ( Bell, 1991 ; Bell and Puterka, 2004 ; Butt et al., 1988 , 1989 ; Puterka, 1997 ; Robert et al., 1999 ). Observation of breeders’ selections in the orchard suggested

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