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  • Author or Editor: F.A. Bliss x
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Control of pollen production without the difficulties of mechanical emasculation allows crosses to be made efficiently in many plant species that would otherwise be disregarded commercially because of problems of hybridization. Development of male-sterile inbreds is facilitated by the use of cytoplasmic-genic male sterility in a manner similar to the system proposed by Jones and Clarke for use in onions (5). This method is now commonly used in F1 hybrid development of such crops as maize (6), sorghum (9), sugar beets (8), and sudan grass (1), and has been suggested for use in other crops (4).

Open Access
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Abstract

The germplasm for a cultivated crop is generally regarded as the gene pool of cultivars, species and genera that can be utilized as sources of additional genetic variation for crop improvement. When developing strategies for the optimum use of vegetable germplasm, several problems not found in field crops, ornamentals and fruits should be considered. In vegetables, a part of the immature plant is often utilized. Because it is still physiologically immature, arbitrary judgments concerning time of harvest may greatly affect yield and quality, compared to crops in which the mature seeds are harvested. Second, unlike most ornamentals, tree fruits and small fruits, many vegetables are propagated by seed rather than asexually. An efficient means of stabilizing the commercial genotype(s) must be developed before widespread use is feasible.

Open Access
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Seedlings of Prunus mahaleb are often used as rootstocks for sweet cherry (P. avium) scion cultivars in commercial orchards. While they are desirable based on ease of propagation and economical production of nursery stock, seedlings may be variable resulting in nonuniform compound trees, and they are susceptible to several important diseases. Seedling sources have shown substantial variability for population uniformity of plant growth, and reaction to crown gall, powdery mildew and Phytophthora root rot. Segregating families also vary for pollen fertility, inbreeding response and control of scion growth. Multiple screening for favorable trait combinations is underway to develop improved sources of cherry rootstocks.

Free access
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Kiwifruit (Actinidia deliciosa) is a functionally dioecious plant where fruit size is dependent on number of seeds set. Pollen fertility was estimated in 1990 and 1991 by percentage stainability and percentage germinability in vitro. Profiles of the isozymes AAT, GPI and PGM were used to assess if any large differences in pollen fertility could be attributed to genotypic variation. Based on these three isozymes, eight different genotypes were discovered. Although significant differences were found among vines within orchards and among orchards, all vines can be considered good pollenizers (stainability > 87%). A positive correlation was found in 1991 between percentage stainability and percentage germination.

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Genetic linkage maps for many organisms are being produced using molecular markers. The utility of these maps depends on the ability to place genes of known, important effects on the map. It is often useful lo saturate the chromosome around these loci with many linked molecular markers. This study used Bulked Segregant Analysis and Random Amplified Polymorphic DNA to identify linked markers to loci in peach, Prunus persica L. Batch and almond Prunus dulcis Mill populations. Linkages to isozyme loci were first sought to test the suitability of this technique to long-lived perrenials. Several RAPD markers were found to be linked to three isozyme loci in a segregating F3 population from a peach × almond cross. PAPD markers have also been identified which are linked to the yellow-flesh locus of peach in a heterozygous peach population. Thus, this method has proven useful for identifying molecular marker linkages to important loci in peach and almond. These RAPDs may now be placed on a linkage map generated in our lab using a peach/almond hybrid population which will allow these loci to be studied and manipulated more easily in a breeding program.

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Studies of genetic variation at the DNA level in the tree fruit and nut crop species of Prunus have been very limited. Recently molecular markers based on random amplified polymorphic DNA (RAPD) markers have been shown to be highly useful and efficient gene markers in other plant and animal species. We have used a total of 50 primers (10-mers) with arbitrary nucleotide sequence to identify cultivars of cherry, plum, apricot, peach and almond. A total of 120 accessions of different cultivars were assayed. The variation revealed by RAPD markers was highly species specific in the five Prunus species examined. High levels of polymorphism were observed for almond cultivars whereas sweet cherry revealed the lowest levels of polymorphism for the RAPD primers examined. The implications of these results in the germplasm diversity in the cultivated species of Prunus will be discussed.

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The discovery of bruchid resistance in wild beans and the demonstration that theArcelin protein is responsible for the resistance, provide an opportunity to develop resistant cultivars of common bean, Phaseolus vulgaris L. Arcelin expression is controlled by multiple alleles, which impart different levels of insect resistance. In field tests in Honduras and Brazil, backcross-derived lines with the Arl-1 allele were most resistant, especially to Mexican bean weevil. Seed mixtures of 0.80 Arl-1:0.20 susceptible and equal amounts of Arl-1,Arl-2, and Arl-3, and Arl-4 containing seeds showed resistanc elevels and seed yields similar to lines homogeneous for Arl-1. Breeding lines uniform for appearance and agronomic performance, but heterogenous for resistance genes are being tested as potential new dry bean cultivars having stable insect resistance.

Free access

Abstract

Genic male steriles of common bean (Phaseolus vulgaris L.) showed an average of 68% outcrossing. Outcrossing estimates are conservative due to selfing or sibbing made possible by unexpected fertility restoration in plants initially classified as male sterile. In growth chamber studies, a temperature regime of 30° day/18°C night for 2 weeks after flowering altered the expression of unstable sterile plants from partial sterile to male sterile. The reverse shift was conditioned by an 18° day/7° night temperature regime. Sterility was restored again by returning plants to the higher temperatures. The sterile F1 progenies of the cross male sterile x Swedish Brown-10 were all unstable. Temperature-stable steriles were obtained by selfing cold-treated, unstable steriles or by using these plants to pollinate stable steriles.

Open Access

Crown gall is an important disease of many fruit and nut crops, but little is known about sources of resistance. We screened germplasm from Prunus armeniaca L., P. angustifolia Marsh., P. argentia L., P. avium L., P. besseyi Bailey, P. bokhariensis Schneid., P. brigantica L., P. cerasifera Ehrh., P. cerasus L., P. dulcis (Mill.) D.A. Webb, P. fruiticosa Pall., P. hortulana Bailey, P. insititia L., P. japonica Thunb., P. mahaleb L., P. persica (L.) Batsch, P. serotina Ehrh., P. simonii Carr., P. sogdiana L., and P. webbii (Spach) Vieh. When either main stems or lateral branches of seedlings were inoculated with strains K12 and C58 of Agrobacterium tumefaciens (Smith and Townsend) Conn., the incidence of resistance was less than 10% except in some accessions of P. mahaleb L. where up to 30% of the plants were resistant. Some resistant plants were identified in other species, with P. insititia L. being the most promising. Symptoms based on presence and size of galls should be allowed to develop for up to 90 days after inoculation to reduce the likelihood of misclassifying plants as resistant when they are slightly susceptible.

Free access

Abstract

A method was developed to evaluate tomato plants by means of excised leaves for reaction to Cornynespora cassiicola (Berk. & Curt) Wei using the toxin in the cell-free filtrate of virulent isolates. This test should be useful for identifying resistant families and segregates.

Open Access