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- Author or Editor: Juan J. Ruiz x
- Journal of the American Society for Horticultural Science x
Parthenocarpy in pepino (Solanum muricatum Aiton) can overcome poor fruit set caused by pollination deficiencies. In two families involving a parthenocarpic parent (Pp), a nonparthenocarpic parent (Pnp), and the generations Pp⊗, Pnp⊗, F1, BCp, BCnp, and F2, we studied three traits that are often confused: parthenocarpy, efficiency of parthenocarpy over seeded fruit set, and the degree of facultative parthenocarpy. Plants were trained to two stems (A and B). On stem A we emasculated six flowers per truss; three were pollinated and the other three were left unpollinated. We considered that a plant was parthenocarpic if it set one or more seedless fruit similar in size and shape to those seeded, and nonparthenocarpic if it only set seeded fruit. The efficiency of parthenocarpy over seeded fruit set was measured with a parthenocarpic fruit set index (PFSI), defined as twice the ratio of seedless to total fruit on stem A. In stem B all flowers were left to self-pollinate naturally. We quantified the degree of facultative parthenocarpy as the percentage of seedless fruit of the total. Parthenocarpy is controlled by one dominant gene for which we propose the symbol P. Parthenocarpic fruit set in the homozygote PP was as efficient as the seeded one (PFSI ≈ 1); in the heterozygote Pp it was less efficient (PFSI ≈ 0.6). The dose of gene P explained the differences found between generations for the PFSI and made it possible to predict the PFSI of a given generation from the proportions of PP and Pp genotypes. Although for the Pp hybrids parthenocarpic fruit set was less efficient than the seeded one, their ability to set seedless fruit in conditions of deficient pollination, together with their high degree of heterosis, makes them agronomically useful. The degree of facultative parthenocarpy seemed to be a complex trait with low heritability. In environments unfavorable for pollination, parthenocarpic genotypes set seedless fruit, thus ensuring crop production and yield stability. Using the degree of facultative parthenocarpy to classify plants for parthenocarpy is not recommended. Developing parthenocarpic cultivars can help spread this crop and stabilize yields.
We studied the genetic variability of some traditional tomato (Lycopersicon esculentum L. Mill.) cultivars of Spain, and established their relationships using both simple sequence repeats (SSR) and sequence related amplified polymorphism (SRAP) markers. These included cultivars from different locations of three main types, Muchamiel, De la pera, and Moruno. Additionally we tested two other local cultivars, `Valenciano' and `Flor de Baladre', plus a small sample of commercial cultivars and a few wild species. Both types of markers resolved the cultivars from different groups, but SSR failed to distinguish some of those classified under the same group. All the De la pera cultivars clustered together by genetic similarity with the SRAP markers. The other traditional cultivars, which are grown in a wider geographic range, formed a more diffuse group, which included the commercial cultivar Roma. The Mexican cultivar Zapotec, a breeding line, and the virus-resistant commercial hybrid `Anastasia' were the most distant of all the cultivars. The latter hybrid had higher similarity to the wild species due to introgressed segments from them carrying the resistance genes. Similar results were observed for SSR markers but with a lower level of resolution. This information would be useful to facilitate tomato germplasm conservation and management efforts.
Resistance to Celery mosaic virus (CeMV) in celery [Apium graveolens L. var. dulce (Mill.) Pers.] is recessive and determined by the single gene, cmv. We report discovery of two polymerase chain reaction-based dominant markers tightly linked to cmv in segregating F2 and BC1 populations. Marker me1em2 is associated to the dominant (susceptibility allele) and the second marker, me8em2, to the recessive (resistance allele). Simultaneous screening for both markers in segregating populations allows for identification of both homozygous and heterozygous genotypes for disease resistance. This marker system can be used for early seedling selection, which will simplify and speed development of celery cultivars resistant to CeMV.