Effect of a traditional control method (tree removal) on the spread of sharka in an apricot orchard in Southeastern Spain

The spatial spread of sharka disease (Plum pox virus, PPV) was studied from 1990 to 2002 in a traditional apricot (Prunus armeniaca L.) orchard located in Murcia (Southeast of Spain). The occurrence of sharka was determined by the visual observation of symptoms on leaves and fruits during the ripening stage, when symptoms are most visible. To ascertain PPV in doubtful samples, an ELISA-DASI assay was applied to the leaves. All trees infected the previous year were pulled up and were not replanted. Results showed that the virus was introduced to the farm by natural vectors (aphids) from a neighbouring sharka-infected plum orchard. It was then transmitted from these infected trees mainly to nearby trees by the same vectors, although also often to trees standing quite a distance away. The long interval between infection and symptom appearance makes eradication of the disease more difficult. Pulling up infected trees as a control method reduced the percentage of trees ultimately lost, and over the long term could stop the further spread of the disease

Effect of a traditional control method (tree removal) on the spread of sharka in an apricot orchard in Southeastern Spain

The spatial spread of sharka disease (Plum pox virus, PPV) was studied from 1990 to 2002 in a traditional apricot (Prunus armeniaca L.) orchard located in Murcia (Southeast of Spain). The occurrence of sharka was determined by the visual observation of symptoms on leaves and fruits during the ripening stage, when symptoms are most visible. To ascertain PPV in doubtful samples, an ELISA-DASI assay was applied to the leaves. All trees infected the previous year were pulled up and were not replanted. Results showed that the virus was introduced to the farm by natural vectors (aphids) from a neighbouring sharka-infected plum orchard. It was then transmitted from these infected trees mainly to nearby trees by the same vectors, although also often to trees standing quite a distance away. The long interval between infection and symptom appearance makes eradication of the disease more difficult. Pulling up infected trees as a control method reduced the percentage of trees ultimately lost, and over the long term could stop the further spread of the disease

Pedigree analysis of 220 almond genotypes reveals two world mainstream breeding lines based on only three different cultivars

Loss of genetic variability is an increasing challenge in tree breeding programs due to the repeated use of a reduced number of founder genotypes. However, in almond, little is known about the genetic variability in current breeding stocks, although several cases of inbreeding depression have been reported. To gain insights into the genetic structure in modern breeding programs worldwide, marker-verified pedigree data of 220 almond cultivars and breeding selections were analyzed. Inbreeding coefficients, pairwise relatedness, and genetic contribution were calculated for these genotypes. The results reveal two mainstream breeding lines based on three cultivars: “Tuono”, “Cristomorto”, and “Nonpareil”. Descendants from “Tuono” or “Cristomorto” number 76 (sharing 34 descendants), while “Nonpareil” has 71 descendants. The mean inbreeding coefficient of the analyzed genotypes was 0.041, with 14 genotypes presenting a high inbreeding coefficient, over 0.250. Breeding programs from France, the USA, and Spain showed inbreeding coefficients of 0.075, 0.070, and 0.037, respectively. According to their genetic contribution, modern cultivars from Israel, France, the USA, Spain, and Australia trace back to a maximum of six main founding genotypes. Among the group of 65 genotypes carrying the Sf allele for self-compatibility, the mean relatedness coefficient was 0.125, with “Tuono” as the main founding genotype (24.7% of total genetic contribution). The results broaden our understanding about the tendencies followed in almond breeding over the last 50 years and will have a large impact into breeding decision-making process worldwide. Increasing current genetic variability is required in almond breeding programs to assure genetic gain and continuing breeding progress

Genetic analysis for physical nut traits in almond

Peer ReviewedPublishe

Caracterización de embriones múltiples en almendro

Multiple embryos within the same tegument occur spontaneously in certain almond [Prunus dulcis (Mill.) D.A. Webb]cultivars including Nonpareil and Mission. Seedlings from the same polyembryonic seed are frequently viable, thoughoften one of the seedlings shows weak growth and develops poorly. These dwarf seedlings have been characterised in aprevious work as haploid. In this work, we have characterised 450 seedlings from polyembryonic seeds of the Californiancultivar Nonpareil, and 100 seedlings from polyembryonic seeds of the Spanish selections D97396 and D97407,including their germination and later growth. Isozyme and Simple Sequence Repeat markers were used to geneticallyanalyse seedling genetic structure. In addition, individual mitotic karyotypes were determined following staining of roottips. The percentage of twin embryos showing aberrant growth was approximately 25% with mortality rates of about 90%.Results suggested the sexual origin of both embryos. Seedlings from the same seed are genetically identical with a similargrowth, though often one of the seedlings from the secondary embryo loses part of the genomic contents and becomesan aneuploid plant and showed a weak development. The use of this material in almond breeding is also discussed.La aparición de embriones múltiples dentro del mismo tegumento es un fenómeno espontáneo que ocurre en semillas de algunas variedades de almendro [Prunus dulcis (Mill.) D.A. Webb] como "Nonpareil" o "Mission". Las plántulas procedentes de estas semillas poliembriónicas son viables, aunque a menudo muestran un crecimiento más debil y retrasado. Estas plántulas enanas han sido caracterizadas como haploides en trabajos previos. En este trabajo hemos estudiado 450 plántulas procedentes de semillas poliembriónicas de la variedad californiana "Nonpareil" y 100 plántulas procedentes de semillas poliembriónicas de las selecciones españolas "D97396" y "D97407", observando su germinación y posterior crecimiento. Estas plántulas han sido caracterizadas molecularmente mediante marcadores isoenzimáticos y microsatélites (...

Breaking dormancy of GF305 peach and Real Fino apricot trees during the evaluation of resistance to sharka (plum pox potyvirus)

In countries like Spain or France, where sharka (plum pox potyvirus) is not as widespread as it is in Greece or Central Europe, experiments to evaluate apricot resistance have to be carried out in controlled conditions using insect-proof greenhouses. One of the most important aspects of such growth conditions is the application of periods of artificially induced dormancy in cold chambers so that tree species from temperate zones can undergo the necessary endodormancy-breaking step. In the experiment described in this paper, GF305 peach and Real Fino apricot seedlings were exposed to artificial periods of cold (7 $^\circ$C) and darkness lasting 3 to 12 weeks (between 504 and 2016 hours of cold) in order to determine the optimum period for subsequent good vegetative growth. After removal from the cold chamber, the plants were placed in a greenhouse and weekly recordings were made of the percentage of leaf buds sprouted and vegetative growth. The optimal periods were found to be 5 weeks (840 hours of cold) for GF305 and 8 weeks (1344 hours of cold) for Real Fino.Levée de dormance du pêcher GF305 et de l'abricotier Real Fino pendant l'évaluation de la résistance à la sharka (plum pox potyvirus). Dans des pays comme la France ou l'Espagne, où la sharka n'est pas aussi répandue qu'en Grèce ou en Europe Centrale, les expériences pour évaluer la résistance de l'abricotier doivent être conduites dans des conditions contrôlées en utilisant des serres indemnes d'insectes. Un des aspects les plus importants des ces conditions de culture est la nécessité d'appliquer des périodes d'induction artificielle de dormance pour que ces arbres des zones tempérées puissent passer l'étape indispensable de la levée de dormance. Dans l'expérience décrite, des plantules du pêcher GF305 et de l'abricotier Real Fino ont été exposées à des périodes artificielles de froid (7 $^\circ$C) et d'obscurité durant 3 à 12 semaines (entre 504 et 2016 heures de froid) pour définir la période optimale permettant une bonne croissance végétative subséquente. A la sortie de la chambre froide, les plantes ont été placées en serre et des mesures hebdomadaires ont été faites du pourcentage de bourgeons de feuilles démarrés et de la croissance végétative. Les périodes optimales ont été de 5 semaines (840 heures de froid) pour GF 305 et de 8 semaines (1344 heures de froid) pour Real Fino

Behaviour of apricot (Prunus armeniaca L.) cultivars in the presence of sharka (plum pox potyvirus): a review

Information concerning the evaluation of apricot resistance to sharka (plum pox potyvirus) has in many cases been published in journals of limited circulation. In an attempt to assess the actual status of this resistance, a global review has been made, including 222 cultivars, 175 of which can be considered as susceptible, 27 as resistant and 20 as cultivars of uncertain classification. Such a doubtful classification could be due to differences in evaluation methods, the isolates used, or to the authenticity of the plant material. The results seem to indicate that the main origin of resistance to sharka could be North American cultivars, although other resistant sources have been found in Central Europe.Comportement des cultivars d'abricotier (Prunus armenica L.) à la sharka (plum pox potyvirus) : une revue. Les informations concernant l'évaluation du comportement de l'abricotier à la sharka sont fréquemment publiées dans des journaux à faible audience. La présente revue se propose de synthétiser ces informations dispersées : 222 cultivars sont pris en compte, 175 d'entre eux pouvant être considérés comme sensibles, 27 comme résistants et 20 pour lesquels la classification est incertaine. Cette classification douteuse peut être due à des différences dans les méthodes d'évaluation, aux isolats utilisés ou à l'authenticité du matériel végétal. Les résultats semblent indiquer que la principale source de résistance à la sharka aurait pour origine les cultivars nord-américains bien que d'autres sources de résistance ont été trouvées en Europe centrale