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Genetic diversity of the Spanish national almond (Prunus amygdalus Batsch) collection was characterized with 19 simple sequence repeat (SSR) markers selected because of their polymorphism in almond and other Prunus L. species. A total of 93 almond genotypes, including 63 Spanish cultivars from different growing regions, as well as some international cultivars and breeding releases were analyzed. All primers produced a successful amplification, giving a total of 323 fragments in the genotypes studied, with an average of 17 alleles per SSR, ranging from 4 (EPDCU5100) to 33 (BPPCT038). Allele size ranged from 88 bp at locus PMS40 to 260 bp at locus CPPCT022. The heterozygosity observed (0.72) was much higher not only than in other Prunus species, but also than in other almond pools already studied. The dendrogram generated using the variability observed classified most of the genotypes according to their geographical origin, confirming the particular evolution of different almond ecotypes. The SSR markers have consequently shown their usefulness for cultivar identification in almond, for establishing the genetic closeness among its cultivars, and for establishing genealogical relationships. Almond {Prunus amygdalus (syn. P. dulcis (Mill.) D.A. Webb)} is a species in the Rosaceae family with a genome 2n = 16. The almond is the most important tree nut crop in terms of production and is one of the most polymorphic fruit species (Kester et al., 1991; Socias i Company and Felipe, 1992). This high polymorphism may be due to its self-incompatibility (Socias i Company, 1998) and to the utilization of open- pollinated seedlings in traditional almond culture (Grasselly, 1972; Rikhter, 1972). The almond originated in central Asia (Grasselly, 1976) and is probably the oldest tree nut crop to be domesticated, possibly during the third millennium BCE (Spiegel-Roy, 1986). Over several centuries, almond spread from its center or origin toward the Mediterranean Basin, and was introduced by the Phoenicians, Greeks, and Romans into the different Mediterranean regions, expanding from Greece and the Balkans to Spain and Portugal. In all the Mediterranean Basin, both in the northern and southern shores, almond production became concentrated in specific areas, mostly with a traditional cultural system, adapted to the drought-resistant and frost-sensitive characteristics of the available almond germplasm, resulting as a consequence in the emergence of adapted land races associated with specific production areas (Grasselly and Crossa-Raynaud, 1980). Although seedling propagation resulted in the proliferation of a large number of

The pistil (S-RNase) and the pollen [S-haplotype-specific F-box protein (SFB)] components of the Sf allele, presumably conferring self-compatibility in almond {Prunus amygdalus Batsch [syn. P. dulcis (Mill.) D.A. Webb]}, were identified and sequenced in ‘Ponç’, a local Spanish almond cultivar, confirming their identity with the published sequences of these components. Despite the presence of the Sf allele, the ‘Ponç’ phenotype was self-incompatible as confirmed by different pollination tests, including self pollen tube growth, fruit set after self-pollination, and fruit set in bagged branches. However, the pistil and the pollen of ‘Ponç’ were fully viable when pollinated by a cross-compatible pollen or used on a cross-compatible pistil. The fact that ‘Ponç’ presents two different S-proteins with RNase activity may indicate an active function of its Sf -RNase, whereas in the self-compatible almond cultivars thus far studied, the Sf -RNase has been inactive. This activation indicates that the presence of the Sf allele may not be the exclusive source of self-compatibility in almond, and other factors may also be involved in the expression of almond self-compatibility.

Nut and kernel dimensions and sphericity, shelling percentage, oil content, and fatty acid composition were studied over 2 years in 15 advanced almond (Prunus amygdalus Batsch) selections. The aim was to test the effect of pollination type on these fruit traits for this group of new self-compatible selections of a mostly self-incompatible species as well as the yearly effect on these variables. Variability between selections was much higher than that between years, showing a moderate level of year-stability and a significant year effect only for some variables. The different pollination treatments affected all chemical components studied, as well as nut and kernel weight, but not the other physical traits. Self-pollination decreased kernel weight and volume as well as oil content and percentage of linoleic acid but increased the percentage of oleic acid. These variations in the fatty acid composition were in the trend of increasing kernel quality. Inbreeding depression could also negatively affect several aspects of nut and kernel quality. Thus, autogamous almond genotypes without apparent symptoms of inbreeding depression may yield kernels of increased nutritional and industrial quality.

ADDITIONAL INDEX WORDS. Prunus amygdalus, pollen tube growth, breeding ABSTRACT. Pollen tube growth after selfi ng was studied in four almond (Prunus amygdalus Batsch) families derived from crosses between self-compatible ʻTuonoʼ and self-incompatible ʻFerragnesʼ and ʻFerraliseʼ in both directions, in order to ascertain the phenotypic expressions of the different genotypes. A differential expression of self-compatibility was observed in the seedlings of the different families. The genetic self-compatible offspring of ʻFerraliseʼ showed a lower percentage of pistils with pollen tubes at the style base and a lower number of pollen tubes at the pistil base after self-pollination than those observed in the self-compatible offspring of ʻFerragnesʼ. This low level of self-compatibility expression observed in some ʻFerraliseʼ seedlings may be due to the inbreeding present in ʻFerraliseʼ. As a consequence, caution must be taken in almond breeding to avoid the increase of inbreeding by the utilization of related parents and to diversify the sources of self-compatibility, at present mostly limited to ʻTuono.ʼ

An F2 population from a single F1 plant from the cross of peach (Prunus persica (L.) Batsch) rootstock cultivars Harrow Blood (HB) × Okinawa (Oki) was used to locate the Mi locus, which conditions resistance to Meloidogyne incog- nita (race 1) (Kofoid and White) Chitwood. These data and comparison of common markers among published genetic linkage maps placed the Mi locus on Prunus L. linkage group 2. Two restriction fragment length polymorphisms (RFLPs) (linked at 4.8 and 6.8 centimorgan (cM), repulsion phase) and one random amplifi ed polymorphic DNA (RAPD) marker (linked at 9.5 cM, coupling phase) were linked to Mi. The RAPD marker was cloned, sequenced, and converted to a polymerase chain reaction (PCR)-based cleaved amplifi ed polymorphic sequence (CAPs) marker. Clones of resistance gene analogs (RGA) developed from Oki were highly polymorphic when used as RFLP probes. The RGAʼs mapped to four linkage groups but clustered on two of the four linkage groups, providing limited coverage of the genome. Even so, they may be useful as markers for disease resistance genes that occur in other populations. The linkage maps of the HB × Oki F2 population and a peach × almond (Prunus amygdalus Batsch) F2 population were colinear in certain regions, however, a signifi cant number of markers mapped to different linkage groups among the two populations. The locus for the blood-fl esh trait (red-violet mesocarp) mapped to the top of linkage group 4. Most stone fruit and nut trees grown commercially and in home gardens are compound plants consisting of a genetically distinct scion grafted on a rootstock. Root-knot nematode infestation of peach tree roots lowers yields and shortens the lifespan of an orchard. The most agronomically important root-knot nematodes (genus Meloidogyne Goeldi) are Meloidogyne incognita, M. javanica (Treub) Chitwood, and M. arenaria (Neal) Chitwood, which are found in all arable regions of the world (Mai, 1985), with M. incognita being most widespread and damaging in Cali- fornia peach orchards (McKenry, 1989). Genetic resistance of the rootstock, while only one of several methods used to control nematodes, is the most economical, effective, and ecologically acceptable (Mai, 1985; Opperman et al., 1994). Currently, only three peach rootstock cultivars, Nema- guard, Nemared, and Lovell, are used extensively in California (Yoshikawa et al., 1989), with Nemaguard and Nemared being resistant to root-knot nematodes. However, both have limitations, including sensitivity to wet soil conditions and zinc defi ciency, susceptibility to damage by root lesion nematode (Pratylenchus vulnus Allen and Jensen), ring nematode (Criconemella xenoplax (Raski) Luc. and Raski), bacterial canker (Pseudomonas syringae

Scanning electron microscopy was used to examine almond [Prunus dulcis (Mill.) D.A. Webb (syn. Prunus amygdalus Batsch, Amygdalus communis L.)] flower bud development for three cultivars (Nonpareil, Carmel, and Butte) from four California locations (which span the range of almond production in California) for 2 years, and for `Nonpareil' in a single location for a third year. The objectives were to document timing of floral developmental events and to better understand the extent of variation that exists within and among cultivars, locations, and years. Results indicated that the time of floral initiation relative to hull split varied among cultivars. Median time for floral initiation in `Nonpareil' was more than 3 weeks after the onset of hull split. For `Butte' and `Carmel', median time of floral initiation preceded the onset of hull split. Extensive variation in the timing of bud development events within a cultivar was apparent. Timing of developmental events varied among locations, but no patterns emerged consistent with the north to south range which spanned 4°15' latitude and 520 km. Among years, development occurred earliest in 1997, a relatively warm year, and was delayed in 1998 and 1999, relatively cool years. Results indicate an earlier onset of floral initiation than reported in the classical literature on the subject.

Seed of California almond [Prunus dulcis (Mill.) D.A. Webb, syn. P. amygdalus Batsch, and P. communis (L.) Arcangeli, non-Huds.] genotypes contained very low saturated fatty acids, high monounsaturated fatty acids, and low polyunsaturated fatty acids. Kernel oil consisted primarily of five fatty acids: palmetic, palmetoleic, stearic, oleic, and linoleic. Linolenic acid was only present in amounts of

Prunus accessions were screened in a greenhouse for suitability as hosts for Criconemella xenoplax (Raski) Luc and Raski. All 410 accessions examined were suitable hosts for the nematode. Included in this study were 266 Prunus persica L. Batsch cultivars and cultivars representing 25 other Prunus species: P. americana Marsh., P. andersonii A. Gray, P. angustifolia Marsh., P. argentea (Lam.) Rehd., P. armeniaca L., P. besseyi L. H. Bailey, P. cerasifera Ehrh., P. cistena N.E. Hansen, P. davidiana (Carriere) Franch., P. domestica L., P. dulcis (Mill.) D. Webb, P. emarginata (Dougl. ex Hook.) Walp., P. hortulana L. H. Bailey, P. insititia L., P. kansuensis Rehd., P. maritima Marsh., P. munsoniana W. Wright & Hedr., P. pumila L., P. salicina Lindl., P. simonii Carriere, P. spinosa L., P. tenella Batsch, P. texana D. Dietr., P. tomentosa Thunb., and P. webbii (Spach) Vierh. Also, another 66 interspecific hybrids were tested. Although a few accessions seemed to exhibit an unstable form of resistance, it seems unlikely that Prunus selections that exhibit useful resistance to population increase by C. xenoplax will be found.

Six cross-incompatibility groups, which contain most of commercially important California almond cultivars (Prunus dulcis (Mill.) D.A. Webb, syn. Prunus amygdalus Batch), and their self-incompatibility (S) allele genotypes are identified. Incompatibility groups include 'Mission' (S aSb), 'Nonpareil' (ScSd), and the four groups resulting from the 'Mission' x 'Nonpareil' cross: (SaSc), (SaSd), (SbSc), and (SbSd), as represented by 'Thompson', 'Carmel', 'Merced' and 'Monterey', respectively. All seedlings from the 'Mission' x 'Nonpareil' cross were compatible with both parents, a result indicating that these two cultivars have no alleles in common. Crossing studies support a full-sib relationship for these progeny groups and the origin of both parents from common germplasm. Cultivars in these six groups account for ≈ 93% of present California production, a result demonstrating a limited genetic base for this vegetatively propagated tree crop. About 65% of the world almond production is in California, with >166,500 ha in production in 1990 (California Agricultural Statistics Service, 1990). The interplanting of cross-compati ble pollinizer cultivars in what previously were often single-cultivar orchards led to dramatic improvements in productivity and production consis- tency (Tufts, 1919; Tufts and Philp, 1922). Self-incompatibility in almond, a diploid tree crop (2n = 16), seems to be of the monogenic, gametophytic type (Socias i Company, 1991 ) as are other self-incompatible crops in the Rosaceae (Crane and Brown, 1937; Crowe, 1964). The self-incompatibility (S) locus controls self- and intra-specific cross-incompatibility (CI), and a series of many distinct alleles seems to exist (Socias i Company, 1991). Crossa-Raynaud and Grasselly (1985) have assigned the genotypes (S 1S2), (S3S4), and (S7S8) to 'Cristomorto', ' Ai', and 'Tardy Nonpareil', respectively. Tufts and Philp (1922), in their analysis of 23 early almond cultivars, established two CI groups (CIGs): a) 'Nonpareil' and 'I.X.L.' and b) 'Mission' (also known as 'Texas Prolific'), the main pollinizer for 'Nonpareil' at that time, and 'Languedoc' (different from the French cultivar of the same name). 'Long I.X.L.' and 'Profuse' have been added to the 'Nonpareil' CIG and 'Ballico' has been added to the 'Mission' CIG (Kester, 1963). Other early cultivars proposed by Kester and Asay, (1975) to be cross-incompatible include 'Jordanolo' and 'Harpareil', produced from a 'Nonpareil' × 'Harriott' cross; 'Reams' and 'Jubilee'; 'Kutsch', 'Rivers Nonpareil', 'Sultana', and 'Bigelow'; and 'Smith X.L.' and 'Drake', although crossing data no longer are available. Of these cultivars, only 'Mission' and 'Nonpareil' remain exten- sively planted. Newer cultivars, selected for improved horticul- tural performance and pollinizer efficacy, are being planted in- creasingly. Most of these new cultivars seem to be chance seed- lings from 'Nonpareil' × 'Mission' crosses (Hauagge et al., 1987). Four CIGs would be expected in the progeny of a 'Nonpareil' × 'Mission' cross if parents shared no common S alleles.