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Jordi Canals, Jorge Pinochet, and Antonio Felipe

The influence of temperature and age of the plant was determined on nematode reproduction on a susceptible almond (Prunus amygdalus Batsch.) and on a resistant peach-almond hybrid (P. persica Stok. × P. amygdalus Batsch.) rootstock inoculated with Meloidogyne javanica (Treub) Chitwood. Experiments were conducted under greenhouse conditions in heated and unheated sand beds. `Garrigues' almond inoculated with 3000 nematodes per plant showed extensive galling, high final nematode population levels, and high counts of nematodes per gram of root at 27 and 32C. The hybrid G × N No. 1 showed minimal galling and reproduction at 27C but higher levels of galling and final population and nematode counts per gram of root at 32C, suggesting a partial loss of resistance with temperature increase. One-month-old and 1-year-old plants of `Garrigues' were susceptible following inoculation with 2000 nematodes per plant, although plantlets (l-month) were significantly more affected. Plantlets of hybrid G × N No. 1 were also susceptible, but 1-year-old plants were resistant. Resistant genotypes (G × N selections) seem to require root tissue maturation before expressing full resistance.

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Bridget M. Lamp, Joseph H. Connell, Roger A. Duncan, Mario Viveros, and Vito S. Polito

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.

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Patrick M. McCool and Robert C. Musselman

Almond (Prunus amygdalus Batsch cv. Nonpareil), apricot (Prunus armeniaca L. cv. Royal Blenheim), and peach [Prunus persica (L.) Batsch cv. Halford] grafted nursery stock seedlings were exposed once per week for 4 hours to a maximum O3 concentration of 0.25 μl·liter-1 in field exposure chambers. Exposures were repeated for a total of 4 months in 1986 (year 1) and 1987 (year 2). Trunk caliper, number of shoots, and net growth (total seasonal weight increase) were measured at the end of each year. Almonds appeared to be the most sensitive to O3. Almond seedlings exhibited extensive foliar injury from O3, while apricot and peach seedlings were relatively insensitive. Total net growth of O3-exposed almond was reduced during both years relative to the controls and an impact on caliper was evident after year 2. Apricot seedlings exposed to O3 developed a thinner trunk but more shoots than the controls in both years. Peach tree seedlings exposed to O3 had fewer shoots than the controls at the conclusion of year 2 but thicker trunks after both years. No significant difference in variance or shape of distribution of net growth within the treatment populations between O3-exposed seedlings and controls was detected for any of the three fruit crops. The impact of O3 on young, nonbearing perennial fruit crops may be most evident in specific growth characteristics, such as net growth or trunk caliper.

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Anne M. Gillen and Fred A. Bliss

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 incognita (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 amplified 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 amplified polymorphic sequence (CAPs) marker. Clones of resistance gene analogs (RGA) developed from Oki were highly polymorphic when used as RFLP probes. The RGA's 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 significant number of markers mapped to different linkage groups among the two populations. The locus for the blood-flesh trait (red-violet mesocarp) mapped to the top of linkage group 4.

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A.R. Biggs and R. Scorza

Suberin accumulation in mechanically wounded bark tissue was determined fluorimetrically in greenhouse-grown peach [Prunus persica (L.) Batsch] and F2 progeny from peach × almond [P. amygdalus (Mill.) DA. Webb] hybrids. In general, suberin accumulation following wounding was significantly greater for progeny from almond-type than for peach-type hybrids. Hybrids from parents with almond tree type combined with peach fruit type accumulated the highest suberin levels. These data may partially explain the differences observed among peach and peach × almond hybrids in relative susceptibility to Leucostoma canker [Leucostoma persoonii Hohn. and L. cincta (Fr.) Hohn.] and injury caused by lesser peachtree borer. The association of higher suberin accumulation with specific phenotypic characteristics could simplify the selection of desirable seedlings in a breeding program that includes canker resistance as an objective.

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Pere Arús, Carmen Olarte, Miguel Romero, and Francisco Vargas

Ten isozyme genes were studied after analyzing the variability of eight enzyme systems—glucose phosphate isomerase (GPI), phosphoglucomutase (PGM), aspartate aminotransferase (AAT), leucine aminopeptidase (LAP), 6-phosphogluconate dehydrogenase (6PGD), isocitrate dehydrogenase (IDH), shikimate dehydrogenase (SDH), and aconitase (ACO)—in the progeny of five crosses among almond [Prunus amygdalus Batsch, syn. P. dulcis (Miller) D. A. Webb] cultivars. Six of these loci were found to be located in two linkage groups, one containing four loci (Pgm-2, Gpi-2, Aat-2, and Lap-1) and two more in the other (Idh-2 and Aat-1). Genetic configurations of pairs of loci specific to segregating F1 progeny of crosses between heterozygous parents were found in our data, for which we derived the estimate of the recombination fraction and its variance. Linkage data for the gene pairs that could be estimated in various crosses were used to obtain a joint estimation of the recombination fraction.

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A.M.S. Nyomora, P.H. Brown, K. Pinney, and V.S. Polito

The effect of boron (B) on in vivo and in vitro development of almond [Prunus dulcis (Mill.) D.A. Webb (syn. P. amygdalus Batsch)] pollen and pollen tubes and the resultant effect on fruit set was studied in mature trees. The cultivars Mono (pistil donor) and Butte (pollinizer) in an orchard with low soil B in Fresno, California were sprayed with B at 0, 0.8, 1.7, or 2.5 kg·ha-1 during Fall 1993. Pollen viability as indicated by the fluorescein diacetate method (FDA) was >85% and was not affected by field-applied B, however, in vivo pollen germination and tube growth were enhanced by foliar-applied B. More effect of applied B on in vivo growth appeared as pollen tubes progressed toward the ovary. For in vitro germination, foliar-applied B reduced bursting of tubes, and addition of B to the culture media significantly increased pollen germination and pollen tube growth.

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José Manuel Alonso and Rafael Socias i Company

Pollen tube growth after selfing was studied in four almond (Prunus amygdalus Batsch) families derived from crosses between self-compatible `Tuono' and self-incompatible `Ferragnès' and `Ferralise' 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 `Ferralise' 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 `Ferragnès'. This low level of self-compatibility expression observed in some `Ferralise' seedlings may be due to the inbreeding present in `Ferralise'. 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 `Tuono.'

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Yan Shi and D. H. Byrne

A standardized screening procedure for tolerance to bicarbonate-induced Fe chlorosis using a commercial fertilizer mix (Plantex) as the nutrient source, high solution pH (8.5) and 1.5 m m bicarbonate to simulate a calcareous soil situation was used with a 1 vermiculite:1 perlite (v/v) support media, small pots and topping (pinching back the tops of shoots). The tolerance level of peach [Prunus persica (L.) Batsch] rootstock could be assessed by leaf visual-chlorosis ratings and Spad-502 chlorophyll readings instead of extractable leaf-chlorophyll concentration or plant Fe concentration. Although most of the tolerant genotypes had almond [P. amygdalus (Mill.) D.A. Webb] in their parentage, a few peaches (`Swat', NJ672281007) showed high to moderate levels of tolerance.

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Patrick H. Brown

Concentrations of N, P, K, Ca, Mg, B, Fe, Cu, Zn, and Mn in mature commercial fig (`Calimyrna'; `Sari Lop') leaves are presented throughout the growing season. These data can be used as preliminary norms for the interpretation of tree nutrient status for high-yielding commercial fig orchards. In comparison with other deciduous tree crops growing in the same regions {almond [Prunus amygdalus Batsch syn. P. dulcis (Mill) D.A. Webb], walnut (Juglans regia L.), peach [Prunus persica (L.) Batsch]}, productive fig trees have relatively low leaf N, P, and K concentrations (2.1%, 0.1%, and 1.0% dry weight, respectively) in July, although tissue Mn and Ca concentrations often exceed those typically found in other deciduous species growing in the same soils. Seasonal variations in fig leaf nutrient concentrations are similar to those of other tree crops. Marked declines in tissue K and N concentrations toward the end of the season may indicate a need for supplemental N and K fertilization in highly productive orchards. The potential for K deficiency in fig also is indicated by the generally lower leaf K concentrations in the low-vigor orchards examined.