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Abstract
Pistillate flowers from walnut trees having > 80% pistillate flower abscission (PFA) were examined from the time of anthesis until shortly before abscission. In addition to normally developing flowers, two types of abortive flowers were found. One abnormal flower type, seen in only two cases, lacked a developed embryo sac and had cellular degeneration in the nucellus. The second type of damaged flowers, which were more commonly observed, had apparently normal development of the nucelli and embryo sacs, but cell and tissue necrosis became evident beginning at the tip of the stigma, in the integuments, and throughout the placental evaginations. No cell or tissue damage was observed until after ovary growth in these flowers had stopped. We conclude that this second type of damage is associated with PFA.
We investigated the basis for fruit drop in walnut (Juglans regia L.) following bloom period applications of streptomycin as a potential control treatment for walnut blight, a bacterial disease incited by Xanthomonas campestris pv. juglandis (Pierce) Dye. Experiments were conducted on streptomycin-treated field plots of `Vina' walnut. Four streptomycin treatments were applied at different times relative to anthesis. Fruit from all treatments grew similarly for four weeks following anthesis when high levels of fruit abscission began to occur in the treatment sprayed during the bloom period. Microscopy revealed that in this treatment ovules failed to develop normally, and neither embryo nor endosperm developed. The pattern of fruit development and timing of fruit drop following streptomycin treatment at bloom is similar in all ways to that of unpollinated walnut flowers where growth appears normal until abscission occurs 3 to 5 weeks after anthesis. Pollen germination and pollen tube growth were inhibited in the bloom-period treatments. Pollen germination in vitro was not affected by addition of streptomycin to a germination medium. If streptomycin were to be used in a walnut blight control program, application timed to coincide with the period of pistillate bloom and pistillate flower receptivity should be avoided.
Abstract
Easy-to-root ‘Colt’ showed cell divisions leading to root initials beginning within 2 days after exposure to auxin. By contrast, juvenile (i.e., 2-year-old seedling) rooting Mazzard (P. avium) and invigorated (i.e., by co-culture) rooting ‘46-1 Mazzard’ required 4 and 5 days. Root initials appeared in the phloem parenchyma in ‘Colt’ and in the cambium region in both seedling Mazzard and invigorated ‘46-1 Mazzard’. Peroxidase activity (PA) was low in shoot tips of ‘Colt’, intermediate in juvenile Mazzard, and high in adult non-rooting ‘46-1 Mazzard’. In basal shoot tissue, PA activity was low in both ‘Colt’ and invigorated ‘46-1 Mazzard’ prior to root initiation, but increased sharply when root initiation started. The appearance of root initials was associated with an increase in intensity of anodic band A for isoperoxidase.
Seventeen olive (Olea europaea L.) cultivars, including oil and table olive cultivars originating from throughout the Mediterranean area, were screened using random amplified polymorphic DNA (RAPD) markers. The results indicate that a high degree of polymorphism is evident in the olive germplasm reexamined. Forty random decamer primers were screened; seventeen of these produced 47 reproducible amplification fragments useful as polymorphic markers. Each of the 17 cultivars can be discriminated with a few primers. Results were analyzed for similarity among the cultivars and a cluster analysis was performed. These analyses revealed two main groups: one comprising primarily small-fruited cultivars grown mainly for oil production, and the other characterized by having large fruit. There was no apparent clustering of olive cultivars according to their geographic origins.
Abstract
Investigation of pollen grain germination and retention on the stigma, and pollen tube frequency in the style following compatible (cross) and incompatible (self) pollinations in ‘Nonpareil’ almond [Prunus dulcis (Mill.) D.A. Webb Syn. Prunus amygdalus Batsch.J revealed that rejection of incompatible male gametophytes occurs on the stigma as well as in the style. Self-pollinations are characterized by lower pollen grain retention on the stigma, reduced and delayed pollen germination, and, where pollen germination had occurred, a low frequency of pollen tubes growing through the style. Pollen tube growth slowed greatly after the tubes entered the ovarian locule before they reached the ovule.
Abstract
Microscopic examination of sectioned germinating olive seed (Olea europaea L.) did not reveal differences from many other seed types. No seedcoat-imposed mechanical restrictions were found during germination. The seed was 4% and the embryo 1% of the mature, whole fruit dry weight. Maximum embryo dry weight was achieved by early October. Germination was 90% when the embryo had gained 60% of its final dry weight. No dormancy factors were evident in the excised embryos.
The Random Amplified Polymorphic DNA (RAPD) technique was used to characterize 15 cultivars of pistachio (Pistacia vera L.). A total of 37 polymorphic markers were considered in this study. Each cultivar exhibited a unique molecular phenotype and, as a consequence, can be uniquely fingerprinted. A similarity and cluster analysis based on the amplified fragments produced two distinct groups which are consistent with the known geographical origin of the cultivars. Our results suggest that RAPD analysis can provide a new alternative for cultivar identification and classification of pistachio.
We have been screening olive (Olea europea L.) cultivars using the Random Amplified Polymorphic DNA (RAPD) technique. We examined 23 olive cultivars selected to represent the important olive-growing regions of the world. These include oil and table olive cultivars originating from throughout the Mediterranean area. A high degree of polymorphisms is evident in the olive germplasm we examined. Early results indicate that polymorphisms that exist within the species are sufficient to enable efficient development of RAPD markers for distinguishing olive cultivars.
The Random Amplified Polymorphic DNA (RAPD) technique was used to develop molecular markers linked to sex expression in Pistacia vera, a dioecious species. Progenies from two female parents (`Lassen' and `Kerman') pollinated by a common male parent (`Peters') were studied. Two bulks of DNA were made in each cross, one from males and one from females. DNA was extracted from each bulked sample as well as from each of the contributing individuals and from 14 additional P. vera cultivars. Twelve hundred decamer oligonucleotide primers were used to perform DNA amplification on the bulk DNA. This analysis led to the identification of one primer (OPO08) that produces a 945 bp. amplification band present only in females and absent in males. The relationship between band presence and female sex expression was conserved in every individual obtained from the two crosses and in 14 cultivars unrelated to the crosses. This band, which we propose is tightly linked to the gene(s) controlling sex determination, provides a reliable marker for sex of pistachio seedlings and should be a useful tool in pistachio breeding.
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.