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.
V.S. Polito, K. Pinney, R. Buchner, and W. Olson
J.I. Hormaza, L. Dollo, and V.S. Polito
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.
A. Fabbri, J.I. Hormaza, and V.S. Polito
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.
J.I. Hormaza, L. Dollo, and V.S. Polito
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.
A. Fabbri, J.I. Hormaza, and V.S. Polito
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.
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.
J.G. Luza, R. van Gorsel, V.S. Polito, and A.A. Kader
Fruits of mid- (`O'Henry'), late (`Airtime'), and extra-late-season (`Autumn Gem') peach [Prunus persica (L.) Batsch] cultivars were examined for changes in cell wall structure and cytochemistry that accompany the onset of mealiness and leatheriness of the mesocarp due to chilling injury. The peaches were stored at 10C for up to 18 days or at SC for up to 29 days. Plastic-embedded sections were stained by the Schiff's-periodic acid reaction, Calcofluor white MR2, and Coriphosphine to demonstrate total insoluble carbohydrates, ß-1,4 glucans, and pectins, respectively. Mealiness was characterized by separation of mesocarp parenchyma cells leading to increased intercellular spaces and accumulation of pectic substances in the intercellular matrix. Little structural change was apparent in the cellulosic component of the cell walls of these fruits. In leathery peaches, the mesocarp parenchyma cells collapsed, intercellular space continued to increase, and pectin-positive staining in the intercellular matrix increased greatly. In addition, the component of the cell walls that stained positively for ß-1,4 glucans became thickened relative to freshly harvested or mealy fruit. At the ultrastructural level, dissolution of the middle lamella, cell separation, irregular thickening of the primary wall, and plasmolysis of the mesocarp parenchyma cells were seen as internal breakdown progressed.
G.S. Sibbett, G. McGranahan, V. Polito, P. Catlin, L. Hendricks, K. Kelley, W. Coates, and J. Grant
Preliminary studies with controlled pollinations have shown that pistillate flower abscission (PFA) in walnut (Juglands spp.) is associated with heavy pollen loads on the flowers. This study measured percent pistillate flower abscission (PFA), pollen grains per flower, yield and yield efficiency on Serr walnut from trees adjoining pollinizing cvs and at sequential intervals up to 197m away in twelve orchard locations. A highly significant, negative correlation in PFA existed as distance from the foreign pollen source increased. Pollen grains per flower were highly correlated with percentage PFA. Yield and yield efficiency, measured in two of the test orchards, were positively correlated with distance from the pollen source.
G. S. Sibbett, V. Polito, P. Catlin, G. McGranahan, J. Grant, K. Kelley, B. Olson, and D. Ramos
In both laboratory and field experiments, excessive pollen has been found to be a major cause of pistillate flower abscission (PFA) and reduced yields of sensitive English Walnut cultivars (CVs) (especially “Serr”). In the field, PFA and reduced yields develop when substantial overlap of male and female walnut bloom occurs. PFA and poor yields can be further aggravated when pollenizing CV's have been included into an orchard to maximize pollen availability for the commercial CV Field experiments, conducted in 1992 and 1993, demonstrated that mechanically shaking trees to remove male flowers pre-bloom from either pollenizer CV's or the main CV reduced pollen load, PFA, and substantially improved yields.