scholarly journals Pollination of English Walnuts: Practices and Problems

2000 ◽  
Vol 10 (1) ◽  
pp. 127-130
Author(s):  
William H. Krueger
Keyword(s):  
Fruit Set ◽  
Juglans Regia ◽  
Pistillate Flower ◽  
San Joaquin Valley ◽  
Pollen Load ◽  
Fruit Drop ◽  
Flower Abortion ◽  
English Walnut ◽  
Cultivar Susceptibility ◽  
Pollen Shed

English walnut (Juglans regia, L.) is a monoecious species bearing staminate and pistillate flowers separately on the same tree. Walnuts are generally self-fruitful, cross-compatible and dichogamous, having incomplete overlap of pollen shed and female receptivity. It is this characteristic which led to the recommendation that about 10% of the trees in a commercial planting be a cultivar with a pollen shed period overlapping pistillate flower receptivity of the main cultivar. Excessive pollen load has been implicated in the `Serr' cultivar in pistillate flower abortion (PFA), the loss of the female flowers early in the season before fruit drop due to lack of pollination. PFA can be reduced and yield improved in `Serr' orchards by reducing pollen load. This can be accomplished by pollinizer removal, or catkin removal at the beginning of pollen shed by mechanical shaking. In years of significant bloom overlap between staminate and pistillate bloom, PFA can be further reduced and yield improved by removing `Serr' catkins. PFA occurs to a lesser extent in other cultivars such as `Chico', `Chandler', `Vina' and `Howard'. This information has led to the reevaluation of pollinizer recommendations. Research focused on optimum pollinizer levels in `Chandler', a cultivar of increasing importance to the California walnut industry, has been inconclusive. Lack of pollinizers may impact yields to a greater extent in the in the northern San Joaquin Valley and Sacramento Valley than in the southern San Joaquin Valley. In any case the previously recommended 10% appears to be excessive. Two to three percent is probably adequate to limit losses due to lack of pollination without resulting in excessive PFA, and is currently being recommended by extension farm advisors and specialists. Factors to consider when determining the number of pollinators to plant include: cultivar susceptibility to PFA, walnut pollen load in the area and local pollination and fruit set experiences.

First Report of Alternaria alternata and Fusarium spp. Causing Brown Apical Necrosis in Walnut Fruit in Southern Chile

2021 ◽  
Author(s):  
Ernesto Antonio Moya-Elizondo ◽  
María Jose Lagos ◽  
Juan G. San Martín ◽  
Braulio E. Ruiz
Keyword(s):  
Alternaria Alternata ◽  
Fungal Pathogens ◽  
Juglans Regia ◽  
Bacterial Pathogen ◽  
Southern Chile ◽  
Fusarium Spp ◽  
First Report ◽  
Fruit Drop ◽  
English Walnut ◽  
Apical Necrosis

This is the first report of Alternaria alternata and Fusarium spp. causing brown apical necrosis (BAN) in walnut fruit in southern Chile. English walnut (Juglans regia L.) is the second most widely grown fruit in Chile. The bacterial pathogen Xanthomonas arboricola pv. juglandis affects walnut production in Chile and has been associated with apical necrosis symptom and premature fruit drop; this research focused on determining if fungal pathogens were associated with this damage. The presence of BAN in commercial walnut orchards in southern Chile reveals the need for improved phytosanitary programs to control this disease.

scholarly journals Occurrence and Etiology of Brown Apical Necrosis on Persian (English) Walnut Fruit

Plant Disease ◽  
2002 ◽  
Vol 86 (6) ◽  
pp. 599-602 ◽  
Author(s):  
A. Belisario ◽  
M. Maccaroni ◽  
L. Corazza ◽  
V. Balmas ◽  
A. Valier
Keyword(s):  
Complex Disease ◽  
Juglans Regia ◽  
Disease Symptoms ◽  
Brown Patch ◽  
Fruit Drop ◽  
Diseased Fruit ◽  
Pathogenicity Tests ◽  
English Walnut ◽  
Apical Necrosis

In 1998, a severe fruit drop was observed in Italy, principally on cv. Lara Persian (English) walnut (Juglans regia). Dropped fruit showed a brown patch at the blossom end and blackening and rot of inner tissues. The disease, called brown apical necrosis (BAN), was investigated on fruit collected in Italy and France in 1999. In 2000, studies were carried out in three walnut orchards located in Italy and in France to substantiate the etiology of BAN. Isolations performed from inner diseased fruit tissues yielded several fungi, in decreasing frequency of isolation: species of Fusarium and Alternaria, and one species each of Cladosporium, Colletotrichum, and Phomopsis. However, only Fusarium spp. were recovered from stigmas of BAN-affected fruit. The fungi associated with BAN-diseased fruit and species composition differed among locations and over time, confirming results obtained in previous investigations. The species of Fusarium used in pathogenicity tests reproduced BAN-disease symptoms when inoculated on fruit, whereas an Alternaria alternata isolate caused only limited necrosis of the style. However, the role of the other fungi commonly isolated from BAN-diseased fruit remains to be defined. The walnut blight pathogen, Xanthomonas arboricola pv. juglandis, occasionally was isolated from BAN-diseased fruit. No correlation was found between the extent of external brown patches and the size of inner lesions. Repeated isolations from and inoculations of fruit demonstrated that BAN can be considered a complex disease, and the inner infections originate from the style of the fruit.

scholarly journals Streptomycin Applications to Control Walnut Blight Disease Can Prevent Fertilization and Increase Fruit Drop

HortScience ◽  
2002 ◽  
Vol 37 (6) ◽  
pp. 940-942 ◽  
Author(s):  
V.S. Polito ◽  
K. Pinney ◽  
R. Buchner ◽  
W. Olson
Keyword(s):  
Pollen Germination ◽  
Xanthomonas Campestris ◽  
Juglans Regia ◽  
Pistillate Flower ◽  
Control Treatment ◽  
Bacterial Disease ◽  
Bloom Period ◽  
Fruit Drop ◽  
Walnut Blight

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.

scholarly journals Apical Necrosis and Premature Drop of Persian (English) Walnut Fruit Caused by Xanthomonas arboricola pv. juglandis

Plant Disease ◽  
2011 ◽  
Vol 95 (12) ◽  
pp. 1565-1570 ◽  
Author(s):  
Concepció Moragrega ◽  
Josep Matias ◽  
Neus Aletà ◽  
Emilio Montesinos ◽  
Mercé Rovira
Keyword(s):  
Growing Season ◽  
Fusarium Spp ◽  
Disease Epidemiology ◽  
Fruit Drop ◽  
Major Increase ◽  
Xanthomonas Arboricola ◽  
English Walnut ◽  
Cultivar Susceptibility ◽  
Apical Lesions ◽  
Apical Necrosis

Etiological and epidemiological aspects of apical necrosis of walnut fruit were studied on cultivars Chandler, Franquette, and Hartley in a Spanish walnut orchard during 2007 and 2008. Affected fruit showed brown necrosis beginning at the blossom end of nuts; these symptoms differed from lesions of common blight of walnut (Xanthomonas arboricola pv. juglandis). X. arboricola pv. juglandis was consistently isolated from apical lesions throughout the growing season. Field isolates reproduced symptoms observed in the orchard when inoculated on immature detached walnut fruit in the laboratory. Sporadic occurrence of Fusarium spp. and Alternaria spp., mainly in dropped fruit, was attributed to secondary colonization of apical lesions that were originally caused by X. arboricola pv. juglandis. Apical necrosis and common blight were similar in disease epidemiology and cultivar susceptibility; a major increase in epidemics occurred at initial fruit development, and cvs. Chandler and Hartley were more affected than cv. Franquette. Our results suggest that apical necrosis is a new manifestation of walnut blight characterized by distinct symptoms and severe premature fruit drop.

scholarly journals Relationship between Fruiting, Specific Leaf Weight, and Subsequent Spur Productivity in Walnut

1991 ◽  
Vol 116 (3) ◽  
pp. 426-429 ◽  
Author(s):  
I. Klein ◽  
S.A. Weinbaum ◽  
T.M. DeJong ◽  
T.T. Muraoka
Keyword(s):  
Fruit Set ◽  
Light Exposure ◽  
Juglans Regia ◽  
Pistillate Flower ◽  
Kernel Weight ◽  
Specific Leaf Weight ◽  
Shell Weight ◽  
Unit Leaf ◽  
Leaf Weight ◽  
Carry Over

Localized and carry-over effects of light exposure [as inferred from specific leaf weight (SLW)] on spur viability, flowering, and fruit set were monitored in selected spurs throughout walnut (Juglans regia, cvs. Serr and Hartley) tree canopies. Shaded spurs (i.e., average SLW <4 mg·cm-2) were predisposed to die during the winter, and spur mortality was accentuated among spurs that had borne fruit that season. More catkins and distillate flowers per spur were characteristic of the more exposed positions within the canopy (as indicated by SLW) during the previous summer and following an “off” year. In exposed `Serr' canopy positions (SLW >5 mg·cm-2), catkin and Pistillate flower maturation was reduced in fruiting spurs by 60% and 30%, respectively, in the subsequent year relative to vegetative spurs. In `Hartley', the number of distillate flowers was also reduced by 35% on spurs that fruited the previous year relative to spurs that had been vegetative. Maximum rates of return bloom and fruit set were evident in spurs exhibiting the highest SLW and N per unit leaf area (NA), specific to each cultivar. Among spurs of both cultivars, distillate flower development was more sensitive to shading in the previous season than was catkin development. Shell weight of `Serr' varied positively with SLW, but kernel weight, fruit N, and oil concentration did not vary “with SLW in either cultivar.

scholarly journals Foliar Application of Zinc and Boron Improves Walnut Vegetative and Reproductive Growth

2011 ◽  
Vol 21 (2) ◽  
pp. 181-186 ◽  
Author(s):  
Karim Keshavarz ◽  
Kourosh Vahdati ◽  
Mahmoud Samar ◽  
Behzad Azadegan ◽  
Patrick H. Brown
Keyword(s):  
Vegetative Growth ◽  
Pollen Germination ◽  
Fruit Set ◽  
Foliar Application ◽  
Juglans Regia ◽  
Foliar Spray ◽  
Pistillate Flower ◽  
Nutrient Concentrations ◽  
Kernel Length ◽  
Chlorophyll Index

An experiment was conducted in a persian walnut (Juglans regia) orchard in the north of Iran to evaluate the effects of zinc (Zn) as zinc sulfate and/or boron (B) as boric acid in foliar spray with different concentrations and combinations. Three B and three Zn concentrations (0, 174, and 348 mg·L−1 for B and 0, 1050, and 1750 mg·L−1 for Zn) were applied either independently or in combination. Leaf nutrient concentrations, pollen germination, fruit set, leaf chlorophyll index, nut and kernel characteristics, vegetative growth, nut weight, and nut yield were measured to assess the effects of treatments. The results showed that all B and Zn applications and combinations had a significant effect on all traits except nut and kernel diameter, shell percent, husk thickness, and pistillate flower abscission (PFA). Pollen germination, fruit set, vegetative growth, nut weight, kernel percent, nut and kernel length, and chlorophyll index were highest when B and Zn were applied simultaneously at 174 and 1050 mg·L−1 concentrations, respectively.

scholarly journals 323 REDUCING POLLEN LOAD MINIMIZES PISTILLATE FLOWER ABSCISSION AND IMPROVES COMMERCIAL ENGLISH WALNUT YIELDS UNDER FIELD CONDITIONS

HortScience ◽  
1994 ◽  
Vol 29 (5) ◽  
pp. 476f-477
Author(s):  
G. S. Sibbett ◽  
V. Polito ◽  
P. Catlin ◽  
G. McGranahan ◽  
J. Grant ◽  
...  
Keyword(s):  
Field Experiments ◽  
Pistillate Flower ◽  
Field Conditions ◽  
Pollen Load ◽  
Male And Female ◽  
English Walnut ◽  
Male Flowers ◽  
Flower Abscission

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.

Hazelnut Pollination

HortScience ◽  
1998 ◽  
Vol 33 (3) ◽  
pp. 555d-555
Author(s):  
J.L. Olsen ◽  
S.A. Mehlenbacher ◽  
A.N. Azarenko
Keyword(s):  
Single Gene ◽  
Pistillate Flower ◽  
Temperature Dependent ◽  
Multiple Alleles ◽  
Anisogramma Anomala ◽  
Molecular Aspects ◽  
Management Recommendations ◽  
Pollen Shed ◽  
Resistant Genotypes ◽  
Pollination And Fertilization

Hazelnuts are wind-pollinated, monoecious, mostly dichogamous, and self-incompatible of the sporophytic type. About 90% of the cultivars studied are protandrous. Anthesis of the pistillate flower is temperature-dependent and occurs from December through February, with its peak in January. Stigmatic surfaces may remain receptive for up to 3 months. Four to 5 months separate pollination and fertilization of the ovule, which usually occurs between mid-May and the end of June in Oregon. A 10% pollinizer density has been the standard, with a recommended distance of <20 m between the main cultivar and the nearest pollinizer. Two or three different pollinizer varieties with different times of pollen shed are recommended. The Oregon hazelnut industry is presently combating the fungal disease, Eastern Filbert Blight, Anisogramma anomala. Part of the current management recommendations are to reduce the susceptible pollinizer varieties to a density of around 5%, and then gradually replace those left with immune or more-resistant genotypes. Recent research by S.A. Mehlenbacher refined methods of using fluorescense microscopy to quickly determine genotype compatibility. The self-incompatiblity is controlled by a single gene with multiple alleles. The biochemical, physiological, and molecular aspects of sporophytic self-incompatiblity are being research by A.N. Azarenko.

Sign in / Sign up

Export Citation Format

Share Document