scholarly journals Photosynthesis of Blueberry Leaves as Affected by Septoria Leaf Spot and Abiotic Leaf Damage

Plant Disease ◽  
2004 ◽  
Vol 88 (4) ◽  
pp. 397-401 ◽  
Author(s):  
I. Roloff ◽  
H. Scherm ◽  
M. W. van Iersel
Keyword(s):  
Leaf Area ◽  
Disease Severity ◽  
Leaf Spot ◽  
Abiotic Factors ◽  
Lesion Size ◽  
Leaf Conductance ◽  
Yield Potential ◽  
Leaf Spots ◽  
Virtual Lesion ◽  
Septoria Leaf Spot

Leaf spots caused by fungal pathogens or abiotic factors can be prevalent on southern blueberries after harvest during the summer and fall, yet little is known about how they affect physiological processes that determine yield potential for the following year. In this study, we measured CO2 assimilation and leaf conductance on field-grown blueberry plants affected by Septoria leaf spot (caused by Septoria albopunctata) or by edema-like abiotic leaf blotching. Net assimilation rate (NAR) on healthy leaves varied between 6.9 and 12.4 μmol m-2 s-1 across cultivars and measurement dates. Infection by S. albopunctata had a significant negative effect on photosynthesis, with NAR decreasing exponentially as disease severity increased (R2 ≥0.726, P < 0.0001). NAR was reduced by approximately one-half at 20% disease severity, and values approached zero for leaves with >50% necrotic leaf area. There was a positive, linear correlation between NAR and leaf conductance (R2 ≥ 0.622, P < 0.0001), suggesting that the disease may have reduced photosynthesis via decreased CO2 diffusion into affected leaves. Estimates of virtual lesion size associated with infection by S. albopunctata ranged from 2.8 to 3.1, indicating that the leaf area in which photosynthesis was impaired was about three times as large as the area covered by necrosis. For leaves afflicted by edema-like damage, there also was a significant negative relationship between NAR and affected leaf area, but the scatter about the regression was more pronounced than in the NAR-disease severity relationships for S. albopunctata (R2 = 0.548, P < 0.0001). No significant correlation was observed between leaf conductance and affected area on these leaves (P = 0.145), and the virtual lesion size associated with abiotic damage was significantly smaller than that caused by S. albopunctata. Adequate carbohydrate supply during the fall is critical for optimal flower bud set in blueberry; therefore, these results document the potential for marked yield losses due to biotic and abiotic leaf spots.

scholarly journals Survival Analysis of Time to Abscission of Blueberry Leaves Affected by Septoria Leaf Spot

2005 ◽  
Vol 95 (1) ◽  
pp. 108-113 ◽  
Author(s):  
P. S. Ojiambo ◽  
H. Scherm
Keyword(s):  
Survival Analysis ◽  
Disease Severity ◽  
Leaf Spot ◽  
Accelerated Failure Time Model ◽  
Yield Potential ◽  
Parameter Estimates ◽  
Disease Progress ◽  
Assessment Period ◽  
Starting Point ◽  
Septoria Leaf Spot

In the southeastern United States, Septoria leaf spot, caused by Septoria albopunctata, can result in premature defoliation of blueberry plants during summer and fall, thereby reducing yield potential for the following year. The effects of disease severity and leaf attributes (leaf age and leaf location in the canopy) on the dynamics (timing and extent) of defoliation were quantified in field plots of Premier rabbiteye blueberry (Vaccinium ashei) in 2002 and 2003. In each year, 50 shoots were selected for assessment in early spring, and all leaves on these shoots (n = 410 and 542 in 2002 and 2003, respectively) were monitored individually for disease progress and time of abscission at 3- to 10-day intervals throughout the season. In both years, disease progress was characterized by an exponential increase in disease severity up to late September, followed by a decline toward the end of the assessment period in late November. Defoliation was sporadic up to late August, followed by more rapid and sustained levels of leaf loss. Abscission of severely infected leaves could explain the decline in disease severity toward the end of the season. Final disease severity (i.e., disease severity on the last assessment date before leaf drop) was highest for leaves that abscised early and lowest for leaves that had not abscised by the end of the assessment period. Survival analysis revealed that older leaves (located on the lower halves of shoots) and leaves with high levels of disease (≥5 spots/leaf at the time of fruit harvest in mid-June) abscised significantly (P < 0.0001) earlier than younger leaves and leaves with lower disease severity. Relative to their respective reference groups, mean times to abscission were ≈2 weeks shorter for the older leaf group and ≈3 weeks shorter in the leaf group afflicted by high disease severity. When an accelerated failure time model was fitted to the data, the resulting parameter estimates indicated that each additional leaf spot present at harvest accelerated time to leaf abscission (expressed using late August as a starting point) by 1.9 and 4.5% in 2002 and 2003, respectively. Leaf location in upper or lower portions of the canopy had no significant effect on time to abscission (P > 0.05).

scholarly journals CONTROL OF SEPTORIA LEAF SPOT OF PISTACHIO (PISTACIA VERA)

HortScience ◽  
1994 ◽  
Vol 29 (12) ◽  
pp. 1408f-1409
Author(s):  
Robert E. Call ◽  
Michael E. Matheron
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Pistacia Vera ◽  
Apparent Effect ◽  
Leaf Spots ◽  
Crop Maturity ◽  
Experimental Plots ◽  
Septoria Leaf Spot

Studies were established in 1992 and 1993 in a mature commercial pistachio orchard to determine the effectiveness of several fungicides for control of septoria leaf spot (Septoria pistaciurum). Fungicide treatments used in 1992 were Bravo 720F at 3.0 lbs./A (ai.) and 4.5 lbs./A a.i.; Kocide 101 50W at 8.0 lbs./A a.i. plus Benlate 50W at 1.0 lb./A a.i. Fungicide treatments in 1993 were Bravo 825 WDG at 3.0 and 4.5 lbs./A a.i. and Benlate 50W at 2.0 lbs./A a.i. Treatment replications consisted of two treated trees separated by nontreated trees within the row and nontreated tree rows dividing treated rows. At crop maturity, disease severity was determined by counting the number of leaf spots caused by septoria on ten leaves collected at random from each of the two trees of each replicated plot. All treatments significantly reduced disease severity compared to trees receiving no fungicide treatments. Experimental plots were too small to detect any apparent effect of fungicide treatments on yield. Leaves around nut clusters not receiving fungicide treatments were senescent at crop maturity, while leaves on treated trees showed no sign of senescence.

scholarly journals Septoria Leaf Spot Reduces Flower Bud Set and Yield Potential of Rabbiteye and Southern Highbush Blueberries

Plant Disease ◽  
2006 ◽  
Vol 90 (1) ◽  
pp. 51-57 ◽  
Author(s):  
P. S. Ojiambo ◽  
H. Scherm ◽  
P. M. Brannen
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Field Trials ◽  
Fruit Weight ◽  
Early Spring ◽  
Yield Potential ◽  
Flower Bud ◽  
Bud Set ◽  
Southern Highbush ◽  
Septoria Leaf Spot

In field trials on Premier rabbiteye blueberry, individual shoots were selected and tagged in the fall of 2001, 2002, and 2003 to quantify the effects of Septoria leaf spot severity and disease-induced premature defoliation on flower bud set and return yield. Experiments were carried outsimilarly on Bluecrisp southern highbush blueberry using shoots tagged after fruit harvest in the summer of 2002 and 2003. Leaves on the distal 20-cm segments of these shoots were monitored for disease severity (number of spots per leaf) through the remainder of the growing season; at the same time, defoliation (expressed as the proportion of nodes with missing leaves) was recorded for each of the shoot segments. Flower bud set was assessed subsequently in winter or early spring, and berries were harvested as they matured the following summer to determine return yield. For both cultivars, higher flower bud numbers were more likely to occur on shoots with lower disease levels the previous fall (P ≤ 0.0462 based on a Kolmogorov-Smirnov test). The data further showed that flower bud set potential (i.e., the maximum number of buds on shoots within a given disease severity range) decreased linearly as disease severity increased (r2 ≥ 0.926, P ≤ 0.0005). Based on the slope of this relationship, flower bud set potential decreased by one bud per shoot as disease severity the previous fall increased by 18 and 12 spots per leaf for Premier and Bluecrisp, respectively. Relationships between yield and disease variables were similar to those of flower bud numbers and disease, except that the decrease in yield potential (i.e., the maximum fruit weight per shoot within a given disease severity range) was less gradual than for flower bud set potential. On Premier, yield potential dropped markedly and significantly as disease severity the previous fall exceeded about 50 to 60 spots per leaf on average (P < 0.0001 based on a Kruskal-Wallis test). Evidence for such a threshold effect was weaker on Bluecrisp, presumably because of the lower number of data points for this cultivar combined with lower yields due to poor pollination.

scholarly journals Heritability of peach tree resistance to bacterial leaf spot

2017 ◽  
Vol 52 (5) ◽  
pp. 366-369 ◽  
Author(s):  
André Luiz Varago ◽  
Idemir Citadin ◽  
Marcos Robson Sachet ◽  
Gener Augusto Penso ◽  
Maria do Carmo Bassols Raseira
Keyword(s):  
Leaf Area ◽  
Disease Severity ◽  
Leaf Spot ◽  
Field Conditions ◽  
Broad Sense Heritability ◽  
Peach Tree ◽  
Bacterial Leaf Spot ◽  
Tree Resistance ◽  
Leaf Area Duration ◽  
Xanthomonas Arboricola

Abstract: The objective of this work was to evaluate the broad-sense heritability reaction to bacterial leaf spot (Xanthomonas arboricola pv. pruni), in peach tree populations obtained from directed crosses. Disease severity and defoliation of the genotypes were evaluated in field conditions, with posterior measurement of the healthy leaf area duration (HAD). The observed average heritability (0.51) indicates that the use of the evaluated genitors can be effective for the development of cultivars with higher resistance to the disease.

scholarly journals Temperature and incubation period affect Septoria pistaciarum conidium germination: disease forecasting and validation

2021 ◽  
Vol 60 (1) ◽  
pp. 113-117
Author(s):  
Thomas THOMIDIS ◽  
Konstantinos MICHOS ◽  
Fotis CHATZIPAPADOPOULOS ◽  
Amalia TAMPAKI
Keyword(s):  
Incubation Period ◽  
Disease Severity ◽  
Leaf Spot ◽  
Disease Risk ◽  
Generic Model ◽  
High Disease Severity ◽  
Conidium Germination ◽  
Effects Of Temperature ◽  
Important Disease ◽  
Septoria Leaf Spot

Septoria leaf spot is an important disease of pistachio trees in Greece. This study aimed to determine effects of temperature and the incubation period on germination of conidia of Septoria pistaciarum, and to evaluate a generic model to forecast pistachio leaf spot under the field conditions of Aegina Island, Greece. The optimum temperature for conidium germination was 23°C, and germination was inhibited at 35 and 4°C. At constant temperature of 23°C, conidia commenced germination after 9 h. The predictive model indexed disease risk close to 100 at 10 May at two locations (Rachi Moschona and Vigla) in 2017, and first leaf spot symptoms were observed on 17 May. Moderate to high disease severity (>25% leaves infected) were observed in unsprayed trees at the end of May. In 2018, the model indexed risk close to 100 on 9 May at Rachi Moschona, and first symptoms were observed on 18 May. Moderate to high disease severity (>25% leaves infected) were observed in unsprayed trees on 25th of May. This study has shown that the forecasting model can be used in Aegina Island, Greece, to predict the severity of Septoria leaf spot of pistachio.

Directional Spread of Septoria Leaf Spot in Tomato Rows

Plant Disease ◽  
1997 ◽  
Vol 81 (3) ◽  
pp. 272-276 ◽  
Author(s):  
S. K. Parker ◽  
F. W. Nutter ◽  
M. L. Gleason
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Logistic Model ◽  
Disease Spread ◽  
Infection Rates ◽  
Fresh Market ◽  
Tomato Plants ◽  
Septoria Leaf Spot

Disease severity of Septoria leaf spot in rows of fresh-market tomato plants that were not staked was assessed in 1992 and 1993 following inoculation of the center plant in each row. Both temporal disease increase and spatial disease gradients were best described by the logistic model. Apparent infection rates for Septoria leaf spot epidemics averaged 0.282 day-1 (SE = 0.015, r2 = 0.96, P < 0.0001) in 1992 and 0.260 day-1 (SE = 0.011, r2 = 0.96, P < 0.0001) in 1993. Apparent infection rates remained relatively constant at increasing distances from initial foci. Estimated values for disease gradient slopes 3 to 5 weeks after inoculation ranged from -0.26 to -1.05 m-1. Velocities of disease spread ranged from 0.3 to 1.3 m/day. Results of analysis of disease severity data for these 2 years suggest that Septoria leaf spot epidemics can develop at rapid rates, but steep disease gradients limit the velocity of spread.

scholarly journals Optimum Sample Size for Determining Disease Severity and Defoliation Associated with Septoria Leaf Spot of Blueberry

Plant Disease ◽  
2006 ◽  
Vol 90 (9) ◽  
pp. 1209-1213 ◽  
Author(s):  
P. S. Ojiambo ◽  
H. Scherm
Keyword(s):  
Sample Size ◽  
Leaf Area ◽  
Disease Severity ◽  
Total Variation ◽  
Leaf Spot ◽  
Variance Components ◽  
Optimum Sample Size ◽  
The Mean ◽  
Time Required ◽  
Optimum Sample

In a 3-year field study, Premier rabbiteye blueberry plants were sampled at three hierarchical levels (leaf, shoot, and bush) to assess severity of Septoria leaf spot (caused by Septoria al-bopunctata) and incidence of defoliation. A positive linear relationship (R 2 = 0.977, P < 0.0001, n = 2127) was observed between the number of spots per leaf and percent necrotic leaf area, both assessed on individual leaves in mid- to late October. For data summarized at the shoot level, percent defoliation increased nonlinearly (R 2 = 0.729, P < 0.0001, n = 224) as disease severity increased, with a rapid rise to an upper limit showing little change in defoliation above 60 spots per leaf. Variance components were calculated for disease severity to partition total variation into variation among leaves per shoot, shoots per bush, and bushes within the field. In all cases, leaves per shoot and shoots per bush accounted for >90% of the total variation. Based on the variance components and linear cost functions (which considered the time required to assess each leaf and select new shoots and bushes for assessment), the optimum sample size for assessing disease severity as number of spots per leaf (with an allowable variation of 20% around the mean) was 75 leaves, one each selected from three shoots per bush on 25 bushes (total time required for assessment: 36.1 min). For disease severity expressed as percent necrotic leaf area, the corresponding values were 144 leaves, two each sampled from three shoots per bush on 24 bushes (total time required: 21.7 min). Thus, given the strong correlation between the two disease variables demonstrated in this study, visual assessment of percent necrotic area was the more efficient method. With an allowable variation of 10% around the mean, a sample of 27 shoots from nine bushes was the optimum sample size for assessing defoliation across the 3 years.

scholarly journals Temporal Progress of Septoria Leaf Spot on Rabbiteye Blueberry (Vaccinium ashei)

Plant Disease ◽  
2005 ◽  
Vol 89 (10) ◽  
pp. 1090-1096 ◽  
Author(s):  
P. S. Ojiambo ◽  
H. Scherm
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Developmental Stages ◽  
Disease Incidence ◽  
Disease Onset ◽  
Parameter Estimates ◽  
Vaccinium Ashei ◽  
Leaf Emergence ◽  
Temporal Progress ◽  
Septoria Leaf Spot

Septoria leaf spot, caused by Septoria albopunctata, is an important disease on blueberry in the southeastern United States, yet its epidemiology is largely unknown. Disease severity and dissemination of pycnidiospores were monitored from 2002 to 2004 in a planting of susceptible Premier rabbiteye blueberry to characterize the temporal progress of the disease and determine the effect of inoculum dynamics and selected leaf attributes on disease development. Disease onset was observed between late April and mid-June, followed by a rapid increase in disease severity until mid- to late September; thereafter, disease severity decreased until the end of the season due to abscission of severely infected leaves. A logistic model was fitted to disease severity data using nonlinear regression, and parameter estimates were used to compare the effects of leaf position on the shoot and shoot location in the canopy on disease progress. Based on this model, the highest absolute rate of disease increase and the highest upper asymptote of disease severity were predicted for leaves in intermediate positions on the shoot and for shoots in the lower canopy. Data collected with funnel spore samplers showed that splash-dispersed pycnidiospores of S. albopunctata were available throughout most of the period from April through late October. Final disease severity on individual leaves was more strongly correlated with cumulative spore numbers throughout the entire season (from leaf emergence to the end of the assessment period in November) than with cumulative spore numbers during shorter periods around the time of leaf emergence; this suggests that infection is not limited to young, expanding leaves, but rather that leaves at all developmental stages can become infected by S. albopunctata seasonlong. Disease incidence on leaves of potted trap plants exposed to natural inoculum in the field during rain events in 2003 and 2004 was >70.0% irrespective of leaf developmental stage at the time of exposure. Taken together, the results of this study indicate that inoculum of S. albopunctata is present throughout most of the growing season and that infection can occur season-long on leaves of any age, giving rise to a polycyclic epidemic.

Temporal Dynamics of Septoria Leaf Spot of Blueberry and its Relationship to Defoliation and Yield

2007 ◽  
Vol 8 (1) ◽  
pp. 68
Author(s):  
Peter S. Ojiambo ◽  
Harald Scherm ◽  
Phillip M. Brannen
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Temporal Dynamics ◽  
Field Trials ◽  
Flower Bud ◽  
Bud Set ◽  
Crop Development ◽  
Septoria Leaf Spot

In field trials on Premier rabbiteye blueberry in Georgia, onset of Septoria leaf spot (caused by Septoria albopunctata) occurred between late April and mid-June. Average disease severity increased sigmoidally until late September, after which it declined due to the abscission of severely affected leaves. Disease severity was highest on early-emerging leaves and on those located on shoots closer to the ground. Pycnidiospore inoculum was present throughout the season, and leaves became infected by S. albopunctata season-long. Disease severity, defoliation, flower bud set, and next season's yield were interrelated; severely affected leaves abscised earlier in the fall than those with low disease severity, and shoots with severely diseased leaves and/or high levels of defoliation had reduced flower bud set. Furthermore, such shoots consistently had low yields the following year. The results form the basis for identifying disease levels that can be tolerated during specific periods of crop development without negatively impacting flower bud set and yield. Accepted for publication 15 March 2007. Published 26 July 2007.

Reemergence of Septoria leaf spot caused by Septoria cannabis on hemp in the Kentucky

Plant Disease ◽  
2021 ◽  
Author(s):  
Mostafa Rahnama ◽  
Desiree Szarka ◽  
Hua Li ◽  
Ed Dixon ◽  
Lisa Castlebury ◽  
...  
Keyword(s):  
Phylogenetic Analysis ◽  
Leaf Spot ◽  
Sequence Data ◽  
Morphological Characteristics ◽  
Gene Sequences ◽  
Leaf Spots ◽  
New Information ◽  
The Us ◽  
Septoria Leaf Spot

Hemp reemerged in 2014 after being illegal for over 50 years and restricted for 90 years. Today, hemp is primarily grown for production of cannabidiol (CBD) with limited acreage dedicated to fiber. One of the most frequent and destructive leaf spot diseases of hemp cultivars grown for CBD is Septoria leaf spot. Symptoms are mostly observed in lower leaves and inner canopy. Leaf spots begin as small, irregular, brown to gray spots that rapidly expand to about 5.0 to 7.5 mm in diameter. Pycnidia are scattered, round, dark brown to black in color and measure 38.8 to 145.0 μm in diameter. Conidia are hyaline, curved but occasionally straight, pointed at the apex, and contain 3 to 4 septa. Morphological characteristics were like those reported for S. cannabis. Gene sequences from seven diagnostic loci (EF, TUB, RPB2, LSU, ITS, ACT and CAL) did not match any published accessions. There are no published sequences for S. cannabis available for comparison. Phylogenetic analysis of concatenated sequences showed that isolates from hemp grouped separately from other Septoria spp. Similarity of morphological characteristics and lack of matching sequence data to other Septoria spp. led to the conclusion that isolates collected from hemp in Kentucky are S. cannabis. This new information will serve as an update for Septoria leaf spot diagnostics, especially as hemp acreage continues to increase across the US.

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