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Article

Reaction of Mandarins to the Alternaria Brown Spot and Huanglongbing: Identification of Potential Varieties for These Diseases to Be Managed in the Field

by
Marinês Bastianel
1,
Rodrigo Martinelli
1,
Fernando Trevizan Devite
1,
Mariangela Cristofani-Yaly
1,
Rodrigo do Vale Ferreira
1,
Eduardo Sanches Stuchi
2 and
Fernando Alves de Azevedo
1,*
1
Centro de Citricultura Sylvio Moreira, Instituto Agronômico, Rod. Anhanguera, km 158, Cordeirópolis 13492-442, SP, Brazil
2
Embrapa Mandioca e Fruticultura, Cruz das Almas 44380-000, BA, Brazil
*
Author to whom correspondence should be addressed.
Horticulturae 2023, 9(6), 641; https://doi.org/10.3390/horticulturae9060641
Submission received: 27 April 2023 / Revised: 20 May 2023 / Accepted: 26 May 2023 / Published: 30 May 2023
(This article belongs to the Special Issue Advances in Citrus Pathology and Disease Management)
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Abstract

:
Mandarins occupy the third group among citrus produced in Brazil. Primarily aimed at the fresh fruit market, commercial orchards have suffered significant production losses due to the high incidence of diseases, such as the alternaria brown spot (ABS) and huanglongbing (HLB). The fact that 80% of the orchards are composed of two varieties, Ponkan mandarin and Murcott tangor, which are highly susceptible to both diseases, demands intensive chemical control of the diseases in the field, which has resulted in a significant increase in production costs and a negative environmental impact. A total of one hundred and seventy-three mandarin accessions, including several species and hybrids belonging to the Collections of the Instituto Agronômico de Campinas (IAC), were evaluated in the field in an endemic location for the diseases. Evaluations of the incidence and severity of the diseases showed a range of genotypes tolerant to ABS that could replace the current commercial varieties, mainly within the clementine and willow leaf mandarin groups. Although, with differences in incidence and susceptibility to HLB, there are no tolerant varieties to this disease, which significantly impacts the loss of fruit quality.

1. Introduction

Mandarins constitute the main group among citrus for fresh fruit consumption, covering several species of the genus Citrus and their hybrids, which have many physicochemical characteristics. The mandarin group includes common mandarins (C. reticulata), satsumas (C. × unshiu), clementines (C. × clementina), willow leaves (or Mediterranean mandarins) (C. × deliciosa), tangors (mandarin × sweet orange hybrids), and tangelos (mandarin × grapefruit hybrids), which share characteristics that make them suitable for in natura consumption, such as the ease of peeling compared to other citrus fruits and balanced flavor, among others.
Among the fruits produced worldwide, mandarins are the main ones in terms of volume. According to the FAO data for 2020 [1], the world production of this citrus group was 38.60 million t. China leads as the world’s largest producer, with a production of 23.13 million t, much higher than the other producers of Spain (2.17 mi t), Turkey (1.59 mi t), Morocco (1.37 mi t), Brazil (1.03 mi t), and Egypt (0.971 mi t). In the fruit productivity world ranking, among the ten most significant producers of mandarins, the USA is the first (33.7 t ha−1), Brazil is the eighth (18.7 t ha−1), and China is the tenth (10.4 t ha−1) [1]. Among the factors that led to this lower Brazilian productivity are those associated with phytosanitary problems [2].
The State of São Paulo (SP) led mandarin production in 2020 at around 340 thousand tons in just over 10 thousand ha, corresponding to one-third of the country’s total production. The states of Minas Gerais (MG), Paraná, and Rio Grande do Sul produced in the same year, respectively 244, 157, and 122 thousand tons of fruit [3]. These data demonstrate that more than 60% of Brazilian production is concentrated in the country’s southeastern region, mainly in the SP and MG states.
Interestingly, when analyzing agricultural production data in the country, a decrease in area and production volume has been observed in recent years. In 2005, for example, production was more than 1230.0 tons in 61.0 thousand ha. In 2020, there was a reduction of 10% in the area (55.5 thousand ha) and 16% in the volume produced (1.03 thousand tons) [3].
Among the factors involved in the cultivated area decline, one can highlight the rise in production costs given the phytosanitary problems that occurred in the country during this period that mainly impacted the alternaria brown spot (ABS) and huanglongbing (HLB; ex-greening), which may have demotivated the maintenance of orchards since the main mandarin varieties planted in Brazil, Ponkan mandarin and Murcott tangor, are highly susceptible to these diseases.
The ABS is caused by the fungus Alternaria alternata (Fr.) Keissl, whose germinate spores infect an alternaria citri toxin (ACT) that kills host cells, causing necrotic lesions on leaves, fruits, and young branches and, consequently, premature leaf and fruit drop [4,5]. The disease has made it impossible to maintain commercial variety orchards in Brazil and the main mandarin-producing regions of the world [6,7]. Symptoms under field conditions are particularly severe on some mandarins, grapefruit (C. × paradisi Macf.), and their hybrids, including important economic varieties such as ‘Emperor’, ‘Fortune’, ‘Nova’, and ‘Murcott’ [8,9], among others. Previous studies have shown that there are disease-tolerant varieties, such as Fremont mandarin, Ortanique tangor, clementines, and willow leaf mandarins, among others [10,11,12].
The disease causes a reduction in production due to fruit drops and the presence of symptoms that depreciate the fruits for the fresh fruit market. This leads to the need for intensive control of the fungus, from 4 to 30 fungicide applications per year, increasing production costs [2,13]. Problems related to the loss of sensitivity of the pathogen to commercial fungicides of several active principles have already been reported [14,15], possibly due to constant use in orchards.
Huanglongbing was reported in Brazil in 2004 [16], and today it is the most critical disease in citrus cropping systems worldwide. Caused by the bacteria ‘Candidatus liberibacter spp.’ and transmitted by the psyllid Diaphorina citri, it is a highly destructive and aggressive disease, causing damage, increasing production costs, and making citrus production unfeasible in several regions of the world. The severity of disease symptoms of mandarin and hybrids was demonstrated in previous studies [17,18,19]. Most commercial citrus cultivars are susceptible to HLB, with a few more tolerant exceptions, such as the “LB8-9” Sugar Belle® mandarin [20]. Furthermore, significant differences in physical and biochemical parameters of HLB-infected and healthy mandarin and sweet orange fruits were related [21].
The search for resistant varieties that meet consumer demand has been one of the most significant demands in citriculture. The Centro de Citricultura ‘Sylvio Moreira’ of the Instituto Agronômico (CCSM/IAC) has one of the most extensive citrus collections in the world [22], enabling the establishment of dozens of accessions in the field for the selection of new commercial varieties. In this paper, we related the results of three years of observations on the reaction of 178 mandarins to the ABS and HLB.

2. Material and Methods

2.1. Experimental Area and Treatments Description

The experiment was established in February 2015 and conducted for three agricultural years (2018 to 2020) at CCSM/SP, Cordeirópolis, State of São Paulo, Brazil (22°27′29.82″ S and 47°24′16.62″ W), with an average altitude of 709 m above sea level. The on-site climate is classified as subtropical (Cwa) and humid, with dry winters (temperatures below 18 °C) and hot summers (temperatures above 22 °C) [23]. The soil was classified as an Orthic Ferralsol (WRB/FAO: oxisol, Rhodic Hapludox, USDA Soil Taxonomy; Latossolo Vermelho distrófico, Brazilian classification), with 64.6% clay, 21.3% sand, and 14.1% silt, and the average results of the last four years of the soil chemical analysis presented pH at 5.3 ± 0.4 and organic matter content at 3.5 ± 0.8%.
A total of 69 accessions of mandarins, including (Citrus reticulata), 5 satsumas (C. × unshiu), 16 clementines (C. × clementina), 27 willow leaf mandarins (C. × deliciosa Tenore), 51 tangors (C. reticulata × C. × sinensis), and 10 tangelos (C. reticulata × C. × paradisi), composed of a total of 178 genotypes. The accessions came from the Active Citrus Germplasm Bank of the IAC (BAG Citrus IAC) and the Bebedouro Experimental Station (EEAB) (Supplementary Table S1). All plants were grafted onto Rangpur lime (C. × limonia Osbeck) and established in a randomized block design, with four replications and two plants per plot, spaced at 7.0 × 4.0 m and totaling 1424 plants and 39.872 m2 of the experimental area.

2.2. Alternaria Brown Spot (ABS) Evaluations

The alternaria brown spot (ABS) was evaluated for three consecutive years (2018 to 2020) in plants using a qualitative rating scale, ranging from zero (no symptoms) to four (plant with burnt shoots and leaf fall) [24]. In fruits, the ABS was evaluated by a diagrammatic scale to assess alternaria brown spot severity on the mandarin leaves’ diagrammatic severity scale, corresponding to the relative fruit area with lesions [25]. For each evaluated year, the means of the variable incidence and severity in plants and fruits were assessed, and the data was used to calculate the area under the disease progress curve (AUDPC) by the trapezoidal integration method [26].

2.3. HLB Evaluations

All plants in the experimental area were inspected for HLB symptoms for three consecutive years, starting in 2017. The percentage of the canopy that had disease symptoms on the leaves was visually inspected and determined. Each plant was assigned a percentage, where 0 means the absence of symptomatic leaves and 100% means the absence of healthy leaves [27]. As for the ABS, assessments were used to calculate the AUDPC.

2.4. Fruit Quality and ‘Candidatus Liberibacter asiaticus’ (CLas) Detection through qPCR

After the HLB incidence assessments, in the 2019 harvest, four varieties with contrasting severity levels were selected and evaluated for the influence of the presence of the pathogen on fruit quality. Leaves and fruits of Murcott IAC 221 tangor, Ponkan IAC 172 mandarin, Dekopon IAC 2009 tangor, and Rio IAC 194 willow leaf mandarin were sampled from symptomatic and asymptomatic branches, respectively, for HLB detection through qPCR (leaves) and physical–chemical analysis (fruits). Analyses were conducted on three samples of five fruits each. Were evaluated average mass (g), the height/width ratio (cm) of the fruit, and juice yield (JY) titratable acidity, obtained by titration with a standardized solution of 0.3125 N of NaOH using phenolphthalein as an indicator, with estimates based on volume. Total soluble solids were determined by a refractometer, and the ratio was calculated with the relationship between soluble solids/acidity.
DNA samples were analyzed for the presence of the 16SrDNA from CLas with an HLBaspr primer/probe (5′FAM/BHQ1, Macrogen, Seoul, Republic of Korea) through qPCR [19]. For each reaction, 1.0 μL of DNA was used, Master Mix [1x], 0.5 μM of HLBas and HLBr primers, and 0.2 μM HLBp probe, in a final reaction volume of 12 μL. The polymerase chain reaction consisted of the denaturation phase at 50 °C (2 min) and 95 °C (10 min), followed by 45 cycles of 15 s at 95 °C and 45 s at 59 °C. The controls used were healthy (absence of CLas), positive (DNA with the presence of CLas), and negative (water—the absence of DNA). A fluorescence assessment of the qPCR was carried out with a StepOnePlus™ Real-Time PCR System (Applied Biosystems, Waltham, MA, USA) at each amplification cycle and was analyzed by StepOne™ Software v2.3. CLas titer values were obtained by threshold cycle (Ct) values, obtained for qPCR targeting. The 16S ribosomal DNA sequence below 36 was considered as CLas positives (CLas+). Log10 of CLas genomes per gram of tissue were estimated [28].

2.5. Data Analysis

All data were submitted to a normality analysis, variance analysis (ANOVA), and, when necessary, a multiple mean comparisons test by Tukey’s honestly significant difference test (HSD) (α = 0.05). The correlations between the variables were submitted by Pearson’s linear correlation test (α = 0.05). Normality, Pearson’s correlation, and ANOVA tests were provided by R software (v. 4.1.0). Multivariate analyses using the principal component analysis (PCA) were made via a correlation matrix, using the ABS and HLB data to identify the response of the citrus groups. PCA data were normalized and demonstrated by the principal component’s distance biplot by their average values [29]. PCAs were performed by FactoMineR and Factoextra packages [30,31], while means separation tests were performed using the Agricolae package [32].

3. Results

3.1. Alternaria Brown Spot (ABS) Severity and Incidence

The first symptoms of the ABS were observed in the field after three years of planting. Rating carried out in the years after the emergence of symptoms observed that there was a higher incidence (% of genotypes with symptoms) in plants (leaves and branches) and fruits in the tangelo and tangor groups when compared to the common mandarins and hybrids on the other hand clementine; willow leaf (WL) mandarin and satsuma (plants and fruits) remained asymptomatic (p < 0.001) (Figure 1A–C). The same was observed for ABS severity in plants (p < 0.001) (Figure 1D). Among the 69 varieties of common mandarin evaluated, there were tolerant ones to the ABS. A total of 26 showed no symptoms on leaves (37.7%) and 53 on fruits (76.8%); likewise, 18 tangors (35.3%) showed no symptoms on leaves and 23 on fruits (45.1%); and, for the tangelos, one did not show any symptoms on leaves (10%; the Ellendale early variety) and three on fruits (30%) (Supplementary Table S1).
The main citrus varieties among the horticultural groups were used in the principal component analysis (PCA) to distinguish the varieties regarding their susceptibility to ABS. It was possible to identify one main component that comprised most of the variance in this study (PC1: 87.4% of the total variance) (Figure 2). This component showed a strong positive correlation with plant ABS incidence (r = 0.969) and severity (r = 0.977) and fruit incidence (r = 0.965) and severity (r = 0.821). This result was expected since the leaves, branches, and fruits are sources of A. alternata inoculum.
Among all varieties, Fortune (common mandarin group) showed the highest levels of severity and incidence in both plants and fruits, followed by the Murcott and TMxLP (Murcott tangor × Pera sweet orange) hybrids, such as the 61, 124, 246, 253, 321, 353, 370 (tangor group). The Nova, Nova SPA and Lee (tangelo group), and Loose Jacket (common mandarin group) also showed high ABS susceptibility (Figure 2 and Supplementary Table S1).

3.2. HLB Severity and Incidence

The AUDPC for HLB incidence and severity in different mandarin groups demonstrates significant differences in the incidence and symptom severity among the common mandarin group (p < 0.05) (Figure 3). A higher AUDPC for HLB incidence (% of infected plants) was observed in tangors and tangelos, followed by common mandarins, clementines, and willow leaf mandarins (WL). Field observations showed that HLB symptoms are more expressed in common mandarins and clementines, followed by tangelos and tangors. The satsumas group was the least affected by both HLB incidence and HLB severity, followed by WL mandarins.
Examining the PCA of the HLB data, the two main components comprised all the variance (100.0%) (Figure 4). HLB incidence and severity positively correlated (r = 0.746) with the PC1 component, demonstrating no separation between incidence and severity, as both are mainly in PC1. Interestingly, HLB incidence data did not correlate with HLB severity (r = 0.114), as the common mandarin varieties that were shown to be infected by HLB did not always show high severity values. The Ponkan IAC 722, Ponkan Nanine (common mandarin group), and IAC 2019Maria (tangor group) demonstrated higher HLB severity symptoms, as the Ortanique IAC 554, TMxLP 253, W Murcott, TMxLP 124, and Thomas (tangor group) demonstrated higher HLB incidence. Contrarily, the Fremont 9-3 common mandarin, TCxLP 24 tangor, Hashimoto and Wase satsumas, and 16MPF21 clementine showed lower HLB incidence values.

3.3. Fruit Quality and Clas Detection through qPCR

In the analysis of symptomatic and asymptomatic fruits and branches, a decrease in mass, fruit size, total soluble solids, ratio, and, consequently, a lower technological index between healthy fruits collected from healthy branches and symptomatic fruits from symptomatic branches was observed for all the varieties studied (Table 1). These results demonstrate that the bacterium negatively influences fruit quality, limiting the cultivation of mandarins in the presence of HLB disease.
Another point to highlight is that even in asymptomatic sectors of the plant, there was the presence of bacteria (‘Ca. Liberibacter asiaticus’) in samples of the Murcott and Dekopon tangors (Table 1).

4. Discussion

4.1. Citrus Varieties’ Responses to ABS

The willow leaf or Mediterranean mandarins and satsumas remained asymptomatic to the ABS. Although initially, symptoms were observed in satsumas under in vitro inoculation conditions [33]. Several studies have been carried out to determine the resistance or susceptibility to the ABS in citrus. Although there are some discrepancies among the results of these studies, resistance is present in clementine, willow leaf, and satsuma mandarins [34,35,36]. From a diploid progeny analysis, it has been proposed that a single recessive allele controls the inheritance of ABS resistance in mandarins [37]. Therefore, resistant cultivars are considered to be recessive homozygous for this locus, whereas susceptible cultivars could be heterozygous or homozygous dominant [11].
Among the common mandarins, six clones of ‘Fremont’ obtained from irradiated buds of the Fremont mandarin [38], the IAC 2019Maria mandarin, the first variety developed and protected by the IAC, TMxTP 09, and TMxLP 11 hybrids, remained asymptomatic to the ABS. The particularity of Fremont clones is their great commercial potential, as they are seedless and have excellent organoleptic fruit characteristics, in addition to smaller plant size; therefore, ABS resistance adds even more value to a new cultivar. Some authors have reported the tolerance of the Fremont mandarin to A. alternata [10,35]
The reasons for the resistance of the Fremont genotype to the ABS have not yet been fully clarified. Evidence shows that the resistance is controlled by a single recessive allele inherited from C. × clementina [39,40], a parental of the hybrid Fremont. ABS resistance to the Fremont genotype may be related to its ability to detoxify reactive oxygen species, in addition to not responding to inoculation through the accumulation of H2O2 and showing no damage to plasma membranes [41].
Likewise, the IAC 2019Maria mandarin is a new variety resulting from the IAC Breeding Program, recently licensed (2019) and commercially planted. The TMxLP 09 hybrid is another variety resulting from the Program, whose fruits meet the demand of the Brazilian consumer, with similar characteristics to ‘Ponkan’, the most consumed variety, but with a later maturation period.
All clementine accessions remained asymptomatic, confirming the tolerance of this group to the ABS [11]. However, clementine hybrids were very susceptible to the disease, such as Fortune and Caçula 3 IAC 1330 and Caçula 4 IAC 1318 (Figure 2). Because these three genotypes are hybrids between clementine and Cravo mandarin and both are tolerant to disease, other factors may be involved in the inheritance of resistance/susceptibility to the ABS [11,12].
Identifying tolerance to the ABS in mandarin genotypes makes them potentially interesting for use in commercial orchards or as parents in breeding programs. Recent studies indicate the potential of using molecular markers in the assisted selection of breeding progenies [5,36] since they allow the early selection of hybrids that are resistant to directed crosses, which is an affordable and efficient strategy to obtain new resistant varieties.
The severity observed among all accessions was very variable. ‘Fortune’ mandarin was one of our study’s most susceptible varieties to the ABS. Among the mandarins’ varieties and their cultivated hybrids ‘Dancy’ and ‘Fortune’ have been reported as the most susceptible [42], as well as the ‘Minneola’, ‘Orlando’, ‘Sunburst’, and ‘Nova’ tangelos [43]. This high susceptibility to the Fortune has been widely reported and cited as the probable cause of its reduction in planting in Spain over the years, where it is no longer found in orchards [6,7]. Recently characterized by molecular markers as a clementine × Orlando tangelo hybrid [44], the Fortune mandarin appears to have inherited the high susceptibility of the tangelo. The four tangelos abovementioned (Minneola, Orlando, Sumbusrt, and Nova) have a Dancy mandarin as a parental. This fact can be the reason for their extreme susceptibility to the ABS. Unfortunately, ‘Dancy’ was not evaluated in this study, but it is known that all are these tangelos.
This study evaluated dozens of mandarins and hybrids under field conditions. Differences in ABS incidence and susceptibility were observed over the natural inoculation of the pathogen, and a range of genotypes tolerant to the ABS could replace the current commercial varieties, reducing production costs and environmental damage caused by the intensive application of fungicides, which can be currently dispensed with the cultivation of tolerant varieties. However, evaluating fruit production and quality can also indicate potential varieties for the Brazilian citrus industry.

4.2. Citrus Varieties’ Responses to HLB

Although no known HLB-resistant citrus species or varieties have been identified, some citrus accessions are reportedly tolerant [45,46]. Differential anatomical responses of tolerant and susceptible citrus species were observed to the ‘Candidatus Liberibacter asiaticus’ infection [45]. An experiment conducted in a greenhouse by McCollum et al. [46] showed good agreement with trends observed in the orchard for susceptibility to HLB. The authors observed that Citrus macrophylla e C. medica trees were most susceptible to ‘Ca L. asiaticus’, with 100% infection by the end of the test period, while the complex genetic hybrids’ US 1-4-59’ and ‘Fallglo’ were consistently the least susceptible, with approximately 30% infection.
Recently, some citrus cultivars released by the UF-CREC breeding program have exhibited tolerance to HLB, specifically “LB8-9″ (Sugar Belle®) and “7-6-27″ mandarin [20]. Mira et al. [47], studying some hybrids populations of mandarins, observed that the tolerant trees represent a very low percentage (5.3%) compared to the other categories in the field evaluation for symptoms of HLB disease. Based on the number of trees in every cross, more than 30% of the cross {(Clementine × Temple) × C. ichangensis} was tolerant trees, followed by {(Clementine × Temple) × Swingle} at the ratio of 22.72% tolerant trees. The cross {(Clementine × Temple) × C. ichangensis} includes most HLB tolerant trees in a visual evaluation. In the present work, field observations showed that the symptoms are more expressed in tangors, tangelos, and mandarins than clementines and willow leaf mandarins (WL mandarin), as these seem less affected by the disease. Interestingly, HLB incidence data did not correlate with HLB severity, as the citrus varieties that were shown to be infected by HLB did not always show high severity values.
Recently, 448 diverse mandarin hybrids have been assessed from 30 crosses and 45 additional accessions, and some hybrids were reported to exhibit reduced sensitivity to HLB [19]. Likewise, although we observed differences in susceptibility in the 178 varieties evaluated, no HLB-asymptomatic varieties were found in this study. The citrus varieties are closely related to a narrow genetic base and lack HLB resistance [18].
A decrease in mass, fruit size, total soluble solids, ratio, and, consequently, a lower technological index between healthy fruits collected from healthy branches and symptomatic fruits from symptomatic branches was observed for all varieties studied. Sajid et al. [21] also reported differences in physical and biochemical parameters between infected and healthy citrus fruits. The authors observed that the fruit diameter, leaf area, and juice weight of samples infected with HLB were significantly lower than those of HLB-infected samples and healthy Kinnow mandarin and Mosambi sweet orange samples. Infected fruits of both varieties showed greater skin thickness, lower juice percentage, higher juice acidity, and lower total soluble solids. These results demonstrate that the bacterium negatively influences fruit quality, limiting the cultivation of mandarins in the presence of HLB disease.

5. Conclusions

Evaluations of the incidence and severity of the diseases showed a range of genotypes tolerant to ABS that could replace the current commercial varieties, mainly within the clementina and willow leaf mandarin groups. Among the common mandarins, Fremont and its six clones, the IAC 2019Maria mandarin and TMxTP 09 and TMxLP 11 hybrids remained asymptomatic to the ABS. Although, with differences in incidence and susceptibility to HLB, there are no tolerant varieties to this disease, which significantly impacts the loss of fruit quality.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/horticulturae9060641/s1. Table S1: ABS and HLB presence (+) or absence (−) after three years of evaluations on mandarin groups and hybrids from the Genebanks of the Instituto Agronômico de Campinas (IAC) (BAG Citros IAC), IAC Breeding Program and the Estação Experimental de Citricultura de Bebedouro (EECB).

Author Contributions

Conceptualization, M.B., F.A.d.A. and M.C.-Y.; methodology, M.B., F.A.d.A., F.T.D., E.S.S., R.d.V.F. and M.C.-Y.; formal analysis, M.B., F.A.d.A., F.T.D., R.M. and M.C.-Y.; investigation, M.B., M.C.-Y. and F.A.d.A.; resources, M.B., M.C.-Y. and F.A.d.A.; data curation, M.B., R.M. and F.A.d.A.; writing—original draft preparation, M.B, R.M., F.A.d.A., F.T.D., E.S.S. and M.C.-Y.; writing—review and editing, R.M., M.B., F.A.d.A., F.T.D., E.S.S., R.d.V.F. and M.C.-Y. All authors have read and agreed to the published version of the manuscript.

Funding

This study was partially funded by the following research projects: Fapesp No. 2014/50880-0, 2017/24564-1, and 2020/07045-3, and CNPq No. 465440/2014-2.

Conflicts of Interest

The authors declare no conflict of interest.

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Horticulturae 09 00641 g001 550
Figure 1. The area under the disease progress curve (AUDPC) for the alternaria brown spot (ABS) on citrus groups: clementine, common mandarin, tangelo, tangor, and willow leaf mandarin (WL mandarin). ABS incidence on plants (A) and fruits (B), and ABS severity on plants (C) and fruits (D). Means followed by the same letter do not differ from Tukey’s HSD test (α = 0.05).
Figure 1. The area under the disease progress curve (AUDPC) for the alternaria brown spot (ABS) on citrus groups: clementine, common mandarin, tangelo, tangor, and willow leaf mandarin (WL mandarin). ABS incidence on plants (A) and fruits (B), and ABS severity on plants (C) and fruits (D). Means followed by the same letter do not differ from Tukey’s HSD test (α = 0.05).
Horticulturae 09 00641 g001
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Figure 2. Biplot of the principal component analysis (PCA) by the correlation matrix for the alternaria brown spot (ABS) data within the citrus groups and varieties. AUDPC: area under disease progress curve; SEV: severity; INC: incidence; PL: plant; FR: fruit; WL mandarin: willow leaf mandarin.
Figure 2. Biplot of the principal component analysis (PCA) by the correlation matrix for the alternaria brown spot (ABS) data within the citrus groups and varieties. AUDPC: area under disease progress curve; SEV: severity; INC: incidence; PL: plant; FR: fruit; WL mandarin: willow leaf mandarin.
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Figure 3. The area under the disease progress curve (AUDPC) for HLB incidence (A) and severity (B) in citrus groups: clementine, common mandarin, tangelo, tangor, and willow leaf mandarin (WL mandarin). Means followed by the same letter do not differ from Tukey’s HSD test (α = 0.05).
Figure 3. The area under the disease progress curve (AUDPC) for HLB incidence (A) and severity (B) in citrus groups: clementine, common mandarin, tangelo, tangor, and willow leaf mandarin (WL mandarin). Means followed by the same letter do not differ from Tukey’s HSD test (α = 0.05).
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Figure 4. Biplot of the principal component analysis (PCA) by the correlation matrix for the HLB data within the citrus groups and varieties. AUDPC: area under disease progress curve; SEV: severity; INC: incidence; WL mandarin: willow leaf mandarin.
Figure 4. Biplot of the principal component analysis (PCA) by the correlation matrix for the HLB data within the citrus groups and varieties. AUDPC: area under disease progress curve; SEV: severity; INC: incidence; WL mandarin: willow leaf mandarin.
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Table
Table 1. HLB influence on mandarin fruits. +: symptomatic HLB; −: asymptomatic HLB; H/L: mass (M) height (H)/width (W) of the fruit; juice yield (JC); ratio; acidity (A); TSS: total soluble solids (°Brix); TI (technological index) of juice; and, CLas titer.
Table 1. HLB influence on mandarin fruits. +: symptomatic HLB; −: asymptomatic HLB; H/L: mass (M) height (H)/width (W) of the fruit; juice yield (JC); ratio; acidity (A); TSS: total soluble solids (°Brix); TI (technological index) of juice; and, CLas titer.
GenotypeFruitBranchMass (g)Height (H)Width (W)H/WJuice Yield (%)AcidityTSS RatioTI CLas Titer
(log10 16S rDNA Copy)
Murcott (Tangor) −−185.8 a6.6 a7.6 a0.87 a49.9 a0.52 b9.8 a15.1 a1.98 a4.50 (+)
−+150.2 a6.1 ab6.9 a0.87 a49.4 a0.64 ab7.9 b14.2 ab1.83 ab4.77 (+)
++87.6 b5.2 b5.6 b0.92 b49.1 a0.86 a7.3 b9.9 b1.45 b5.03 (+)
Ponkan (Mandarin) −−268.7 a9.2 a9.5 a0.97 b50.1 a0.40 a8.1 a19.8 a1.64 a0 (−)
−+148.9 b6.9 b6.7 b1.00 ab47.7 a0.42 a7.4 a19.2 a1.47 a0 (−)
++124.6 b6.8 b6.5 b1.06 a31.7 b0.48 a7.6 a17.5 a1.05 b3.60 (+)
Dekopon
(Tangelo) 		−−444.1 a11.2 a9.6 a1.16 a47.3 a0.87 b10.4 a9.2 a1.86 a4.21 (+)
−+278.2 b9.6 a8.0 b1.18 a45.9 a1.11 ab7.4 b7.7 b1.43 b4.23 (+)
++85.6 c6.1 b5.2 c1.16 a44.0 a1.34 a8.1b6.7 b1.50 ab4.90 (+)
Rio IAC 194 (WL mandarin) −−97.0 a5.2 a6.1 a0.85 b55.4 a0.85 b9.5 a11.0 a1.98 a0 (−)
++66.1 b5.2 a4.6 b1.19 a47.1 b0.95 a7.1 b8.1 b1.82 b3.92 (+)
Means followed by the same letter do not differ statistically (Tukey 5%). F = fruit; Br = branches; no asymptomatic fruits were found in symptomatic branches of Rio IAC 194 mandarin.
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Bastianel, M.; Martinelli, R.; Devite, F.T.; Cristofani-Yaly, M.; Ferreira, R.d.V.; Stuchi, E.S.; Azevedo, F.A.d. Reaction of Mandarins to the Alternaria Brown Spot and Huanglongbing: Identification of Potential Varieties for These Diseases to Be Managed in the Field. Horticulturae 2023, 9, 641. https://doi.org/10.3390/horticulturae9060641

AMA Style

Bastianel M, Martinelli R, Devite FT, Cristofani-Yaly M, Ferreira RdV, Stuchi ES, Azevedo FAd. Reaction of Mandarins to the Alternaria Brown Spot and Huanglongbing: Identification of Potential Varieties for These Diseases to Be Managed in the Field. Horticulturae. 2023; 9(6):641. https://doi.org/10.3390/horticulturae9060641

Chicago/Turabian Style

Bastianel, Marinês, Rodrigo Martinelli, Fernando Trevizan Devite, Mariangela Cristofani-Yaly, Rodrigo do Vale Ferreira, Eduardo Sanches Stuchi, and Fernando Alves de Azevedo. 2023. "Reaction of Mandarins to the Alternaria Brown Spot and Huanglongbing: Identification of Potential Varieties for These Diseases to Be Managed in the Field" Horticulturae 9, no. 6: 641. https://doi.org/10.3390/horticulturae9060641

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