Temporal dynamics of wheat blast caused by Pyricularia oryzae Triticum lineage throughout the successive wheat cycles

Wheat blast, caused by Pyricularia oryzae Triticum lineage (PoTl), can infect wheat leaves and heads. The pathogen biology and disease epidemiology of the isolates PoTl still need more profound insights for the integrated management of wheat blast in Brazilian wheat �elds. This study aimed to characterize the incubation period, latent period, and the temporal progress of wheat blast and to �t the best nonlinear model, describing the nature of an epidemic of the PoTl isolate 12.1.146 compared with the PoTl isolate Py6038, throughout �ve successive infection cycles of PoTl on wheat leaves and heads. Wheat blast occurred in all infection cycles. The incubation period and latent period of the PoTl isolate 12.1.146 were signi�cantly shorter than that of the PoTl isolate Py6038. The secondary inocula produced by the PoTl isolates on symptomatic wheat leaves caused blast symptoms when inoculated on wheat heads. The area under the disease progress curve (AUDPC) was calculated based on disease severity. In all infection cycles, the AUDPC of the PoTl isolate 12.1.146 was signi�cantly higher than that of the PoTl isolate Py6038. The nonlinear logistic model had the best �t to describe the intensity of the disease progress curves (DPCs) of PoTl isolates on wheat leaves and heads, �tting classic sigmoid-shaped curves. Our �ndings show that the disease severity of the PoTl isolate 12.1.146 did not reduce under grow chamber conditions, even after �ve successive infection cycles. These �ndings may imply the integrated management of the disease wheat blast pathogen in Brazilian �elds.


Introduction
Wheat (Triticum aestivum) is one of the most important cereal staple crop produced worldwide contributing to global food security (Acevedo, 2018).In 2019, Brazil produced 6.6 million tons of wheat, representing 0.9% of the 735 million tons produced globally (Colussi et al., 2022).Wheat production can be threatened by several pests and diseases, though (FAOSTAT, 2020).Wheat blast, caused by Pyricularia oryzae Triticum lineage (PoTl), is one of the major diseases threatening the crop yields.Wheat blast disease was rst reported in 1986 in Parana state, Brazil.Since then, the pathogen has rapidly spread to wheat elds in south-central Brazil and neighbouring countries, including Argentina, Bolivia, and Paraguay (Ceresini et al., 2018a, Gladieux et al., 2018).In 2016, the disease was reported outside South America, rstly, in Bangladesh, southeast Asia, and secondly, in 2017, in Zambia, eastern Africa, causing outbreaks that signi cantly harmed production in both countries (Callaway, 2016, Islam et al., 2016, Tembo et al., 2020).These two outbreaks have been linked to introductions via contaminated seed lots (Singh et al., 2021).The fungal pathogen is able to infect both wheat leaves and heads, but head blast is the most destructive symptom (Castroagudin et al., 2015).Head blast associated yield losses ranging from 10 to 100% have been reported in wheat crops from South America countries, Bangladesh and Zambia (Bonjean et al., 2016, Islam et al., 2016, Tembo et al., 2020).More recently, the blast disease was found in Germany, in 2022, in central Europe (Barragan et al., 2022).
Managing wheat blast disease is still challenging.The deployment of wheat resistant cultivars and calendar-based preventive fungicide spraying are the main management strategies in Brazil (Goulart et al., 2007, Pagani et al., 2014).However, resistance is not considered durable across geographical regions due to the pathogen´s high diversity in virulence, and to the limited e cacy of fungicides (Ceresini et al., 2018a, Ceresini et al., 2018b).For many years, the limited e cacy of systemic site-speci c fungicides has been associated with application technologies di culties in systematically reaching the pathogen infection sites on wheat heads where infection occurs with the highly favourable environmental conditions for the disease; and with the high susceptibility of wheat cultivars.Not surprisingly, the e cacy of this spraying approach in managing wheat blast has rarely been higher than 60% (Ceresini et al., 2018b).To make the situation even worse, PoTl has a wide host range, including other poaceous hosts, which grow near wheat elds and may be an important reservoir or source of inoculum in the early phases of a wheat blast epidemic, hindering the management of the disease (Castroagudin et al., 2015, Castroagudin et al., 2016, Dorigan et al., 2019).Furthermore, multiple Pyricularia species, including P. pennisetigena and P. urashimae associated with other poaceous hosts, can also cause blast disease on the heads of adult wheat plants (Dorigan et al., 2023).
Although wheat blast has been reported in Brazil for more than 30 years, there are still unanswered questions about the pathogen´s ecology and disease epidemiology, especially related to the timing and temporal dynamics of wheat heads infection.Few studies have clari ed the epidemiological importance of PoTl secondary inocula produced from symptomatic wheat leaves to the temporal progression of blast on heads, and much more research is needed to better characterize the incubation period and latent period on wheat leaves and heads (Rios et al., 2016).Furthermore, it is unknown whether the disease severity of PoTl isolates keeps the same temporal dynamics after successive cycles of infection.Knowledge about variation in the long-range temporal progress curves of PoTl isolates is essential to guide the adoption of management strategies that include timing for fungicide spraying.For instance, as a smarter alternative for the calendar-based preventive and successive fungicide sprays, epidemiology-based advice on the right timing for fungicide spraying could be applied instead, delaying disease emergence in the early phases of a wheat blast epidemic.
Several statistical models have been applied to describe the temporal dynamics of epidemics and to compare epidemic-based management tactics (Vanderplank, 1963, Campbell & Madden, 1990).Applying such models could help determining: i) if the wheat blast disease progress curves (DPCs) maintain the same shape over many infection cycles; ii) whether the parameters rate (r) and initial inoculum (y0), which are t in the regression models, varied along successive infection cycles; and iii) the disease severity in the fungal progeny arising from each infection cycle is not reduced.On barley, P. oryzae mutants tested under both saprophytic and infections conditions did not show differences in the disease severity of the isolates throughout four infection cycles (Avila-Adame & Koller, 2003).
Therefore, the aim of this study was (i) to verify whether the PoTl isolate 12.1.146and the PoTl isolate Py6038 secondary inoculum produced in symptomatic wheat leaves during ve successive infection cycles could develop blast on wheat heads; (ii) to characterize the temporal dynamics of wheat blast, the area under the disease progress curve (AUDPC), incubation period and latent period for both wheat leaves and heads over the course of ve successive infection cycles of PoTl isolates; and (iii) to t empirical models to describe the wheat blast dynamics in each infection cycle of the PoTl isolates.

Fungal material, inoculum preparation, and plant material
The Pyricularia oryzae Triticum lineage (PoTl) 121146 isolate and the Py6038 isolate were used for testing the relevant hypotheses in this study.These isolates were deposited in the Molecular Plant Pathology fungal collection from São Paulo State University, Ilha Solteira, SP.The 12.1.146isolate was obtained in 2012 from symptomatic heads from wheat elds in Mato Grosso do Sul (MS) state, Brazil.
The Py6038 isolate was collected in Goiás (GO) state, Brazil, in 2006, using the same procedure.The sampling methods adopted in wheat elds were performed as described by Castroagudin et al. (2015).
For inoculum preparation, mycelial discs (7-mm diameter) of the PoTl isolates were transferred from a colony with 7 days of growth to 15 plates containing PDA medium (42 g L − 1 potato-dextrose-agar, KASVI, India) and 15 plates containing oatmeal agar medium (OA, 60 g of oatmeal our, 12 g of agar).For each plate containing PDA or OA, 50 µg mL − 1 streptomycin sulphate and chloramphenicol were added.These plates were incubated for 15 days at 25°C under constant light using 1,060-lumen Osram® uorescent lamps.To facilitate the release of conidia, 4 mL of distilled water with the surfactant Tween 80 (10 µL L − 1 ) was added to each plate containing the culture medium.The conidial suspensions were obtained by scraping the mycelia with a sterile spatula.The conidial concentration was measured using a Neubauer chamber.
Concomitantly with inoculum preparation, three 'Anahuac 75' wheat plants were grown in a 770-mL plastic pot containing plant substrate Tropstrato HT potting mix (Vida Verde, Campinas, São Paulo, Brazil).The plants were kept in a greenhouse and irrigated daily, and every 15 days, a dose of 0.84 grams of N-P 2 O 5 -K 2 O (10-10-10) was applied per pot.The PoTl isolates were inoculated on the leaves of 1month-old wheat plants, at growth stage 14 (Zadocks et al., 1974).On heads, the inoculations were carried out at the beginning of anthesis, at growth stage 60, in 2-month-old immature heads (Zadocks et al., 1974).Using a manual sprayer, conidial suspensions with 10 5 conidia mL − 1 of 12.1.146and Py6038 PoTl isolates were uniformly inoculated either onto the adaxial leaf surfaces or onto the heads until draining.For inoculation of each isolate, 25 mL of the conidial suspension were inoculated in twelve wheat heads distributed on four pots, each containing three plants.For the rst 24 hours after inoculation, the plants were incubated in a growth chamber in the dark at 25°C and > 90% relative humidity.Then, the plants were kept in a growth chamber under the same conditions but with a 12-hour photoperiod supplied by 33,354-lumen Osram® sodium vapour lamps (400W, model HQI-T NDL E40 5200K) for 21 days.An Even® digital thermo-hygrometer was used to monitor the temperature and relative humidity.
In the growth chamber, the wheat plants inoculated with each isolate were incubated separately and completely isolated from one another using transparent plastic bags, avoiding lateral contamination.
Five successive infection cycles of the PoTl isolates were performed on wheat leaves.For PoTl isolates, the infection cycles on leaves and heads lasted 21 days.The 1st, 3rd and 5th cycles were assessed.For the secondary inoculum production on infected wheat leaves with typical blast lesions, the plants were kept in a growth chamber under the same conditions described in this section.Twelve wheat leaves with sporulating lesions from each isolate were collected from four pots, each containing three wheat plants.The wheat leaves were placed into plastic tubes containing 10 mL of distilled water.The conidia were dislodged from the blast lesions by vortexing the plastic tube for 1 minute.The number of conidia recovered from sporulated wheat leaves was quanti ed using a Neubauer chamber.Between one infection cycle and another, every 21 days, the conidia produced by PoTl isolates on wheat leaves were inoculated on healthy plants of the subsequent cycle.The secondary inoculum obtained from wheat leaves with typical blast lesions in the 1st, 3rd and 5th cycles was inoculated simultaneously on wheat heads.

Experimental design
The experimental design was completely randomized, with four replicates per treatment.The experiments were repeated once.The temporal dynamics of the PoTl isolates was assessed among infection cycles, and the factorial arrangement was 5 × 2, combining ve infection cycles and two treatments, the PoTl isolate 121146 and the PoTl isolate Py6038, which were inoculated on wheat leaves and heads.For each experiment, four pots containing three plants and/or three wheat heads each were prepared for inoculation of each isolate, and disease severity, incubation period and latent period were assessed in twelve wheat leaves and heads.
Assessment of disease severity and the ability of PoTl secondary inoculum to develop wheat blast over time For PoTl isolates, in each infection cycle, the ability of the secondary inoculum produced on symptomatic wheat leaves to develop blast on wheat heads was assessed based on disease severity values.For each infection cycle, the disease severity on wheat leaves and heads was determined at 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 d.a.i.The non-destructive method was used to measure the disease severity on wheat leaves and heads over the course of each infection cycle.A Canon® digital camera (EOS Rebel T1i model) was used to photograph wheat leaves and heads with typical blast symptoms.
The digital camera was attached to a 1.55-m-high monopod at a distance of 20 cm from the wheat leaves and heads.Assess 2.0 (APS, St. Paul, Minnesota), a software program for analyzing digital photographs, was used to determine the percentage of each wheat leaf or head area affected in relation to the total leaf or head area (i.e., the disease severity caused by PoTl isolates on wheat leaves and heads).Two sides of each head were photographed, and the disease severity was calculated as the arithmetic mean between the two images obtained.For each infection cycle, disease severity values of PoTl isolates on wheat leaves and heads were plotted, obtaining the disease progress curves (DPCs).
The infection rate of PoTl isolates was determined on wheat leaves and heads.

Area under the disease progress curve
The AUDPC was calculated to compare the disease severity of PoTl isolates within each cycle and between infection cycles.The disease severity values from the 12 blast assessments were integrated as AUDPC for wheat leaves and heads, according to (Shaner & Finney, 1977): where AUDPC = area under the disease progress curve, Yi = proportion of disease at the i th observation, Ti = time in days at the i th observation, and n = total number of observations.

Assessment of incubation period and latent period
For each infection cycle, the incubation period and latent period were estimated by monitoring wheat leaves inoculated until the rst symptoms and signals of the fungal reproductive structures.The length of the incubation period was estimated between inoculation and appearance of the rst symptoms of the disease.The length of the latent period was assessed between inoculation and the rst conidia emergency (reproductive structures) on wheat leaves inoculated with PoTl isolates.

Model tting to disease progress curves
For each infection cycle, nonlinear models were tted, and the data from the 12 assessments of disease severity of PoTl isolates on wheat leaves and heads were used for the tting.Different models were tted, including exponential y = (y0) × exp (rt) (1), Gompertz's y = exp (-(-ln (y0)) × exp (-rt)) (2), logistic y = 1/[1 + ((1/ y0) -1) × exp (-rt)](3), monomolecular y = 1 -(1 -y0) × exp (-rt) (4), and linear (y = y0 + r × t) (5).For these equations, y represents the disease severity percentage at time t, y0 is the disease severity at time t0 and r is the disease progress rate of each model, with time in days (Campbell & Madden, 1990).The best model was chosen according to the highest coe cient of determination in the regression analysis (R 2 ), the smallest mean-square of the residuals (MSR), the signi cance of the parameters of the tted regression models, and the lowest dispersion of points in the residuals plot.

Data analysis
For the analysis of data, results from two replicates of each experiment were combined.The value of the quotient between the largest and smallest square mean residual from two replicates of each experiment was less than seven, admitting the homogeneity of residual variances, which allowed the joint analysis of the data (Gomes, 1990).The Shapiro-Wilk tests was applied to assess the assumptions of the ANOVA for blast severity, AUDPC, incubation period and latent period (p = 0.05).The severity, incubation period and latent period of PoTl isolates on wheat plants were compared by ANOVA's F test using a factorial arrangement between isolate and cycle.The PoTl isolates were compared within each cycle and between infection cycles.Within each cycle, the isolates were compared by ANOVA's F test and between them with the Scott-Knott test (p ≤ 0.05).All analyses were performed using the ExpDes.ptpackage of the statistical software RStudio version 1.2.5033 (Ferreira & Cavalcanti, 2009).

Disease progress curve and disease progress rate
The wheat blast occurred in all infection cycles, and symptoms were observed on both wheat leaves and heads.For each infection cycle, the secondary PoTl inoculum produced on symptomatic 'Anahuac 75' wheat leaves at 21 d.a.i. was able to develop blast symptoms on wheat heads.There was continuous progress of blast symptoms on leaves and heads, from 0.0 to 60.0-100.0%severity throughout 15 days.The PoTl isolate 12.1.146had maximum disease intensity at 10 d.a.i, (i.e., earlier than the 15 d.a.i of the PoTl isolate Py6038) (Fig. 1).
The sigmoid-shaped disease progress curve of the PoTl isolate 12.1.146was maintained from the rst to the last infection cycle on wheat leaves and heads (Fig. 1).There was a signi cant interaction between cycle and isolate on 'Anahuac 75' wheat leaves and heads (p ≤ 0.001).In all infection cycles, at 7 d.a.i, the PoTl isolate 12.1.146caused the highest disease severity on wheat leaves and heads (p ≤ 0.001) (Fig. 1).
On the heads, the highest levels of disease severity for the PoTl isolate 12.1.146,at 7 d.a.i, was at 1st infection cycle (Fig. 1).At the end of the 1st and 5th cycles, at 15 d.a.i, there was 100.0%disease severity on wheat leaves and heads inoculated with the isolates of PoTl (Fig. 1).In contrast, at the end of the 3rd infection cycle, for wheat plants inoculated with PoTl isolate 12.1.146,there was 98.7% and 82.7% disease severity on wheat leaves and heads, respectively, while for plants inoculated with PoTl isolate Py6038, the disease severity was 79.8% and 63.9%, respectively (Fig. 1).
Within each infection cycle, there were signi cant differences between infection rate of PoTl isolate 12.1.146and PoTl isolate Py6038 inoculated on wheat leaves (p ≤ 0.01) and wheat heads (p ≤ 0.1), according to ANOVA's F test.In all infection cycles, the infection rate of 12.1.146and Py6038 PoTl isolates increased with the continuous progress of blast symptoms on leaves and heads, which occurred from 5 to 10 d.a.i.(Fig. 1).For the 1st and 5th infection cycle on wheat leaves and heads, at 7 d.a.i, the infection rate of PoTl isolate 12.1.146was higher than that of PoTl isolate Py6038 (p ≤ 0.001) (Fig. 1).Between the 10 and 15 d.a.i, the infection rate of 12.1.146and Py6038 PoTl isolates decreased in the 1st and 5th infection cycle, since 100% blast symptoms on leaves and heads were reached (Fig. 1).

Area under the disease progress curve
For AUDPC within each infection cycle, there were signi cant differences between 12.1.146and Py6038 PoTl isolates (p ≤ 0.001), according to ANOVA's F test.Among the infection cycles, the interaction between cycle and isolate on wheat leaves and heads were statistically signi cant (p ≤ 0.001).In all infection cycles, higher AUDPC values were observed on the wheat leaves and heads inoculated with the PoTl isolate 12.1.146,and the AUDPC was lower for the PoTl isolate Py6038 (p ≤ 0.001) (Fig. 2).The highest AUDPC values were observed for PoTl isolates on wheat leaves and heads at 1st infection cycle (Fig. 2).

Incubation period and latent period
Within each infection cycle, signi cant differences between 12.1.146and Py6038 PoTl isolates for incubation period and latent period (p ≤ 0.001) were identi ed by ANOVA's F test.Among the infection cycles, there were a signi cant interaction between cycles and PoTl isolates for incubation period on wheat leaves (p ≤ 0.001) and heads (p ≤ 0.1) and latent period (p ≤ 0.001).In all infection cycles, a shorter incubation period and latent period were observed on the wheat leaves and heads inoculated with the PoTl isolate 12.1.146,and the incubation period and latent period were longer for the PoTl isolate Py6038 (p ≤ 0.001) (Fig. 3).At the end of the 5th infection cycle, the incubation time of the 12.1.146and Py6038 PoTl isolates on wheat leaves increased signi cantly from 2.6 to 3.2 and from 3.2 to 3.7 days, respectively (p ≤ 0.001) (Fig. 3A).Similarly, between the 1st and 5th infection cycle, the incubation period on wheat heads increased signi cantly from 2.7 to 2.9 days for PoTl isolate 12.1.146and from 3.7 to 3.9 days for PoTl isolate Py6038 (p ≤ 0.001) (Fig. 3B).For the latent period of the PoTl isolate 12.1.146on wheat leaves, there was no effect of the infection cycles in the time necessary for conidial production.Conversely, the latent period of the PoTl isolate Py6038 on wheat leaves increased signi cantly from 6.6 to 7.2 days between the 1st and 5th infection cycle (p ≤ 0.001) (Fig. 3C).

Model tting to disease progress curves
In all infection cycles, for both wheat leaves and heads, the logistic model was the best t for the wheat blast progress curve (Fig. 4).In the infection cycles, on wheat plants inoculated with the isolates 12.1.146and Py6038, overall, the logistic model resulted in the highest R 2 and the lowest MSR on wheat leaves and heads (Table 1 and Table 2).Additionally, in all infection cycles, for both wheat leaves and heads, the disease progress rate (r) and the initial inoculum (y0) under the logistic model were signi cant parameters for isolates of PoTl (Table 1 and Table 2).When comparing the disease progress rate (r) of PoTl on leaves between the 1st infection cycle (rc1) and the 5th infection cycle (rc5) under the logistic model, the rc5 of PoTl isolate 12.1.146was 1.70 times higher than rc1, while in heads the rc5/rc1 ratios was 1.07.c Coe cient of determination tted in the regression analysis (R 2 ).The signi cance codes used were: *** p < 0.001; ** p < 0.01; * p < 0.05.Na: not tted.
d Mean square of the residual of the linear regression analysis (MSR).
e y 0 : initial severity of wheat blast.
f r: progression rate of wheat blast.

Discussion
Even though the wheat blast has been reported in Brazil for more than 30 years, there are still unanswered questions about the pathogen´s ecology and disease epidemiology; in this study, we assessed the effect of successive infection cycles of the 12.1146 and Py6038 PoTl isolates on the temporal development of blast on wheat leaves and heads (Dorigan et al., 2022).Knowledge about the biology and epidemiology of the PoTl isolate may lead us to understand better and to develop integrated disease management strategies against PoTl that cause blast in wheat elds in Brazil.This information may also provide a safer basis for employing models capable of supporting decision making in the application of fungicides in controlling the wheat blast disease.
Firstly, our study reports that 12.1.146and Py6038 PoTl secondary inoculum produced on wheat leaves was pathogenic and e cient in causing wheat blast on wheat leaves and heads throughout ve successive infection cycles.Moreover, the secondary inoculum of the isolates PoTl harvested from wheat leaves with typical blast symptoms and sporulated lesions caused blast symptoms when inoculated on wheat heads.This result reveals an important role for the PoTl inoculum produced on symptomatic wheat leaves in the development of blast on wheat heads.The PoTl inoculum is capable of oryzae Triticum on wheat, the PoTl inoculum and blast symptoms also spread from leaves to heads, following a vertical movement (Gongora-Canul et al., 2020).In our study, the time between inoculation and the rst conidia emergency on wheat leaves (latent period) was shorter for PoTl isolate 12.1.146than that of the PoTl isolate Py6038 in all infection cycles (Fig. 3C), which was consistent with the previous report in P. oryzae on rice, where the latent period of the isolates ranged from 5 to 7 days on rice leaves (D' Avila et al., 2022).
Secondly, in all infection cycles, the period in days between inoculation and the rst symptom on wheat leaves and heads (incubation period) was shorter for PoTl isolate 12.1.146than that of the PoTl isolate Py6038 (Fig. 3A and Fig. 3B), which was consistent with previous report in PoTl isolates, where the incubation period of the isolates ranged from .Although the disease severity was lower at the 3rd infection cycle, the infection levels went back up in later cycles.These differences in the 3rd infection cycle on wheat leaves and heads can be explained by several factors, including longer incubation of PoTl isolates (Fig. 3), as well as lower infection rate and expansion of lesions on infected wheat leaves and heads (Fig. 1).
For the 1st and 5th infection cycles, the levels of disease severity of PoTl isolate 12.1.146were higher (more than 60% at 9 d.a.i), and the rate of disease progress was higher at the 5th cycle than at the initial infection cycle on leaves and heads.Similarly, to what was observed for PoTl isolate 12.1.146,P. oryzae isolates have caused a high level of infection, more than 60% of the disease incidence at 10 d.a.i, in combination with the increase in the rate of disease progression (Rios et al., 2016).Furthermore, our results demonstrate a continuously decreasing infection rate of PoTl isolates ranging from near 0.0 between 10 and 15 d.a.i (Fig. 1).Therefore, decreasing the probability of occurrence of secondary infections on wheat leaves 15 d.a.i (Fig. 1).
Thirdly, regarding the AUDPC, based on the disease severity values on wheat leaves and heads, the PoTl isolate 12.1.146had higher values than the PoTl isolate Py6038 in all infection cycles (Fig. 2).When inoculated on wheat leaves and heads for each infection cycle, there were differences in the behaviour of the temporal progress of blast and AUDPC between the PoTl isolate 12.1.146and the PoTl isolate Py6038.The continuous progression of blast symptoms on wheat leaves and heads ranged from near 0.0 to maximum severity in 1.5-2.0weeks from each infection cycle (Fig. 1).In addition to progression of wheat blast, the PoTl isolate 12.1.146led to maximum severity of disease faster than the PoTl isolate Py6038 (Fig. 1).In contrast to what was observed in our study, some isolates of P. oryzae has shown a reduced infection e ciency and reduced aggressiveness compared to the sensitive isolates over the course of four disease cycles in rice plants (D' Avila et al., 2022).
Fourthly, the nonlinear model that best t the sigmoid progress curves over the course of time, for both the isolate 12.1.146and the isolate Py6038, was the logistic model (Fig. 4).This model was also selected by other authors to describe the wheat blast epidemic, although on crop elds ( infecting wheat plants from vegetative stages of the host up to the head stage (Cruz et al., 2015, Cruz & Valent, 2017, Martínez et al., 2019).The development of wheat blast symptoms in the middle canopy of plants in combination with the natural senescence of basal leaves contributes to the formation of an important source of secondary inoculum of PoTl (Cruz et al., 2015).Similar to what was observed for P.

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Figure 1 Disease
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Table 1
Parameters used in the regression analysis to t the nonlinear models for blast disease progress curve on wheat leaves, inoculated with two isolates of Pyricularia oryzae Triticum.On wheat leaves, ve successive infection cycles of the PoTl 12.1.146and Py6038 isolates were performed.
b d Mean square of the residual of the linear regression analysis (MSR).e y 0 : initial severity of wheat blast.f r: progression rate of wheat blast.

Table 2
Parameters used in the regression analysis to t the nonlinear models for blast disease progress curve on wheat heads inoculated with two isolates of Pyricularia oryzae Triticum.On wheat heads, ve successive infection cycles of the PoTl 12.1.146and Py6038 isolates were performed. b 2.54 to 2.95 days and wheat leaves, and from 2.88 to 3.16 days on wheat heads (Dorigan et al., 2022).The wheat blast severity from both 12.1.146and Py6038 isolates increased over time on wheat leaves and heads.At 7 d.a.i, the disease intensity of PoTl isolate 12.1.146on leaves and heads at the initial infection cycle was 1.54 and 1.82 times higher than that of the PoTl isolate Py6038, respectively.Similarly, to what was observed for the initial infection cycle, in successive infection cycles, at 7 d.a.i, PoTl isolate 12.1.146caused higher disease severity than the PoTl isolate Py6038 Bedimo et al., 2007, van den Bosch et al., 2014)The Gompertz model has also been cited for its temporal t of wheat blast (Gongora-Canul et al., 2020).Both logistic and Gompertz models have similar curve shapes and are often used to describe and model polycyclic epidemics (MouenBedimo et al., 2007, van den Bosch et al., 2014).Therefore, we can highlight some important ndings of this study: i) for each infection cycle, the secondary inoculum of PoTl isolate 12.1.146andPoTlisolatePy6038producedonsymptomatic wheat leaves infected and colonized wheat heads; ii) disease severity in both 12.1.146andPy6038isolatesincreasedoverthecourse of time in each infection cycle on wheat leaves and heads; iii) after the 5th infection cycle, the PoTl isolate 12.1.146didnotreducethediseaseseverityon wheat leaves and heads.As a nal highlight, iv) the logistic model can be used to describe and model wheat blast epidemics caused by PoTl isolates under controlled conditions.When analyzing the likely contributions of our results to the management of the PoTl, the questions and answers about successive wheat crop cycles in Brazil and the occurrence of isolates such as 12.1.146(intermsofblast severity) have important implications for the integrated management of wheat blast in wheat elds.Certain cultural practices should be implemented, for example, the management of secondary inoculum of PoTl isolates in wheat elds, in basal leaves, which is a potentially important inoculum source for new epidemics, as well as the crop planting date, which according toGoulartet al. (2007) should be adjusted as a strategy to escape infection by the PoTl pathogen (Goulart et al., 2007, Cruz et al., 2015).Other management strategies can be implemented and contribute to the reduction of PoTl populations in wheat elds, for example, applications of multisite fungicides in mixtures with effective active ingredients of single-site inhibitors.Multisite fungicides can be employed as mixing partners with other fungicides at an early stage of the disease epidemic (Cook et al., 1999, Hobbelen et al., 2011, van den Bosch et al., 2014).Moreover, biological control spraying labelled biofungicides formulated with Bacillus methylotrophicus, Chaetomium globosum, and Tricoderma harzianum can also be used to manage wheat blast (Park et al., 2005, Singh et al., 2012, MAPA, 2021).These important management strategies would be essential in reducing wheat blast severity in Brazilian wheat elds.Declarations Acknowledgements Adriano Francis Dorigan was supported by Brazilian Coordination for the Improvement of Higher Education Personnel (CAPES, nance code 001).Silvino Intra Moreira was supported by PDJ/CNPq Postdoc Scholarship (152074/2022-8).Paulo Cezar Ceresini was supported by São Paulo Research Support Foundation, Brazil (Fapesp 2020/07611-9).Eduardo Alves is supported by the National Council for Scienti c and Technological Development (CNPq 305482/2017-3, 313825/2018-1, 432445/2018-8, and 306133/2021-0).