Wheat (
The amount of water available for crops is defined by the balance between precipitation and evapotranspiration [
Because most farmers are focused on grain yield potential, irrigation technology has become an important tool both to maximize production [
Central pivot irrigation is the dominant technique used in this region, but it is not clear whether this technology affects disease susceptibility. This method wets the foliage, thus reducing its temperature while increasing the relative humidity and the length of time during which the leaves remain wet; both of them can promote foliar diseases.
Foliar diseases are the main biotic restrictions that reduce wheat yield in Argentina [
However, the negative effects of foliar diseases on wheat yield and quality have increased in Argentina over the last several years due to, among other things, the expansion of no-till, the dissemination of susceptible genotypes, and the use of infected seed [
The major foliar fungal diseases caused by necrotrophic pathogens in Argentina have historically been tan spot (DTR) and septoria leaf blotch (SLB); the latter is caused by
According to Fernández and Corro Molas [
Serrago et al., cited by Simón et al. [
Additionally, in Argentina, the losses caused by the DTR can reach values as high as 14% in grain yield, as well as an 8 to 11% reduction in thousand grain weight and between 1.2 and 4.5% in hectoliter weight [
Wheat cultivars that are susceptible to LR regularly suffer yield reductions of 5–15% or greater, depending on the stage of crop development [
Seed quality is also essential; the health status of a seed lots is the main criterion for seed quality, together with purity, energy, and germinative power [
Few studies have investigated wheat diseases grown under supplementary central pivot irrigation in Argentina. Work carried out in southern Alberta (Canada) showed that wheat foliar diseases increased in the presence of sprinkler irrigation [
The concepts outlined above highlight the importance of obtaining local information about health problems in cultivated wheat and their possible effects on grain production, that is, comparing the yield maximization achieved through supplementary irrigation with the potential negative effects of irrigation on the evolution of diseases.
The objective of this work was to assess the relation between the health of a wheat crop (grown in the greenhouse or field) and the water management conditions used in the eastern/central region of Santa Fe.
The experiment was carried out over two successive growing seasons (2009-2010) in the “Miraflores” area (latitude 32°10′14′′ S, longitude 60°59′57′′ W), located in the eastern/central region of the Santa Fe province, with 800 ha under central pivot irrigation with water from the Coronda River. The system that they have has an intake in the river, which drives through channels, partly excavated and partly on an embankment, with four pumping stations. The central pivot covers an area of 32 ha (six towers, 325 m) with average irrigation flow and depth of 125 m3 h−1 and 8 mm day−1, respectively. The applied drops are between 1 and 2 mm, and the passage time on the leaves varies from a few minutes (extreme towers) to a few hours (central towers), depending on the applied depth.
The climate analysis considered historical information for the central region (Oliveros and Santa Fe), including rainfall, temperatures, pressure vapor, wind, radiation, and evaporation.
The soil is a Typic Argiudolls, which is suitable for agriculture (class I, INTA, 1992). Surface composite samples of soil (0–0.2 m) were extracted for chemical analysis (pH, total nitrogen, organic matter, phosphorous, sulfur) in order to calculate the fertilizer doses required.
The treatments were as follows: D (rainfed, no irrigation) crops located outside the circle; TI, with irrigation managed according to the maximum expected yield and maximum demand for water; CDI, with irrigation managed strategically according to the water deficit. Three plots (replicates of 100 m2 each) in each treatment area were selected for evaluation.
The Cronox cultivar was used for all treatments. Cronox is a short-intermediate cycle plant with moderate susceptibility to DTR and LR, and moderate-to-low susceptibility to SLB, according to the information provided by their respective breeder. Seeding was carried out on June 10 with a density of 150 kg ha−1 seed, resulting in a density of 453 plants m−2. Fertilizer was applied based on a prior analysis of the soil: 150 kg ha−1 urea (broadcast applied), 70 kg ha−1 of diammonium phosphate, and 50 kg ha−1 calcium sulfate, and the harvest was on November 12. In the 2010 season, Cronox was sowed on June 23 but at a higher density (160 kg ha−1), 409 plants m−2. Plants were fertilized with 120 kg ha−1 urea (broadcast applied), 100 kg ha−1 of ammonium phosphate, and 80 kg ha−1 calcium sulfate, and the harvest was on November 14. Management practices, which were usually carried out by the farmers, included the preventive treatment of seeds with an antifungal agent (25% carbendazim + 25% tiram).
Seed samples with and without treatment (4 samples of 100 seeds each) were obtained and incubated to measure germination energy (GE) and germinative power (GP). Incubation was carried out using the top of paper method according to Peretti [
Incubation was carried out at 21 ± 1°C, a relative humidity of 80%, 12 h light, and 12 h of darkness [
The Zadoks scale was used to monitor crop phenology [
Fusarium head blight (FHB) results from the development of a complex of pathogenic fungi.
Distrain software was also used to estimate the severity of several diseases, including LR, powdery mildew, SLB, striated rust, stem rust, and DTR [
To estimate the total aboveground biomass (TAB), samples were taken from plants at three timepoints,
Yield was determined from two samples extracted at random from physiologically mature plants along one linear meter per plot. In the laboratory, plants and stems were counted for each sample, and subsamples (20 stems) were separated by components (stalk and spike); the number of spikelets per spike and fertile and infertile spikelets was counted. Each component and the rest of the sample were dried separately at 65°C to a constant weight. Each sub-sample of spikes was threshed manually, and the resulting grains were subsequently weighed and counted.
The experiment was conducted in a random block design with three replicates, and analysis of variance (ANOVA) was used to evaluate the severity, impact, LAI, and yield parameters using the program INFOSTAT/professional-version 2009 [
In addition to epidemiological studies in the field, we evaluated plants grown in a greenhouse in order to compare the health and yield of this cultivar under different irrigation conditions.
The same variety of wheat was used (Cronox) with a sowing date of May 31, 2010, in furrows of 0.3 m and separated by 0.2 m. Greenhouse plants received either TI (irrigated at 100% field capacity) or CDI (75% of field capacity) treatments, but it was not feasible to use D (rainfed, no irrigation). Cultivation occurred normally with a density of 47 pl per treatment, equivalent to 400 plants m−2. The treatments began with an initial moisture equivalent to field capacity.
The plants were kept in a greenhouse with a temperature of 22°C and a photoperiod of 16 : 8 (light and dark) [
Interval irrigation was initiated when 75% of the available water had been depleted. A 20 mm fixed dose was used, representing the estimate of useful water in the container, and a pressurized sprayer (Giber) was used to simulate sprinkler irrigation.
Given that wheat stubble constitutes a natural reservoir of many fungi that cause necrotrophic “leaf spots,” such as
Nondestructive methods (i.e., weekly observation through manual magnifiers) were used to evaluate disease from the beginning of tillering to the filling of grains. LAI was estimated by subsampling 10 plants per treatment and was repeated at three phenological timepoints:
Yield was determined using the same methodologies that were used in the growing field. The trial was conducted in a randomized block design with four replicates, and severity, impact, LAI, and yield parameters were evaluated using analysis of variance (ANOVA).
The GE and GP values obtained for the seeds from the 2009 season were 100% and 99%, respectively, for untreated seeds and 99.5% and 97.5%, respectively, for treated seeds; in 2010, these values were 98.75%, 98.25%, 99.5%, and 99%, respectively. According to Peretti [
In the untreated seeds from 2009, the incidence of microorganisms was 30.5%, predominantly “black point” grains caused by
The conditions of high humidity and high temperatures that occurred towards the end of the growing season in 2009, coupled with poor storage conditions, increased the incidence of the pathogens that cause discoloration and deterioration of seeds. This result was verified in the analyses performed on seeds that were stored by the farmer and used for seeding in the 2010 season, which contained
Incidence (%) and genera of pathogens identified through blotter tests of seeds treated with fungicide or untreated in 2009 and 2010.
Treatment | Year | ||||||
---|---|---|---|---|---|---|---|
Seeds treated | 2009 | 0 | 0 | 0 | 0 | 0 | 0 |
2010 | 1.25 | 0 | 10.5 | 0 | 0 | 0.25 | |
Seeds untreated | 2009 | 22 | 5 | 0 | 2.5 | 0.5 | 0 |
2010 | 26.5 | 0 | 28 | 0 | 6.25 | 11.25 |
Exposure to fungi in the field and during storage affects germination, seedling stand, grain size and weight, and industrial quality. In the case of wheat, these fungi are associated with the grain spotting known as “black scutellum,” or “blackpoint.” This pathology is characterized by a black or brown coloration in the area of the embryo, which could also be extended to the surrounding area and the groove [
A total of 310 mm effective rainfall was received in 2009, which was greater than the historical average (Figure
Average, minimum, and maximum air temperature values (°C) and precipitation during the 2009 growing season.
The daily average air temperatures were lower than 16°C in June, July, and September, as well as in the first ten days of August and the second ten days of October. The lowest temperature was recorded on July 14 (−8°C). Three consecutive days with temperatures greater than 21°C were recorded during August and October (last ten days) and two days in November (second ten days).
The ambient relative humidity remained above 60%, and wet leaves were still observed after 15 hours on two consecutive days during the second ten days of July and the first ten days of September.
The three most frequent leaf pathologies, LR, DTR, and SLB, were identified in all treatments.
The incidence of foliar diseases was higher in the D treatment than in the other treatments, although the severity remained below 1% in all treatments. The average disease incidence (percentage of sick leaves with respect to the total number of leaves), both in general and at different phenological stages, was significantly different (Table
Incidence (%) of foliar disease onset for total irrigation (TI), irrigation with controlled deficit (CDI) and dry (D) wheat at various phenological timepoints.
Treatment | Incidence (%) | |||||||
10/09/2009 | 16/09/2009 | 30/09/2009 | 15/10/2009 | |||||
TI | 17.1 | A | 19.6 | A | 14.2 | A | 27 | A |
CDI | 18.8 | A | 13.5 | A | 15.7 | A | 16.8 | A |
D | 51.3 | B | 31.3 | B | 46.7 | B | 59.5 | B |
Different letters indicate significant differences according to Tukey (
This pattern was likely observed because the nonirrigated wheat did not achieve total coverage of furrows, even at advanced stages of development (
The individual development of each foliar disease present during the crop cycle was analyzed. In general, epidemics of SLB is caused by a combination of favorable climatic conditions (usually characterized by long periods of light rain and moderate temperatures), certain cultivation practices, the availability of inoculum and the presence of susceptible varieties [
DTR was the most frequently observed disease throughout the analysis period, with an average incidence value of 20.07%. DTR also made up 31.58% of leaf injuries, together with LR. These injuries were observed on both FL and FL-1. The fungus survives in the stubble and, under humid conditions and adequate rainfall, releases spores that infect the lower leaves. From there, the disease advances to higher leaves by rain splashing or air circulation [
There were significant differences between the D treatment and the irrigation treatments (CDI and TI), with the exception of the sampling on September 16, in which the differences were not significant (Table
Incidence (%) of tan spot (DTR) for total irrigation (TI), irrigation with controlled deficit (CDI), and dry (D) treatments at different sampling dates in 2009.
Treatment | Incidence (%) DTR | |||||||
10/09/2009 | 16/09/2009 | 30/09/2009 | 15/10/2009 | |||||
TI | 16.7 | A | 19.1 | A | 14.2 | A | 11 | A |
CDI | 18.8 | A | 12.3 | A | 15.7 | A | 3.3 | A |
D | 49.73 | B | 20.1 | A | 46.7 | B | 29.5 | B |
Different letters indicate significant differences according to Tukey (
The average incidence of LR was 11.52% over two sampling dates. LR was first identified in
On September 30 (the sampling that was conducted before the new LR attack), the conditions in the experimental area were highly favorable for pathogen development. According to INTA Gálvez, in the first ten days of October, the maximum, minimum, and average temperatures were 22.1°C, 4.7°C, and 13.5°C, respectively. Rainfall of 101 mm accumulated in just 15 days (for comparison, the historical average for October is 105 mm), and several days were misty and foggy, which resulted in water accumulation on the leaves.
At
Incidence (%) of (LR) for total irrigation (TI), irrigation with controlled deficit (CDI), and dry (D) treatments at different sampling dates in 2009.
Treatment | Incidence (%) LR | |||
16/09/2009 | 15/10/2009 | |||
TI | 0.5 | A | 10.2 | A |
CDI | 1.2 | A | 7.7 | A |
D | 11.7 | B | 48.2 | B |
Different letters indicate significant differences according to Tukey (
In addition to all of the observed foliar diseases of fungal origin, large, dry, grayish-green lesions corresponding to bacterial blight caused by
Finally, at physiological maturity (November 12), spikes were analyzed using wet chamber method. The presence of stained glumes caused by the saprotroph fungus
Although foliar diseases were common throughout the growing season, high yields were obtained in all treatments, as evaluated by the number of spikes. The only significant differences observed between D and irrigation (DIC and TI) were in the weight of 1000 grains (Table
1000 grains weight, biomass of harvested grain (BHG) and index harvest (HI) measured during 2009 for total irrigation (TI), irrigation with controlled deficit (CDI) and dry (D) treatments.
Treatment | 1000 grains weight (g) | BHG (kg ha−1) | HI | |||
TI | 33.57 | A | 8057 | A | 0.5 | A |
CDI | 33.95 | A | 8128 | A | 0.48 | A |
D | 30.88 | B | 6919 | B | 0.42 | B |
Different letters indicate significant differences according to Tukey (
The critical period for the main component of wheat yield (grains m−2) ranges from 20 to 30 days before and 10 days after flowering. This is therefore the period during which leaf health is the most crucial for the plant to take advantage of incident radiation to maximize the growth and viability of the grains. Serious losses can also occur when the flag leaf is infected prior to anthesis. However, even the most prevalent diseases never exceeded 4% incidence or 1% severity in FL, so those were considered unlikely to have caused yield loss, regardless of the time of occurrence. Furthermore, crop health was generally very good, and yield differences between treatments were attributed to other causes (e.g., water availability differential, LAI achieved in each treatment).
During the wheat growing season, from implantation until the harvest, a total of 184 mm effective rainfall was received, well below the normal rainfall for the area of study. Due to the lack of rainfall, four irrigations were conducted, with a net sheet total of 180 mm. The first irrigation consisted of 40 mm conducted on August 7 (
The average daily temperature was below 16°C during the last third of June and during July, August, September, and October. In the first days of November, the daily average temperature exceeded 22°C (Figure
Average, minimum, and maximum air temperature (°C) and precipitation (mm) during the 2010 growing season.
Similar to the results from 2009, all three basic foliar diseases (LR, DTR and, to a lesser extent, SLB) were observed. Disease was significantly more prevalent in the D treatment than in either irrigation treatment (
The first sampling was carried out in
Leaf area index (LAI) at two sampling points for total irrigation (TI), irrigation with controlled deficit (CDI), and dry (D) treatments.
Treatment | LAI | |||
16/09/2010 | 13/10/2010 | |||
TI | 6.39 | A | 7.95 | A |
CDI | 6.38 | A | 6.15 | AB |
D | 3.17 | B | 5.52 | B |
Different letters indicate significant differences according to Tukey (
At the following sampling at
In the following sample, which was collected at
Incidence (%) of foliar disease onset for individual phenological states under total irrigation (TI), irrigation with controlled deficit (CDI), and dry (D) treatments.
Treatment | Incidence (%) | |||||
16/09/2010 | 30/09/2010 | 13/10/2010 | ||||
TI | 10.3 | A | 20.1 | A | 50.2 | A |
CDI | 11.7 | A | 23.7 | A | 48.2 | A |
D | 21.6 | B | 52.7 | B | 74.3 | B |
Different letters indicate significant differences according to Tukey (
SLB infection levels were low due to the low rainfall and limited hours of wet leaves, which did not allow SLB establishment and dispersal. The registered incidence values were 1.22% in D, 3.14% in CDI, and 3.44% at TI.
DTR was present from the tillering stage to the end of the growing season. The stay of wheat straw at the soil surface, associated with moderately conducive weather conditions, favored the emergence and constant development of DTR throughout the entire crop cycle, with a variable but consistently increasing incidence according to phenological state. Significant differences were observed between D and the irrigated treatments (Table
Incidence (%) of tan spot (DTR) in various phenological states for total irrigation (TI), irrigation with controlled deficit (CDI), and dry (D) treatments.
Treatment | Incidence of DTR (%) | |||||
16/09/2010 | 30/09/2010 | 13/10/2010 | ||||
TI | 6.8 | A | 20.1 | A | 46.77 | A |
CDI | 9.3 | A | 23.7 | A | 45.2 | A |
D | 20.4 | B | 52.7 | B | 71.2 | B |
Different letters indicate significant differences according to Tukey (
The spread and infection of
The onset of LR was significantly delayed in 2010 relative to 2009 and was first registered only at the beginning of flowering. According to INTA Galvez, the maximum, minimum, and average temperatures during the second ten days of September were 27.5°C, 8.1°C, and 16.8°C, respectively. A total of 56.4 mm of rainfall was recorded in the last two weeks of September and the first ten days of October, and leaves were wet for up to 17 consecutive hours for several days in the last third of September.
Statistical analysis showed significant differences in LR incidence between D and irrigation treatments (37.07% versus 8.73% in CDI and 9.5% in TI).
The disease reached FL-1 with an incidence of 40% in D, 2% in CDI, and 10% in TI. The severity reached levels of 15% in D but was less than 1% with only one to two pustules per leaf in the irrigation treatments. LR was observed in FL only in the D treatment, with an incidence of 6% and a maximum severity of 10%.
Finally, on November 11, samples were extracted to analyze the crop yield. Very good results were obtained in all treatments, although a significant difference (
1000 grains weight, biomass of harvested grain (BHG) and harvest index (HI) measured during 2010 for total irrigation (TI), irrigation with controlled deficit (CDI) and dry (D) treatments.
Treatment | 1000 grains weight (g) | BHG (kg ha−1) | HI | |||
---|---|---|---|---|---|---|
TI | 30.3 | B | 8898 | B | 0.49 | A |
CDI | 27.2 | BA | 7820 | BA | 0.47 | A |
D | 25.7 | A | 6899 | A | 0.48 | A |
Different letters indicate significant differences according to Tukey (
In terms of the health of the spikes and grains,
Additionally,
The first irrigation was conducted during
The first symptoms were observed during full tillering (
Incidence (%) of foliar disease onset at different times of measurement for total irrigation (TI) and irrigation with controlled deficit (CDI) treatments.
Treatments | Incidence of foliar disease (%) | |||||||||
13/08/2010 | 24/08/2010 | 02/09/2010 | 14/09/2010 | 28/09/2010 | ||||||
CDI | 9.12 | A | 32.12 | A | 30.08 | A | 17.08 | A | 36.67 | A |
TI | 9.63 | A | 31.38 | A | 33.21 | A | 57.38 | B | 70 | B |
Different letters indicate significant differences according to Tukey (
DTR infection reached both FL-1 and FL. The maximum incidence in FL-1, observed at
It should be noted that lower levels of incidence and severity were reported in CDI in the greenhouse trials than under field conditions.
LAI values were similar between treatments (Table
Leaf area index (LAI) measured during different phenological states under total irrigation (TI) and irrigation with controlled deficit (CDI) treatments.
Treatments | LAI | |||||||
13/07/2010 | 24/08/2010 | 02/09/2010 | 14/09/2010 | |||||
CDI | 6.57 | A | 6.16 | A | 5.63 | A | 3.56 | A |
TI | 7.14 | A | 6.56 | A | 5.56 | A | 3.86 | A |
Different letters indicate significant differences according to Tukey (
1000 grains weight, biomass of harvested grain (BHG) and harvest index (HI) measured for total irrigation (TI) and irrigation with controlled deficit (CDI) treatments.
Treatments | 1000 grains weight (g) | BHG (kg ha−1) | HI | |||
---|---|---|---|---|---|---|
TI | 31.75 | A | 7328 | A | 0.39 | A |
CDI | 28.59 | B | 4898 | B | 0.34 | A |
Different letters indicate significant differences according to Tukey (
The genera of fungi identified in this analysis correspond to those recognized by Can Xing et al. [
During the two agricultural cycles evaluated, DTR and LR were the dominant foliar diseases. The cultivated plants remained healthy until advanced stages of development, and the severity of both foliar diseases was low in all of the treatments tested. In the 2009 season, 100% of plants in all treatments exhibited some degree of infection, although the severity was very low (less than 1%). Similarly, in the 2010 season, 100% of the experimental plants exhibited some degree of infection, again with relatively low severity (less than 15% in D, below 5% in CDI and 1% in TI).
Plants that received irrigation treatments exhibited lower levels of foliar diseases in both years. These results conflict with those of a previous study [
The lower disease burden of irrigated plants, observed during both years, may be attributed to the fact that better nourished plants (i.e., plants with greater water accessibility) are generally more tolerant of or less affected by foliar diseases. The work of Annone et al. [
SLB was minimal (trace levels) in both years and was observed more frequently in D plants than in irrigated plants, especially during the more humid 2009 season. These results can be attributed to the density of plants generated in each treatment; as discussed above, plants in the D treatment did not fully cover the grooves, unlike the plants under irrigation, thus allowing the disease to develop further. This finding is consistent with the work of Massaro et al. [
The results of our greenhouse experiments should not override those obtained in the field; significant differences in the parameters severity and incidence for both irrigation systems have not been verified.
Finally, significant differences in productivity were observed between irrigation and rainfed treatments. These differences were due to the application of water during the stem elongation stage (
Based on tests carried out over two consecutive years, supplementary sprinkler irrigation of cultivated wheat at opportune moments, even in small quantities, increases grain weight and thus yield without increasing the incidence of foliar disease. Two fundamental principles should be considered for the correct management of wheat diseases: (1) the initial health of the crop should be optimized by using seeds with a low pathogen load and (2) appropriate monitoring should be conducted to properly quantify the diseases present in the field.