1. Introduction
Sugarcane (Saccharum spp.) is one of the world’s most important agricultural crops, with Brazil being the largest producer, responsible for 42% of global production. In the 2023/2024 harvest season, 713.2 million tons of sugarcane were harvested on 8.33 million hectares [1]. The raw material has a wide range of uses, not only for the production of sugar and ethanol, but also for the production of industrial by-products. Furthermore, the use of waste from the processing of the raw material makes sugarcane one of the agricultural crops best suited to the circular economy.
Sugarcane smut, caused by Sporisorium scitamineum (Syd.), is an important fungal disease which reduces the quality and yield of sugarcane, resulting in significant economic losses. The disease was first identified in 1877 in Natal, South Africa [2], and in Brazil, it was first observed in 1946 in the region of Assis, São Paulo [3]. Sugarcane plants infected by S. scitamineum exhibit a modified apical meristem, known as a “whip”, which is the main symptom used to identify the presence of the disease. There is also a reduction in diameter and over sprouting of tillers. The primary mode of spread is by spores (teliospores) transported by wind, rain, humans, and insects [4].
Screening of sugarcane varieties, clones, and germplasm accessions for smut resistance has been adopted by breeding programs in Australia, Indonesia, and Japan. These programs have used artificial inoculation and field evaluation to identify resistant genotypes for use as parents in crosses, aiming to increase the frequency of resistant individuals in the progeny [5,6].
Sugarcane exhibits two distinct forms of resistance: (i) external resistance, controlled by the structural barrier of bud scales and/or chemical compounds within the buds, such as flavonoids (glycosidic substances), which impair teliospore germination; and (ii) internal resistance, driven by the interaction between the plant and the fungus within the plant tissue [7,8,9]. This internal resistance involves the production of pathogenic-related proteins, the balance between oxidative burst and antioxidant enzyme activity, and antimicrobial compounds such as phytoalexins and glycoproteins, for example [10,11].
The immersion method is used to assess external resistance, wherein the hyphae of S. scitamineum is unable to penetrate the epidermis due to structural and biochemical changes in the cell wall of the host plant, including the accumulation of lignin and phenolic compounds [7]. Internal resistance is evaluated using the needle-bud puncture method [8,9], where a suspension of teliospores is introduced into the bud scales by a needle, disrupting its structural barrier and triggering various induced sugarcane defense responses. This method is most suitable for screening parental sources of smut resistance.
Greenhouse resistance trials offer several advantages, including the ability to evaluate a greater number of genotypes, the use of controlled conditions, and the containment of the inoculum, which reduces the spread of spores. Although the resistance observed under these conditions may not fully reflect the resistance seen in the field, greenhouse trials are a crucial first step in eliminating the most susceptible genotypes and identifying those with potential smut resistance. This approach allows for the evaluation of genotype responses in a relatively short period, which is advantageous for sugarcane breeding programs dealing with a large number of genotypes [12].
The evaluation of smut resistance considers the incidence of the disease, measured by the number of stalks with whips or infected plants per plot [13]. Additionally, epidemiological parameters such as the Area Under the Disease Progress Curve (AUDPC) [14,15,16] allow the disease’s behavior to be monitored over time. While incidence measures the percentage of infected plants, the AUDPC provides a single value that accounts for both the incidence and severity of the disease over time.
According to Campbell and Madden (1990) [14], genotypes that exhibit rapid symptom expression tend to accumulate higher AUDPC values, reflecting the dynamics of infection and pathogen–host interaction. A correlation between genotype susceptibility and AUDPC was observed for Septoria tritici in winter wheat, with the most susceptible wheat cultivars recording higher AUDPC values [17].
In this study, the response to smut infection of 165 sugarcane genotypes, artificially inoculated using the needle-bud puncture method, was evaluated under greenhouse conditions. Resistance was assessed through a combination of disease incidence and AUDPC data, as well as the relative Area Under the Disease Progression Curve (rAUDPC). This allowed the genotypes to be classified into four resistance levels: highly resistant, resistant, moderately susceptible, and susceptible. The practical applications of this approach in a sugarcane breeding program are discussed.
2. Materials and Methods
2.1. Material
The trial was conducted at the Sugarcane Center of the Agronomic Institute of Campinas (IAC) in Ribeirão Preto, São Paulo, Brazil. It began in August 2022 (bud inoculation) and continued until May 2023. A total of 165 sugarcane genotypes were screened for smut resistance, including S. robustum, S. officinarum, and S. spontaneum accessions, as well as commercial cultivars from Brazilian sugarcane breeding programs and IAC clones. Known resistant and susceptible cultivars were included as controls.
2.2. Greenhouse and Field Ttrial Experimental Design
The greenhouse experiment was conducted using a randomized complete block design with three replicates. Each experimental plot consisted of a 50-cell tray (150 buds per genotype), with buds extracted from 10-month-old stalks selected for uniformity and quality [18]. The buds were artificially inoculated using the needle-bud puncture method. SP80-3280 and IAC66-6 genotypes served as resistant and susceptible controls, respectively.
For the field experiment, two-month-old, inoculated plants were arranged in a randomized block design with three replicates. Each plot consisted of a 2 m row with 4 plants (0.5 m spacing) and 1.5 m between rows, totaling 12 plants per genotype.
2.3. Inoculum Source and Viability Test
Enclosed whips covered with a silver film were collected from a previously infected experimental field plot at the Sugarcane Center in Ribeirão Preto, São Paulo, Brazil, from the IAC09-8047 clone of the IAC sugarcane breeding program, which is susceptible to sugarcane smut infection. The whips were dried at 38 °C for four hours before the silver film was removed to extract the teliospores. The teliospores were sieved (200 mesh), packed in a permeable plastic bag, and stored in a desiccator with silica gel to maintain viability [19]. Viability was assessed through germination tests on a 1% (w/v) water–agar culture medium. A suspension of 150 µL of teliospores at 105 was spread on a microscope slide, placed in a Petri dish with moistened cotton wool, covered with a dark plastic bag, and incubated at 28 °C for seven hours. Teliospores with a germination tube length greater than or equal to the mean diameter were considered viable, with a minimum of 90% germination indicating viability.
2.4. Bud Inoculation
Single buds from 10-month-old were inoculated using the needle-bud puncture method [12]. A suspension of 4.5 × 105 (spores/mL) was prepared in a sterilized porcelain crucible (0.2 g of teliospores, 1.5 mL of distilled water, and 2 µL of 10% Tween 80). Each bud was punctured with a hypodermic needle (25 mm × 0.70 mm) on both sides, preserving the germination pole, and planted in 50-cell trays filled with Carolina soil Class XVI (Figure A1a). The trays were kept in a sprouting chamber at 30 °C and >85% humidity for 48 h to promote germination and infection (Figure A1b). Temperature was then increased to 35 °C for a week to enhance sprouting. The trays were transferred to the greenhouse with sprinkler irrigation applied twice a day for 15 min until the end of the evaluations (Figure A1c).
2.5. Sugarcane Smut Incidence
Evaluations began two months after planting the inoculated buds, when the first signs of the disease (black whip-like sorus) were observed and continued weekly for 198 days (Figure A1d). Disease incidence was calculated as the percentage of plants with whips (infected plants) out of the total number of plants in each plot (total emerging buds), i.e., disease incidence (%) = (number of infected plants/total number of emerged buds) × 100. The same procedure was applied in the field experiment.
2.6. Area Under the Disease Progress Curve (AUDPC)
The AUDPC was calculated according to the equation of Shaner and Finney (1977) [20].
where yi = proportion of disease in the i-th observation; ti = time in the i-th observation (in days); and n = total number of observations in a time t.The AUDPC was used to estimate genetic and environmental variance, and broad-sense heritability (h2) was measured using the R software version 4.2.3. VCA (Variance Component Analysis) package. Broad-sense heritability of individual plants was estimated with the following equation:
where VG is the genotypic variance and VE is the environmental variance.2.7. Genotypes Categorization for S. scitamineum Resistance
The genotypes were classified for smut resistance based on the relative Area Under the Disease Progress Curve (rAUDPC). The rAUDPC was calculated by dividing each genotype’s AUDPC by that of the most susceptible genotype, multiplied by 100, resulting in values from 0 (highly resistant) to 100% (highly susceptible). The genotypes were categorized into four resistance classes: highly resistant (0%), resistant (0.1% to 5%), moderately susceptible (5.1% to 20%), and susceptible (>20%).
2.8. Statistical Analysis
Statistical analyses were conducted using R statistical software with a 5% significance level (p ≤ 0.05) for analysis of variance. Data were normalized using the Neperian logarithm (ln) transformation, by the formula ln(x + 5), where “x” is the value to be transformed. Spearman’s correlation (r2) compared disease expression in the greenhouse and field. Cultivars SP80-3280 and IAC66-6 were used as resistance and susceptibility standards, respectively. The whip incidence data from the greenhouse experiment was analyzed using a mixed model procedure (PROC MIXED) in SAS package version 9.4 [21], with random effects for genotype and fixed effects for block and evaluations. This analysis allowed for the calculation of the Best Linear Unbiased Prediction (BLUP) of the Expected Difference from the Parent (EDP), indicating each genotype’s positive or negative effects relative to the reference experiment.
3. Results
3.1. Greenhouse Smut Incidence
The incidence of sugarcane smut (black whip sorus) ranged from 0 to 88%, with an average of 9.5%. The resistant standard genotype (SP80-3280) exhibited no incidence of whips throughout the entire evaluation period. The genotypes SP91-1049 and IACSP04-2516 had a very low whip incidence observed around 85 days after the start of the evaluation, while the genotype IAC16-2144 reached 88% of whip incidence, exceeding the susceptible standard genotype IAC66-6 (63% of whip incidence).
The average number of whips of 10 of the 165 genotypes over 198 days of evaluation (October 2022 to April 2023) is shown in Figure 1.
Although the average number of whips was higher in IAC16-2144 than in the standard susceptible genotype (IAC66-6), the first whip observation in IAC66-6 occurred earlier (13 days after the start of evaluations; 55 days after inoculation) compared to IAC16-2144 (43 days after the start of evaluations; 72 days after inoculation). Maximum incidence occurred at 142 and 172 days after the start of evaluations for IAC66-6 and IAC16-2144, respectively, showing differences not only in disease progression but also in the latent period, i.e., time interval between bud inoculation and the first appearance of symptoms (whip). In addition to the IAC16-2144 genotype, nine genotypes were also found to be more susceptible than the original standard; six of these genotypes (IAC16-2134, IACSP04-2503, Co213, IACSP99-4011, IN84-58, and IACCTC05-3616) had an average whip number starting at 36 days after the start of evaluations, followed by a stabilization between 150 and 198 D.A.I., a consistent pattern across all the most susceptible genotypes.
The distribution of whip incidence (Table 1) showed a predominance of genotypes with a low incidence of whips, with the majority (115 genotypes) displaying a maximum of 10% of incidence. One hundred and forty-four genotypes had an incidence value ranging from 0 to 40%.
3.2. Area Under the Disease Progress Curve (AUDPC)
The AUDPC values increased throughout the experiment, reflecting the speed at which the disease developed. Most of the genotypes (131) showed AUDPC values between 0 and 500 (Table 2). Additionally, some genotypes exhibited slight susceptibility, with AUDPC values of approximately 1000. A low frequency of genotypes with high AUDPC values (>1000) was also observed, indicating susceptibility to smut. The genotypes with the lowest AUDPC value, recorded as zero, reflect the complete absence of the disease (whips), highlighting them as the most putative resistant. Conversely, the highest AUDPC value was 2629 (IAC16-2144), which exceeded the value (1369) of the susceptible standard genotype (IAC66-6).
3.3. Categorization of Genotypes Resistance by rAUDPC
The AUDPC of all genotypes was divided by the AUDPC of the most susceptible genotype (IAC16-2144) to calculate the relative AUDPC values (rAUDPC). The rAUDPC values ranged from 20.97% (IACBIO277) to 100% (IAC16-2144), with an average of 46.42% for the susceptible resistance class. The moderately susceptible class encompasses genotypes with rAUDPC values ranging from 6.09% (IACSP04-3148) to 19.21% (IACSP04-3150), with an average of 11.49%. For the genotypes classified as resistant, the rAUDPC values ranged from 0.02% (IACCTC07-8008) to 5.08% (IAC16-2053), with an average of 1.31%. Of the 165 genotypes from the panel, 33 (20%) were classified as susceptible, 18 (11%) as moderately susceptible, 60 (36%) as resistant, and 54 (33%) as highly resistant (Table 3).
The sugarcane genotypes classified as susceptible (rAUDPC values above 20%), as well as the ranking of the 10 genotypes with the lowest rAUDPC values within the moderately susceptible (MS) and resistant (R) classes, are summarized in Table 4. The well-known smut-susceptible cultivars IAC66-6 and NCo 310 exhibited rAUDPC values of 52% and 38.61%, respectively, compared to the most susceptible genotype (IAC16-2144) identified in the greenhouse trial (Table 4). The well-known intermediate variety Co419 showed a rAUDPC value of 6.87% and was classified as moderately susceptible. In addition to the resistance standard cultivar SP80-3280, a further 54 genotypes exhibited an rAUDPC value of 0% (highly resistance), indicating the absence of whip incidence during the evaluation period, as shown in Table A1.
3.4. Comparison Between Greenhouse and Field Trial
The number of genotypes with smut incidence in the field experiment (143 or 86.66%) was higher than the observed in the greenhouse (111 genotypes or 67.27%). Of the 165 genotypes, 106 (64.24%) developed whips either in the greenhouse or field conditions, 37 (22.42%) showed whip incidence only in the field conditions, while 5 (3.03%) showed it only in the greenhouse. Moreover, 17 genotypes (10.30%) showed no whips in either condition (Table 5) and remained highly resistant (Table A1). Of the 37 genotypes showing whip incidence only in the field, 10 were rated as susceptible (S), 9 as moderately susceptible (MS), and 18 as resistant (R), (Table A1). The Spearman correlation (r) between the incidence of whips in the field and in the greenhouse was 61%, indicating a positive and moderately strong correlation.
3.5. Genetic Parameters
According to the analysis of variance (Table 6) the genotypes differ significantly at the 1% level for the AUDPC values showing variability for this measure among the 165 genotypes of the panel evaluated at greenhouse. No significant differences were observed between blocks. The broad-sense heritability value was 74.70%, while the error (environmental variance) represented 25.30% of the total phenotypic variation.
The mixed model analysis of the greenhouse experiment revealed 82 genotypes with negative EPD values at a probability of less than 0.0001 of being 0, of which 54 showed predicted genetic means of zero (Table A1). These results indicate their potential as genitors for breeding smut-resistant sugarcane. Of the 10 genotypes with the lowest rAUDPC values in the resistant class, as presented in Table 4, 8 belong to these 82 genotypes. They displayed EDP values ranging from −0.05554 (SP71-6163) to -0.05086 (IAC80-3480) and predicted genetic means ranging from 0.00071 to 0.00539. The remaining two genotypes, IACSP01-2417 and IACSP93-6006, had EDP values of −0.04749 and −0.04662, with a probability of being 0 at 0.0002, and predicted genetic means of 0.00876 and 0.00963, respectively.
On the other hand, 28 genotypes exhibited positive EDP values with a probability of less than 0.0001 of being 0 (Table A2). These genotypes belong to the susceptible and moderately susceptible classes and should be avoided as parentals in sugarcane breeding. This group includes the susceptible standard genotypes IAC16-2144 and IAC66-6, which showed EDP values of 0.3489 and 0.2979, and predicted genetic means of 0.40515 and 0.35415, respectively.
4. Discussion
Screening for disease resistance is by far the most crucial and challenging step in any genetic breeding program, especially for a genetically complex crop like sugarcane. Sugarcane exhibits high levels of ploidy and heterozygosity, multiple growing cycles (ratoons), and a long-term breeding process that spans 8 to 15 years to release a new commercial variety. The high ploidy level and heterozygosity imply the presence of multiple homoeologous copies of each gene (allele dosage at each locus), which can promote variation in expression levels and variable phenotypic effects. Therefore, the association between genotypic and phenotypic data is not straightforward [22]. Additionally, due to allele dosage and heterozygosity, segregation is more complex [23]. Consequently, susceptible genotypes at low frequency can occur even in crosses between resistant parents.
Considering that the evaluation of disease resistance is time-consuming, establishing pre-screening tests that allow for the assessment of numerous clones in a confined space and require fewer spores for inoculum preparation could be a promising routine tool for breeders.
The needle-bud puncture inoculation method enabled us to effectively study the response of 165 sugarcane genotypes to smut infection at the physiological level, specifically, internal resistance driven by plant-fungus interactions within the plant tissue [9,24]. Although the needle-bud puncture method bypasses the external disease resistance mechanisms provided by the bud’s structural characteristics, it is recommended for preliminary disease testing. This method effectively eliminates the most susceptible clones and allows for the evaluation of a large number of clones within a relatively short time frame [12]. These authors emphasize that, despite being considered excessively rigorous and leading to increases in the absolute infection value, the relative infection value among varieties remains consistent. This consistency allows for differentiation between the extremes of the disease rating scale and minimizes the risk of discarding intermediate and resistant genotypes. Therefore, in our panel, it was possible to identify potential genotypes that likely possess resistance mechanisms which help to limit pathogen multiplication, its systemic establishment in the host, and symptom expression (whip incidence). Notably, the well-known smut-resistant cultivar SP80-3280 [25] exhibited no symptom expression (incidence of whips) over the 198-day evaluation period. In contrast, genotypes such as IAC16-2144 showed a high incidence of smut, surpassing the standard susceptible variety IAC66-6 used in several Brazilian sugarcane smut studies [12,25] under both artificial inoculation and natural infection in the field. A similar result was reported by Rago et al. (2009) [3], who observed a higher incidence of whip in the sugarcane intermediate variety Co421 than in the susceptible variety SP84-2066, which exhibited a shorter latent period than the Co421 variety. Moreover, the range of smut incidence (0% to 88%) observed in our panel reflects the variability in smut reaction response among the genotypes. This variability can be further explored in association mapping studies to identify potential resistant clones for the breeding program.
In addition to the incidence of whips, the overall latent period observed for the genotypes in the greenhouse (47 to 191 days) was consistent with that reported by Hidayah et al. (2024) [26] in the field, where symptoms appear 2 to 7 months (60 to 210 days) after infection, depending on host susceptibility. Typically, 60 to 180 days are required for smut symptoms to develop [27].
The resistance response to smut in the 165 genotypes was assessed using a combination of disease incidence and AUDPC data, as well as the relative Area Under the Disease Progression Curve (rAUDPC). The AUDPC provides an integrated measure of disease progression over time, allowing for a better understanding of host response to the pathogen and the establishment of resistance rankings among genotypes [3,13].
The AUDPC values for the 165 genotypes revealed that the majority exhibited low levels of disease incidence (smut whips), indicating a notable prevalence of resistance. Thirty-three percent of the genotypes showed no smut incidence throughout the evaluation period. These genotypes have great potential to be used as parents in crosses for developing resistant varieties. This outcome is somewhat expected, as most of the genotypes are clones or commercial varieties that have already undergone selection processes. In breeding programs, the strategic selection of genotypes with low AUDPC values indicates high resistance to smut. Based on AUDPC values, Hoepers et al. (2024) [13] classified 41 sugarcane genotypes as highly resistant (7.3%), resistant (43.9%), moderately resistant (29.3%), moderately susceptible (7.3%), and susceptible (12.2%). In addition, the estimation of the genetic predicted value (genotype effect on whip incidence) by the EPD approach has practical applications for sugarcane breeders, as it can identify potential “resistant genotypes” to be used in breeding programs, given that their estimated effects are known.
Due to the emission of new whips over time, periodic disease evaluation is important. Consequently, using a variable that accounts for the entire duration of the epidemic, such as AUDPC, is more appropriate for genotype classification [13]. Given the significant number of genotypes evaluated in our study and to facilitate the interpretation of the results in terms of resistance levels, we divided the AUDPC value of each genotype by the AUDPC of the most susceptible genotype (IAC16-2144) to obtain the relative Area Under the Disease Progression Curve (rAUDPC). This approach allows for a better categorization of the genotypes into resistance classes. This method was proposed by Lima (2020) [28] to classify the genotypes as resistant, intermediate, or susceptible to sugarcane brown and orange rust. The rAUDPC aligns with the assumption of Matsuoka et al. (1986) [12], which recommends performing the rating based on the infection observed in the standard controls in each test, rather than using predetermined infection levels when applying the needle-bud puncture method.
It is important to keep in mind that although the resistant and susceptibility standard controls behaved as expected, the smut reaction reported for the 165 genotypes evaluated in greenhouse conditions was against a smut population from Ribeirão Preto, São Paulo, where the teliospores were collected for artificial inoculation. According to Rago (2009) [3], there is considerable variability in the aggressiveness of S. scitamineum populations in the State of São Paulo, with Piracicaba and two populations from Jaú behaving as the most aggressive compared to Ribeirão Preto. However, there were no changes in virulence among the populations studied. Each sugarcane breeding program has its own strategy for disease screening based on their operational capacity and available financial resources. However, to standardize pre-screening tests across different breeding programs or regions and facilitate broader applicability, it is important to use a mixture of spores from different regions as the source of inoculum for artificial inoculation in screening trials [3].
The moderately strong correlation between greenhouse and field evaluations (61%) indicates that the greenhouse is a reliable tool for identifying smut-resistant genotypes. This correlation is satisfactory, as smut is a disease with difficult symptom reproducibility, meaning inoculated plants do not always manifest the disease [3]. Genotypes that emit whips in both conditions could be discarded, while those that do not are likely resistant and should be advanced. This approach ensures only the most promising genotypes proceed to costly and time-consuming field evaluations. In fact, the field conditions are less controlled than the greenhouse, where factors like soil type, and especially high temperature, and low humidity can affect disease expression. Of the genotypes with whip incidence only in the field, 18% were susceptible, while the rest were moderately susceptible or resistant. In addition, as stated by Rajput (2021) [29], sugarcane smut disease affects meristematic tissues, with the pathogen propagating only in young and actively growing plant tissues. Thus, field conditions can promote better plant growth compared to a cell tray.
Significant differences in smut AUDPC among genotypes is indicative of genetic variability within our panel whilst the lack of significant differences between blocks demonstrates experimental uniformity, reinforcing the reliability of the results.
Smut resistance is considered polygenic [3,30], and varietal resistance has been durable in most sugarcane production areas [31]. Chao et al. (1990) [32] reported that smut reaction is significantly affected by genotype and genotype by environment interaction, leading to changes in infection levels of parent clones between plant cane and first ratoon cane.
The high broad-sense heritability value (74.70%) estimated by variance components for AUDPC indicates that most of the phenotypic variance captured for smut incidence over the evaluation period in greenhouse conditions is due to genetic effects, with less influence from the environment. Previous studies found moderate to high broad-sense heritability (0.68 and 0.75) for smut resistance in sugarcane under field conditions [33,34]. In a bi-parental mapping population, moderately high broad-sense heritability was estimated for smut rating (0.64) and incidence [31]. The pre-inoculated buds used in our experiment were kept in a sprouting chamber at 30 °C and >85% humidity, which matches the conditions described in the literature [35,36] as favorable for teliospore germination and infection. Therefore, environmental factors such as soil type and nutrition (sterilized substrate in the greenhouse versus field soil), irrigation (controlled in the greenhouse versus rainfall in the field), and temperature influenced the genotype x environment interaction and consequently disease expression.
The use of resistant genotypes in breeding programs has significantly increased the proportion of resistant plants over time [5,6,32,37,38]. As noted by Chao et al. (1990) [32], many traits are considered beyond smut resistance in parental choice. By identifying and minimizing the use of susceptible clones as parents, the proportion of smut-resistant genotypes in breeding programs can be increased. Therefore, the identification and careful selection of superior genotypes for resistance are essential for developing resistant varieties, contributing to crop sustainability and productivity.
Conceptualization, L.d.F.S. and L.R.P.; Data Curation, L.d.F.S.; Formal Analysis, L.d.F.S., F.B.d.S. and M.F.d.S.; Funding Acquisition, A.d.G.; Investigation, L.d.F.S., F.B.d.S., L.O.S.A., L.L.R.J., I.A.d.A. and T.d.C.F.; Methodology, D.P.; Project Administration, L.d.F.S. and L.R.P.; Resources, L.d.F.S. and A.d.G.; Software, M.F.d.S., D.P. and L.R.P.; Visualization, L.d.F.S.; Writing—Original Draft, L.d.F.S.; Writing—Review and Editing, L.O.S.A., L.L.R.J., I.A.d.A., D.P., A.d.G. and L.R.P. All authors have read and agreed to the published version of the manuscript.
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.
To the Agronomic Institute of Campinas, Sugarcane Center (Centro Avançado de Pesquisa e Desenvolvimento de Cana), Ribeirão Preto, São Paulo and São Martinho Mill. L.F.S received a CAPES scholarship; T.C.F received the TT3 FAPESP (22/09652-0) scholarship; F.B.S received a scientific initiation scholarship from FUNDAG; and L.L.R.J received a post-doctoral scholarship from UNESP.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Footnotes
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Enlarge this image.Figure 1. Average number of whips in ten sugarcane genotypes (IAC66-6; SP91-1049; IACSP04-2516; IAC16-2144; IAC16-2134; IACSP04-2503; IACSP99-4011; IN84-58; Co213; and IACCTC05-3616) screened in greenhouse over period of 198 days.
Distribution of whip incidence (S. scitamineum) in sugarcane genotypes observed in greenhouse.
| Incidence Intervals (%) | Number of Genotypes |
|---|---|
| 0 to 20 | 126 |
| 20 to 40 | 18 |
| 40 to 60 | 9 |
| 60 to 80 | 10 |
| 80 to 100 | 2 |
Distribution of AUDPC values in sugarcane genotypes observed in greenhouse.
| AUDPC Intervals | Number of Genotypes |
|---|---|
| 0 to 500 | 131 |
| 500 to 1000 | 14 |
| 1000 to 1500 | 12 |
| 1500 to 2000 | 5 |
| 2000 to 2500 | 2 |
| 2500 to 3000 | 1 |
Range and average of rAUDPC values for resistance classes: susceptible (S), moderately susceptible (MS), and resistant (R).
| Resistance Classes | Range | Average | Number of Genotypes |
|---|---|---|---|
| Susceptible | 20.97 to 100 | 46.42 | 33 (20%) |
| Moderately susceptile | 6.09 to 19.21 | 11.49 | 18 (11%) |
| Resistant | 0.02 to 5.08 | 1.31 | 60 (36%) |
| Highly resistant | 0 | 0 | 54 (33%) |
Relative Area Under the Disease Progress Curve (rAUDPC) for sugarcane genotypes susceptible to S. scitamineum and 10 lowest rAUDPC values within moderately susceptible and resistant classes in greenhouse trial.
| Genotypes | rAUDPC (%) | Class | Genotypes | rAUDPC (%) | Class |
|---|---|---|---|---|---|
| IAC16-2144 | 100 | S | IAC16-2044 | 29.11 | S |
| IAC16-2134 | 83.9 | S | IACSP95-5037 | 26.57 | S |
| IACSP04-2503 | 83.65 | S | IACSP01-8034 | 24.78 | S |
| Co213 | 71.65 | S | RB855156 | 24.56 | S |
| IACSP99-4011 | 71.42 | S | IAC16-2060 | 22.29 | S |
| IN84-58 | 69.77 | S | IACBIO277 | 20.97 | S |
| IACSP93-3046 | 65.42 | S | IACSP04-3148 | 6.09 | MS |
| IACCTC05-3616 | 64.22 | S | Co419 | 6.87 | MS |
| IACCTC05-9552 | 53.72 | S | RB92579 | 7.14 | MS |
| IACSP04-5065 | 52.30 | S | IACBIO266 | 7.33 | MS |
| IAC66-6 | 52.10 | S | IACCTC05-9634 | 8.04 | MS |
| IAC91-1099 | 51.59 | S | IACSP95-3028 | 8.08 | MS |
| IJ76-293 | 51.15 | S | IAC16-2059 | 8.24 | MS |
| NG5712 | 42.36 | S | IAC86-2480 | 10.25 | MS |
| IAC16-2086 | 41.06 | S | IACSP97-6628 | 10.38 | MS |
| IACCTC05-8069 | 40.71 | S | IACSP97-2053 | 11.14 | MS |
| IAC16-2036 | 39.82 | S | IACCTC07-8008 | 0.02 | R |
| IACSP99-3369 | 38.96 | S | IACSP01-2417 | 0.02 | R |
| NCo310 | 38.61 | S | IACSP01-5503 | 0.02 | R |
| IACBIO275 | 38.07 | S | IACSP04-3123 | 0.02 | R |
| IACSP01-8082 | 37.34 | S | IACSP93-6006 | 0.02 | R |
| IACBIO270 | 37.14 | S | CTC08 | 0.03 | R |
| IAC16-2014 | 33.93 | S | IAC80-3480 | 0.03 | R |
| IACCTC05-9630 | 32.96 | S | IACSP02-3025 | 0.03 | R |
| RB867515 | 32.13 | S | IN84-82 | 0.03 | R |
| IACBIO271 | 30.00 | S | SP71-6163 | 0.03 | R |
| IACSP94-2094 | 29.53 | S |
R—resistant; MS—moderately susceptible; S—susceptible.
Comparison between number of genotypes with whip incidence (S. scitamineum) in greenhouse and field trial.
| Trial | Number of Genotypes with Smut Incidence (Whips) |
|---|---|
| Greenhouse | 111 (67.27%) |
| Field trial | 143 (86.66%) |
| Either greenhouse or field trial | 106 (64.24%) r: 61% *** |
| Only field trial | 37 (22.42%) |
| Only greenhouse | 5 (3.03%) |
| No symptom (greenhouse or field trial) | 17 (10.30%) |
r: Spearman correlation; *** p < 0.0001.
Analysis of variance for Area Under the Disease Progress Curve (AUPDC) for 165 sugarcane genotypes assessed for their reaction to smut in greenhouse.
| Source of | D.F. | SM | MS | F | Pr > Fc |
|---|---|---|---|---|---|
| Genotypes | 164 | 2052.8 | 12.5171 | 9.9522 | 0.0000 |
| Blocks | 2 | 6.4 | 3.2177 | 2.5584 | 0.0789 |
| Error | 328 | 412.5 | 1.2577 | ||
| Total | 494 | 2471.8 | |||
| CV: 33.63% | |||||
D.F.: degree of freedom; SM: sum of squares; MS: mean square; F: F statistics.
Appendix A
Genotypes that exhibited relative Area Under the Disease Progress Curve (rAUDPC) value of 0 (highly resistant) and also predicted genetic means of 0 in greenhouse trial with respective classification in field trial.
| Genotypes with AUPDC Value and Equal to 0 | ||
|---|---|---|
| US571415 (R) | IACSP01-5501 (MS) | IACSP93-2060 (R) |
| IACSP04-6007 (S) | IACSP01-5519 (HR) | IACSP94-2101 (R) |
| IACSP04-6059 (R) | IACSP02-2125 (R) | IACSP95-5000 (R) |
| IACSP95-3028 (HR) | IACSP04-2503 (R) | IACSP95-5094 (R) |
| KRAKATAU (MS) | IACSP04-2510 (R) | IACSP96-7569 (R) |
| IS76155 (MS) | IACSP04-3259 (HR) | KASSOER (HR) |
| IACSP01-2421 (S) | IACSP04-5081 (HR) | SP70-1143 (MS) |
| IACSP04-6058 (HR) | IACSP04-6073 (HR) | SP80-185 (HR) |
| IACSP99-1020 (S) | IACSP95-3018 (S) | SP80-3280 (HR) |
| IACSP99-3357 (R) | IACSP95-6114 (S) | SP81-3250 (R) |
| IACCTC05-9578 (HR) | IACSP96-3056 (HR) | SP90-1638 (MS) |
| IACSP97-6680 (S) | IACSP96-3069 (HR) | SP903-414 (S) |
| IAC91-4168 (MS) | IACSP97-3384 (S) | U557-14105 (MS) |
| IACBIO232 (HR) | SP83-2847 (R) | CTC12 (HR) |
| IACCTC05-6518 (R) | IAC16-2081 (R) | CTC06 (R) |
| IACCTC05-9607 (S) | IAC87-3396 (R) | R570 (HR) |
| IACCTC06-1050 (MS) | IACCTC05-2562 (MS) | VERTIX9 (HR) |
| IACCTC06-9741 (R) | IACSP01-3127 (S) | POJ2878 (HR) |
HR—highly resistant; R—resistant; MS—moderately susceptible; S—susceptible.
Genotypes with positive EDP values with probability of less than 0.0001 of being zero with their rAUDPC (%) values and resistance class.
| Genotypes | rAUDPC (%) | Class | EDP (Estimate) | t_Value | Pr > |t| | PGM |
|---|---|---|---|---|---|---|
| IACBIO279 | 18.62 | MS | 0.2678 | 18.96 | <0.0001 | 0.32405 |
| IACBIO277 | 20.97 | S | 0.5215 | 41.03 | <0.0001 | 0.57775 |
| IAC16-2060 | 22.29 | S | 0.07245 | 5.7 | <0.0001 | 0.1287 |
| RB855156 | 24.56 | S | 0.05191 | 4.08 | <0.0001 | 0.10816 |
| IAC16-2044 | 29.11 | S | 0.07592 | 5.97 | <0.0001 | 0.13217 |
| IACSP94-2094 | 29.53 | S | 0.1129 | 8.88 | <0.0001 | 0.16915 |
| IACBIO271 | 30.00 | S | 0.6258 | 49.24 | <0.0001 | 0.68205 |
| IACCTC05-9630 | 32.96 | S | 0.07749 | 6.1 | <0.0001 | 0.13374 |
| IAC16-2014 | 33.93 | S | 0.05898 | 4.64 | <0.0001 | 0.11523 |
| IACBIO270 | 37.14 | S | 0.4701 | 36.99 | <0.0001 | 0.52635 |
| IACBIO275 | 38.07 | S | 0.2252 | 17.72 | <0.0001 | 0.28145 |
| NCo310 | 38.61 | S | 0.06734 | 5.3 | <0.0001 | 0.12359 |
| IACSP99-3369 | 38.96 | S | 0.05063 | 3.98 | <0.0001 | 0.10688 |
| IACCTC05-8069 | 40.71 | S | 0.09616 | 7.57 | <0.0001 | 0.15241 |
| NG5712 | 42.36 | S | 0.1389 | 10.93 | <0.0001 | 0.19515 |
| IJ76-293 | 51.15 | S | 0.5509 | 43.35 | <0.0001 | 0.60715 |
| IAC91-1099 | 51.59 | S | 0.0781 | 6.15 | <0.0001 | 0.13435 |
| IAC66-6 | 52.10 | S | 0.2979 | 23.44 | <0.0001 | 0.35415 |
| IACSP04-5065 | 52.30 | S | 0.114 | 8.97 | <0.0001 | 0.17025 |
| IACCTC05-9552 | 53.72 | S | 0.1243 | 9.78 | <0.0001 | 0.18055 |
| IACCTC05-3616 | 64.22 | S | 0.1726 | 13.58 | <0.0001 | 0.22885 |
| IACSP93-3046 | 65.42 | S | 0.2304 | 18.13 | <0.0001 | 0.28665 |
| IN84-58 | 69.77 | S | 0.3562 | 28.03 | <0.0001 | 0.41245 |
| IACSP99-4011 | 71.42 | S | 0.1825 | 14.36 | <0.0001 | 0.23875 |
| Co213 | 71.65 | S | 0.2207 | 17.36 | <0.0001 | 0.27695 |
| IACCTC05-5580 | 83.65 | S | 0.1444 | 11.37 | <0.0001 | 0.20065 |
| IAC16-2134 | 83.90 | S | 0.1703 | 13.4 | <0.0001 | 0.22655 |
| IAC16-2144 | 100.00 | S | 0.3489 | 27.45 | <0.0001 | 0.40515 |
Enlarge this image.Figure A1. Greenhouse trial. (a) Inoculated buds planted in 50-cell trays; (b) sprouting chamber promoting germination and infection; (c) greenhouse experiment setup; (d) black whip-like sorus.
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Details
; Luciana Oliveira Souza Anjos 2
; Laudecir Lemos Raiol Júnior 1
; dos Anjos, Ivan Antônio 2 ; Tanuza de Carvalho Fernandes 2 ; da Silva, Marcel Fernando 2
; Perecin, Dilermando 1
; de Goes, Antônio 1 ; Luciana Rossini Pinto 2 1 Faculdade de Ciências Agrárias e Veterinárias, Campus de Jaboticabal, Universidade Estadual Paulista, Jaboticabal 14884-900, SP, Brazil;
2 Centro Avançado de Pesquisa e Desenvolvimento de Cana, Instituto Agronômico Campinas, Rodovia Prefeito Antônio Duarte Nogueira, Anel Viário Contorno Sul, km 321, Ribeirão Preto 14001-970, SP, Brazil;