How low soil nutrient availability increases anthracnose severity and limits forage quality and yield in Bolivian Giant Sorghum

ABSTRACT

Soil nutrient availability affects economically significant crops, yet its influence on forage sorghum remains poorly understood. This study aimed to assess the impact of soil fertility on Bolivian Giant Sorghum AGRI 002E (Sorghum bicolor) across morphological, sanitary, yield, chemical, and nutritional attributes. A completely randomized experimental design was employed, comprising two treatments and ten replicates, representing two soil fertility conditions: A (fertile) and B (low fertility). The experiment was conducted in the Brazilian savanna. Soils A and B differed mainly in potassium (K), phosphorus (P), base saturation, manganese (Mn), and zinc (Zn) (0.00-0.20 m), and potassium (K), phosphorus (P), sulfur (S), and Al³⁺ saturation (0.00-0.40 m). Sorghum cultivated in soil A exhibited a remarkable 64.83 % increase in green forage mass compared to soil B, translating to a difference of 24.04 Mg ha^-1 in dry matter. Furthermore, sorghum in soil A maintained a significantly higher number of live leaves, approximately 5.6 more than soil B, albeit experiencing a 33.59 % reduction in estimated leaf area under the lower soil fertility condition. Significantly, a conspicuous negative correlation emerged between the severity of anthracnose and morphological and yield traits. Under conditions of low soil fertility, the severity of anthracnose was six times higher, the dry forage yield was 13.04 Mg ha^-1, and this hindered structural development, increased fibrous structures, diminished crude protein, and reduced digestibility.

Keywords
diases; digestible; Colletotrichum sublineola ; NIRS

INTRODUCTION

Sorghum (Sorghum bicolor (L.) Moench), native to Africa, is recognized as an economically significant crop in several tropical regions, owing to its remarkable versatility. It can be used for both human and animal consumption (Fernandes et al., 2020; Bvenura and Kambizi, 2022), as well as for biodiesel and biofuel production (Stamenković et al., 2020). Additionally, sorghum can be an interesting option when used in intercropping systems with other plants (Rezende et al., 2020; Shi et al., 2023).

Sorghum biotypes diversity is a result of cross-compatibility between different sorghum varieties, whether commercial or wild types, contributing to agricultural advancements (Wang et al., 2016). Sorghum heterogeneity, both in terms of grain or biomass production, morphological traits and genetic composition, implies unique yield requirements and behaviors for each cultivar (Diallo et al., 2018).

The adaptability of sorghum renders it a valuable crop, with the potential to increase production in response to reduced fluctuations in the availability of other important cereals, such as corn, which are influenced by geopolitical factors (Ben Hassen and El Bilali, 2022).

While sorghum exhibits remarkable resilience and reduced water requirements in comparison to other cereals, it remains susceptible to various abiotic and biotic stresses especially in a climate change scenario (Chadalavada et al., 2021). Therefore, genetic improvement programs prioritize the identification and integration of stress-tolerant genes to bolster sorghum resistance against these adversities and low soil nutrient availability (Bernardino et al., 2019; Hao et al., 2021).

Bolivian Giant Sorghum is a relatively new forage-type cultivar with various purposes, especially due to its morphological traits. It reaches significant heights without yielding viable grains in its panicles, and these plants are primarily used to contribute to silage bulk or serve as a source for straw production within no-till planting systems (Latina Seeds, 2023). However, despite its potential for forage production, studies on its agronomic performance remain scarce, particularly regarding its interaction with soil fertility and how this affects key productivity parameters. The available literature provides limited information on its growth dynamics, nutrient uptake, and resistance to biotic and abiotic stresses, making it difficult to establish precise recommendations for its management (Theodoro et al., 2021). This knowledge gap underscores the need for further investigation into the relationship between soil characteristics and the performance of Bolivian Giant Sorghum, particularly in terms of forage yield, nutritional value, and disease susceptibility impacts.

In the context of soil nutrient extraction, the interplay between nutrient availability and the inherent genetic capacity of the plant exerts a significant influence (Abdelhalim et al., 2019; Almeida et al., 2023). Therefore, soil quality is crucial not only for meeting plant nutritional requirements but also for preventing processes such as degradation, organic matter loss, and decreased nutrient cycling efficiency (Kibblewhite et al., 2008). This concern is further compounded in the current landscape, as numerous nations globally grapple with challenges in meeting their domestic fertilizer production requirements. It is estimated that trade disruptions resulting from the Ukraine conflict could lead to a price surge of up to 30 % in fertilizers, posing a substantial threat to food security (Lin et al., 2023). Furthermore, deficiency in certain minerals can inhibit the growth and chemical composition of forage-suitable plants. Zinc application increases plant height and leaf area per plant but does not affect neutral detergent fiber (NDF), acid detergent fiber (ADF), and ash percentage in forage sorghum (Ahmad et al., 2018).

Mineral nutrition also exerts an influence on plant health, especially concerning diseases of varied etiology (Gupta et al., 2017). Sorghum anthracnose is one of the most significant diseases affecting sorghum cultivation, with reports of grain yield reductions ranging from 35 to 72 % (Cota et al., 2017). Soils in tropical regions are highly weathered and typically acidic, conditions that enhance phosphorus sorption by iron and aluminum oxides and result in low P availability, representing one of the main challenges for agricultural production in these areas (Fink et al., 2014; Alovisi et al., 2020). This limitation is associated with the relatively high zero point of charge (ZPC) of highly weathered tropical soils, whereby soil pH values below the ZPC generate net positive surface charge and increase the adsorption of anions such as phosphate (Baldotto and Velloso, 2014). Additionally, organic matter indirectly influences phosphate adsorption by preventing the crystallization of aluminum oxides (Borggaard et al., 2005). In Brazilian savanna soils, phosphorus sorption and desorption processes depend on the interaction of various soil properties (Pinto et al., 2013). However, intensive soil management and fertilization have contributed to improvements in soil fertility under advanced agricultural practices, particularly in the Brazilian savanna (Benites et al., 2023). However, knowledge of the effects of soil nutrient availability on forage sorghum anthracnose is limited, and no studies in the literature have assessed the impact of soil conditions on disease susceptibility and yield losses caused by anthracnose in Bolivian Giant Sorghum.

We hypothesize that lower soil fertility increases anthracnose severity and reduces the yield and nutritional quality of Bolivian Giant Sorghum cultivated in Brazilian savanna soils, whereas higher soil fertility enhances plant performance and disease resistance. This study aimed to evaluate how soil fertility affects the agronomic performance and nutritional quality of Bolivian Giant Sorghum AGRI 002E.

MATERIALS AND METHODS

Experimental area

The experiment was conducted during the 2021/2022 growing season at the Experimental Farm of the Federal University of Mato Grosso do Sul (UFMS), located in the municipality of Terenos, Mato Grosso do Sul (MS), Brazil, at coordinates 20° 26’ 17” S and 54° 51’ 24” W, at an altitude of 407 m.

The soil at the experimental site was classified as a Typic Hapludox (Soil Survey Staff, 2014) or Ferralsol (IUSS Working Group WRB, 2015), corresponding to a Latossolo Vermelho distrófico (Santos at al., 2018a), featuring a very clayey texture. The experimental units comprised seven 5-meter rows, with an inter-row spacing of 0.7 m and a plant density of 8.4 plants per linear meter. The plot area was 25 square meters, with the central 16 square meters designated as the useful area (Figure 1).

Figure 1
Experimental area location and schematic representation of the experimental unit.

The climate of the region is characterized as a tropical type Aw with a defined dry season (Kottek et al., 2006). During December to April (Figure 2), the period in which the experiment took place, the total precipitation was 638.40 mm, with a maximum temperature of 33.10 °C, a minimum of 25.62 °C, and an average of 20.94 °C, as per bi-weekly data from the National Institute of Meteorology (Inmet, 2022).

Figure 2
Meteorological data during the cultivation period of forage sorghum in Terenos, MS (Inmet, 2022).

Experimental design

In the last crop seasons, the areas had distinct land use histories. In area A, a crop rotation system was adopted, including corn (Zea mays), sorghum (Sorghum spp.), and pigeon pea (Cajanus cajan), whereas in area B, only corn was cultivated.

The minimum tillage of the area was carried out as described by Theodoro et al. (2018). The hybrid used was AGRI 002E (Bolivian Giant Sorghum), mechanically sown on December 10, 2021, without basal or topdressing fertilization, at a spacing of 0.7 m, with a population of 120,000 plants per hectare.

The experimental design employed was a completely randomized design in strips, with each strip corresponding to a soil type. There were two treatments (A = fertile; B = less fertile) with 10 replications, for a total of 20 experimental units. Physical and chemical properties of the evaluated soils are found in table 1. The main differences between soils A and B were in the levels of potassium (K), phosphorus (P), base saturation (V %), manganese (Mn), and zinc (Zn) in the 0.00-0.20 m layer. In the 0.00-0.40 m layer, K, P, sulfur (S), and aluminum (Al³⁺) saturation were the factors that showed the greatest difference between soils A and B.

Table 1
Average soil chemical properties in the experimental area at layers of 0.00-0.20 and 0.20-0.40 m

Area	pH(1)	K	P	S	Ca2+	Mg2+	Al3+	H+Al	SB	t	MO	V	m
		–– mg dm-3 ––			–––––––––––––––––––– cmolc dm-3 ––––––––––––––––––––							g dm -3	––––– % –––––
0.00-0.20 m layer
A	5.3	522.0	101.7	1,009.89	6.24	3.40	0.00	3.94	10.98	10.98	41.37	73.59	0.00
B	5.1	205.0	6.9	657.23	4.95	2.39	0.00	5.03	8.86	8.86	35.07	63.79	0.00
Area	Micronutrients					Physical analysis
	B	Cu	Fe	Mn	Zn	Sand			Clay			Silt
	–––––––––––– mg dm-3 ––––––––––––					–––––––––––– g kg-1 ––––––––––––
A	0.59	10.40	28.20	81.80	15.40	231			580			189
B	0.39	13.50	33.40	103.2	1.70	198			608			194
0.20-0.40 m layer
Area	pH(1)	K	P	S	Ca2+	Mg2+	Al3+	H+Al	SB	t	MO	V	m
		–– mg dm-3 ––		–––––––––––– cmolc dm-3 ––––––––––––							g dm -3	––––– % –––––
A	4.9	235.0	24.1	8,608.11	3.96	2.41	0.13	4.87	6.97	7.10	28.54	58.87	1.83
B	4.9	68.00	3.3	705.32	4.07	2.58	0.45	5.77	6.82	7.27	25.07	54.17	6.19
Area	Micronutrients
	Cu			Fe			Mn			Zn		B
	––––––––––––––––––––––––– mg dm-3 –––––––––––––––––––––––––
A	10.40			32.40			48.60			4.10		0.47
B	13.10			39.20			60.30			0.80		0.33

• ⁽¹⁾
  CaCl.
• SB: Sum of bases; t: Effective cation exchange capacity; MO: Organic matter; V: Base saturation; m (%): Aluminum saturation; P: extraction by Mehlich^-1; H+Al: titrated method.

Chemical, structural, yield, and agronomic characteristics

The evaluations were conducted 126 days after sowing, during the pre-tasseling stage, when 20 plants were cut at ground level per plot. Chlorophyll content was measured using a portable Minolta SPAD-502 chlorophyll meter (Soil and Plant Analysis Development) on the middle portion of the third fully expanded leaf, from the apex to the base of the plant (SPAD), and on the middle leaf (SPADML), located at the midpoint of the stem height.

A variety of morphological characteristics of the plant species under investigation was measured. Plant height (PH) was assessed, in meters, using a graduated ruler, focusing on the central stem's length from the ground level to the terminal node featuring leaf attachment. Medium stem diameter was measured in millimetres as MSD (measured at the average plant height just below the leaves) and GSD (measured at ground level, at the plant base) using a digital caliper.

The determination of the number of live leaves (NL) involved summing the count of fully expanded, viable leaves on each plant. Leaf area (denoted as LA) was estimated by analyzing the third fully expanded leaf from its apex to its base. To achieve this, the selected leaf was carefully removed, and its dimensions, including width and length, were meticulously measured in centimeters using a graduated ruler. Subsequently, the leaf area index (LAI) was estimated by multiplying the leaf measured length and width by a constant factor of 0.747 (Sharma, 1983).

Green forage mass was obtained by weighing 20 plants harvested per plot immediately after cutting. The green mass was estimated for production in Mg per hectare, considering a population of 120,000 plants per hectare. A subsample of the harvested plants per plot was identified, weighed, and dried in a forced-air oven at 55 °C for three days to measure dry matter (DM), which was later corrected to obtain dry forage mass (DF kg ha^-1 of DM).

The assessment of sorghum anthracnose severity (ANTRAC) was conducted visually using a modified version of the diagrammatic scale introduced by Sharma (1983). This scale accounts for the approximate percentage of leaf area showing typical disease symptoms (0, 2.5, 5, 10, 20, 35, 50, 75, and 100 %).

After the morphological evaluations, ten plants were divided, weighed, cut, homogenized, identified, and dried in a forced-air oven at 55 °C for three days to measure dry weight. Subsequently, the samples were ground using a Wiley mill (1 mm) and analyzed using near-infrared reflectance spectroscopy (NIRS), following Marten (1985), to measure the content of dry matter (DM), mineral matter (MM), crude protein (CP), NDF, ADF, acid detergent lignin (ADL), cellulose (CEL), silica (SIL), and in vitro organic matter digestibility (IVOMD).

Statistical analysis

The data for the evaluated variables were subjected to analysis of variance using the F-test, and means were compared using the Student t-test at a 5 % significance level. Subsequently, a Pearson correlation analysis was performed between the variables. Statistical analyses were conducted using PROC GLM and PROC CORR in the SAS statistical software version 9.3.

RESULTS

A significant effect (p<0.001) was observed for the morphological and agronomic traits of sorghum as a function of soil fertility, except for GSD, which had an average of 18.97 mm regardless of the soil type (Table 2).

Table 2
Morphological traits of Bolivian Giant Sorghum AGRI 002E cultivated in soils with different fertility levels

Morphological traits	Soil		SEM	p-value
	A	B
SPAD	44.71	24.87	0.9714		<0.0001
SPADML	51.38	27.43	1.0437		<0.0001
PH (m)	3.56	1.99	0.06383		<0.0001
MSD (mm)	19.48	15.35	0.4186		<0.0001
GSD (mm)	19.53	18.42	0.4183		0.1147
NL	14.60	9.00	0.3612		<0.0001
LAI (cm²)	578.89	384.43	17.5656		<0.0001

• SPAD: Chlorophyll content in the third fully expanded leaf from apex to base of the plant. SPADML: Chlorophyll content in the middle leaf. PH: Plant height; GSD: Stem diameter at the base of the plant; MSD: Stem diameter in the middle of the plant; NL: Number of live leaves; LAI: Leaf area index; SEM: Standard error of the mean; m: meter; mm: millimeters; p-value: Probability of significant effect.

The leaves of the plants grown in soil A had approximately 1.79 fold more chlorophyll in the second fully expanded leaf (SPAD) when compared to those grown in soil B. In the middle leaf (SPADML), this difference was even greater, about 1.84 fold (Table 2). The Bolivian giant sorghum grown in fertile soil (Soil A) reached a height 1.57 m taller than that of sorghum grown in low-fertility soil (Soil B). Plants in soil A had approximately 1.6 fold more NL than plants in soil B, as well as 50 % greater estimated leaf area (LA).

Yield traits were affected by soil conditions, with Bolivian sorghum grown in soil A exhibiting greater resilience to disease and higher yield indices compared to sorghum grown in low-fertility soil (soil B) (Table 3). The severity of anthracnose on sorghum leaves was sixfold higher in soil B compared to soil A. Green forage mass (GFM), dry forage mass (DFM), and dry matter (DM) were influenced by soil fertility, with the highest values observed in plants grown in soil A (Table 3). The GFM of Bolivian sorghum was was twice as high in soil A compared to soil B. Anthracnose showed a strong negative correlation with all morphological and productivity traits (Table 4).

Table 3
Yield traits of Bolivian Forage Sorghum AGRI 002E cultivated in soils with different fertility levels

Yield traits	Soil		SEM	P-value
	A	B
ANTRAC (%)	2.40	14.68	1.0884	<0.0001
GFM (Mg ha-1)	123.09	54.14	6.3428	<0.0001
DFM (Mg ha-1)	37.08	13.04	0.9398	<0.0001
DM (%)	30.13	24.83	7.8763	0.0022

• ANTRAC: Anthracnose severity; GFM: Green forage mass; DFM: Dry forage mass; DM: Dry matter; SEM: Standard error of the mean; p-value: probability of significant effect.

Table 4
Pearson correlation between variables of Bolivian Sorghum AGRI 002E plants cultivated in soils with different fertility levels

	SPAD	SPADML	PH	MSD	GSD	NL	LAI	ANTRAC	GFM	DFM	DM
1.000	0.983*	0.963*	0.916*	0.403	0.958*	0.927*	-0.928*	0.943*	0.629*	0.957*
SPADML		1.000	0.979*	0.918*	0.443	0.973*	0.934*	-0.958*	0.935*	0.639*	0.950*
PH			1.000	0.896*	0.507*	0.960*	0.893*	-0.955*	0.913*	0.614*	0.919*
MSD				1.000	0.630*	0.962*	0.924*	-0.834*	0.954*	0.600*	0.434
GSD					1.000	0.530	0.446*	-0.449*	0.502*	0.149	0.954*
NL						1.000	0.938*	-0.908*	0.979*	0.586*	0.967*
LAI							1.000	-0.852*	0.941*	0.512*	0.935*
ANTRAC								1.000	-0.841*	-0.853*	-0.581*
GFM									1.000	0.519	0.697*
DFM										1.000	0.968*
DM											1.000

• ^*
  Significant at the 5 % probability level.
• Chlorophyll content (SPAD); Chlorophyll content in the middle leaf (SPADML); Plant height (PH); Stem diameter in the middle of the plant (MSD); Stem diameter at the base of the plant (GSD); Number of live leaves (NL); Leaf area index (LAI); Anthracnose severity (ANTRAC); Green mass (GFM); Dry forage mass (DFM); Dry matter (DM) of AGRI 002E sorghum plants as a function of soils with different fertility levels.

Plant height showed a high positive correlation with SPAD, SPADML, MSD, GSD, NL, LAI, GFM, DFM, and DM. Meanwhile, variables SPAD, SPADML, NL, and DFM correlated with all other variables except GSD. The DFM did not show a significant correlation with GFM and GSD (Table 4).

Soil fertility did not influence (p>0.05) the levels of DM, MM, ADF, LIG, and SIL in Bolivian giant sorghum. Levels of NDF and CEL were higher in plants cultivated in soil B, while CP and IVOMD variables had greater levels in plants grown in soil A (Table 5).

Table 5
Chemical characteristics of Bolivian Giant Sorghum AGRI 002E cultivated in soils with different fertility levels

Chemical characteristics	Soil		SEM	p-value
	A	B
DM (%)	91.29	90.44	0.4349	0.2507
MM (% of DM)	8.58	8.54	0.4440	0.2902
CP (% of DM)	9.58	4.27	0.8738	0.0010
NDF (% of DM)	77.69	81.31	0.8286	0.0073
ADF (% of DM)	42.43	46.51	1.2376	0.0821
ADL (% of DM)	5.41	5.38	0.1858	0.8256
CEL (% of DM)	35.82	38.23	0.7015	0.0470
SIL (% of DM)	1.77	2.86	0.4057	0.1132
IVOMD (% of DM)	40.41	31.80	2.3682	0.0456

• DM: Absolute dry matter; MM: Mineral matter; CP: Crude protein; NDF: Neutral detergent fiber; ADF: Acid detergent fiber; ADL: Acid detergent lignin; CEL: Cellulose; SIL: Silica; IVOMD: In vitro organic matter digestibility; SEM: Standard error of the mean; p-value: Probability of a significant effect.

The CP of Bolivian sorghum decreased by approximately 55 % when grown in soils with unfavorable chemical characteristics (soil B). The CP showed a strong negative correlation with the variables NDF and CEL. On the other hand, there was a positive correlation of 85.79 % with the IVOMD variable. The NDF and CEL showed a high positive correlation between them (Table 6). Mineral matter showed a significant correlation only with DM and SIL, with the former being negative (73 %) and the latter being positive (77 %).

Table 6
Pearson correlation between chemical variables of Bolivian Sorghum AGRI 002E cultivated in soils with different fertility levels

	DM	MM	CP	NDF	ADF	ADL	CEL	SIL	IVOMD
DM	1.000	-0.737*	0.333	-0.269	-0.645*	-0.473*	-0.358	-0.934	0.646*
MM		1.000	0.213	-0.157	0.255	0.244	-0.073	0.772*	-0.185
CP			1.000	-0.911*	-0.835*	-0.472*	-0.900*	-0.397	0.858*
NDF				1.000	0.843*	0.636*	0.911*	0.362	-0.873*
ADF					1.000	0.779*	0.927*	0.705*	-0.951*
ADL						1.000	0.746*	0.447*	-0.758*
CEL							1.000	0.416	-0.881*
SIL								1.000	-0.679*
IVOMD									1.000

• ^*
  Significant at the 5 % probability level.
• Absolute dry matter (DM); mineral matter (MM); crude protein (CP); neutral detergent fiber (NDF); acid detergent fiber (ADF); acid detergent lignin (ADL); cellulose (CEL); silica (SIL); and in vitro organic matter digestibility (IVOMD) of dry matter (DM); mineral matter (MM); crude protein (CP); neutral detergent fiber (NDF); acid detergent fiber (ADF); acid detergent lignin (ADL); cellulose (CEL); silica (SIL); and in vitro organic matter digestibility (IVOMD).

DISCUSSION

Low soil fertility in the Brazilian Cerrado increases the susceptibility of Bolivian Giant Sorghum to anthracnose and reduces its yield, chemical composition, and nutritional quality. Soils with higher availability of K, P, Zn, and S favored the agronomic and chemical performance of the plants, enhancing disease resistance and improving nutritional quality. Additionally, plants grown in less fertile soils exhibited greater development of fibrous structures, while those in more fertile soils showed higher crude protein content and in vitro organic matter digestibility. Thus, the results demonstrate that soil fertility plays an essential role in the productivity and quality of Bolivian Giant Sorghum Agri 002E.

The discussion will be based on the interpretation of nutrient levels in the two soil layers, using the chemical analyses performed and a reference for soils in the Brazilian Cerrado biome (Sousa and Lobato, 2004). Soil A had higher levels of K, P, S, and Zn in both the 0.00-0.20 m and 0.20-0.40 m layers compared to soil B. According to reference values, K levels were high in both soils (>80 mg dm^-3) in the 0.00-0.20 m layer. In the 0.20-0.40 m layer, K levels became adequate in soil B. Phosphorus levels were high in the 0.00-0.20 m layer in both soils (>12 mg dm^-3 for clayey soil - soil A; and >6 mg dm^-3 for very clayey soil - soil B) and in the 0.20-0.40 m layer, P levels were moderate in soil B (3.1 to 4 mg dm^-3 for very clayey soil).

The average S content in the 0.00-0.40 m layer was 30 and 4 mg dm^-3 for soils A and B, respectively, the content was high (≥10 mg dm^-3) in soil A and low (≤4 mg dm^-3) in soil B. Zinc content was high in both soils in the 0.00-0.20 m layer (>1.6 mg dm^-3) and in the 0.20-0.40 m layer, the nutrient was in low concentration in soil B (0 to 1 mg dm^-3).

Zinc presence inhibits the accumulation of reactive oxygen species (ROS), which are responsible for damaging cell membranes and impeding the normal functioning of cells in plant tissues (Cakmak, 2000; Duc et al., 2018). Although zinc (Zn) is an essential micronutrient for plant metabolism, only small amounts are required for sorghum fertilization (Ahmad et al., 2018). Zinc concentrations in the 0.00-0.20 m soil layer were likely sufficient to meet the specie basal requirements in both fertility conditions. In the 0.20-0.40 m layer, potassium (K), phosphorus (P), and Zn levels were higher in soil A, which also exhibited sulfur (S) content within the range considered adequate for sorghum cultivation.

Soil nutrient availability can influence the severity of plant infections. According to Dordas (2008), nutrients such as N, K, P, Mn, Zn, B, and Si play fundamental roles in plant tolerance and resistance to pathogens. In the present study, higher soil availability of K, P, Zn, and S was associated with improved agronomic and chemical performance of Bolivian Giant Sorghum Agri 002E, thereby enhancing its resistance to anthracnose.

Different physiological mechanisms can explain the influence of nutrients on disease resistance. In this study, greater availability of K and P in the soil was associated with greater resilience to anthracnose and better sorghum performance, respectively, corroborating existing literature. Potassium can reduce plant susceptibility to pathogens up to a certain limit, promoting balanced growth and improving cell membrane integrity (Dordas, 2008). Phosphorus, in turn, exerts a variable effect on plant resistance, potentially reducing the severity of root infections, as reported in previous studies on cereals (Kiraly, 1976; Huber, 1980).

Higher Zn availability was associated with better chemical performance in sorghum, suggesting a potential effect on anthracnose resistance. In this context, micronutrients such as Mn and Zn are essential components of plant defense against pathogens. Manganese strengthens structural barriers against fungal penetration, while Zn may influence plant susceptibility to diseases (Dordas, 2008).

Conversely, nutrient deficiency can increase plant susceptibility to diseases. In sorghum grown in less fertile soils, lower nutrient availability was associated with poorer morphological performance and an increase in fibrous structures, possibly related to reduced resistance toanthracnose. Pathogens can interfere with nutrient absorption, translocation, and utilization, leading to nutritional deficiencies and exacerbating the effects of infection (Huber and Graham, 1999).

Potassium promotes plant mass growth in grasses, while P is essential for energy production and plays a crucial role in root development. However, considering the levels of P found in the two evaluated soils, it is considered that the differences observed in the plants grown in these two areas are not attributable to P. Sorghum is adapted to West African Savanna, characterized by low soil phosphorus levels, and breeding programs aim to develop cultivars that exhibit better phosphorus use efficiency (Bernardino et al., 2019). Supporting this, Damian et al. (2017) did not observe any effect of P or K fertilization on the dry mass and protein content of forage sorghum cultivated for silage in Cerrado soils with very high potassium and phosphorus levels.

Nevertheless, it is important to note that phosphorus fertilization has been shown to increase sorghum grain yield (Iwasaki et al., 2022), highlighting the role of P management in optimizing sorghum productivity depending on soil fertility status. Bolivian Giant Sorghum Agri 002E has an aggressive and deep root system (Latina Seeds, 2023), allowing it to access nutrients located in deeper soil layers. Therefore, better fertility conditions in the 0.20-0.40 m soil layer improved sorghum morphological traits.

The increase in plant height is accompanied by greater numbers of nodes and leaves, justifying the better responses in height and leaf number in sorghum cultivated in soil A. Sorghum cultivated in soil B produced 68.95 Mg ha^-1 less green mass than in soil A, and this was significantly correlated with all morphological characteristics. Additionally, K levels in the 0.20-0.40 m layer and S levels in the 0.00-0.40 m layer were lower in soil B, contributing to lower mass production.

Plants cultivated in soil A had higher values of height (3.56 m); green mass (123.09 Mg ha^-1); dry mass (37.0.8 Mg ha^-1), and lower dry matter content (30.13 %). In soil B, the results for height (1.99 m), green mass (54.14 Mg ha^-1), dry mass (13.04 Mg ha^-1), and dry matter content (24.83 %) were lower. In a study conducted by Theodoro et al. (2021), Agri 002E presented height, green mass, dry mass, and dry matter results of 2.77 m; 87.96 Mg ha^-1; 33.11 Mg ha^-1; and 34.68 at 97 days after sowing.

The correlation of all variables with SPAD, SPADML, NL and DM, except for GSD, indicates that chlorophyll and the number of live leaves are directly related to the overall performance of the plant, influencing its growth and productivity. The severity of ANTHRAC was negatively correlated with most productive variables, including PH, SPAD, SPADML, NL and DM. This result reinforces that greater disease severity compromises plant growth and productive capacity.

At 126 days after sowing, plants in soil A showed the best performance, demonstrating that soil conditions provided the best results for the cultivar. Plants from soil B experienced a drastic reduction in morphological and production characteristics, which occurred due to lower nutrient levels and higher disease severity.

The lower soil concentration of these minerals influenced the development and resilience of sorghum under adverse environmental conditions. The higher zinc content in the 0.20-0.40 m layer (Table 1) resulted in better sorghum yields in soil A, as this nutrient enhances chlorophyll synthesi and, N uptake and accelerates plant development even under drought (Dimkpa et al., 2019). The increase in chlorophyll content directly influences the production of photoassimilates, which, as they accumulate, increase plant height and stem diameter (Buso et al., 2011). The increase in photoassimilates also resulted in larger leaf size and, therefore, greater leaf area, with better results observed in sorghum cultivated in soil A.

Antracnose severity was 12.28 % higher in plants from soil B, possibly due to the nutritional status of the plant. Plants with better nutritional status significantly enhance resistance to disease, as reported by Huber et al. (2012) and supported by the findings in this paper. Building upon the established cultural practices delineated for managing forage sorghum anthracnose disease (Mofokeng et al., 2017), we suggest incorporating the practice of sowing in nutrient-rich soils in this paper, even considering that it is a plant defined as rustic.

From an epidemiological perspective, the reduced severity implies a lower primary inoculum source in subsequent crops that may also be host of C. sublineola in the same area, as this pathogen can survive in crop debris (Gaffoor et al., 2021). The lower photoassimilate production in soil B-grown plants, due to lower chlorophyll content and higher anthracnose severity, led to shorter plant height, fewer live leaves, and a smaller LAI, resulting in reduced green and dry mass and dry matter production.

Few studies published in high-impact journals have investigated the relationship between soil nutrition and anthracnose severity, and the literature on this topic remains limited. Research evaluating the effects of minerals on disease mitigation yields mixed results. Muniz et al. (1991) concluded that bean cultivar resistance to anthracnose was not related to the Ca content in the tissues, even when different doses of this mineral were applied in nutrient solution to the Jalo and Ouro cultivars. On the other hand, Moraes et al. (2006) analyzed the influence of silicon on reducing anthracnose caused by Colletotrichum lindemuthianum in common bean (Phaseolus vulgaris), observing that foliar application of sodium metasilicate reduced disease severity by 62.4 % and prolonged healthy leaf area maintenance, despite no external silicon barrier formation being observed in the plant tissues. These studies highlight the complexity of the interaction between nutrients and anthracnose resistance, underscoring the need for further research on the roles of various minerals in reducing disease severity across crops.

Soil condition influenced the chemical characteristics PB, NDF, CEL, and IVOMD. An increase in CP and IVOMD reduces CEL and NDF because they have a strong negative correlation.

The NDF and CEL showed a strong positive correlation, indicating that the increase in the NDF fraction is directly associated with the increase in cellulose, which is expected, given that cellulose is one of the main structural components of fibre. The ADF and acid detergent lignin (ADL) showed a positive correlation with CEL, reinforcing that these structural components accumulate simultaneously in the plant. The IVOMD showed significant negative correlations with NDF (-87 %), ADF (-95 %), and CEL (-88 %), indicating that greater levels of these structural constituents reduce the digestibility of the plant material.

On the other hand, CP showed a significant negative correlation with NDF (-91 %), ADF (-83 %) and CEL (-90 %), suggesting that the increase in the fibrous fraction occurs at the expense of the protein content, a relevant factor for the nutritional quality of the forage. These results highlight the strong interactions between plant structural components and their implications for the forage digestibility and nutritional value. Increasing the fibrous fraction, especially NDF and ADF, can reduce the digestibility and nutritional quality of sorghum. At the same time, the mineral and protein composition is influenced by growing conditions and soil fertility.

Plants under stress scenarios mobilize nutrients to provide energy to other tissues (Habermann et al., 2019), resulting in a reduction in protein content and, consequently, in the digestibility of the material. The CP and NDF results found in plants cultivated in soil A were higher than the values found by Rodrigues Filho et al. (2006). In their study with four forage sorghum genotypes, CP ranged from 4.85 to 6.97%, and NDF ranged from 37.29 to 53.05 %. In accordance with forage sorghum breeding programs, genotypes are typically chosen if their crude protein (CP) content in dry matter exceeds 6 % (Bhat, 2019). Consequently, we deduced that, despite the potential for Giant Bolivian Sorghum to attain sufficient CP levels, the specific environmental conditions in soil B fostered the growth of less nutritionally enriched plants with lower CP content.

Base saturation in the 0.00-0.20 m layer was higher in soil A, but both soils were in the ideal range for sorghum cultivation, which is a minimum of 50 %, according to Sousa and Lobato (2004). Aluminum saturation in the 0.20-0.40 m layer was higher in soil B, but in both soils it was less than 20 %, and exchangeable calcium was above 0.5 cmol_c dm^-3; no gypsum application was necessary for Cerrado. Assessing Al³⁺ saturation at 40 % in a study involving 20 grain sorghum genotypes, Santos et al. (2018b) reported a notable decrease in yield. However, the study also revealed that 10 hybrids yielded at high levels under both low and high Al³⁺ saturation conditions.

Bolivian Giant Sorghum altered its developmental pattern in soils with lower nutrient availability, yet still produced 13.04 Mg ha^-1 of dry mass, although CP content was significantly lower. In conditions of scarce soil nutrient availability due to war or capital constraints in the agricultural sector, this plant can be a good strategy to support animal production temporarily, especially for livestock farmers who can supplement silage to increase CP content. Thus, this study expands knowledge on the influence of soil fertility on the resistance of Bolivian Giant Sorghum Agri 002E to anthracnose, filling a gap in the literature and highlighting the importance of nutrient management in mitigating the disease and improving crop quality.

CONCLUSION

Lower soil fertility in the Brazilian savanna increased the susceptibility of Bolivian giant sorghum Agri 002E to anthracnose and reduced its productivity, chemical composition, and nutritional quality. In more fertile soils, there was greater biomass production, higher crude protein levels, improved organic matter digestibility, and a lower incidence of the disease. Adequate soil fertility management is essential to maximize the agronomic performance and health of forage sorghum. Although the crop has demonstrated the ability to adapt to less fertile soils, nutritional limitations have compromised its nutritional quality and disease resistance. Bolivian giant sorghum Agri 002E exhibits enhanced performance when grown in soil with high nutrient availability within the 0.00-0.40 m soil layer; in soils with lower nutrient availability, it was able to produce 13.04 Mg ha^-1 of dry mass, although the CP content was lower (4.27 %). Strategies that promote soil nutrient balance are essential to optimize crop productivity and sustainability.

ACKNOWLEDGEMENTS

The authors thank the Universidade Federal de Mato Grosso do Sul (UFMS) and Embrapa Beef Cattle. We extend our gratitude to the Foundation for the Support of Education, Science, and Technology of the State of Mato Grosso do Sul (FUNDECT), the Coordination for the Improvement of Higher Education Personnel – Brazil (CAPES), under Financing Code 001, and the National Council for Scientific and Technological Development (CNPq) for their financial support for this research.

• How to cite:
  Corado HS, Difante GS, Theodoro GF, Fernandes CD, Gomes RC, Lima ND, Frontado NEV, Rodrigues JG, Santana JCS. How low soil nutrient availability increases anthracnose severity and limits forage quality and yield in Bolivian Giant Sorghum. Rev Bras Cienc Solo. 2026;50:e0240178. https://doi.org/10.36783/18069657rbcs20240178
• FUNDING
  This study was funded by Universidade Federal de Mato Grosso do Sul and in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

Data Availability

The data that support this study cannot be publicly shared due to ethical or privacy reasons of the Brazilian Agricultural Research Corporation (Embrapa) and may be shared upon reasonable request to the corresponding author if appropriate.

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Edited by

• Editor:
  José Miguel Reichert https://orcid.org/0000-0001-9943-2898 and Edicarlos Damacena Souza https://orcid.org/0000-0003-3719-8615

Publication Dates

• Publication in this collection
  16 Mar 2026
• Date of issue
  2026

History

• Received
  21 Aug 2024
• Accepted
  01 Aug 2025