Chronic renal failure (CRF) associated with elevated dietary cadmium (Cd) among farming communities in the irrigated agricultural area under the River Mahaweli diversion scheme has reached a significantly higher level of 9,000 patients. Cadmium, derived from contaminated phosphate fertilizer, in irrigation water finds its way into reservoirs, and finally to food, causing chronic renal failure among consumers. Water samples of River Mahaweli and its tributaries in the upper catchment were analyzed to assess the total cadmium contamination of river water and the possible source of cadmium. Except a single tributary (Ulapane Stream, 3.9 μg Cd/l), all other tested tributaries carried more than 5 μg Cd/l, the maximum concentration level accepted to be safe in drinking water. Seven medium-sized streams carrying surface runoff from tea estates had 5.1-10 μg Cd/l. Twenty larger tributaries (Oya), where the catchment is under vegetable and home garden cultivation, carried 10.1-15 μg Cd/l. Nine other major tributaries had extremely high levels of Cd, reaching 20 μg Cd/l. Using geographic information system (GIS), the area in the catchment of each tributary was studied. The specific cropping system in each watershed was determined. The total cadmium loading from each crop area was estimated using the rates and types of phosphate fertilizer used by the respective farmers and the amount of cadmium contained in each type of fertilizer used. Eppawala rock phosphate (ERP), which is mostly used in tea estates, caused least pollution. The amount of cadmium in tributaries had a significant positive correlation with the cadmium loading of the cropping system. Dimbula Tea Estate Stream had the lowest Cd loading (495.9 g/ha/year), compared with vegetable-growing areas in Uma Oya catchment with 50,852.5 g Cd/ha/year. Kendall's τ rank correlation value of total Cd loading from the catchment by phosphate fertilizer used in all crops in the catchment to the Cd content in the tributaries was +0.48. This indicated a major contribution by the cropping system in the upper catchment area of River Mahaweli to the eventual Cd pollution of river water. Low soil pH (4.5-5.2), higher organic matter content (2-3%), and 18-20 cmol/kg cation exchange capacity (CEC) in upcountry soil have a cumulative effect in the easy release of Cd from soil with the heavy surface runoff in the upcountry wet zone. In view of the existing water conveyance system from upcountry to reservoirs in North Central Province (NCP) through diversion of River Mahaweli, in addition to their own nonpoint pollution by triple superphosphate fertilizer (TSP), this demands a change in overall upper catchment management to minimize Cd pollution through agriculture inputs to prevent CRF due to elevated dietary cadmium among NCP farmers.

The cell-wall-degrading enzymes (CWDE) secreted by necrotrophs are important virulence factors. Although not unequivocally demonstrated, it has been suggested that necrotrophs induce hosts to cooperate in disease development through manipulation of host CWDE. The necrotrophic fungus Macrophomina phaseolina causes charcoal rot disease in Sorghum bicolor. An RNA-seq experiment was conducted to investigate the behavior of sorghum CWDE-encoding genes after M. phaseolina inoculation. Results revealed M. phaseolina's ability to significantly upregulate pectin methylesterase-, polygalacturonase-, cellulase-, endoglucanase-, and glycosyl hydrolase-encoding genes in a charcoal rot-susceptible sorghum genotype (Tx7000) but not in a resistant genotype (SC599). For functional validation, crude enzyme mixtures were extracted from M. phaseolina- and mock-inoculated charcoal-rot-resistant (SC599 and SC35) and -susceptible (Tx7000 and BTx3042) sorghum genotype stalks. A gel diffusion assay (pectin substrate) revealed significantly increased pectin methylesterase activity in M. phaseolina-inoculated Tx7000 and BTx3042. Polygalacturonase activity was determined using a ruthenium red absorbance assay (535 nm). Significantly increased polygalacturonase activity was observed in two susceptible genotypes after M. phaseolina inoculation. The activity of cellulose-degrading enzymes was determined using a 2-cyanoacetamide fluorimetric assay (excitation and emission maxima at 331 and 383 nm, respectively). The assay revealed significantly increased cellulose-degrading enzyme activity in M. phaseolina-inoculated Tx7000 and BTx3042. These findings revealed M. phaseolina's ability to promote charcoal rot susceptibility in grain sorghum through induced host CWDE.

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Stalk rot diseases are among the most ubiquitous and damaging fungal diseases of sorghum (Sorghum bicolor (L.) Moench) worldwide. Although reports of quantitative yield losses to stalk rots are available, the impact of stalk rot on grain quality attributes is unknown. This study was conducted to test whether stalk rot diseases could affect grain mineral (N, P, K; Ca, Mg, Cu, Fe, Mn, and Zn) and macronutrient (protein, fat, and starch) content, ash content, and physical traits (unit grain weight, hardness, and diameter). A field experiment was conducted in 2013 and 2014 with four sorghum genotypes (two hybrids and two lines). Plants from each genotype were inoculated with four stalk rot pathogens (Fusarium andiyazi, F. proliferatum, F. thapsinum, and Macrophomina phaseolina) and mock-inoculated with phosphate-buffered saline (control). Grains collected from infected and control plants were analyzed for macronutrient and ash content using near-infrared reflectance spectroscopy, grain hardness and diameter using the single-kernel characterization system, and mineral content using the Rapid Flow Analyzer (Model RFA-300 for N) and inductively coupled plasma spectrometer (for P, K, Ca, Mg, Cu, Fe, Mn, and Zn). Although stalk rot pathogens significantly reduced unit grain weight, they did not significantly affect grain hardness and diameter and, therefore, may not affect milling quality. Pathogens significantly reduced all macronutrient and most mineral contents across genotypes and environments on a per-unit-grain basis, except N and Mg, which were affected in a genotype- and environment-specific manner, and Fe, which was not significantly affected. Most minerals tested were significantly and negatively correlated with disease severity (lesion length) and total grain weight per panicle. The hybrid tested (Pioneer 84G62) exhibited reduced mineral and macronutritional changes after stalk rot infection, providing insights into the possibility of producing high-yielding, nutritionally stable hybrids under stalk rot disease pressure through dedicated breeding efforts.

Stalk rots are among the most prevalent and destructive sorghum diseases worldwide. Although experimental evidence is limited, delayed postflowering senescence due to the staygreen trait is accepted as a physiological means of stalk rot resistance. Staygreen has been shown to be correlated with chlorophyll content (as measured by a soil and plant analytical development [SPAD] meter). Field experiments were conducted to test the effects of Fusarium stalk rot and charcoal rot on SPAD readings at three developmental stages, to test whether staygreen genotypes are more resilient to stalk-rot-mediated chlorophyll degradation, and to examine the relationships between SPAD and stalk rot resistance and tolerance when plants were inoculated with causal organisms. Staygreen and nonstaygreen lines (two) and hybrids (two) established in the field were inoculated with Fusarium thapsinum, F. proliferatum, F. andiyazi, and Macrophomina phaseolina at 14 days after flowering. SPAD readings were obtained at soft-dough, hard-dough, and physiological maturity. Most pathogens significantly reduced the SPAD of the genotypes over the mock-inoculated control at three developmental stages. The stalk-rot-resistant and staygreen check line, SC599, showed a remarkable feature of negative senescence from soft dough to physiological maturity under disease pressure. Disease severity was significantly and negatively correlated with SPAD at all developmental stages, revealing the potential impact of the staygreen trait on stalk rot resistance. The difference between control and pathogen-treated total seed weight per panicle (i.e., tolerance) was significantly and positively correlated with the difference between control and pathogen-treated SPAD at physiological maturity, demonstrating the ability of staygreen trait to enhance stalk rot tolerance under disease pressure.

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