Producción de HCN en sorgo y su interacción frente a estreses bióticos y abióticos

Sorghum (Sorghum spp.), the fifth most important cereal crop worldwide, stands out for its remarkable tolerance to water stress, making it a strategic crop in arid and semi-arid regions. In Uruguay, its increasing integration into agricultural systems has recently been threatened by the invasion of the yellow sugarcane aphid (Melanaphis sorghi), an emerging and highly damaging pest characterized by rapid parthenogenetic reproduction, wide dispersal capacity, and challenging management. Although strategies such as genetic resistance, early sowing, and seed treatments have been promoted, the defensive role of compounds like hydrogen cyanide (HCN), derived from the hydrolysis of cyanogenic glucosides, remains underexplored against piercing-sucking pests such as Melanaphis sorghi (M. sorghi), despite its proven efficacy against chewing insects like Spodoptera frugiperda. In this context, the present thesis evaluated, under controlled conditions, the interaction between water stress and the stress caused by M. sorghi in three sorghum hybrids: one with high and another with low HCN synthesis capacity (both with unknown responses to the aphid), and a third hybrid susceptible to the insect, with unknown cyanogenic capacity. Variables related to aphid population dynamics, plant physiological responses, and forage quality were analyzed. The results revealed significant differences among hybrids. The genotype with the lowest cyanogenic capacity (H3) consistently showed lower infestation, greater above-ground biomass, thicker stem, and higher SPAD index under combined stress, which contradicts the hypothesis that higher HCN production confers greater resistance. This suggests the involvement of alternative defense mechanisms, possibly environmentally induced, such as the accumulation of secondary metabolites or phloem-specific proteins. Ex situ assays showed no significant differences among hybrids, reinforcing the idea that such defenses are not structural (e.g., waxes or trichomes), but chemical and dependent on the plant's physiological state. Combined stress intensified losses in aerial biomass, chlorophyll content (SPAD), and stem thickness, particularly in the more susceptible hybrids (H1 and H2). In all cases, forage quality declined under stress conditions, reflected in increased lignin (ADL) content and reduced essential minerals, as indicated by higher NDF, ADF, and lower ash content. These findings highlight the complex, multifactorial nature of resistance to M. sorghi and emphasize the need for integrative approaches in breeding more resilient hybrids capable of withstanding increasingly frequent multiple stress scenarios.