Lacunas de produtividade em soja no Rio Grande do Sul e caracterização fisiológica de genótipos com tolerância a déficit hídrico

Abstract

The average soybean yield in Rio Grande do Sul (RS) is 50% of yield potential, being the main limiting factor water deficit. Estimates of yield gaps provide important information about the possibility of increasing production through improvements in agricultural systems. In addition, new technologies for drought tolerance come to the market with the promise of mitigating productivity losses due to water deficit. In this sense, the objectives of this work are: i) to decompose the factors responsible for the soybean yield gap in RS, identifying opportunities for improvements in crop management, and ii) determine the response of transpiration to soil water content, represented by the fraction of transpirable water in the soil (FTSW), in soybean with transcription factor (TF) HaHB4® and TF AtAREB. The yield potentials were estimated with the crop model CSM CROPGRO - Soybean. Yield gaps and the analysis of possible causes were calculated based on those obtained through 853 field soybean data applied in four agricultural years (2017/18, 2018/2019, 2019/2020 e 2020/2021) in RS. The FTSW experiments were installed in greenhouses at EMBRAPA Soja in Londrina/PR and at Tropical Melhoramento e Genética – TMG in Cambé/PR. In the experiment in Cambé/PR, four soybean cultivars were used (2 commercial cultivars and 2 HB4® soybean lines), and in the Londrina/PR experiment six soybean cultivars were used (2 AtAREB lines and 4 commercial cultivars). The annual increase in yield of changes in RS depends on management methods (46%), genetic improvement (42%) and climate (12%). We identified a gap of 995.3 kg ha-¹, 2006.2 kg ha-¹ and 1436.5 kg ha-¹ regarding the positioning of cultivars and sowing dates, water availability during the cycle and management improvements, respectively. A gap of 2431.7 kg ha-¹ can be closed by adjusting cultivar management, sowing date, plant density, soil pH, P and K contents, no-tillage, crop rotation and crop succession. The lines with TF AtAREB1 present reduced daily transpiration, in the irrigated and rainfed environments, in relation to the commercial cultivars. The higher drought tolerance of lines with TF AtAREB1 is due to the lower threshould FTSW for transpiration rate, higher root/shoot ratio and longer drought survival. Hybridization of cultivars with high yield potential can improve soybean drought tolerance with FT AtAREB. The HaHB4® line with higher drought tolerance maintains potential transpiration at low FTSW values and has 14% higher water use efficiency than the sensitive cultivar under water deficit. Under well-irrigated conditions, HaHB4® gene showed higher transpiration coefficient values, that indicate physiological processes with good functioning. This study indicates that soybean cultivars with TF AtAREB1 or TF HaHB4® may be an alternative to increase soybean tolerance to water deficit in regions with drought.