RESUMEN
Soybean plants under heat and drought generate a multiplicity of responses in photosynthesis and senescence, impairing growth, yield, and seed quality. The goal of this study was to analyze and quantify independent and combined effects of heat and drought during seed filling on photosynthesis and senescence, and its subsequent effects on the filling duration in soybean genotypes contrasting on seed protein. Two field experiments were conducted using high and low seed protein genotypes. During seed filling plants were exposed to four treatments: control (ambient temperature and soil water content near field capacity), heat stress (HS, episodes above 32 °C 6 h d-1) during 15-d, drought stress (DS, soil water content ≤ 25% of field capacity) during the entire seed filling, and HS × DS. We found non-genotypic variation in leaf photosynthesis in both experiments. Irrigated HS, did no alter photosynthesis and senescence. Drought, regardless of heat, reduced photosynthesis, carbohydrate production and affected membranes integrity, leading to premature leaf senescence and shortening the filling duration. The magnitude of responses was similar between drought alone and stresses combined, indicating a dominant role of drought over heat. The seed filling duration was not shorter in high protein compared to low protein genotype, nor was senescence pattern altered across treatments. These results indicated that the higher seed protein content exhibited by some genotypes are not necessarily associated with an earlier onset of senescence and shortening of the filling period as suggested by previous studies analyzing genotypes differing in protein concentration.
Asunto(s)
Glycine max , Fotosíntesis , Sequías , Hojas de la Planta , Semillas , Glycine max/genéticaRESUMEN
In subtropical environments where sugarcane (Saccharum spp.) crops are frequently limited by the duration of the growth cycle, earliness in maturity is a key genotypic trait. Using the concept of source-sink relationships, we hypothesised that earliness is controlled by the dynamics of tillering (DT), which define sink strength early in the growth cycle. Five modern commercial sugarcane genotypes with similar sucrose yields and varying degrees of earliness in ripening were grown in the field over three years and their DT, dynamics of sucrose accumulation (DS), and source-sink relationships over time were characterised. Canonical correlations and principal components analysis revealed that DT explained 68% of the total variance in DS. Early ripening genotypes exhibited the shortest thermal time to the end of tiller mortality (θTilmort), the lowest tiller survival and millable tiller number, and greatest sugar content at θTilmort (Sconc,Tilmort). The rate and duration of the sucrose accumulation phase did not explain the genotypic variation either in final sugar content or in earliness when considered in isolation without taking into account the effect of Sconc,Tilmort. In the set of genotypes examined, the variation in final sucrose yield was most explained by the variation in stalk number. We conclude that the dynamics of tiller appearance and senescence modified the early source-sink relationships and thus determined the differential sucrose contents around θTilmort and the earliness of maximal sugar accumulation. θTilmort, which was closely associated with the 14-leaf phenological stage, emerged as a candidate trait to screen for genotypic variation in early ripening, crop cycle duration, and yield.