Morphological root responses of soybean to rhizosphere hypoxia reflect waterlogging tolerance

Abstract

Jitsuyama, Y. 2015. Morphological root responses of soybean to rhizosphere hypoxia reflect waterlogging tolerance. Can. J. Plant Sci. 95: 999Á1005. Excess soil moisture induces hypoxia, causing waterlogging injury in soybeans [Glycine max (L.) Merr.]. Twelve Japanese soybean cultivars with varying hypoxia tolerance were used. Of these, 11 (all but Hayahikari) were evaluated for waterlogging tolerance using a scaled index with data from previous studies. To investigate hypoxic responses, cultivars were grown under hydroponic conditions for 2 wk a year for 2 yr, with aerobic or hypoxic oxygen concentrations artificially maintained in the rhizosphere. Hypoxic responses (measured as plant dry weight and root morphology) were assessed at the early vegetative stage. The effects of hypoxic treatment on root dry weight were significant, and the effect of year on soybean dry weight was not significant. The change in root dry weight, and particularly, in coarse root length, was significantly correlated with waterlogging tolerance index at the 0.001 probability level. This study showed that root responses to rhizosphere hypoxia might reflect waterlogging tolerance in soybeans.Key words: Hypoxia, soybean, root, temperature, waterlogging tolerance Jitsuyama, Y. 2015. Les re´actions morphologiques des racines du soja a`l'hypoxie de la rhizosphe`re refle`tent la tole´rance a`l'engorgement du sol. Can. J. Plant Sci. 95: 999Á1005. Une trop grande quantite´d'eau dans le sol entraıˆne l'hypoxie, ce qui cause des dommages au soja [Glycine max (L.) Merr.]. Les chercheurs ont recouru a`douze cultivars japonais de soja tole´rant l'hypoxie de fac¸on variable. Ils ont e´value´la tole´rance a`l'engorgement de onze cultivars (tous sauf la varie´te´Hayahikari) avec un indice gradue´en se servant des donne´es d'e´tudes ante´rieures. Pour ve´rifier la re´action a`l'hypoxie, les chercheurs ont cultive´les varie´te´s de fac¸on hydroponique en maintenant deux semaines par an pendant deux ans la concentration d'oxyge`ne requise pour reproduire les conditions ae´robies ou hypoxiques dans la rhizosphe`re. La re´action a`l'hypoxie (mesure´e d'apre`s le poids sec de la plante et la morphologie des racines) a e´te´e´value´e au de´but de la pe´riode ve´ge´tative. L'hypoxie affecte de fac¸on significative le poids sec des racines, mais l'anne´e n'a aucun effet sensible sur le poids sec du soja. La modification du poids sec des racines mais, surtout, de la longueur brute de ces dernie`res pre´sente une importante corre´lation avec l'indice de tole´rance a`l'engorgement au niveau de probabilite´de 0,001. Cette e´tude indique que la re´action des racines a`l'hypoxie de la rhizosphe`re pourrait affecter la tole´rance du soja a`l'engorgement du sol.

Phenotypic variation in root development of 162 soybean accessions under hypoxia condition at the seedling stage

“…SDW of plants was greater under hypoxia (hydroponic conditions) than under normoxia (Table 1). Soybean SDW has been reported to show no significant changes (Jitsuyama, 2015) or increased SDW (Sakazono et al, 2014) under short-term hypoxia in hydroponic culture. On the other hand, SDW of plants grown in waterlogged soil was significantly lower than that under control conditions (Table 3).…”

“…In a study using hydroponic culture, Iyodaizu was selected from 92 accessions as a hypoxiatolerant cultivar on the basis of the ability of its seedlings to develop roots under hypoxia (Sakazono et al, 2014). In addition, Shoku-kei 32 and Toyohomare showed high waterlogging tolerance (Jitsuyama, 2015).…”

“…Shoku-kei 32, which was bred recently in Hokkaido, Japan, has high waterlogging tolerance at the flowering stage, whereas Toyoharuka is sensitive to waterlogging at this stage (Kousaka et al, 2013). Toyomusume is a major cultivar in Hokkaido and is moderately sensitive to waterlogging at the flowering stage (Jitsuyama, 2015). All seeds were multiplied at the Kyushu University Farm, Fukuoka Prefecture, Japan (33°6′N, 130°5′E), in 2013 or 2014 and stored at 4 °C until they were ready for use.…”

Hypoxia-Responsive Root Hydraulic Conductivity Influences Soybean Cultivar-Specific Waterlogging Tolerance

“…Although the use of a comparative physiological approach might provide new insights into soybean waterlogging tolerance, there are no available reports describing studies involving several cultivars under normal and oxygen-stress conditions in the root zone. The responses of eight Japanese soybean cultivars to hypoxic conditions were compared in a short-term hydroponic culture system [17] [18]. The results revealed a cultivar-specific waterlogging tolerance during the immature growth stage without the development of adventitious roots or aerenchyma.…”

“…The results revealed a cultivar-specific waterlogging tolerance during the immature growth stage without the development of adventitious roots or aerenchyma. Additionally, some susceptible cultivars exhibited decreased shoot and root biomasses due to hypoxia, with some plants suddenly withering, possibly because of reduced root hydraulic conductance [18]. The present study involved a modified hydroponic culture system that enabled the creation of two different oxygen environments.…”