Drought‐Induced Stress Effect on Soybean Seed Calcium and Quality

Abstract

Drought stress can lower seed quality of soybean [Glycine max (L.) Merr.], possibly from stress related changes in seed‐nutrient concentration. Determinate soybean plants were grown under a mobile weather‐shelter near Ames, IA in 1985 and 1986 to determine if the timing of drought stress could influence seed‐Ca concentration and, subsequently, seed germination and quality. A randomized complete‐ block design was used to test the effect of withholding water during flowering (R2), full pod (R4), seed formation (R5), and full seed (R6) on the quality of the harvested seed. Drought stress was quantified by monitoring leaf temperatures. Each drought‐stress period received an equivalent amount of drought stress. Seed from a R5 drought stress had 85% germination compared with 96% germination for the nonstressed seed. This reduction in seed germination coincided with a 343 μg g−1 decrease in seed‐Ca concentration from a Ca level of 1648 μg g−1 in the nonstressed seed. Electrolytic conductivity per seed and seed‐Ca concentration were negatively correlated (r = −0.50). Germination percentage was significantly correlated (r = + 0.57) with seed‐Ca concentration and negatively correlated with P, Fe, and Zn (r = −0.49, −0.44, and −0.43, respectively). Application of 2.0 g L−1 of Ca(NO3)2 to the germination media of the R5‐stressed seed improved germination to the level obtained by nonstressed seed. The application of Ca(NO3)2 also improved the germination of R6‐stressed seed, which had a concentration of seed Ca equal to the control. This suggests that seed‐Ca concentration is not solely responsible for the decrease in germination percentage of drought‐stressed seed. Results indicate that drought stress during seed formation can reduce seed‐Ca concentration, but additional work is needed to clarify the role that Ca and other seed nutrients play in the germination of drought‐stressed seed.

Efeito da irrigação sobre o potencial fisiológico de sementes de soja em semeadura de inverno

“…Os dados da literatura referentes aos efeitos da irrigação na qualidade de sementes mostram a importância desta prática na fase de maior acúmulo de matéria seca (Rassini e Lin, 1981;Smiciklas et al, 1989;Heatherly, 1993). No entanto, o objetivo do presente estudo foi avaliar o efeito da irrigação após o estádio R 7 , ou seja, após a semente já formada.…”

“…Galbiatti et al (2004) verificaram que a suspensão da irrigação aos 20 dias após o florescimento não diferiu do tratamento em que a irrigação foi mantida durante todo o ciclo. Na cultura da soja, entretanto, o uso de irrigação na entressafra pode minimizar os efeitos negativos da deficiência hídrica sobre o potencial fisiológico das sementes, em especial na fase de enchimento de vagens, ou seja, no estádio R 5 , conforme demonstraram vários pesquisadores (Rassini e Lin, 1981;Smiciklas et al, 1989;Dornbos et al, 1989;Heatherly, 1993). Nesse sentido, Albrecht et al (2009) observaram que algumas das cultivares avaliadas em semeadura no período 'safrinha' não produziram sementes com qualidade fisiológica no oeste do estado do Paraná, resultado atribuído à sensibilidade daqueles genótipos ao déficit hídrico associado à baixa capacidade de retenção de água do solo naquela região.…”

Mineral concentrations in soybean seed produced under high day and night temperature

“…Drought stress during seed formation and filling decreased seed Ca concentration (Smiciklas et al 1989).…”

“…A high Ca concentration in the seed coat has been linked to hard seeds and reduced water uptake, which makes soybean unacceptable for making these products (Saio 1976). Most of the phytic acid in soybean is extractable into soymilk and coprecipitates with the proteins in tofu during coagulation (Saio 1979;van der Riet et al 1989). Coagulation occurs more slowly at greater phytic acid concentration and the resulting network can hold more moisture, so there is greater yield and softer tofu (Saio et al 1969;Saio 1979).…”

“…Several minerals are essential to plant growth and two have been implicated in stress-induced quality reductions in soybean seed used for planting. Soybean seed quality has been positively correlated with seed Ca concentration (Smiciklas et al 1989;Keiser and Mullen 1993) and negatively correlated to seed B concentration and B:Ca ratio (Keiser and Mullen 1993).…”