The production of high quality seeds is linked to a good quality control system. In this system, the tetrazolium test plays an important role in the evaluation of the seed physiological quality, not only due to its relative quickness, but also because of the amount of information that the test presents, such as the indexes of viability and vigor, in addition to providing the diagnosis of possible seed quality problems, such as mechanical damage, insect damage, pre-harvest weathering and deterioration during storage. The development of the test had its beginnings at the end of the 19^th century, with great evolution in its concepts and methods in the 20^th century. For that, there was the dedication of dozens of professionals in several countries, such as Germany, Japan, Russia, Serbia (former Yugoslavia), United States, Argentina and Brazil. The test indirectly measures the respiration processes that occur in the mitochondria of the cells that make up the tissues of the seeds. The reducing reaction of the solution of the tetrazolium salt under the action of dehydrogenase enzymes results in triphenylformazan, which presents a red carmin coloration. By the interpretation of the resulting staining patterns, seed viability, vigor and the main problems affecting seed quality are determined.

Due to the climate change of the past few decades, some agricultural areas in the world are now experiencing new climatic extremes. For soybean, high temperatures and drought stress can potentially lead to the “green seed problem”, which is characterized by chlorophyll retention in mature seeds and is associated with lower oil and seed quality, thus negatively impacting the production of soybean seeds. Here we show that heat and drought stress result in a “mild” stay-green phenotype and impaired expression of the STAY-GREEN 1 and STAY-GREEN 2 (D1, D2), PHEOPHORBIDASE 2 (PPH2) and NON-YELLOW COLORING 1 (NYC1_1) genes in soybean seeds of a susceptible soybean cultivar. We suggest that the higher expression of these genes in fully mature seeds of a tolerant cultivar allows these seeds to cope with stressful conditions and complete chlorophyll degradation. The gene expression results obtained in this study represent a significant advance in understanding chlorophyll retention in mature soybean seeds produced under stressful conditions. This will open new research possibilities towards finding molecular markers for breeding programs to produce cultivars which are less susceptible to chlorophyll retention under the hot and dry climate conditions which are increasingly common in the largest soybean production areas of the world.

The effects of lignin on soybean seed quality have been studied since the early 1990s. Initially, higher lignin content in the seed coat was associated with greater resistance to mechanical damage by the seeds. Later, positive relationships of lignin content in the seed coat were associated with tolerance to stresses caused by weathering in pre-harvest, resulting in improved seed quality. Additional studies have shown that higher lignin content in the pod wall of soybean is also related to production of seeds with high physiological and sanitary qualities. Colored soybean seeds (black or brown) are known to have higher seed quality due to higher lignin content in the seed coat; in addition, the presence of anthocyanin in the seed coat of colored seeds also contributes to improve seed quality. Finally, the effects of boron on lignin synthesis are also highlighted in this review article. As demonstrated in this review article, lignin content in the seed coat and pod wall of soybean plays an important role in relation to physical, health, and physiological seed qualities. These parameters should be considered in studies related to evaluation of the quality of soybean seeds as affected by genetic factors. These parameters should also be strongly considered for inclusion in breeding programs to improve soybean seed and grain quality.

Hot and dry weather conditions during soybean [Glycine max (L.) Merrill] seed maturation can cause forced maturation of the seed, resulting in the production of high levels of green seed, which may be detrimental to seed germination. These stressful conditions were imposed on soybean plants during seed maturation to investigate the production of green seeds and seed quality. Plants of the CD 206 cultivar were grown in a greenhouse until the R5.5 growing stage and then transferred to phytotrons at R6 and R7.2 for stress induction. Plants were subjected to two temperature regimes, high (28ºC to 36ºC) and normal (19ºC to 26ºC), and four soil water availability conditions, control (adequate water supply), 30% gravimetric moisture (GM), 20% GM and no water supply. Seed were harvested at R9. Green seed percentages and 100-seed weights from the lower, middle and upper thirds of each plant were determined. Seed quality was assessed by germination, tetrazolium (viability and vigor) and electrical conductivity tests. Occurrence of green seed varied from 9% to 86%, depending on the severity of the stresses imposed. High temperature, coupled with no water supply at R6, resulted in a pronounced occurrence of green seeds. There was no difference in the percentage of green seeds among the plant segments. Seed quality was negatively affected by the incidence of green seeds. A procedure for screening soybean genotypes in a phytotron for their tolerance and/or susceptibility to the production of green seeds was developed.

Mechanical damage is a serious problem for the physiological potential of soybean seeds, especially when combined with chemical treatment. The aim of this study was to investigate the effects of chemical treatment on the physiological potential of soybean seeds with increasing levels of mechanical damage. Soybean seeds (cv. M6410 IPRO) of two lots with differences in vigor were subjected to five levels of mechanical damage (zero, one, two, three, and four impacts) brought about in a controlled manner. After characterization of the effect of the impacts on seed physical integrity (X-ray, X-ray microtomography, tetrazolium, and sodium hypochlorite), the seeds were subjected to four combinations of chemical treatment with fungicides (carbendazim and thiram), insecticides (imidacloprid and thiodicarb), micronutrients (cobalt and molybdenum), polymer (Peridiam®), and drying powder (Talkum Gloss®). Seed germination and vigor were evaluated sixty days after chemical treatment. A progressive increase in mechanical damage, especially that which causes cracks in the seed coat, reduces the physiological potential of soybean seeds and increases their sensitivity to the phytotoxic effect of the chemical treatment. The physical integrity of the seed coat is crucial for the success of technologies used for chemical seed treatment.

The Seed Symposium of the 27^th ISTA Congress was held in Budapest, Hungary in May 2004. This paper presents a review of the oral and poster papers presented in seven sessions under the theme 'Towards the future in seed production, evaluation and improvement', namely application of advanced technologies; organic and conventional seed production; viability and vigour: evaluation and impact; seed systems in developing and emerging economies; seed lot hygiene; seed improvement; physiological basis of seed quality.