Identification of soybean genotypes with high stability for the Brazilian macro-region 402 via biplot analysis.

Biplot analysis has often been used to recommend genotypes from different crops in the presence of the genotype x environment interaction (GxE). The objective of this study was to verify the association between the AMMI and GGE biplot methods and to select soybean genotypes that simultaneously meet high grain yield and stability to the environments belonging to the Edaphoclimatic Region 402, from Soybean Cultivation Region 4 (Mid-West), which comprises the Center North and West of Mato Grosso, and the southern region of Rondônia. Grain yield of 12 soybean genotypes was evaluated in seven competition trials of soybean cultivars in the 2014/2015 harvest. Significant GxE interaction revealed the need to use methods for recommending genotypes with adaptability and yield stability. The methods were complementary regarding the recommendation of the best genotypes. The AMMI analysis recommended MG/BR46 (Conquista) (G10) widely for all environments evaluated, whereas the BRY23-55012 (G9) and BRAS11-0149 (G2) were the most indicated genotypes by the GGE biplot method. However, the methods were concordant as to Porto Velho (PV1) environment that contributed least to the GxE interaction.

Soybean physiology and gene expression during drought.

Soybean genotypes MG/BR46 (Conquista) and BR16, drought-tolerant and -sensitive, respectively, were compared in terms of morphophysiological and gene-expression responses to water stress during two stages of development. Gene-expression analysis showed differential responses in Gmdreb1a and Gmpip1b mRNA expression within 30 days of water-deficit initiation in MG/BR46 (Conquista) plants. Within 45 days of initiating stress, Gmp5cs and Gmpip1b had relatively higher expression. Initially, BR16 showed increased expression only for Gmdreb1a, and later (45 days) for Gmp5cs, Gmdefensin and Gmpip1b. Only BR16 presented down-regulated expression of genes, such as Gmp5cs and Gmpip1b, 30 days after the onset of moisture stress, and Gmgols after 45 days of stress. The faster perception of water stress in MG/BR46 (Conquista) and the better maintenance of up-regulated gene expression than in the sensitive BR16 genotype imply mechanisms by which the former is better adapted to tolerate moisture deficiency.

Cloning and quantitative expression analysis of drought-induced genes in soybean.

We determined the expression levels of DREB transcription factor (Gmdreb1) and of the genes Gmgols, Gmpip1b, Gmereb, and Gmdefensin in drought-tolerant (MG/BR46-Conquista) and drought-sensitive (BR16) genotypes of soybean, during drought. The trial was carried out in a controlled-environment chamber, set up to provide drought conditions. Sequences of Arabidopsis thaliana DREB-family proteins were used to build a phylogenetic tree through the alignment of the conserved regions near the AP2 domain. We found that Gmdreb1 is similar to Atrap2.1, which is located near the AtDREB1 and AtDREB2 families. The amplified fragment was cloned and sequenced; alignment with the sequence available at Genbank showed total similarity. Expression analysis showed that under drought: a) Gmdreb1 expression increased in leaves and roots of both genotypes and expression level changes occurred that were correlated with the length of the water-deficit period; b) there were increased expression levels of Gmdefensin in roots of MG/BR46; c) expression of Gmgols increased in leaves and roots of the two genotypes; d) Gmpip1b expression generally increased, except in roots of BR16, and e) the same was found for Gmereb, except in roots of MG/BR46.

Phytotoxicity of a Culture Filtrate Produced by Stemphylium solani of Cotton.

Stemphylium solani, which causes a new leaf blight of cotton, was suspected of producing a phytotoxin. Studies were conducted to examine the relationship between the reaction of different cotton cultivars and of some unrelated host species to the pathogen and its toxin-containing culture filtrates. Seven single spore isolates of S. solani from cotton and their toxin-containing culture filtrates were used for leaf and root bioassays. An isolate of S. solani from tomato was also used for comparison. The phytotoxic effect was isolate dependent. Culture filtrates of five isolates killed 40 to 60% of the cotton seedlings when incubated for 4 days at 10-1 dilution. At 10-2 dilution, the culture filtrates of most of the isolates affected the development of the root system but failed to kill any seedling. The phytotoxic effect of the culture filtrate was not degraded by autoclaving. A high correlation coefficient between the percentage of the leaf area infected (LAI) by S. solani and the percentage of the necrotic leaf area (LAN) by the culture filtrate was observed when one of the aggressive isolates and its culture filtrate were tested against adult plants of 38 cotton cultivars (r = 0.86). Cultivars CNPA T-1180-23, CNPA-PRECOCE 2, PR 94-215, and PR 94-82 demonstrated resistance to the pathogen as well as insensitivity or moderate sensitivity to its toxin. Cultivars showing intermediate reaction to the pathogen also showed intermediate reaction to its culture filtrate. Similarly, the highly susceptible cultivars Paraná 3, PR 93-129, and PR 94-216 also were highly sensitive to the culture filtrate. Of the 18 plant species belonging to 18 genera, eight were susceptible to the pathogen. With two exceptions, susceptible hosts were also sensitive to the culture filtrate, whereas nonsusceptible hosts were insensitive. A component of the culture filtrate was regarded as a pathogenicity factor.