Sunflower and drought stress during early development

ANDRADE, ANDREA; CASTILLO, PAULA; VIGLIOCCO, ANA; ALEMANO, SERGIO; ABDALA, GUILLERMINA

Sunflower: cultivation, nutrition and biodiesel uses

Nova Science Publishers

Año: 2011; p. 99 - 134

Sunflower (Helianthus annuus L.) is an important oil crop world-wide. Responses of inbred sunflower lines (B59, B67, B71, R415, R049, R419, R423, R432, HA89, RHA274, HAR4) to drought stress imposed at germination and seedling growth stages were evaluated in field and laboratory experiments. In the field, B59, R419, and B67 showed major reduction of seed and oil yield under drought, whereas no reduction was observed for R432, HAR4, or B71, and HA89, R415, R049, RHA274, and R423 showed intermediate reduction. In the laboratory, seeds of B59 showed reduced germination percentage in the presence of 200 and 400 mM mannitol (simulated drought condition), whereas germination of R432, B71, HAR4, RHA274, and HA89 was reduced only with 400 mM mannitol. On the basis of these results, we characterized line B59 as drought-sensitive, and B71 as drought-tolerant, and used them in subsequent experiments. Dry and germinated seeds from B59 and B71 plants grown under drought and irrigation conditions were evaluated for content of phytohormones: jasmonates (JAs), abscisic acid (ABA), and ABA catabolites. Germination percentage, in general, was correlated with endogenous hormone levels. Seeds from plants grown under drought had lower content of total JAs, and higher germination percentage, than seeds from plants grown under irrigation. For plants of both lines, grown under both soil moisture conditions, content of total JAs was higher in germinated seeds than in dry seeds. ABA was the major hormonal compound in dry seeds of B59 plants grown under drought. Under drought, ABA level was higher in dry seeds of B71 than of B59. ABA content declined after germination, for both lines under both soil moisture conditions. Composition patterns of JAs and ABA varied in sunflower seeds depending on environmental conditions experienced by the mother plant, and drought modified the hormonal content of seed progeny. We investigated interactions between sunflower and associated bacteria isolated from plants grown under irrigation and drought. Twenty-nine endophytic bacterial strains were investigated. Strains identified as Bacillus pumilus (SF3 and SF4) and Achromobacter xylosoxidans (SF2) were selected for further experiments, based on their characterization as plant growth-promoting bacteria (PGPB). Plant growth of B59, B71, and a commercial hybrid (Paraiso 24) following inoculation with the three bacterial strains was enhanced more strongly for Paraiso 24 and B71 than for B59, under both drought and irrigation. All three strains produced salicylic acid (SA) in control medium, with higher levels for SF3 and SF4 than for SF2. Under drought stress (Øa = – 2.03 MPa), all three strains showed significantly increased SA. SA and jasmonic acid caused a modest reduction in growth of the pathogenic fungi Alternaria and Verticillum, and a major reduction in growth of the fungus Sclerotinia. Bacterial pellets inhibited fungal growth more efficiently than bacterial supernatants. In summary, endophytic bacteria were found to improve sunflower seedling growth under drought stress, to produce SA, and to inhibit growth of pathogenic fungi. Our findings suggest that growth and yield of sunflower under drought stress condition can be improved by inoculation with a suitable PGPB such as SF2, SF3, or SF4. The characteristics of these bacterial strains, and effects of their inoculation on sunflower seedlings, have technological implications for formulation of more effective inoculants.