Cultivated Helianthus annuus differs from two wild relatives in germination response to simulated drought stress

Abstract

Wild sunflowers are a source of desirable traits for improving cultivated sunflower Helianthus annuus (ANN). Two wild species of sunflower, H. argophyllus (ARG) native to coastal sand dunes and H. niveus ssp. tephrodes (TEPH) native to the desert sand dunes, have been hypothesized to be drought resistant. We tested the expectation that these wild species would have higher percent germination and more uniform germination under simulated drought stress conditions compared to cultivated ANN. In a growth chamber study, we assessed germination of ANN, ARG and TEPH (three representative accessions for each species) under four osmotic stress treatments imposed using polyethylene glycol to simulate varying levels of drought stress: 0, -0.4, -0.8 and -1.2 MPa. As expected, all three species responded to increasing simulated drought stress with decreased percent germination assessed after seven days and delayed germination timing and uniformity assessed with logistic regressions. ARG responded marginally better than ANN with a greater percent germination at -1.2 MPa and greater uniformity at 0 and -0.4 MPa. Although the ARG advantage was small, this suggests that ARG × ANN recombinant hybrids may deserve further investigation to see if desirable alleles can be identified for improving cultivated ANN germination and establishment under mild drought conditions. In contrast, TEPH responded with substantially lower percent germination and less uniformity than ANN, suggesting that it is unlikely that TEPH will be useful as a donor of desirable drought resistance alleles.