Our study demonstrates that Hakea is an exception to the more commonly described shift from insect to bird pollination. However, we note that only one previous phylogenetic study involved Australian plants and their honeyeater pollinators and that our finding might prove to be more common on that continent.

No abstract

Water availability is a major factor limiting plant productivity in both natural and agronomic systems. Identifying putative drought resistance traits in crops and their wild relatives may be useful for improving crops grown under water-limiting conditions. Here, we tested the expectation that a desert-dwelling sunflower species, Helianthus niveus ssp. tephrodes (TEPH) would exhibit root and leaf traits consistent with greater ability to avoid drought than cultivated sunflower H. annuus (ANN) in a common garden environment. We compared TEPH and ANN at both the seedling and mature stages under well-watered greenhouse conditions. For traits assessed at the seedling stage, TEPH required a longer time to reach a rooting depth of 30 cm than ANN, and the two species did not differ in root:total biomass ratio at 30 cm rooting depth, contrary to expectations. For traits assessed at the mature stage, TEPH had a higher instantaneous water use efficiency and photosynthetic rate on a leaf area basis, but a lower photosynthetic rate on a mass basis than ANN, likely due to TEPH having thicker, denser leaves. Contrary to expectations, ANN and TEPH did not differ in leaf instantaneous stomatal conductance, integrated water-use efficiency estimated from carbon isotope ratio, or nitrogen concentration. However, at both the seedling and mature stages, TEPH exhibited a lower normalized difference vegetative index than ANN, likely due to the presence of dense leaf pubescence that could reduce heat load and transpirational water loss under drought conditions. Thus, although TEPH root growth and biomass allocation traits under well-watered conditions do not appear to be promising for improvement of cultivated sunflower, TEPH leaf pubescence may be promising for breeding for drought-prone, high radiation environments.

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.