Classic Genetics and Breeding - Genetics, Genomics and Breeding of Crop Plants - page 74

2.4.5 Insects Affecting Seed Yield (from Vear and Miller 1992)
Sunflower is a host to a number of insect pests. In North America,
approximately 15 species of sunflower insects cause plant injury and
economic loss, depending upon the severity of infestation (Schultz 1978).
The existence of this number of insect pests coincides with the evolution of
wild sunflowers in North America. To date, these insect species have not
been transferred to other production areas of the world. However, two
species of insects attack sunflower other than in North America. These are
the European Sunflower Moth in Europe and Russia, and the Rutherglen
bug in Australia.
Head-infesting species of insects producing economic damage include:
Sunflower moth, Homoesoma electellum (Lepidoptera: Pyralidae); European
Sunflower Moth, Homeosoma nebulella (Lepidoptera: Pyralidae); Banded
Sunflower Moth, Cochylis hospes (Lepodoptera: Cochylidae); Sunflower
Budworm, Suleima helianthana (Lepidoptera: Tortrichidae); Seed Weevil,
Smicronyx fulvus and S. sordidus (Coleoptera: Curculionidae); and Sunflower
midge, Contarinia schulzi (Diptera: Cecidomyiidae). Foliage and stem feeding
species include: Sunflower Beetle, Zygogramma exclamationis (Coleoptera:
Chrysomelidae); Painted Lady, Cynthia cardui (Lepidoptera: Nymphalidae)
and Stem Weevil, Cylindropterus adspersus (Coleoptera: Curculionidae).
The most important insects in North America are the Sunflower Moth,
Banded Sunflower Moth, Seed Weevil and Sunflower Midge. Resistance to
the Sunflower Moth and European Sunflower Moth has been associated
with the armored layer, a pigmented substance between the outer layer and
the adjoining sclerenchyma tissue in the sunflower hull. Few resistance
mechanisms have been determined for the other species. Other mechanisms
for decreasing damage have been investigated and include: biological control,
chemical deterrents derived from wild Helianthus species, pheromones to
trap insects, chemical feeding deterrents and cultural controls.
2.4.6 Drought Resistance
Sunflowers are most often grown in areas where irrigation is not possible or
is restricted to use on maize crops. When water is not a limiting factor,
sunflowers absorb and transpire relatively large amounts, with production
of what may be an excessive leaf area if drought occurs later in the cycle
(Merrien 1992). However, compared with many crops, sunflowers are
relatively drought tolerant in the sense that they are able to extract water
from a large depth of soil and at low soil water potentials.
Robelin (1967) showed that yield is affected if sunflowers lack sufficient
water in the period of six weeks around flowering. Among cultivated hybrids,
ratios of yield in dry and irrigated conditions may vary by 100%, but such