Abstract
Shattercane (Sorghum bicolor (L.) Moench subsp. drummondii) and weedy sunflower (Helianthus annuus L.) are two examples of crop wild relatives (CWRs) that have become troublesome weeds in agriculture. Shattercane is a race belonging to a different subspecies than domesticated sorghum (Sorghum bicolor (L.) Moench subsp. bicolor). Weedy sunflower populations are natural hybrids between wild and domesticated sunflower (Helianthus annuus L.). Both species have key weedy characteristics, such as early seed shattering and seed dormancy, which play an important role in their success as agricultural weeds. They are widely reported as important agricultural weeds in the United States and have invaded various agricultural areas in Europe. Shattercane is very competitive to sorghum, maize (Zea mays L.), and soybean (Glycine max (L.) Merr.). Weedy sunflower causes severe yield losses in sunflower, maize, soybean, pulse crops, and industrial crops. Herbicide resistance was confirmed in populations of both species. The simultaneous presence of crops and their wild relatives in the field leads to crop–wild gene flow. Hybrids are fertile and competitive. Hybridization between herbicide-tolerant crops and wild populations creates herbicide-resistant hybrid populations. Crop rotation, false seedbed, cover crops, and competitive crop genotypes can suppress shattercane and weedy sunflower. Preventative measures are essential to avoid their spread on new agricultural lands. The development of effective weed management strategies is also essential to prevent hybridization between sorghum, sunflower, and their wild relatives and to mitigate its consequences.
Highlights
Crop wild relatives (CWRs) are wild plant species closely related to domesticated crops
The use of CWRs is recommended for crop improvement in dominant multipurpose crops such as sorghum (Sorghum bicolor (L.) Moench subsp. bicolor) and sunflower (Helianthus annuus L.) [2,12]
As for Europe, Vrbnicanin et al [98] collected two sunflower populations in Serbia from fields treated with nicosulfuron in consecutive years. These authors found that the application of nicosulfuron at the recommended field dose had no effect on the relative fitness and fecundity of the two potentially resistant populations. This is not an official case where herbicide resistance was confirmed in doseresponse experiments, these results suggest that herbicide-resistant weedy sunflower may be evolving in Europe
Summary
Crop wild relatives (CWRs) are wild plant species closely related to domesticated crops. Drummondii), and weedy sunflower (Helianthus annuus L.) are prominent examples of weedy relatives of rice, sorghum, and sunflower, respectively [13,14,15] All these species are competitive and have undesirable agronomic characteristics, such as early seed shattering and seed dormancy, which play an important role in their success as weeds in agriculture [15,16,17]. Shattercane and weedy sunflower are among the most competitive weeds against their closely related domesticated crop species, namely sorghum and sunflower, respectively [22,23]. Weedy rice exclusively infests rice fields and causes severe yield losses everywhere in the world where direct-seeded rice is cultivated [15,19] Apart from their competitive ability, populations of these weedy crop relatives have developed resistance to common herbicides used to control weeds in summer field crops [29]. Emphasis is placed on the role of weed management in preventing gene flow from crops to their wild relatives
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