PlantwisePlus Blog

Striga infected field. USDA APHIS PPQ Archive, Bugwood.org

A group of scientists from the Netherlands, UK and Africa have studied upland NERICA rice cultivars to identify those that exhibit multi-level striga resistance. In two separate research papers, the 18 NEw RICe for Africa (NERICA) cultivars and their parents were screened for pre- and post- attachment striga resistance. One particular cultivar NERICA 1 was shown to possess high levels of both these types of resistances.

NERICA cultivars are interspecific upland rice cultivars developed by a team of scientists and their partners at The Africa Rice Center. These are crosses between the two traditional cultivated rice species, both of which are grown in Africa. The Asian species, Oryza sativa is known for its high yielding potential while its African counterpart (O. glaberrima) is known to be more resistant to local biotic and abiotic stresses. The resulting NERICA cultivars were widely accepted by African subsistence rice farmers and resulted in a consistent increase in rice production.

To further increase this production however, other production constraints have to be alleviated. One such is the noxious weed plant striga (Striga hermonthica and S. asiatica) that results in significant yield losses in many rice growing areas. Striga is also called witch weed and is found to infect a wide range of cereal hosts including sorghum, maize and rice. It is an obligate parasite that requires a host for survival and its seeds are found commonly in the soil. The germination of striga seeds is triggered by host-derived signals like strigolactones. Once they germinate, they attach to the roots of host plants and form specialized structures called haustoria. Using these structures, the parasite absorbs nutrients from the host leaving it severely stunted. Following this striga plants emerge from the ground, flower profusely, producing a large number of seeds that lay dormant in the ground awaiting the next host.

Scientists Jamil et al. studied the production of strigolactones to identify pre-attachment striga resistance of NERICA cultivars. They found that the quantity and quality of strigolactones produced by NERICA cultivars varied and had an effect on germination, attachment and emergence rate of striga. They found that cultivars that produced less strigolactones (like NERICA 1) were less infected by striga than those cultivars that produced more strigolactones (NERICA 7, 8, 11, 14).

In another study, scientists Cissoko et al. studied the ability of these cultivars to resist the parasite after its germination, during attachment. They found that some of the cultivars (NERICA 7, 8, 9, 11 and 14) were highly susceptible to this stage while others (NERICA 1, 10) showed considerable resistance.

These studies suggest that rice cultivars with both these resistances (like NERICA 1) will be particularly useful in striga infected fields. This information is thus important not just to improve current integrated management practices for striga, but also helps plant breeders develop cereal cultivars with resistance to biotic stresses.

References

• Cissoko, M.; Boisnard, A.; Rodenburg, J.; Press, M.C.; Scholes, J.D. (published online 29 Aug 2011) New Rice for Africa (NERICA) cultivars exhibit different levels of post-attachment resistance against the parasitic weeds Striga hermonthica and Striga asiatica. New Phytologist. DOI: 10.1111/j.1469-8137.2011.03846.x

• Jamil, M.; Rodenburg, J.; Charnikhova, T.; Bouwmeester, H. (published online 29 Aug 2011) Pre-attachment Striga hermonthica resistance of New Rice for Africa (NERICA) cultivars based on low strigolactone production. New Phytologist. DOI: 10.1111/j.1469-8137.2011.03850.x