Physiological and genetic study of the three-way interactions between rice, arbuscular mycorrhizal fungi and the parasitic weed Striga

Striga constitutes a major limitation to cereal crop production and efficient control methods are scant, because the parasite damages the host plant before it emerges. Therefore, identifying cultivars that avoid or reduce the impact of the parasites on the host plant is crucial. This study screened a diverse collection of rice cultivars for Striga resistance, evaluates the influence and nature of AMF (Rhizophagus intraradices) induced protection against Striga using split-root technique, assesses the genetic variation in host root phytochemical activity on Striga seeds germination and examines evidence that variation in the presence or absence of the MAX1 ortholog gene is implicated in resistance. Upon examination, six of the rice cultivars showed good resistance to Striga while nineteen showed intermediate resistance and six were clearly susceptible. The phenotype of the resistant mechanism was characterized by the ability of the cultivar to support no or few emerged Striga. The product of the PCR analysis showed that the insertion/deletion of MAX1 gene was not associated with host resistance. The influence of AMF on Striga-rice interaction showed a genotypic dependent response in AMF induced protection against Striga. AMF reduced damage by Striga in Bala, RINIL 16.6 and 16.5 but did not protect Azucena. These variations in response of the RINILs to Striga imply a role of signalling between rice and Striga which may be related to strigolactones despite the lack of association between resistance and the MAX1 polymorphism. The AMF-induced protection against Striga act through a systemic mechanism in Azucena but the nature of the induced protection in Bala was inconclusive. The activity of the host root phytochemical on Striga seeds germination differed with Striga ecotype and the optimal dilution required to stimulates specific Striga ecotype is not the same for all cultivars. The outcome of this research provided useful strategies for Striga control, be it breeding or mycorrhizal application. The elucidation of the genetic basis of the AMF enhanced resistance mechanisms and tolerance in susceptible cultivars and manipulation of the presence MAX1 genes might provide strategies for the control and management of Striga infestation.