Evaluation of Pre-Attachment and Post-Attachment Striga Hermonthica (Del.) Benth. Resistance in Pearl Millet (Pennisetum Glaucum (L.)
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Striga species are parasitic weeds, one of the most devastating biological constraint threatening agriculture especially production of cereals in sub-Saharan Africa (SSA), causing approximately 30% to near crop failure, thus endangering the livelihood of more than 300 million poor smallholder famers. One way of combating Striga is having natural host resistance which is cost effective and efficient for tolerance phytopathogenic damages. Such resistance can either be due to failure of the host to stimulate germination of the parasite (pre-germination resistance) or blockage of the parasite penetration by the host (post-germination resistance). From field evaluations, wild pearl millet (Pennisetum glaucum) accession 29 AW was shown to get less Striga attachments compared to the cultivated variety, SOSAT-C88 P10. However, the mechanism of resistance was not established. The aims of this study were to investigate pre- and post-attachment Striga resistance in pearl millet using SOSAT-C88 P10, a cultivated susceptible pearl millet and 29 AW. Pre-germination resistance was determined using an agar-gel assay which measured the maximum germination distance (MGD), whereas post-germination resistance was determined using rhizotron based approach as well as histological analyses. A high Striga germination activity was observed in SOSAT-C88 P10 (MGD= 35.94 + 2.88> 10 mm) coupled with elevated percentage of germinated Striga seeds (>85.04%) compared to 29 AW (MGD= 7.96 +2.75 mm <10 mm) with few sprouts (8.14 %) of the parasite. Moreover, macroscopic screening showed that there were highly significant differences between SOSAT-C88 P10 and 29 AW in terms of number of Striga attachments, Striga dry weight and the length of Striga seedlings (P-value < 0.05). SOSAT-C88 P10 had many Striga attachments, with much longer Striga seedlings with significant weight, while, 29 AW had very few Striga seedlings attachment, smaller and slow growth seedlings with lower biomass. Further histological analyses revealed that the high number of attachments of Striga on SOSAT-C88 P10 compared to 29 AW was due to biochemical or physiological barriers at host endodermis layer. This work therefore demonstrated that there are multiple forms of Striga resistance (pre- and post-attachment) in wild pearl millet 29 AW. These findings will be useful for future resistance breeding of pearl millet.