Genetic basis of striga hermonthica (del.) benth resistance in wild sorghum accessions
Dorothy, Annah Mbuvi
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Striga weeds are root parasitic plants that affect production of food in sub-Saharan Africa. Striga genus includes species; Striga hermonthica, S. gesnerioides, S. aspera, S. asiatica and S. forbesii with S. hermonthica being the most widely spread in the semi-arid tropical African zones. The most effective Striga control strategy is to exploit natural resistance. Wild grasses contain a resistance mechanism that enables them to resist Striga infection resulting in low Striga quantity in feral grasslands as compared to cultivated cereals. In this study, seven wild sorghums accessions (WSE-1,WSA-1,WSA-2,WSA-3,WSD-1,WSD-2 and WSD-3) were evaluated for post-attachment Striga resistance against three common ecotypes of S. hermonthica weeds in Kenya (Alupe, Kibos and Mbita). Cultivated race N13(resistant) for post Striga germination served as control. The resistant accessions were the WSE-1, WSA-1 and WSA-2 which had lowest mean count (<30), mean length (< 0.243cm) and mean biomass (< 9.233mg) of S. hermonthica plantlets growing on their roots as compared to N13 which had mean count (<44), mean length (<0.329 cm) and mean biomass (<23.733mg) of S. hermonthica plantlets while the highly susceptible accessions were WSD-1,WSD-2, WSD-3 and WSA-3, which had the highest mean count (> 80), mean length (> 0.651 cm) and mean biomass (> 36mg) of S. hermonthica plantlets. According to Tukey’s Honest significant Difference test, there were significant differences in the mean counts, mean biomass and mean lengths (P˂ 0.05) of Striga growing on the roots of sorghum accessions. Therefore it was established that resistance response against S. hermonthica among sorghum varied widely. Subsequent to determination of resistance response in wild sorghum accessions, RNA-sequencing was done on WSE-1 infected with Striga seeds at two different stages. This led to identification of two different pathogenesis resistance genes (PR-2 and PR-4). Gene ontology annotation revealed these to be anti-fungal agents involved in cell wall loosening and chitinase, as well as a cell wall degrading enzyme respectively. When the two genes will be transformed in cultivated sorghums, they will act in signaling induction of defensive response and also they will act in defensive mechanism, stabilizing cellular structures against further pathogen or Striga infection. Therefore, these genes will provide a platform for enhancing Striga resistance in sorghum and develop a durable, broad-spectrum resistance in cultivated sorghums.