Strigolactone Profile of Selected Legumes and their Potential for Use as Trap Crops for Striga

Abstract

Striga hermonthica’s non-hosts stimulate parasite seed to germinate without getting infected because the non-hosts produce unique germination stimulants (strigolactones). This phenomenon – called suicidal seed germination is greatly used in S. hermonthica control. For improved efficiency of the suicidal seed germination method in S. hermonthica control, detailed analysis of comparative ability of potential trap crops to stimulate germination is critical. An additional and often ignored determinant of suitability of nonhost intercrops is the extent to which the parasite can penetrate various non hosts and if such interaction can adversely affect the trap crop. This is critical because although the parasite is not able to effectively infect a non-host, it may still cause injuries that can expose the crop to other pathogens such as bacteria and fungi. In this study, suitability of Kenya’s commonly used legumes (cowpea, pigeon pea, common bean, and garden pea) as potential intercrops in the control of S. hermonthica was determined. Firstly, their efficiency to induce germination of S. hermonthica seeds using germination assays was determined. Then, the amounts and types of strigolactones in their root exudates was assayed using a high performance liquid chromatography coupled with tandem mass spectrometer (LCMS/ MS). Finally, the extent of interaction between the legumes and S. hermonthica was determined using histological analysis. There were significant differences in the induction of S. hermonthica germination by the legume root exudates, synthetic GR24, and water (p=0.0001). Analysis of strigolactones in root exudates of legumes revealed that the most abundant strigolactones were 2-epi-5-deoxystrigol and orobanchol with trace amounts of 2-epi-orobanchol and strigol. Expectedly, none of the legumes fully supported growth and development of S. hermonthica to enable the parasite complete its lifecycle. However, the extent of parasite penetration varied greatly in the different legumes. Cowpea and garden pea formed vascular connections with S. hermonthica parasite. However, the parasite did not grow beyond pigeon pea’s endodermis, and in the common bean, the parasite barely attached on the host cortex. These findings suggest that all legumes tested are appropriate for use as intercrops because they induced high S. hermonthica seed germination. Additionally, confounding effects (mixed) on successful penetration of S. hermonthica in non-hosts will require further investigation. Knowledge from this study has provided fundamental insights on the importance of trap crops in induction of suicidal germination of Striga hermonthica seeds, which depletes the parasite’s seedbank in soil.